Combined Cooling, Heating, Power, and Ventilation
(CCHP/V) Systems Integration
Fred Betz
PhD. Dissertation
Center for Building Performance and Diagnostics
School of Architecture
College of Fine Arts
Carnegie Mellon University
Pittsburgh, Pennsylvania
May 11, 2009
Copyright © Frederik Betz, 2009. All rights reserved.
Copyright Declaration
I hereby declare that I am the sole author of this thesis.
I authorize Carnegie Mellon University, Pittsburgh, Pennsylvania to lend this thesis to
other institutions or individuals for the purpose of scholarly research.
I authorize Carnegie Mellon University, Pittsburgh, Pennsylvania to reproduce this thesis
by photocopying or by other means, in total or in part, at the request of other institutions
or individuals for the purpose of scholarly research.
Copyright © Frederik Betz, 2009. All rights reserved.
2
Acknowledgements
I would like to thank Dr. Volker Hartkopf for chairing my thesis committee and for
bringing me to the Center for Building Performance and Diagnostics four years ago. He
helped me gain a new perspective and appreciation for the built environment. His never
ending supply of energy and optimism is truly inspiring.
Dr. David Archer has guided my day to day tasks since my arrival in the Intelligent
Workplace four years ago. Through his tireless efforts he inspired me to persevere
through my entire project from preliminary design ideas all the way through construction
and evaluation of a complex system.
Prof. John Wiss provided me with invaluable insight into engine technology and always
helped me stay grounded with his years of practical experience. I would especially like to
thank Sharilynn and Jim Jarrett who provide support services in the Intelligent Workplace,
which allowed all of the faculty and staff to function as a team.
Flore Marion generously spent months of her time assisting me with her fantastic
TRNSYS programming skills without which an entire chapter of my thesis would never
have existed. I am truly thankful to have had her assistance on this thesis.
I would like to thank all of the students working in the IW for their support and
encouragement over the years. In particular I would like to thank Philip Kwok, Bing
3
Dong, Joonho Choi, and Viraj Srivastava. Their advice and attitude made working long
hours enjoyable.
I would like to thank my parents Karin and Al Betz for helping me develop and maintain
a work ethic that has made all of my success to date possible. Finally, I would like to
thank my brother Ingo, whose sense of humor helped me keep a smile on my face for the
last four years in the face of some tough challenges.
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Dedication
I would like to dedicate this dissertation to my wife Victoria. Without her love and
support everyday for the last four years this dissertation would not have been possible.
5
Abstract
Combined heat and power (CHP) systems are frequently used to reduce energy
consumption in a facility due to the increased energy efficiency. System efficiencies
range between 65% and 85%, whereas the average utility efficiency for electric power
supply is 31% and for heating from a natural gas supply is around 80%, which yields a
combined efficiency of approximately 50% for all energy supplied in the United States of
America. Buildings use 70% of all electricity generated in the U.S., 40% of all U.S.
primary energy to heat, light, ventilate and cool facilities. Therefore, it makes sense to
site power plants near both the electrical and thermal loads to make use of the nearly 70%
of energy that is annually wasted by large central power plants.
CHP systems are frequently reserved for larger facilities due to high first costs and
complex operations, however 75% of all buildings in the U.S. have an area of less than
10,000 ft2 (929 m2). There have been several attempts made by various corporations to
break into the micro CHP market with limited success. Studies commissioned by the
Department of Energy show that two of the key barriers to the adoption of CHP systems
in smaller facilities is the high first cost and the lack of packaged plug-and-play systems.
To address this challenge, the Center for Building Performance and Diagnostics (CBPD)
has designed, installed, operated and evaluated a 25 kWe biodiesel fueled CHP system
that is integrated with an absorption chiller system and an enthalpy recovery ventilation
system with solid desiccant dehumidification in a single system that provides all of the
electric, cooling, heating, and ventilation needs of the Intelligent Workplace, IW. The
6
chiller and ventilation systems are well understood with three published dissertations in
the last four years.
This dissertation integrates elements of each subsystem through the use of calibrated
simulations to determine the effectiveness of operating such a system in a commercial
office building as well as potentially in a data center.
Key contributions of this work include:

A complete accounting of how the CHP system is setup and how it operates with
both Diesel and biodiesel fuel.

A generic preliminary design procedure for the CHP system of a building as well
as the specific design procedures for the biodiesel fueled CHP system.

A simplified TRNSYS CHP system performance model that can be easily
adjusted to be used for different buildings and/or for different prime movers.

A conceptual systems integration model, which identifies how components and
sub-systems may fit together.
Key results in this dissertation include:

The results show that for efficient and effective performance of a CHP system in a
high performance building it is essential to have electrical and thermal grids
available to export and/or import CHP energy. The grids allow the CHP system to
operate continuously at the design load. The grids also provide back up in case of
system outage.
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
The results of operating the biodiesel fueled CHP system in the IW yields an
average annual efficiency of about 66% and a peak of 78%.

A scaled up system for the Building As Power Plant (BAPP) will achieve similar
efficiencies unless a larger load for the coolant energy can be found.

Data centers offer an ideal location for CHP systems as they do not have such
highly variable loads such as office buildings. Furthermore, data centers do not
have latent cooling or heating loads, which simplifies systems integration, as the
only components required for the system are an engine or turbine, heat recovery
equipment, and absorption chillers. A CHP system with absorption chillers has
been calculated in this dissertation to achieve an average efficiency of 78% in
data centers.
There are many possible next steps; however the three most important steps in the
development of the CCHP/V technology are to complete the automation and integration
of the CHP system with the rest of the IW.
Second, to refine the BAPP data for the TRNSYS simulation and to create a modular
CHP system in TRNSYS so the development of BAPP mechanical system can proceed
and provide a future testing ground for packaged CCHP/V systems.
Third, to conceive and develop the means for reducing equipment and installation costs
by a factor of 10 to 20 must be developed.
8
Table of Contents
Copyright Declaration ......................................................................................................... 2
Acknowledgements ............................................................................................................. 3
Dedication ........................................................................................................................... 5
Abstract ............................................................................................................................... 6
Table of Contents ................................................................................................................ 9
List of Figures ................................................................................................................... 12
List of Tables .................................................................................................................... 14
Nomenclature .................................................................................................................... 15
1.0 Introduction ................................................................................................................. 16
1.1 Rationale ................................................................................................................. 16
1.2 Market Size ............................................................................................................. 18
1.3 Why not CHP? ........................................................................................................ 18
2.0 Background ................................................................................................................. 20
2.1 DG & CHP Principles ............................................................................................. 20
2.2 Fuels ........................................................................................................................ 22
2.3 Energy Grids ........................................................................................................... 25
2.4 Prime Movers .......................................................................................................... 26
2.4.1 Central Power Plants ........................................................................................ 26
2.4.2 Boilers and Steam Turbines ............................................................................. 27
2.4.3 Gas Turbine ...................................................................................................... 27
2.4.4 Internal Combustion Engines ........................................................................... 28
2.4.5 Fuel Cells ......................................................................................................... 28
2.4.6 Prime Mover Summary .................................................................................... 28
2.5 Heat Loads .............................................................................................................. 29
2.5.1 Space Heating .................................................................................................. 30
2.5.2 Absorption Cooling.......................................................................................... 30
2.5.3 Desiccant Regeneration ................................................................................... 31
2.5.4 Other Heat Loads ............................................................................................. 31
2.5.5 Storage ............................................................................................................. 32
2.5.6 Heat Loads Summary....................................................................................... 32
2.6 Existing Packaged Systems..................................................................................... 33
2.7 Case Studies ............................................................................................................ 34
3.0 IWESS Components and Subsystems ......................................................................... 37
3.1 Biodiesel Fueled Engine Generator with Heat Recovery ....................................... 37
3.1.1 System Components......................................................................................... 37
3.1.2 Input / Output ................................................................................................... 47
3.1.3 Operating Description and Results .................................................................. 48
3.1.3.1 Engine: Measured Data versus Manufacturer’s Specifications ................ 51
3.1.3.1 Pressure – Time – Crank Angle Measurements ........................................ 53
3.1.3.2 Turbocharger Analysis .............................................................................. 55
3.1.3.3 Combustion Gas and Emissions Analysis ................................................ 56
3.1.3.4 Heat Recovery Analysis ............................................................................ 60
3.1.4 Systems Integration Potential .......................................................................... 63
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3.2 Steam Driven Double Effect Absorption Chiller .................................................... 65
3.2.1 System Components......................................................................................... 65
3.2.2 Input / Output ................................................................................................... 66
3.2.3 Operating Description and Results .................................................................. 68
3.2.4 Systems Integration Potential .......................................................................... 70
3.3 Ventilation System with Enthalpy Recovery and Solid Desiccant Dehumidification
....................................................................................................................................... 71
3.3.1 System Components......................................................................................... 71
3.3.2 Input / Output ................................................................................................... 72
3.3.3 Operating Description and Results .................................................................. 73
3.3.4 Systems Integration Potential .......................................................................... 77
4.0 Preliminary Design Guide........................................................................................... 79
4.1 Generic Design Steps .............................................................................................. 79
4.1.1 Loads ................................................................................................................ 80
4.1.2 Fuel Selection................................................................................................... 81
4.1.3 Energy Grids .................................................................................................... 82
4.1.4 Prime Movers ................................................................................................... 83
4.1.5 Auxiliary and Heat Recovery Equipment ........................................................ 84
4.1.6 Operating Strategy ........................................................................................... 85
4.1.7 CHP System Evaluation ................................................................................... 86
4.2 Design of Biodiesel Fueled CHP System ............................................................... 87
4.2.1 Load Profiles .................................................................................................... 87
4.2.2 Fuel Selection................................................................................................... 88
4.2.3 Energy Grids .................................................................................................... 89
4.2.4 Prime Movers ................................................................................................... 90
4.2.5 Auxiliary and Heat Recovery Equipment ........................................................ 91
4.2.6 Operations ........................................................................................................ 94
4.2.7 Evaluation ........................................................................................................ 94
4.2.8 Submittals ........................................................................................................ 95
5.0 TRNSYS Modeling..................................................................................................... 96
5.1 IWESS Model ......................................................................................................... 96
5.1.1 Biodiesel Fueled Engine Generator with Heat Recovery Modeling ................ 96
5.1.2 Double Effect Steam Driven Absorption Chiller ............................................. 97
5.1.3 Ventilation Unit with enthalpy recovery and solid desiccant wheel................ 98
5.1.4 Computational Model Issues............................................................................ 98
5.1.5 Combined IWESS Model .............................................................................. 100
5.1.6 IWESS Simulations ....................................................................................... 103
5.1.6.1 Mode Zero: Design Operation ................................................................ 104
5.1.6.2 Mode One: Thermal Load Follow .......................................................... 104
5.1.6.3 Mode Two: Regeneration Load Follow .................................................. 106
5.1.6.4 IWESS Simulation Discussion ............................................................... 108
5.2 BAPP Model ......................................................................................................... 108
5.2.1 Engine Modification ...................................................................................... 108
5.2.2 BAPP Simulations ......................................................................................... 112
5.2.2.1 Mode Zero: Design Operation ................................................................ 112
5.2.2.2 Mode One: Thermal Load Follow .......................................................... 113
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5.2.2.3 Mode Two: Regeneration Load Follow .................................................. 113
5.2.2.4 BAPP Simulation Discussion ................................................................. 114
5.3 Data Center CHP Operation.................................................................................. 116
6.0 Systems Integration ................................................................................................... 119
6.1 Individual Systems Integration ............................................................................. 120
6.2 Packaged Systems Integration .............................................................................. 126
7.0 Contributions, Conclusions, and Future Work ......................................................... 130
7.1 Contributions......................................................................................................... 130
7.2 Conclusions ........................................................................................................... 132
7.3 Future Work .......................................................................................................... 134
References ....................................................................................................................... 140
Appendix …………………………………………………….………………………………….143
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List of Figures
Figure 1: U.S. Electrical Energy Flow for Large Central Plants (Quadrillion BTUs) [2] 21
Figure 2: Energy Flow for Distributed Generation with Heat Recovery (Quadrillion
BTUs) (Adapted from Reference 2) ................................................................................. 22
Figure 3: Basic CHP Flow Diagram ................................................................................. 38
Figure 4: CHP System Components ................................................................................. 39
Figure 5: Baldor Engine Generator ................................................................................... 39
Figure 6: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kWe......... 40
Figure 7: Assembled Components: Engine Generator (Left), Steam Generator (Right) .. 41
Figure 8: Steam - Hot Water Converter ............................................................................ 42
Figure 9: Coolant Heat Exchanger with Piping before Insulation .................................... 43
Figure 10: Remote Mounted Radiator .............................................................................. 44
Figure 11: Engine Generator Onboard Interface .............................................................. 44
Figure 12: Engine Generator Onboard Interface .............................................................. 45
Figure 13: Automated Logic CHP User Interface for the Heat Recovery/Rejection System
........................................................................................................................................... 48
Figure 14: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
........................................................................................................................................... 53
Figure 15: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
........................................................................................................................................... 54
Figure 16: Turbocharger Compressor Map [] ................................................................... 55
Figure 17: Summer Operation of the Steam Generator T-Q Diagram.............................. 61
Figure 18: T-Q Diagram for Coolant Heat Exchanger at 25 kWe .................................... 63
Figure 19: Steam Driven Absorption Chiller Flow Diagram [] ........................................ 66
Figure 20: Absorption Chiller Process and Instrumentation Diagram [31] ...................... 67
Figure 21: Automated Logic Absorption Chiller User Interface ...................................... 68
Figure 22: Absorption Chiller Component Heat Transfers vs. Cooling Load [31] .......... 69
Figure 23: Plan View of Ventilation Unit [] ..................................................................... 71
Figure 24: Interior View of the Ventilation Unit [33] ...................................................... 73
Figure 25: Ventilation Unit Flow Diagram [33] ............................................................... 74
Figure 26: Psychrometric Chart for Ventilation System Operation [33] .......................... 74
Figure 27: Enthalpy Removal Breakdown by Component [33] ....................................... 75
Figure 28: Moisture Removal Breakdown by Component [33] ....................................... 75
Figure 29: Operating Cost Breakdown by Component [33] ............................................. 76
Figure 30: IW Heating and Cooling System Flow Diagram\ ........................................... 92
Figure 31: CHP system input / output module.................................................................. 97
Figure 32: Double effect absorption chiller input / output module .................................. 98
Figure 33: Ventilation system input / output module ....................................................... 98
Figure 34: Combined TRNSYS Model........................................................................... 100
Figure 35: Combined/Simplified IWESS TRNSYS Model ........................................... 101
Figure 36: BAPP TRNSYS Simulation .......................................................................... 111
Figure 37: CHP Major Component Diagram .................................................................. 121
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Figure 38: Absorption Chiller Major Component Diagram ........................................... 121
Figure 39: Ventilation System Major Component Diagram ........................................... 122
Figure 40: CCHP/V Energy Cascade .............................................................................. 123
Figure 41: Major Component Piece-wise Systems Integration ...................................... 125
Figure 42: Packaged CCHP/V System ........................................................................... 126
Figure 43: CCHP/V Summer Operation Flow Diagram ................................................. 128
Figure 44: CCHP/V Winter Operation Flow Diagram ................................................... 129
Figure 45: Cost Breakdown of CHP System .................................................................. 138
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List of Tables
Table 1: Prime Mover Performance Summary ................................................................. 29
Table 2: Averaged Summer Diesel Commissioning and Experimental CHP Results ...... 49
Table 3: Averaged Winter Diesel Commissioning and Experimental CHP Results ........ 49
Table 4: Averaged Winter Biodiesel Experimental Results ............................................. 50
Table 5: Diesel Engine Generator Measured Data vs. Manufacturer Specifications ....... 51
Table 6: Biodiesel Engine Generator Data vs. Manufacturer Specifications ................... 52
Table 7: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel ................. 56
Table 8: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel ........................ 56
Table 9: Absorption Chiller Test Program and Results [31] ............................................ 69
Table 10: Typical U.S. Commercial Building Loads ....................................................... 80
Table 11: Prime Mover Performance Summary ............................................................... 83
Table 12: IWESS Design Operation Simulation Results................................................ 104
Table 13: IWESS Thermal Load Follow Simulation Results ......................................... 105
Table 14: IWESS Regeneration Load Follow Simulation Results ................................. 107
Table 15: IWESS 25 kWe CHP Coolant Heat Exchanger Results vs. Power Level ...... 110
Table 16: Estimated BAPP 200 kWe CHP Coolant Heat Exchanger Results vs. Power
Level ............................................................................................................................... 110
Table 17: IWESS 25kWe CHP Air Flow Rate vs. Power Level .................................... 111
Table 18: Estimated BAPP 200 kWe CHP Air Flow Rate vs. Power Level .................. 111
Table 19: BAPP Design Operation Simulation Results .................................................. 112
Table 20: BAPP Thermal Load Follow Simulation Results ........................................... 113
Table 21: BAPP Regeneration Load Follow Simulation Results ................................... 114
Table 22: IWESS Input / Output Table........................................................................... 124
Table 23: IWESS Component List ................................................................................. 125
Table 24: Packaged System Component List ................................................................. 127
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Nomenclature
BAPP: Building As Power Plant
CHP: Combined Heat and Power, also known as cogeneration
CCHP: Combined Cooling Heat and Power, also known as trigeneration
CMU: Carnegie Mellon University
CBPD: Center for Building Performance and Diagnostics
DG: Distributed Generation
IC: Internal Combustion
IW: Intelligent Workplace
IWESS: Intelligent Workplace Energy Supply System
kW: kilowatt
kWc: kilowatt chemical (fuel energy)
kWe: kilowatt electric
kWt: kilowatt thermal
15
1.0 Introduction
The work described in this dissertation covers the preliminary design, procurement,
detailed design, installation, operation, and evaluation of a 25 kWe combined heat and
power subsystem as well as the future integration with installed absorption chillers and an
enthalpy recovery ventilation system with solid desiccant dehumidification as a combined
energy supply system.
The goals of the integration is to show how the three subsystems operate together as a
system by combining three validated simulation models and to show how the first and
operating costs can be reduced through systems integration.
1.1 Rationale
While the cost of energy has dropped substantially in the last year, experts agree that the
price will rebound to historic highs as the world economy recovers [1]. Due to the double
threat of high energy cost and global climate change there is increased interest in the use
of combined heat and power systems, which can reduce the primary energy consumption
of power and heat by up to 50% for building and plant operations.
Currently the U.S. average efficiency for producing electricity is 32% including
transmission and distribution losses [2]. If heating efficiencies are considered, then
standard practice efficiency is around 50% for heating and electricity. Typical CHP
system efficiencies range from 65% to 90% efficiency, including the Intelligent
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Workplace Energy Supply System (IWESS) CHP system which has achieved 76%
efficiency.
Studies commissioned by the Department of Energy [3, 4, 5] show that one of the key
barriers to the use of CHP systems is the high first cost and the availability of packaged
systems. This PhD. dissertation attempts to address these two issues by providing a first
step in the creation of a packaged plug-and-play system that can be delivered to a facility
and be connected rapidly. Furthermore, the packaged system will have reduced overall
costs of design, engineering, and field assembly as compared to a system purchased
piecewise.
One of the key problems when using a CHP system is to find a sufficient heat load that
matches the heat output of the CHP system. CMU’s Intelligent Workplace (IW) offers
two thermal loads during the summer; the regeneration of a desiccant wheel in the
ventilation system and the operation of absorption chillers. During the winter, the IW has
a space heating load. These loads allows the CHP system to operate year round, with the
possible exception of the intermediate seasons, spring and fall, where a properly designed
building should have little need for air conditioning (heating, cooling, or
dehumidification). However, because there are Carnegie Mellon campus electrical, steam,
and chilled water grids, year round export of energy is possible from the IW’s CHP
system.
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1.2 Market Size
Several studies commissioned by the Department of Energy in 2002 have looked into the
market size of CHP systems using current technology [3, 4, 5]. Between 2003 and 2017:

7% of hospitals plan to install CHP systems within 2 years, starting in 2003,

3% of supermarkets plan to install CHP systems within 2 years, starting in 2003,

4% of hotels plan to install CHP systems within 2 years, starting in 2003,

2% of big-box retailers plan to install CHP systems within 2 years, starting in
2003 [4].

Institutions construct new buildings every year, which require power for lighting
and ventilation as well as thermal energy for heating and cooling.

Approximately 42,000 new commercial buildings are built every year; 75% of the
buildings have peak loads below 200 kWe [6].
Several markets would be impacted by improvements in CHP systems most notably
hospitals, supermarkets, and hotels [5]. A total of 3,075 sites were identified for 300-600
kWe CCHP retrofits. For new construction through 2020, 2,464 CHP sites were
identified [5]. It should be noted that this study was conducted in 2002 and 2003, and the
market will have shifted somewhat as fuel and electricity prices have increased several
fold since the publication of this report. Also, the study did not include large institutional
complexes such as universities, in the market sizing.
1.3 Why not CHP?
The advantage of standard electrical and natural gas utilities, boilers and chillers that
provide energy to buildings inefficiently over CHP systems is that it is simple for the
18
building owner and/or occupant. The job of keeping the power on falls to the utility
company and chillers and boilers may include warranties and service contracts in addition
to being mature technologies. Furthermore, the first cost is low for the builder. In essence,
the risk for the consumer is low, while the energy and associated environmental and
economic impacts are large even though CHP systems have existed as long as utilities
have existed.
Currently, CCHP/V systems have a greater perceived risk to the owner or occupant
versus a conventional energy supply system. A buyer would choose a CCHP technology
based on first cost, operating cost, and maintenance cost and reliability.
A major objective of this project is to reduce the first cost by working on systems
integration strategies that reduce the number and complexity of components in the CCHP
system. Reduced first cost would make an owner/occupant more likely to purchase a
CCHP system, which would help refine the technology to the level of relatively simple
boilers and chillers and make it more robust.
An additional objective is the reduction of operating costs by making maximum use of
the fuel energy going into the prime mover (engine, microturbine, etc.). This would
include the electrical energy for office equipment and lighting, high temperature heat for
absorption chillers to make cooling, and low temperature heat for space heating,
dehumidification, and domestic hot water.
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2.0 Background
Buildings account for approximately 40% of all primary energy consumption in the
United States, and consume about 70% of the electricity [6]. Furthermore, approximately
57% of that electricity is generated using coal [7]. These coal power plants use what is
called a Rankine cycle process which entails burning coal in a boiler, to generate steam.
That steam passes through a turbine, which turns a generator. The first steam power
plants in the 1880s had an efficiency of approximately 8%, or in other words 8% of the
heat of combustion of the coal was converted to electrical energy, the rest was rejected as
heat to the surroundings [7]. Steady increases in conversion efficiency occured through
the 1960s, but have peaked at about 35%; the other 65% of the energy is still lost as heat
[8].
In the early 1880s, Thomas Edison realized this large inefficiency and sold the heat to
neighboring buildings in a successful effort to increase his bottom line [8]. In a sense, the
first Edison steam plants were combined heat and power (CHP) plants. The same is true
today of CHP plants. Heat that is normally rejected can be recovered from exhaust gases
and coolant and applied in a useful way. This can improve the efficiency of power
generation facilities from 35% to over 80% [9,10,11,12,13]. This improvement in
efficiency reduces the overall demand for fuel and green house gas emissions.
2.1 DG & CHP Principles
Distributed generation (DG) is simply defined as any electrical generating source with a
capacity of less than five megawatts. Combined heat and power (CHP) is defined as the
20
simultaneous production and use of electricity and heat from a single fuel source. This
concept can be applied to large and small generating facilities. Another term used for
CHP is cogeneration. Also, sometimes cooling is added to the acronym resulting in
combined cooling heating and power (CCHP), or trigeneration.
Figures 1 and 2 show how electrical power is typically generated in the U.S. As shown in
Figure 1, the largest energy flow is the conversion losses seen at the top.
Figure 1: U.S. Electrical Energy Flow for Large Central Plants (Quadrillion BTUs) [2]
In Figure 2, the recoverable conversion losses are highlighted along with the transmission
and distribution losses which are avoided by producing electricity locally.
21
Figure 2: Energy Flow for Distributed Generation with Heat Recovery (Quadrillion BTUs) (Adapted
from Reference 2)
The amount of heat recoverable heat varies depending on the building loads; however the
goal of CHP systems is well described.
2.2 Fuels
There are many fuels available for the operation of CHP systems including: natural gas,
petroleum products (gasoline, Diesel, etc.), biomass (biogas, biodiesel, ethanol, solids),
coal, and waste fuels (waste coal, garbage, etc.). Many of these fuels are associated with a
particular type of prime mover and vary in energy content, cost, availability, and
emissions.
Natural gas is by far the most common fuel type accounting for about 75% of all CHP
systems in operation in the U.S. [14]. The reason for this is that the fuel is readily
available with a nationwide distribution network, the cost per unit of energy is relatively
22
low, and the emissions are relatively clean. However, it should be noted that while the
cost of natural gas is relatively low as compared to many other common fuels, the price is
very volatile making operating costs projections problematic.
Diesel fuel is the most common petroleum product used for CHP systems as Diesel
engines provide a high electrical efficiency. Furthermore, Diesel fuels can be stored
relatively easily adding a margin of security in case of a power outage, which may also
affect the flow of natural gas. The cost is relatively high as Diesel fuel for CHP
applications must still compete with Diesel fuel used for transportation, which is on
average three times as expensive as natural gas per unit energy.
Renewable fuels such as biomass are gaining market share due to their emissions
characteristics and public appeal. Biomass can come in a gaseous, liquid or solid form.
Biogas often comes from landfills and waste water treatment facilities. The first cost of
treatment systems for the fuel is high; however operational costs are very low. Biogas is
typically difficult to distribute, therefore it is often used on site or in nearby locations.
Biodiesel on the other hand has a growing distribution network yet is being primarily
used for transportation rather than power and heat generation. Biodiesel is typically made
from soybean oil in the U.S., but can be made from many different plant oils and animal
fats. The cost is relatively high as biodiesel is primarily used as a transportation fuel and
does divert feed stocks from the food supply.
23
Ethanol, which is typically made from corn is the most common liquid biofuel in the U.S.
and is typically used for transportation, but would work in gasoline fueled engine
generators that have been modified to operate with E85, or a gasoline-ethanol mixture
that is 85% ethanol. Corn based ethanol is a controversial fuel, which may or may not
provide energy independence or a net energy gain, as well as diverting a food source to
fuel production. Ethanol from cellulose (corn husks, grass clippings, etc.) may solve the
issue of diverting food production to fuel production and would be relatively inexpensive,
however cellulosic ethanol is not commercially available yet. Finally, ethanol is a
problematic fuel from an engineering point of view. Ethanol is hygroscopic, meaning it
absorbs water, it has a relatively low energy density, and requires the modification of
engines to run on E85. Cellulosic butanol may be the best of both worlds providing a fuel
that is very similar to gasoline in energy density and performance, while not requiring
engines to be significantly altered [15]. Cellulosic butanol is still in the laboratory scale
development and will not be commercially available for several years.
Solid fuels, referred to as biomass include wood chips, saw dust, grass clippings and any
other solid biological material can be burned in an incinerator to generate steam and drive
a turbine to generate electricity. Biomass is considered a relatively crude fuel and is
somewhat difficult to distribute, however it is usually inexpensive. The emissions vary,
and care must be taken when using biomass to fuel a CHP system, but it can be clean.
Coal is typically used in larger CHP systems and carries with it negative emissions
characteristics including high CO2, particulates, SO2, NOX, heavy metals, etc.. However,
24
the distribution system is relatively good and the cost is relatively low and steady. The
emissions characteristics of coal systems are highly regulated by the EPA and getting
permits may be difficult, especially in urban environments.
Finally, waste fuels such as waste coal, garbage and heavy oils can be used in CHP
systems; however such systems typically require significant emissions controls. Garbage
presents an interesting challenge as the actual fuel composition on site is unknown;
however it can be successfully implemented in a CHP system. For example, the
Hennepin Energy Recovery Center in downtown Minneapolis, MN burns garbage
providing electricity and heat to the downtown area [16].
2.3 Energy Grids
There are several types of energy grids, most commonly the electric utility grid. This grid
is nationwide and offers some flexibility to operators of CHP systems. Each utility grid
operator has different sets of rules and regulations; therefore it is important to contact the
utility when considering the installation of a CHP system. Thermal grids are sometimes
available for CHP operators such as steam, hot water and chilled water. These grids can
provide sources and sinks for thermal energy.
Energy grids enable CHP operators to manage both excess and shortages of energy.
Buildings typically have varying loads over the course of a day as occupants come and go
and as the weather changes. Furthermore, various energy loads may not be coincident.
There may be a large electrical load and a low heating load during the day as the sun is
25
shining and people are present on a fall day. However at night, the temperature drops and
additional heating is required but there is little demand for electricity.
CHP systems tend to operate better with steady conditions simultaneously generating
electricity and heating that should be used. Some energy grids allow CHP systems to
operate flexibly giving and taking a variety of forms of energy as they are needed or not
needed depending on the regulations set by the primary grid operator. Furthermore,
energy grids provide a great backup source of energy in case the CHP system fails.
Energy grids found on college campuses are particularly effective, providing electricity,
heating, and cooling to a mix of institutional and residential applications. As students are
preparing for the day they are using energy in their dormitories, then they move to
laboratories, classrooms, and offices and continue to use energy. In the evening they
return to their dormitories to study, eat dinner, and enjoy recreation, all of which can use
the same CHP system.
2.4 Prime Movers
Prime movers are defined as the device that consumes the fuel, delivers power, and
rejects heat; such as a boiler with a steam turbine, a Diesel engine, or a gas turbine.
2.4.1 Central Power Plants
Many central power plants are of the boiler – steam turbine type and burn coal to
generate steam in a boiler, and then send that high pressure steam through a turbine to
generate electricity. Furthermore, these central power plants typically have very large
26
generating capacity, in excess of 500 MW and sometimes greater than 1,000 MW. The
efficiency of these plants appears to have reached a maximum at about 35%, although
38% efficiency is possible with very sophisticated and expensive equipment [8]. Nuclear
power plants operate in a similar way with the exception of using enriched uranium as a
fuel to provide heat rather than coal. Note, a combination of boiler and steam turbine can
be used on a smaller scale, and are often used with low grade fuels making them cheap to
operate.
2.4.2 Boilers and Steam Turbines
The combination of a boilers and steam turbines is an effective way of using low quality,
inexpensive fuels such as biomass and waste fuels to generate electricity and heat. The
electrical efficiency of these systems is relatively low, 10% to 15%; however a lot of low
quality steam is available for a variety of applications. The emissions generated from this
type of system vary, and will require detailed study for permitting. These systems come
in a variety of sizes, typically 100 kWe and up.
2.4.3 Gas Turbine
Gas turbines for power generation typically use natural gas, however examples of
turbines using kerosene, jet fuel, biogas, and biodiesel among others can be found. Gas
turbines come in a variety of sizes from 30 kW up to 50 MW. The efficiencies of gas
turbines can vary based on the technology used. A simple gas turbine can have an
electrical efficiency as low as 15%, but as high as 45% [8]. This difference is primarily
based on the use of a regenerator to preheat incoming air or the use of a combined cycle
27
process that captures waste heat to generate steam and drive an additional turbine.
Distributed Generation systems typical operate around 15-25% electrical efficiency.
2.4.4 Internal Combustion Engines
Internal combustion (IC) engines can use multiple types of fuel but typically use natural
gas, Diesel, or gasoline for operation. Biodiesel and biogas have also been frequently
used, but are much less common. Efficiencies also vary for reciprocating engines based
on the technology but a natural gas fired IC engine would have a high efficiency of 25%,
whereas a very efficient Diesel engine can reach an efficiency of 40%.
2.4.5 Fuel Cells
Fuel cells have taken on a variety of forms, fuel types, and efficiencies. While fuel cells
are arguably the most efficient form of generating electricity, the high cost both in raw
materials and manufacturing has not allowed them to become a mainstream prime mover
in the last century. Therefore, fuel cells will not be considered in this paper as possible
DG source, although the future potential of this technology is considerable.
2.4.6 Prime Mover Summary
In a CHP system it should be noted that none of these prime movers is inherently better
than another on an energy basis. If each CHP system achieves an efficiency of 80%, then
the factors that vary are the proportion of electricity to heat, and the ability to use the
various fuels effectively. As the goal is to use as much reject heat as possible, a CHP
operator will have to be aware of many issues, including how much heat and electricity
are demanded by the building and its surrounding facilities and how much is available
and in what forms. First costs, cost of fuel, cost of heat and electricity, and maintenance
28
costs will all vary and need to be accounted for. Also, while there isn’t necessarily a cost
associated with emissions, this too may be regulated in the future. Furthermore, the EPA
has designated some locations as non-attainment zones for sulfur oxides, nitrogen oxides,
and particulates, etc. that may have a mitigation cost associated with it. A summary of
prime movers, fuels, and performance is shown in Table 1.
Prime Mover
Boiler + Steam
Turbine
Gas Turbine
IC Engine
-Diesel
Fuels
Nat. gas, coal, waste
fuels, biomass
Natural gas, biogas
Diesel, biodiesel
Gasoline, E85,
natural gas
Electrical
Efficiency
10 - 15 %
15 - 25 %
30 - 40 %
-Spark
20 - 30 %
Fuel Cell
-SOFC
Natural gas
35 - 45 %
-PEM
Hydrogen
35 - 45 %
Table 1: Prime Mover Performance Summary
Recoverable Heat
45 - 65 % low quality
steam
45 - 55 % 600oF exhaust
15 - 20 % 190oF coolant,
15 - 20 % 900oF exhaust
15 - 30 % 190oF coolant,
15 - 20 % 900oF exhaust
25 - 35 % 500oF exhaust
25 - 35 % 300oF exhaust
CHP
Efficiency
Heat to
Power
Ratio
65 - 80 %
60 - 80 %
4.3
2.8
60 - 80 %
1.6
50 - 80 %
2.0
60 - 80 %
60 - 80 %
0.8
0.8
2.5 Heat Loads
The earliest use for reject heat from power generation facilities was in the 1880s with
Thomas Edison’s Pearl street power plant in New York [8]. The plant was only about 8%
efficient and Edison recognized that he could improve his bottom line by selling the
excess heat to neighboring buildings in the winter for space heating [8].
Over the last century additional uses for reject have been found and implemented to
varying degrees around the world, many of which are found in the Intelligent Workplace.
Reject heat temperatures vary greatly depending on the type of prime mover; however
ball park temperatures are available. A Diesel engine would supply exhaust at
29
temperatures in excess of 900oF (482oC) and coolant at 195oF (91oC). A microturbine
might provide exhaust around 600oF (316oC). All of these heat sources provide a high
enough temperature for many applications, which will be discussed below.
2.5.1 Space Heating
Space heating is probably the most common application for reject heat utilization. This
heat can be utilized using radiant and convective systems typically found in many
buildings. Space heat is particularly effective as the temperature is relatively low with a
wide range of useful temperature possible. Operating temperatures range between 90oF
(32oC) for the radiant surfaces in the Intelligent Workplace to 120oF (49oC) common for
air handling units.
2.5.2 Absorption Cooling
A heat pump is a technology that enables the transfer of heat from a low temperature to a
high temperature [17]. Heat pumps can be mechanical driven using electricity and a
motor or by heat. Absorption chillers are heat driven heat pumps [17].
Absorption chillers come in three common types based on the type of refrigerant that they
use; ammonia and water, lithium-bromide and water, and lithium-bromide, water, and
hydrogen [17]. The types of chillers used as part of IWESS are both lithium-bromide and
water. Furthermore, different configurations of absorption chillers are available; single
effect, double effect and triple effect [17]. The higher the number of chiller stages, the
higher the overall efficiency [17]. However, the control system becomes more expensive
and there is an increased cost per unit of cooling. A typical single effect chiller will have
30
a coefficient of performance (COP) of around 0.5 to 0.7, whereas a double effect chiller
can reach a COP of 1.2. It should be noted that normal chillers have a COP of 3.2 on
average or greater [18]. However, the electricity used to drive the chiller must be paid for,
whereas the heat used to drive the absorption chiller is nearly free in the form of solar
energy or engine exhaust as demonstrated in the IWESS project.
2.5.3 Desiccant Regeneration
A common method of humidity control in buildings is to cool incoming outside air to a
temperature at which the water vapor in the air condenses and is removed from the air
stream, and then to reheat the air to the desired set point temperature. Needless to say this
is an energy intensive process that can be accomplished more efficiently using a
desiccant to absorb moisture [19].
As the desiccant absorbs water from the incoming air it becomes saturated overtime.
Therefore, the desiccant needs to be regenerated using a hot air stream, which could come
from a natural gas burner as is presently the case in IWESS or from a hot water heating
coil in the future [19].
2.5.4 Other Heat Loads
There are many other places to utilize waste heat such as domestic hot water, which is
found in almost every building. Additional heat demands include, but are not limited to;
heating pools, drying laundry, process energy, and thawing sidewalks and streets as is
done at Sierra Nevada College in Incline Village, Nevada. Research is being conducted
31
into additional usages of reject heat; however the ones stated above are currently
employed.
2.5.5 Storage
As discussed in section 2.3 CHP systems tend to operate best in steady modes while
buildings operate in dynamic modes. When an energy grid is not available to import and
export energy, storage is an option to be considered by the engineer. While the electric
grid is almost always available, banks of batteries have been used for electrical storage as
well as using electrical resistance heaters to generate hot water or vapor compression
chillers to generate chilled water.
Thermal storage is most commonly used for domestic hot water in most businesses and
homes. The same concept can be used for chilled and hot water, which can provide a
buffer between the CHP system’s outputs and the buildings demands. Based on the loads
an engineer must decide if storage should last for an hour or a day or longer. Ice storage
is a common way of storing large amounts of cooling energy. An absorption chiller can
be used to generate ice, however it must be an ammonia water chiller as lithium-bromide
absorption chillers can only achieve a minimum of 3oC, which is insufficient to create ice.
2.5.6 Heat Loads Summary
As stated in the previous section that there are a number of possible heat sinks that can
provide a use for reject heat from a CHP system. The overall goal is to have a steady
demand for heat year round, which improves the economics of the CHP system. Some
technologies are applied year round, some in a heating season and some in the cooling
32
season; it is up to the CHP system designer to use the given building and site loads to find
the proper balance.
2.6 Existing Packaged Systems
There are a number of packaged units with varying degrees of integration. Some
manufacturers only provide a packaged generator set (prime mover plus generator with
controls). Additional equipment such as automatic transfer switches and soft load
controllers allow the engine generator to provide backup power and/or operate in parallel
with the utility electric supply. Soft load controllers are rarely included in the packaged
engine generator sets.
Integrated heat recovery is found in some 60 and 65 kWe Capstone microturbines as well
as many Schmitt Enertec units [20, 21]. Capstone has the majority of the microturbine
market in the U.S. as they offer a compact, low maintenance system with a small enough
electrical output to open a large market. The Capstone units have a sophisticated onboard
diagnostic system that enables remote diagnosis of faults and speeds repairs.
United Technologies – Carrier has put together a CCHP system with grid paralleling
capabilities. This system can combine four to six 60 kW Capstone microturbines with a
direct fired absorption chiller. The system can be shipped loose or as a skid mounted
package. Furthermore, parallel grid connection control capabilities exist [22].
A search of Ingersoll Rand’s website yielded little in the way of packaged systems. It
does mention that Ingersoll Rand microturbines have been used in CHP systems.
33
Furthermore, Trane, recently acquired by Ingersoll Rand, makes mention of possible
CHP applications for their packaged absorption chiller units yet there is no combination
available at this time [23].
The Baldor unit installed at CMU uses a John Deere Diesel engine, a Stamford generator
and an Intelligen controller. All of these pieces were purchased by Baldor, assembled on
a skid and shipped to CMU. Typically the unit also includes a radiator from ITT for
rejection of heat from the engine coolant; however, a special request was made to
separate the unit from the engine [13].
Units similar to the Baldor package are available from several integrators, including
Kohler Power Systems, Cummins, Caterpillar, Kato, and Generac to name a few. Some
of these companies develop and use their own engines in their generator sets, while
others select engines from the dozens of Diesel, gasoline, and natural gas engine
available on the open market.
2.7 Case Studies
There are literally thousands of DG, CHP and CCHP systems installed throughout the
U.S. varying in size from a few kilowatts to multi-megawatt systems. Many of these
systems are registered in the U.S. CHP database, which outlines location, owner/operator,
installation year, prime mover, capacity, and fuel type [24].
The database was searched for units with a capacity of less than one megawatt and fueled
with biomass (biogas, biodiesel, ethanol, etc.). Sixty-six systems have been identified.
34
Most of these systems use waste from food processing, waste water treatment, or other
agriculture processes that is generated and used on site in reciprocating engines. This is
logical as the fuel for the prime mover would be free other than the fuel treatment costs.
There are only three examples of biomass fueled units being operated on non-locally
sourced fuel, two of which are on the campuses of the University of Montana in Missoula
and California Polytechnic State University in San Luis Obispo and one at a local utility
in Perry, New York.
Two biogas units, one a 30 kW microturbine and one a 30 kW reciprocating unit, both
with a custom heat recovery system are installed and are being operated in Sun Prairie,
Wisconsin at a waste water treatment facility [25]. These units have operated for several
years and have different operating characteristics. The reciprocating unit needs more
maintenance in the form of oil changes, general inspections, and requires a complete
rebuild after 8,000 operating hours. The microturbine has an onboard diagnostic system,
which detects faults and has a lifetime of 40,000 hours before needing replacement.
Furthermore, the first cost of the microturbine is about 20-50% higher than the
reciprocating unit. Both operate with a plant efficiency of about 80%, yet the proportion
of electricity generated by the reciprocating engine is higher than for the microturbine.
The majority of DG, CHP, and CCHP units are natural gas fired as there is little that has
to be done to provide fuel for the prime mover other than piping, which simplifies the
work for the operator of the system. A 60 kW microturbine was installed by the City of
Milwaukee, Department of Public Works to examine the potential economic benefits of
35
CHP systems. At the time of the installation an integrated heat recovery system was not
available, which led to difficulties in the controls of the system. The heat recovery unit
suggested by the manufacturer of the microturbine did not communicate using the same
protocol, making analysis and more importantly control of the heat recovery unit difficult.
A custom solution had to be developed by the engineering staff to rectify this issue,
which the manufacturer has now solved by offering a unit with integrated heat recovery.
In 2007, a 240 kWe CCHP system was installed at the University of Toronto at
Mississauga, Canada and has been operated for nearly two years [26]. The system studied
was a four microturbine system with a double effect absorption chiller system designed
by United Technologies – Carrier as mentioned in section 2.6. The system was a turn-key
contract in which the manufacturer provided all the parts, services, and installation
required to operate the system. It is not explicitly stated in the case study how the
components of the system were delivered or assembled, however, based on the provided
images; the major components (microturbines and chiller) are mounted on a concrete pad
and not on a single skid. This implies that each piece was shipped loose and mounted on
site. Furthermore, the case study does not state whether or not a grid interconnection
system was included or if that had to be purchased separately.
36
3.0 IWESS Components and Subsystems
Three components of the IWESS will be integrated in this dissertation including the
biodiesel fueled engine generator with heat recovery, the steam driven double effect
absorption chiller, and the ventilation system with enthalpy recovery and solid desiccant
dehumidification. Each piece of the system will be assessed in the following sections
with the goals of:

describing the components of the system,

noting the inputs and outputs,

describing the operation of the system, and

describing how these three systems could be integrated.
3.1 Biodiesel Fueled Engine Generator with Heat Recovery
The biodiesel fueled engine generator with heat recovery system has been operating for
over a year achieving a maximum efficiency of 76%, and efficiency comparable to other
CHP systems.
3.1.1 System Components
There are four major components in the biodiesel CHP system:

engine generator,

steam generator,

coolant heat exchanger, and

automatic transfer switch (ATS) / soft load controller (SLC)
shown in Figure 3.
37
Power to
IW/Grid
ATS / SLC
Exhaust
Muffler
Generator
Absorption
Chiller
Steam
Diesel Engine
Radiator
Exhaust Exhaust Gas
Diversion
Valve
To Condensate Tank
Steam
Generator
Hot Water
Converter
Coolant
Loop
Condensate
Tank
Coolant Heat
Exchanger
Chilled Water Supply
and Return (IW/Grid)
To CMU
Campus
Steam Grid
Hot Water Supply and
Return (IW/Grid)
To CMU Campus
Condensate Grid
Regen Exhaust
Condensate from
Exhaust
Air
Absorption Chiller/Grid
Regen
Coil
Hot Water Supply and
Return (IW/Grid)
Ventilation
System
Regen
Air
Return
Air
Outside Air
Dehumidified Air to IW
Figure 3: Basic CHP Flow Diagram
Expanding upon Figure 3, Figure 4 shows the complexity of the CHP system with parts
from no less than twenty-three direct suppliers, manufacturers, and integrators.
Furthermore, this list does not include the installers for the piping, placing the equipment,
masonry work, electrical connections, instrumentation, and programming.
38
Coolant
Heat
Exchanger
Biodiesel
Diesel
Fill
Station 2
Fill
Station 1
Fuel Tank
2
Fuel Tank
1
VFD
Motor
Valve 5
Valve 6
Motor
Radiator
Fan
Motor
Motor
Pump
Starter
Valve 4
Motor
Motor
Valve 3
Engine-Generator
Fuel Pump 1 Day Tank 1
Engine
Generator
Fuel Pump 2 Day Tank 2
Turbocharger
Air
Controler
Electric Grid
Automatic
Transfer
Switch
Intelligent Workplace
Mullion
Steam Generator
Bypass
Tee
Muffler
Blowdown
Separator
Steam
Generator
Back
Pressure
Valve
Control
Column
Steam
Converter
Motor
Valve 2
Fan Coil
Supplier/Manf/Integrator
Baldor
John Deere
Stamford
Intelligen
ASCO
Vaporphase
Kickham
Broad
ITT
Pryco
Magnetek
BorgWarner
Belimo
Bell & Gossett
Highland Tank
Marathon
Penn Separator Corp.
Thermoflo
General Electric
Siemens
Nelson
Pomeco OPW
Marathon Electric
Campus
Steam Grid
Motor
Valve 1
Absorption
Chiller
Radiant
Panel
Cool Wave
Feed
Water
Valve
Condensate
Pumps (2)
Motor (2)
Condensate
Receiver w/
Controller
Figure 4: CHP System Components
The engine generator is a standard engine generator assembled by Baldor Electric
Company shown in Figure 5. It uses a 43 hp (33kW) four cylinder, 2.4 L John Deere
Diesel Engine and a Stamford, Inc. generator. It includes a standard engine generator
controller made by Intelligen, Inc.
Figure 5: Baldor Engine Generator
39
The engine generator is connected to the grid via an ASCO 7000 automatic transfer
switch (ATS) and soft load controller (SLC) shown in Figure 6. The ATS/SLC allows the
engine generator system delivers excess power to the grid during operation, while
allowing the grid to power the mechanical room when the system is offline. The
operation of the ATS/SLC is fully automated, and once a power level is set and the start
command given, the engine generator is started and paralleled to the utility in less than
five seconds.
Figure 6: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kWe.
40
The steam generator made by Vaporphase, Inc. shown in Figure 7 is essentially a double
pass fire tube boiler without a burner. In lieu of a burner, the high temperature exhaust is
routed from the engine to the steam generator. The steam generator also acts as an
exhaust silencer, however the silencing effects are lost if the exhaust is bypassed;
therefore an extra muffler has been installed. Steam is generated at 87 psig (6 bar) in the
summer at 68 pounds per hour (31 kg/hr) for the absorption chiller and at 30 psig (2 bar)
and 65 pounds per hour (29 kg/hr) in the winter, spring, and fall for space heating the IW
and exporting the campus steam grid.
Figure 7: Assembled Components: Engine Generator (Left), Steam Generator (Right)
It should be noted that while there is about 18 kWt of heat recovered from the exhaust,
the system is greatly oversized and can handle up to 250 kWt of heat transfer. This unit
was selected because it is the smallest commercially available exhaust heat recovery
41
steam generator. A steam generator was required for this project as the absorption chiller
used in this project is steam driven. For new systems, direct firing of an absorption chiller
and high pressure hot water heat recovery can be considered to achieve space and cost
savings.
To deliver hot water to the IW, a steam – hot water converter is used that can use steam
from the steam generator or the campus grid. The converter is shown in Figure 8.
Figure 8: Steam - Hot Water Converter
The coolant heat exchanger shown in Figure 9 is a standard plate and frame heat
exchanger made by ITT, Inc. The heat exchanger operates in parallel with a standard
42
engine generator radiator, which has been removed and sits outside of the mechanical
room shown in Figure 10.
Figure 9: Coolant Heat Exchanger with Piping before Insulation
43
Figure 10: Remote Mounted Radiator
There are several control loops within this CHP system that allow for robust control of
the system while also assuring safe operations. The engine controller monitors status,
power level, oil pressure, coolant temperature and level, battery conditions, etc. on an
engine mounted interface shown Figures 10 and 11.
Figure 11: Engine Generator Onboard Interface
44
Figure 12: Engine Generator Onboard Interface
The Soft Load Controller (SLC) and the Automatic Transfer Switch (ATS) takes over
control of the governor in the engine, which was initially controlled by the Intelligen
controller to vary the speed to aid in paralleling the engine to the grid. The SLC/ATS
monitors the grid’s voltage and phase so that the generator output frequency, phase, and
voltage match the grid. The SLC/ATS monitors any disruptions in the grid or the engine
and protect either the grid or the generator from severe damage. If there is a failure the
ATS/SLC will separate the engine generator from the grid and will send a shutdown
order to the engine. The engine will continue to operate for five minutes powering lights,
ventilation, etc. so that occupants have enough time to vacate the lab. Then the engine
will go into its standard shutdown procedure, which includes a five minute cool down.
The steam generator has its own stand alone pneumatic control system that has three
principal tasks. First, it makes sure that the steam generator does not run dry as hot
exhaust gases can warp the coils if the heat is not dissipated. It can call for makeup water
45
based on the output of a low level alarm and if makeup water is not available, it will
bypass the exhaust around the steam generator.
The second task for the pneumatic controller is to maintain the set point pressure inside
the steam generator using a back pressure control valve. The steam pressure is measured
inside the steam generator and downstream from the back pressure valve. If the pressure
inside the steam generator drops below the set point, the back pressure control valve will
restrict the flow of steam until the pressure rises again. The purpose of this controller is to
prevent a sudden drop in steam pressure, which can cause the steam generator to implode.
The third task is to match heat input to the output steam flow. The exhaust gas flow to the
steam generator is modulated by the bypass control valve to maintain a set point pressure
of the output steam flow. This arrangement allows the steam generator to operate at
partial loads, while the engine operates at full power.
The control of the steam is accomplished through a series of two position valves and
pressure reduction valves. During the summer, two two-position valves block flow to the
grid/hot water converter and route the steam flow to the absorption chiller. During the
rest of the year the flow to the chiller is blocked and directed towards the grid and hot
water converter. A pressure reduction valve reduces the steam supply pressure to the hot
water converter to 9 psig (0.6 bar) and the steam from the grid is reduced to 7 psig (0.5
bar) with another pressure reduction valve. The steam from the CHP system is prioritized
over the steam from the grid because the 9 psig steam will prevent the 7 psig pressure
46
reduction valve from opening as the pressure on the outlet side is too high. If there is a
short fall of pressure from the CHP system, the steam grid will start to makeup the
difference once the pressure falls below 7 psig (0.5 bar). Schematics from the steam
system are shown in Appendix A.
The coolant system controller is designed to prevent the engine from over-heating. This is
accomplished by removing heat either through a plate and frame heat recovery exchanger
or a remotely mounted radiator with a fan. The coolant controller has two modulating
valves which allow the controller to proportion flows to control the amount of heat
removed. This arrangement allows the engine to operate at full power, while only
recovering a portion of the coolant energy. This controller is a part of the overall Webbased building automation system (BAS). The BAS operates the overall dispatch of the
CHP system and logs all of the sensor data. The previously mentioned controllers all
function together to allow the system to address varying thermal and electrical energy
demands.
3.1.2 Input / Output
The Inputs for this system include:

fuel (Diesel or biodiesel)

air (fresh air for combustion)

condensate

hot water return
47
The outputs for this system include:

electricity (208 V, 3 phase)

exhaust

steam

hot water

data (Modbus, 4-20mA, 0-5 V converted to BACNET and available on the web)
Data inputs and outputs from sensors and actuators in the heat recovery system are
compiled in the Automated Logic web based user interface shown in Figure 13.
Figure 13: Automated Logic CHP User Interface for the Heat Recovery/Rejection System
3.1.3 Operating Description and Results
The core of the biodiesel fueled engine generator with heat recovery is the engine
generator, which burns fuel in order to generate electricity which is sent to the grid, and
48
generates heat in the forms of high temperature exhaust at 160oC (360oF) and lower
temperature engine coolant at 90oC (190oF). The high temperature exhaust can be
rejected to atmosphere or recovered using a steam generator, which can generate steam at
varying pressure levels. The steam can be used to heat the IW in the winter or drive an
absorption chiller in the summer. Furthermore, the steam system is connected to a
campus grid system, which allows for excess steam to be exported to the grid. The
coolant energy is recovered through another heat exchanger to heat water or rejected
through a radiator. The hot water is used in the winter for space heating in the IW.
Tables 2 through 4 show the compiled commissioning and experimental results, from the
operation of the engine generator, the heat recovery systems (exhaust and coolant), and
the integration with the Intelligent Workplace and campus systems. The engine was
operated at various loads and conditions for over 400 hours as shown in Appendix B.
Summer CHP Diesel Results
Power Output
Fuel Input
Plant Power
Coolant Heat
Exhaust Heat
(kWe)
(kWc)
(kWe)
Recovered (kWt)
Recovered (kWt)
6
25
3
6
3
12
43
3
9
7
18
57
3
12
12
25
76
3
18
18
Table 2: Averaged Summer Diesel Commissioning and Experimental CHP Results
CHP
Efficiency
47%
59%
68%
76%
Winter CHP Diesel Results
Power Output
Fuel Input
Plant Power
Coolant Heat
Exhaust Heat
(kWe)
(kWc)
(kWe)
Recovered (kWt)
Recovered (kWt)
6
25
4
6
4
12
43
4
11
7
18
57
4
14
12
25
76
4
18
17
Table 3: Averaged Winter Diesel Commissioning and Experimental CHP Results
CHP
Efficiency
49%
61%
70%
74%
49
Winter CHP Biodiesel Results
Power Output
Fuel Input
Plant Power
Coolant Heat
(kWe)
(kWc)
(kWe)
Recovered (kWt)
6
26
4
8
12
42
4
10
18
59
4
14
25
76
4
18
Table 4: Averaged Winter Biodiesel Experimental Results
Exhaust Heat
Recovered (kWt)
4
9
13
18
CHP
Efficiency
54%
65%
68%
76%
The results shown in Tables 2 through 4 show average plant efficiency between 47% and
76%, consistent with typical CHP efficiencies. There is a substantial fall off in efficiency
as the power level drops, which indicates that the system operates more efficiently at full
load than part load. This is not surprising as engine efficiency usually peaks at about 80%
of the maximum engine rating, or 25 kWe of 33kWe. Furthermore, the power required to
operate pumps and fans, plant power, remains constant, and becomes a larger percentage
of the total power at the lower loads.
50
3.1.3.1 Engine: Measured Data versus Manufacturer’s Specifications
It has been difficult to precisely compare all of the engine’s specifications with the
measured data as the manufacturer’s specifications are written for operation at 32 kWe,
whereas the engine has been operated at part loads from 6 kWe to 25 kWe electrical.
Note, the specification column is written for the maximum engine rating of 32kWe using
No.2 low sulfur Diesel fuel.
System
Air System
Specification
Data
Notes
Max. temp. rise, amb. to inlet
15 F (8C)
~15 F
Varies due to room air temperature
Steady increase in flow rate with
power (6 kW = 64 CFM, 12kW = 68
CFM, 18kW = 74 CFM)
Engine Air Flow
99 CFM (2.8 m3/min)
83 CFM at 25 kWe
Intake Manifold Pressure
9 psig (64 kPa)
0.4psi (6kWe), 0.9psi (12kWe), 1.6psi (18kWe), 2.3psi (25kWe)
Total Fuel Flow
185 lb/hr (84 kg/hr)
NA
Fuel Consumption (6 kWe)
4.7 lb/hr (2.1 kg/hr)
4.6 lb/hr (2.1 kg/hr)
Fuel Consumption (12 kWe)
7.0 lb/hr (3.2 kg/hr)
7.9 lb/hr (3.6 kg/hr)
Fuel Consumption (18 kWe)
9.8 lb/hr (4.4 kg/hr)
Fuel Consumption (25 kWe)
13.3 lb/hr (6.1 kg/hr)
Fuel Consumption (32 kWb)
17.9 lb/hr (8.1 kg/hr)
NA
Engine Heat Rejection
1303 BTU/min (23
kW)
18 kW at 25 kWe
Coolant Flow
24 GPM (91 L/min)
10.2 GPM
Thermostatic Valve start to
open
185 F (82 C)
Verified by comparing start of coolant
flow and coolant temperature
Thermostatic Valve fully open
201 F (94 C)
Verified by comparing by observing
steady flow above 201 F
Fuel System
10.6 lb/hr (4.8
kg/hr)
14.1 lb/hr (6.4
kg/hr)
The individual fuel flow meters do not
provide independent outputs.
Verified with weigh tank
measurement
Verified with weigh tank
measurement
Verified with weigh tank
measurement
Verified with weigh tank
measurement
Soft load controller will allow a
maximum power of 25 kW
Cooling System
Spec assumes radiator attached to
engine
Exhaust
Exhaust Temperature
963 F (517 C)
930 F (499 C) at 25
kWe
Max allowable back pressure
30 in-H2O (7.5 kPa)
14 in-H2O at 25
kWe
Used a pressure gauge mounted
between the engine exhaust and
steam generator
Table 5: Diesel Engine Generator Measured Data vs. Manufacturer Specifications
51
Table 5 shows that the measured data corresponds well to the manufacturer’s
specifications; however, there is a small margin of error. This margin of error probably
comes from minor differences between engines during manufacturing and the sensors
used by the manufacturer and the IWESS team during testing. Table 6 shows similar
results to Table 5 for biodiesel fuel.
System
Air System
Max. temp. rise,
amb. to inlet
Engine Air Flow
Intake Manifold
Pressure
Fuel System
Total Fuel Flow
Fuel Consumption
(6 kW)
Fuel Consumption
(12 kW)
Fuel Consumption
(18 kW)
Fuel Consumption
(25 kW)
Fuel Consumption
(32 kW)
Cooling System
Engine Heat
Rejection
Coolant Flow
Thermostatic Valve
start to open
Thermostatic Valve
fully open
Exhaust
Exhaust
Temperature
Max allowable back
pressure
Specification
Data
Notes
15 F (8C)
99 CFM (2.8
m3/min)
79 CFM at 25
kWe
Steady increase in flow rate with power (6 kW = 64
CFM, 12kW = 68 CFM, 18kW = 74 CFM)
9 psig (64 kPa)
1.7psi (6kWe), 2.15psi (12kWe), 2.84psi (18kWe), 3.67psi (25kWe)
185 lb/hr (84 kg/hr)
No Measurement Available
4.7 lb/hr (2.1 kg/hr)
Verified with weigh tank measurement
7.0 lb/hr (3.2 kg/hr)
9.8 lb/hr (4.4 kg/hr)
13.3 lb/hr (6.1
kg/hr)
17.9 lb/hr (8.1
kg/hr)
1303 BTU/min (23
kW)
24 GPM (91 L/min)
8.8 lb/hr (4.0
kg/hr)
12.6 lb/hr (5.7
kg/hr)
16.1 lb/hr (7.3
kg/hr)
NA
Verified with weigh tank measurement
Verified with weigh tank measurement
Verified with weigh tank measurement
Soft load controller will allow a maximum power of
25 kW
16 kW at 25 kWe
10.2 GPM
Spec assumes radiator attached to engine
185 F (82 C)
Verified by comparing start of coolant flow and
coolant temperature
201 F (94 C)
Verified by comparing by observing steady flow
above 201 F
963 F (517 C)
890 F (477 C) at
25 kWe
Biodiesel experiments only conducted during winter
at this time, may cause low temp.
30 in-H2O (7.5
kPa)
14 in-H2O at 25
kWe
Used a pressure gauge mounted between the
engine exhaust and steam generator
Table 6: Biodiesel Engine Generator Data vs. Manufacturer Specifications
As shown in Tables 5 and 6, the primary difference between Diesel fuel and biodiesel
fuel is that the fuel flow rate is greater for biodiesel fuel. The reason for this is that the
energy density of biodiesel is lower than Diesel fuel, thus the engine controller naturally
52
increases the fuel demand to meet power demand. As the engine operates below its
maximum, prime power operation, the fuel pump has no problem meeting this challenge.
3.1.3.1 Pressure – Time – Crank Angle Measurements
Pressure sensors have been installed in each engine cylinder to obtain information on
how the combustion process changes when using different fuels. In combination with a
crank angle encoder, the pressure measurements are collected using a high speed data
acquisition system, and plotted as shown in Figure 14.
Figure 14: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
53
Figure 14 shows the pressure vs. crank angle curve, and shows injection combustion
taking place around top dead center (TDC).
Figure 15: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
As can be observed in Figure 15, the wave forms shifts from injection and combustion at
TDC to a delayed combustion of about 15 degrees after TDC. The effect of a delayed
combustion is that the peak combustion temperature is reduced. The purpose of reducing
the peak temperature is to reduce NOX formation to meet U.S. Environmental Protection
Agency regulations. An additional effect of this control strategy is the reduction of engine
capacity and efficiency. Further analysis on these wave forms is under way to compare
the performance of the various fuels.
54
3.1.3.2 Turbocharger Analysis
The engine’s turbocharger was completely instrumented with temperature, pressure and
flow sensors. The data collected from the turbocharger indicates a mass flow rate of
0.053 kg/sec and a maximum compression ratio of 1.25 at 25kWe. These data are plotted
in Figure 16, the compressor map provided in by the turbocharger manufacturer. They
show that this turbocharger is not suited for this engine operating under the specified
conditions.
Figure 16: Turbocharger Compressor Map [27]
It should be noted, that while the turbocharger is not effective for the duty cycle of this
engine, it may operate more efficiently at 33 kWe, the power level for which the
55
turbocharger was designed. CHP system designers should be aware of this fact and
request a turbocharger that will operate more efficiently in the appropriate range.
3.1.3.3 Combustion Gas and Emissions Analysis
Emissions of gas-phase pollutants [carbon dioxide (CO2), carbon monoxide (CO),
nitrogen dioxide (NO2), nitrogen oxide (NO), unburned hydrocarbons (UHC), and
oxygen (O2)] have been measured over four loads using both low sulfur Diesel fuel and
soy based biodiesel fuel.
Load
(kWe)
6
12
18
25
%
O2
16.1
13.9
11.6
9.6
%
CO
0.0
0.1
0.1
0.1
%
CO2
3.7
5.2
6.8
8.2
UHC
(PPM)
4
9
11
12
NO
(PPM)
251
424
466
502
NO2
(PPM)
4
6
5
4
Table 7: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel
Load
(kWe)
6
12
18
25
%
O2
16.3
13.9
11.5
9.7
%
CO
0.0
0.0
0.0
0.0
%
CO2
3.8
5.4
7.1
8.4
UHC
(PPM)
0
1
2
3
NO
(PPM)
224
357
450
498
NO2
(PPM)
5
8
10
9
Table 8: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel
The data in Tables 7 and 8 agree with published results [28, 29, 30] with significant
reductions in CO, and UHC. However, typically soy based biodiesel generates more NOX,
and the averaged data does not reflect that. The NOX emissions for this engine are
reduced due to the engine timing adjustments to meet emissions requirements, which may
account for the similar levels of NOX. Further research into the emissions is warranted if
56
large scale use of biodiesel in CHP systems is to be achieved as emissions must be
understood to meet EPA regulations.
A combustion analysis has been conducted for the engine generator operating at 25 kWe
using Diesel fuel.
The stoichiometric material balance for Diesel fuel.
C12 H 23  aO2  3.76 N 2   bCO2  cH 2O  dN 2
C: 12 = b(1)
b = 12
H: 23 = c(2)
c = 11.5
O: a(2) = b(2) + c(1)
2a = 2x12 + 11.5 = 35.5
a = 17.75
N: a(3.76)(2) = d(2)
d = 66.7
C12 H 23  17.75O2  3.76 N 2   12CO2  11.5H 2O  66.7 N 2
Determine the molar air to fuel ratio.
AFR 
moles _ O2  moles _ N 2 17.75  17.753.76

 84.5
mole _ Fuel
1
Determine quantity of excess air.
57

AFRMeasured 
m air


m fuel
165kg / hr
 25.8
6.4kg / hr
 MWFuel 
167
  25.8 
AFR Measured  AFRMeasured 
 148.6
29
 MW Air 
moles _ O2  moles _ N 2 17.75  17.753.76
AFR 

 84.5
mole _ Fuel
1
EA 
AFR Measured 148.6

 1.76
84.5
AFR
The material balance
C12 H 23  1.7617.75O2  3.76 N 2   aCO2  bH 2O  cN 2  dO2
C: 12 = a(1)
a = 12
H: 23 = b(2)
b = 11.5
O: 1.76 x 17.75 x 2 = a(2) + b(1) + d(2)
62.5 = 2a + b + 2d
62.5 = 24 + 11.5 + 2d
27 = 2d
d = 13.5
N: 1.76 x 17.75 x 3.76 x 2 = c(2)
235 = 2c
c = 117.5
C12 H 23  31.2O2  3.76 N 2   12CO2  11.5H 2O  117.5N 2  13.5O2
The percentage of the emissions on a molar basis of O2 and CO2 and compare to the
results in Table 7 on a dry basis.
Calculated Percentage of CO2 = 8.4%
Calculated Percentage of O2 = 9.4%
58
Both the CO2 and O2 emissions are consistent with the measured data in Table 7.
The heat release from the engine has been calculated.


Q
W



nf
 hP  hR
nf











o
o
o
o


h P  n CO 2 h f   h CO 2  n H 2O h f   h H 2O  n N 2 h f   h N 2  nO 2 h f   h O 2 










o
o
o


h R  n f h f   h f  n N 2 h f   h N 2  nO 2 h f   h O 2 


The number of moles shown below and the necessary enthalpy values with the units of
kJ/kg-mol
C12 H 23  31.2O2  3.76 N 2   12CO2  11.5H 2O  117.5N 2  13.5O2
12 393,520  31,154  9,364CO 2  11.5 241,820  27,125  9,904H 2O  
hP  

117.50  23,085  8,669N 2  13.50  23,850  8,682O 2

h P  12 371,730CO 2  11.5 224,599H 2O  117.514,416N 2  13.515,168O 2 
h P   4,460,760  2,582,888.5  1,693,880  204,768
h P  5,145,000.5kJ / kg  mol 

h R  1 7,014,000  0  f  117.50  0 N 2  31.20  0 O 2

h R  7,014,000kJ / kg  mol 
59
 kg 
6.4 
mf
 kg  mol 
 kg  mol 
 hr 
nf 

 0.0383
 1.065 105 

MW f
 kg 
 hr 
 sec 
167 

 kg  mol 




W
W Electric
Generator


Q
W



nf


25kWe
 kJ 
 28.4 
0.88
 sec 
 hP  hR
nf



Q  W  n f hP  hR


 kJ 
 kg  mol 
 5,145,000.5  7,014,000 kJ 
Q  28.4   1.065  10 5 

 sec 
 sec 
 kg  mol 

 kJ 
 kJ 
 kg  mol 


Q  28.4   1.065  10 5 
1
,
868
,
999
.
5
 kg  mol 
 sec 
 sec 



 kJ 
 kJ 
Q  28.4   19.9  
 sec 
 sec 

 kJ 
Q  48.3   48.3kWt
 sec 
The amount of heat captured by the heat recovery system is approximately 36 kWt from
Tables 2, 3, and 4, which leaves about 12 kWt for radiant and convective losses to the
space from the engine and losses in the pipes and heat exchangers, which is realistic.
3.1.3.4 Heat Recovery Analysis
The steam generator and the coolant heat exchanger have been analyzed using
temperature – heat transfer or T-Q diagrams. T-Q diagrams are an effective way of
describing the operation of heat exchangers by showing the stream temperatures versus
60
heat transfer between them. The required area for heat transfer between the streams, A,
can be calculated from the following function:
A
dq
,
U T
where
U = heat transfer coefficient,
dq = heat transfer,
T = temperature difference between the two streams
Steam Generate T-Q Diagram
1000
900
Temperature (oF)
800
700
Exhaust at 25 kWe
600
500
Exhaust at 6 kWe
400
Saturated Steam
(87psig)
300
Condensate
200
Domestic Hot
Water
100
0
0
5
10
15
Heat Transfer (kWt)
20
25
Figure 17: Summer Operation of the Steam Generator T-Q Diagram
Figure 17 shows the T-Q diagram for the steam generator during summer operation with
exhaust entering on the left at a high temperature. The heat in the exhaust is transferred to
the water inside the steam generator, which evaporates at a rate of 65 lbs/hr (28 kg/hr) at
61
87 psig (6 bar) or 18 kWt. This steam generator uses a pool of water, which is directly
replenished rather than preheating make up condensate, however condensate entering at
212oF (100oC) could be preheated. As shown on the right side of the T-Q diagram,
additional energy is available from the exhaust which leaves the steam generator at
approximately 360oF (160oC). Domestic Hot water is typically delivered at 140oF (60oC),
and is supplied from city water at 50oF (10oC). Recovering additional heat from the
exhaust (8 kWt) to heat domestic hot water represents approximately a 40% increase in
the heat recovery potential, and would increase the CHP efficiency from 78% to 87%.
However, the downside of reducing the exhaust temperature down to below 100oC is that
the moisture in the exhaust will condense, which can form rust in the exhaust pipes.
Therefore, it is necessary to build these sections out of stainless steel.
Additionally, Figure 17 shows the operation of the steam generator when the engine
generator is operating at 6 kWe. The effect of operating at lower loads is that the exhaust
temperature and flow rate are lower, thus reducing steam production.
Figure 18 shows the T-Q diagram for the coolant heat exchanger during both summer and
winter operation. Using engine coolant heat to heat the water used for space heating in
the winter is somewhat problematic as the required temperatures are relatively low,
which forces the temperature of the engine coolant to the relatively low temperature of
185oF, where as an ideal temperature would be about 195oF as shown in Figure 18.
During winter operation the water side of the exchanger typical has a flow rate of four
gallons per minute with an inlet temperature of 95oF and an outlet temperature of 110oF.
62
During the summer, a higher temperature is desired for the regeneration of a solid
desiccant, and therefore a higher over all temperature is maintained.
Coolant Heat Exchanger T-Q Diagram at 25kWe
210
Temperature (oF)
Coolant (12 GPM)
190
Summer Operation
Water (12 GPM)
170
150
130
Coolant (2 GPM)
110
Water (4 GPM)
Winter Operation
90
0
5
10
Heat Transfer (kWt)
15
20
Figure 18: T-Q Diagram for Coolant Heat Exchanger at 25 kWe
To remedy the relatively low coolant operating temperatures during the winter, two
options exist. First, the water flow rate could be further reduced with an improved control
system, which would shift the winter operation water line up to a higher temperature. The
second, option is to bypass some of the water around the coolant heat exchanger
essentially reducing the flow. The two flows would then be mixed and the desired
temperature achieved.
3.1.4 Systems Integration Potential
The CHP system is made up of dozens of components, which include four primary
control systems:
63

engine generator

automatic transfer switch / soft load controller

coolant heat recovery

steam generator
As this system was assembled from disparate components resolving communications
compatibility issues cost a lot of time and money. Integrating these controllers would
reduce installation time and cost. Furthermore, it would simplify the operation of the
CHP system as each controller has its own user interface.
The heat recovery system captures reject heat from the engine and converts it to steam
and hot water via to heat exchangers. The steam could be used in a double effect
absorption chiller to provide cooling during the summer to a building. The steam
generator in this CHP system provides saturated steam at 87 psig (6 bar) and 360oF
(160oC), therefore the exhaust temperature is approximately 370oF (165oC). The
remaining exhaust heat could be used to make domestic hot water at 140oF (60oC) or
drive a single effect absorption chiller.
The coolant energy could be used to drive the desiccant regeneration process of the
ventilation system, which is necessary to provide dehumidified air to the IW.
Alternatively, the coolant energy could be used to drive a single effect absorption chiller
to provide additional cooling.
64
3.2 Steam Driven Double Effect Absorption Chiller
Drs. Hongxi Yin and Ming Qu have both completed dissertations on the steam driven
double effect absorption chiller and the solar thermal high pressure hot water driven
double effect absorption chiller respectively. Each dissertation includes extensive
descriptions of both their components and operation. These chillers were selected as
models for this dissertation as they have both been previously tested and analyzed, both
are on site to allow visual inspection, and both are very compact designs as compared to
other manufacturer’s models. The chillers are nearly identical except for the high
temperature generator as one is designed for steam and the other is designed for high
pressure hot water. Furthermore, the high pressure hot water unit includes an auxiliary
natural gas burner.
3.2.1 System Components
Figure 19 shows a complete cross section of the absorption chiller including the inputs
and outputs of the system. The auxiliary equipment originally installed with this system
will not be included as it was replaced by the CHP system.
65
Figure 19: Steam Driven Absorption Chiller Flow Diagram [31]
This packaged system includes; the absorption chiller, cooling tower, control system,
pumps, valves, and sensors. The same concept of creating a packaged system out of the
chiller components is applied in packaging the biodiesel CHP system, absorption chiller,
and ventilation unit.
3.2.2 Input / Output
The Inputs for this system include:

High pressure steam

Chilled water return

Electricity to operate pumps, fan, control system, etc.

Treated water (for the cooling tower)
The outputs for this system include:

Chilled water supply
66

Water vapor (from cooling tower)

Condensate

Data 1 (Internal control system with separate display)

Data 2 (4-20mA and 0-5 V converted to BACNET and available on the web)
Absorption
Chiller
SS
Finally, extensive information exists
on the instrumentation used to operate and monitor
ESB
WS
BFP
BFT
Absorption
Chiller
the absorption
chiller as shown in Figure 20.
This information will be helpful in
CTW
CR
determining which points are necessary for operation.
ALC control panel
9
10
Cable
Cable
Hot Humid Air
T10
Controller
ME-LGR 25
8
T16
T15
L3
T17 T18
SS
T14
T7
P4 T22 F2
P7 T25
1
P5
WS
T11
T8
T23
T5
Condensate
CWBPV
ESB
BFP
BFT
T19
T13
Absorption
Chiller
F7 T29 P11
CTW
T28 P10
T21 P3
CHWS
T9
T2
3
TLHX
HWS
L2
HWR
CHWS
Campus
4
6
T0
H0
CHWR
Chiller control panel
CR
CHWS
5Building
HWR
Steam Supply
F6
2
CHWR
F6
L1
P1
SV
DV
T6
HWS
DD
RBPV
L4
L5
RP
RPH
T30
P2 T20 F1
B1
T1
B2
CHWR
SP
T3
CTV
T
CHWP
T12
CWP
Chiller
inputs
Chiller
outputs
ALC inputs
ALC
outputs
Timing water Empty
F8
City water
Air
CWV
7
City water
Figure 20: Absorption Chiller Process and Instrumentation Diagram [31]
B
PCHWP
HWR
SS
CHWS
ESB
CCL
BFP
Figure 21
user interface screens for the absorption chiller system.
WSshows one
BFTof the
Absorption
Chiller
CTW
TLHX
CR
HWS
BCL
A
CHWR
67
Figure 21: Automated Logic Absorption Chiller User Interface
The chiller is a very compact unit with a width of 1,143 mm (45 inches) a depth of 660
mm (26 inches) and a height of 1,829 mm (76 inches). The unit does include onboard
controls; however a separate panel is required for running auxiliary equipment. Much of
this auxiliary equipment is not necessary when the unit operates in a CHP mode, and was
only necessary during the stand alone testing phase of the project.
3.2.3 Operating Description and Results
As shown in Table 9, the test program used by Dr. Yin varies five operational parameters
and measures and calculates the effect on the chillers performance and capacity.
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Table 9: Absorption Chiller Test Program and Results [31]
The data in Table 9 provides the necessary information for creating an empirical
operating model of the chiller, which can be integrated with the output of the steam
generator from the CHP system.
Figure 22 provides insight into the operation of the absorption chiller and shows how
each component within the packaged absorption chiller operates versus cooling load.
Heat transfer on chiller component (kW) .
32
Cooling tower
28
24
Absorber
20
Evaporator
16
HTRG
LTRG
12
HTHX
8
Condenser
4
LTHX
0
HRHX
BPHX
0
2
Cooling tower
LTRG
HRHX
4
Absorber
Condenser
BPHX
6
8
Evaporator
HTHX
10
12
HTRG
LTHX
14
16
18
20
Actual cooling load (kW)
Figure 22: Absorption Chiller Component Heat Transfers vs. Cooling Load [31]
69
The evaporator is where the cooling takes place and the primary heat input is into the
high temperature regenerator (HTRG). The cooling tower shows how much heat is
rejected to atmosphere and how much can be captured. These pieces of data further refine
the simulation model and provide insight into what quantity of energy is required to
operate the chiller, and how much energy is produced and rejected.
3.2.4 Systems Integration Potential
Opportunities for improving the chiller system include integration of controls and
recovering cooling tower heat. The control system requires several operational inputs that
are also required for the heat recovery system which could be shared. Furthermore, a
common control system would simplify writing control algorithms for automatic startup,
operation and shutdown.
As can be seen in Figure 22 about 28 kWt of low quality thermal energy is available at
around 35oC (96oF) from the cooling tower, which would be sufficient for preheating
domestic hot water during the summer as city water typically arrives at 13oC (55oF).
Using a heat exchanger rather than a cooling tower would most likely save on first cost as
well as operating costs as removing heat using a pump versus a fan is more efficient [32].
Finally, removing the cooling tower would also save on operating costs for cooling tower
water and chemicals to treat the cooling tower water that is evaporated.
70
3.3 Ventilation System with Enthalpy Recovery and Solid
Desiccant Dehumidification
The ventilation system in the IW has operated for several years and employs both a
passive enthalpy recovery wheel and an active desiccant dehumidification wheel to
condition the air, as well as a heat pump for providing the required heating or cooling
loads of the ventilation air. In her dissertation work at CMU, Dr. Chaoqin Zhai operated
this piece of equipment and focused her work on the performance modeling of the
desiccant wheel and its operation.
3.3.1 System Components
The ventilation unit itself is an example of systems integration. The unit includes a fan
for air handling, two energy wheels (one active, one passive), and a heat pump for
primary heating and cooling. These subsystems are all operated by a single controller and
are packaged by one company. The acceptance of these systems would be greatly reduced
if building operators had to assemble them on site. Instead, the unit arrives on a single
skid and only requires power, gas, and duct connections to operate.
Figure 23: Plan View of Ventilation Unit [33]
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The ventilation unit is also very compact. All of the components are placed inside with an
overall width of 1,753 mm (69 inches) a depth of 737 mm (29 inches) and a height of 991
mm (39 inches). The integrated and packaged enthalpy recovery wheel, desiccant wheel,
heat pump, and necessary controls needed to make this system work serve as an example
for a systematic integration of the three IWESS components.
3.3.2 Input / Output
The Inputs for this system include:

electricity to operate fans, wheels and control system (208 V, 3 phase)

outside air for ventilation, desiccant regeneration, and heat pump operation

return air (from conditioned space)

natural gas (for desiccant regeneration)
The outputs for this system include:

dehumidified ventilation air

exhaust (from desiccant regeneration)

exhaust air (from the heat pump)

exhaust air (from the space)

data (4-20mA and 0-5 V converted to BACNET and available on the web)
While the same user interface capability exists for the ventilation system, there is no
graphical interface like the CHP and chiller systems have in Figures 13 and 21.
72
3.3.3 Operating Description and Results
Figures 24 through 26 describe how the components of the ventilation system operate and
how they affect each other.
Figure 24: Interior View of the Ventilation Unit [33]
Figure 24 shows the operation of the ventilation unit.
1. Outside air enters the unit (and mixes optional return air).
2. The outside air passes through the passive energy recovery wheel.
3. The air goes through a DX coil for cooling and moisture removal.
4. Part of the air passes through an active desiccant and is warmed and dehumidified
by the desiccant wheel.
5. The warmer, drier air is mixed with the cool bypassed air and sent to the space at
the set point humidity and temperature.
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6. A separate outside air stream (regeneration air) is heated by a gas burner to
regenerate the desiccant in the desiccant wheel, and is then rejected to atmosphere.
The flow diagram shown in Figure 25 provides additional insight into how the ventilation
system operates.
Figure 25: Ventilation Unit Flow Diagram [33]
Figure 26: Psychrometric Chart for Ventilation System Operation [33]
Figures 27 through 29 were developed to show the cost and benefit of operating the
ventilation system.
74
Figure 27: Enthalpy Removal Breakdown by Component [33]
Figure 27 shows that the majority of the sensible heat removal is handled by the heat
pump and then followed by the enthalpy recovery module. Nearly zero enthalpy is
removed by the desiccant wheel, which makes sense as the moisture is removed by an
adiabatic process and the temperature increases as shown in Figure 26.
Figure 28 shows that the moisture removal by the active desiccant does account for 52%
of the total moisture removal. Some moisture is removed at the heat pump by the DX coil
due to condensation, and the remainder is transferred to the exhaust air as it picks up
moisture from the enthalpy recovery module.
Figure 28: Moisture Removal Breakdown by Component [33]
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Finally, Figure 29 shows that the active desiccant module has the highest operating cost
mainly due to the high cost of natural gas. Therefore, if reject heat were used to
regenerate the desiccant rather than burning natural gas, the operating cost of ventilation
system would decrease by approximately half. This represents a major opportunity for
using reject heat from the CHP system.
Figure 29: Operating Cost Breakdown by Component [33]
The following has been quoted directly from Dr. Zhai’s thesis justifying the feasibility of
integrating the ventilation system with the CHP system.
“A procedure has been outlined to develop operating strategies for the active
desiccant wheel integrated CHP system. The validated performance model has
been applied in predicting the supply air conditions from the integrated system
under different settings of the control variables. Performance maps that relate the
supply air conditions and different settings of the control variables have been
constructed for the proposed system in the IWESS project. These performance
maps show that the desired supply air condition can be achieved with certain
settings of the control variables, namely the regeneration air temperature, the
regeneration air flow rate, the leaving DX air condition, the wheel rotation speed,
and the bypass ratio. The settings of the control variables to achieve the desired
supply air condition are not unique. It is an optimization problem to determine the
control settings to achieve the lowest system operating energy consumption or
cost, in which the system operating energy consumption or cost is the objective
function, and different control factors are the variables.” [33]
76
The detailed controls of this process are outside the scope of this dissertation; however,
the plumbing, sensor inputs and outputs, and heat transfer calculations will be conducted
to facilitate the integration.
3.3.4 Systems Integration Potential
The desiccant wheel requires a large thermal input, currently in the form of natural gas
combustion, to regenerate the desiccant wheel, which has become saturated from
incoming air. The operation of the desiccant wheel contributes about 62% of the total
operating cost of the ventilation system including the heat pump and the enthalpy
recovery wheel [19]. In lieu of burning natural gas, it has been proposed to use coolant
energy from the engine generator to regenerate the desiccant. This would reduce the
operating costs by about 62%, as the reject coolant heat from the engine would be free
minus the pumping power required to move the thermal energy from the coolant heat
exchanger to the air to water heat exchanger mounted in the ventilation unit.
The setup in the IW would not be ideal as there would be several hundred feet of piping
required to move the heat from the engine to ventilation unit. This would be another
reason for creating a compact packaged unit that would cut down on the overall piping
length.
The control systems could also be integrated to reduce cost and simplify operation. It so
happens that the manufacturer for the ventilation controls is the same as the manufacturer
for the supervisory controls and the ATS/SLC controls. A few sensors (two temperatures
77
and water flow) could be shared between the control system on the engine coolant side
and the regeneration heat exchanger to reduce some first cost as well.
Perhaps the largest first cost saving in creating an integrated CCHP/V package would be
the replacement of the heat pump by a heated and chilled water coil as is also suggested
by Dr. Zhai [33]. Detailed costs are not available at this time, but it is reasonable to
assume that the first cost of a heating and a cooling coil, a control valve and a pump are
much cheaper than an entire heat pump. Furthermore, there would also be operating cost
reductions, as running a pump for the heating and cooling coils would be cheaper than
operating the compressor in the heat pump.
78
4.0 Preliminary Design Guide
This section has two parts: a generic guide for the preliminary design of a cogeneration
system that provides power, cooling, heating, and ventilation to a building and a specific
example based on the biodiesel fueled CHP system designed, installed, operated and
evaluated at Carnegie Mellon University. The design process is iterative; however seven
steps in sequence are recommended. Throughout the design process engineers should be
aware of local code requirements as they affect decisions.
4.1 Generic Design Steps
The general procedure for designing a CHP system is to:
1. determine the electrical and thermal loads, load profiles and the required flow
rates and temperatures of cooling and heating streams.
2. determine which fuel types are locally available, how they are distributed, and
their cost.
3. determine what energy grids are available, what their operating conditions and
costs are, and if it is possible to interface with them.
4. select a prime mover that best fits the load profile and load proportions.
5. select auxiliary and heat recovery equipment to match the prime mover and the
fluids used to transfer energy.
6. choose an operating strategy (thermal or electrical load follow, base load
operation, etc.)
7. evaluate the options on a capital, operating, and environmental cost basis.
79
As these seven steps are carried out the following documents should be created:
1. flow diagram,
2. material and energy balances,
3. equipment descriptions,
4. operating descriptions,
5. process and instrumentation diagram,
6. preliminary layout, and
7. cost estimates for equipment
These documents provide the basis for equipment procurement, detailed design,
installation, and operation.
4.1.1 Loads
The first task is to identify the energy loads for the CHP system. These include, but are
not limited to: electrical (lighting, pumps, fans, computers, etc.), space cooling and
heating, ventilation, dehumidification, and process energy. Lawrence Berkley National
Labs (LBNL) publishes generic annual load values for U.S. buildings on a square foot
basis shown in Table 10 [6].
U.S. Commercial Office Building Energy Intensity (kBTU/ft2-year)
Space
Water
Office
Cooling Cooking Ventilation Lighting Refrigeration
Heating
Heating
Equipment
33.2
11.0
11.4*
1.4
6.1
18.9
0.3
11.1
*Electrical energy for operation of a vapor compression chiller.
Other
7.8
Table 10: Typical U.S. Commercial Building Loads
80
Table 10 shows thermal and electrical loads assuming average furnace and chiller
efficiencies of 80% and COP = 3.2 respectively. The cooking load is not specified as an
electrical or thermal load in the LBNL report. Ventilation energy is assumed to be for a
forced air system that delivers the heating, cooling, and fresh air. The information in
Table 10 gives annual energy demands; however, to properly size and evaluate a CHP
system, peak and base loads and annual hourly load profiles are required.
The full table with IWESS systems applied is shown in Appendix C, which shows the
steps necessary for transforming the average load data for electricity, heating, cooling,
and ventilation into a form for the IWESS systems. These values along with a
conditioned square footage of a building will provide annual total loads for many
building types.
Hourly load data can come from metered data or from building energy simulations.
Simulation data should be used carefully and it is reasonable to add a safety factor of 1.1
when sizing the system, however metered data is best. Over sizing systems will lead to
inefficiency, but reality dictates that metered data are not always readily available. When
analyzing hourly data it important to find the peak (maximum) and base (minimum)
electrical and thermal loads. Details about these loads such as voltage, temperatures, flow
rates, and pressures should be determined as appropriate.
4.1.2 Fuel Selection
There are many fuels available for the operation of CHP systems including: natural gas,
petroleum products (gasoline, Diesel, etc.), biomass (biogas, biodiesel, ethanol, solids),
81
coal, and waste fuels (waste coal, garbage, etc.). Many of these fuels are associated with a
particular type of prime mover. They vary in energy content, cost, availability, and
emissions. The CHP system designer must determine what options are available based on
this list of criteria and tabulate them to assist in the selection of a prime mover, and in the
estimation of the operating costs of the system.
4.1.3 Energy Grids
The availability of energy is an important consideration in the design of a CHP system
for a building. Energy grids can come in many forms; electrical, natural gas, chilled water,
steam, heated water, compressed air, etc. The most common energy grid is the electric
utility grid. The interface with the electric utility grid must be coordinated with the local
electric utility, which will have individual requirements governing the operation of CHP
systems, which will detail voltages, power quality requirements, and cost structures for
providing and accepting power. Larger systems may be required to generate a certain
amount of power.
Thermal grids (steam, chilled water, etc.) are operated by some large utilities or by
smaller private entities. Similar to the electric utility grid, CHP system designers must
contact the grid operators to determine if it is possible to interface with the grids. Typical
performance requirements for interfacing with thermal grids include; temperatures,
pressures, and flows. Furthermore, these temperatures, pressures, and flows may change
throughout the year as thermal demands change throughout the year.
82
The ultimate goal of interfacing with energy grids is to have a source and sink for all the
forms of energy generated by the CHP system and needed by the facility. Many types of
commercial buildings have varying loads throughout the year, whereas CHP systems
operate most efficiently at steady state. Energy grids provide level load profiles for
buildings so that the CHP system can operate independently of the local building loads.
Also, importantly the energy grid can act as a back up in case of a plant failure.
4.1.4 Prime Movers
The fourth step is to select a prime mover that will provide sufficient thermal and/or
electrical energy at the proper conditions. Table 11 lists the prime movers most
frequently considered for CHP systems in buildings along with some of their
performance characteristics. Based on the building load profiles and the fuel data one or
more prime movers will emerge as the best fit for a particular application. As previously
stated, the design process is iterative. Therefore, some prime mover options may be
eliminated in subsequent steps.
Prime Mover
Boiler + Steam
Turbine
Gas Turbine
IC Engine
-Diesel
Fuels
Nat. gas, coal, waste
fuels, biomass
Natural gas, biogas
Diesel, biodiesel
Gasoline, E85,
natural gas
Electrical
Efficiency
10 - 15 %
15 - 25 %
30 - 40 %
-Spark
20 - 30 %
Fuel Cell
-SOFC
Natural gas
35 - 45 %
-PEM
Hydrogen
35 - 45 %
Table 11: Prime Mover Performance Summary
Recoverable Heat
45 - 65 % low quality
steam
45 - 55 % 600oF exhaust
15 - 20 % 190oF coolant,
15 - 20 % 900oF exhaust
15 - 30 % 190oF coolant,
15 - 20 % 900oF exhaust
25 - 35 % 500oF exhaust
25 - 35 % 300oF exhaust
CHP
Efficiency
Heat to
Power
Ratio
65 - 80 %
60 - 80 %
4.3
2.8
60 - 80 %
1.6
50 - 80 %
2.0
60 - 80 %
60 - 80 %
0.8
0.8
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4.1.5 Auxiliary and Heat Recovery Equipment
The fifth step in the design process is to select auxiliary heat recovery equipment that
uses exhaust, coolant or steam to meet the desired loads. This equipment may include:

heat exchangers

absorption chillers (single and double effect)

dehumidifiers

thermal storage arrangements
Section 2.5 discusses the temperature and medium of these thermal outputs with respect
to engine type. There are several ways of transferring heat and there are several types of
heat exchangers that are tailored to particular mediums and applications. An important
tool in selecting and designing equipment for recovery and utilization of thermal energy,
heat, in CHP systems is the T-Q diagram as shown in Figures 16 and 17. T-Q diagrams
should be constructed for each exchange of thermal energy in the system. It may be
necessary to contact several manufacturers to determine the best match for the selected
prime mover and fuel. An effective method for determining if a heat exchanger will meet
the design requirements is using a T-Q diagram, and plotting the inlet and outlet
temperatures versus the heat transfer.
At this point, it is possible to start to develop a preliminary flow diagram so that the CHP
system designer can get an over view of the options thus far. There may be multiple flow
diagrams at this point as a single prime mover and fuel may not have been selected yet,
but there is sufficient information to get started. The preliminary flow diagrams allow the
84
designer to visualize what forms of energy are available and what the loads are. As
information becomes available and decisions are made in subsequent steps, the flow
diagram is revised. Furthermore, it is prudent to develop multiple designs in parallel
using different components and eliminating options as details become available.
4.1.6 Operating Strategy
The sixth step in designing a CHP system is determining an operating strategy. There are
many options available to engineers but they primarily include:

steady state operation at either the peak or base, minimum, loads of the system

thermal or electrical load following operation
Load following may be based on a thermal or electrical load and partially depends on the
available auxiliary equipment and grid types. Electrical load follow is a mandatory
operating method unless battery storage or a grid interconnection exists as more
electricity can not be generated than is consumed, stored or dissipated. Both battery
storage and grid interconnection may be expensive, yet they allow the CHP system to
operate much more efficiently allowing electricity to flow to and from the utility grid so
the CHP operator only has to focus on effectively recovering and utilizing heat.
Design operation typically takes on two forms: base loading and peak loading. Design
operation is defined as operating the prime mover at a constant load and importing or
exporting thermal and electrical energy as appropriate. Base loading has the prime mover
generating the minimum amount of thermal and/or electrical energy that will always be
used by the building. The caveat to this mode of operation is that back up sources of
85
heating, cooling, and electricity must be available to cover the load variability. These
backups can come from standard boilers and chillers and/or the utility grids (electrical
and thermal).
Peak design operation on the other hand has the prime mover operating at a setting that
will always generate sufficient electrical and thermal energy to meet any building load.
The downside to this mode of operation is that there will be instances when there are
excess amounts of thermal and electrical energy, which will have to be exported to an
energy grid or rejected. Rejecting energy decreases over all efficiency, but extra
equipment will not be required to meet peaks (boilers and chillers).
The decisions regarding operating strategies including startup and shut down will
establish the requirements for the sensor, actuator and control system components and
will provide the basis for the piping and instrumentation diagram.
4.1.7 CHP System Evaluation
Evaluation in this step has a dual meaning. First, if multiple CHP system options exist the
designer must weigh these options on an engineering, economic, and environmental basis.
The second meaning of evaluation is that the CHP system designer should determine a
way of evaluating the efficiency, economic, and environmental performance as required
by the conditions set by regulatory bodies, the system owner and the system operator.
Regulatory bodies may want information on the quantity of emissions generated. Owners
may be interested in how much money has been saved by operating the CHP system.
86
CHP system operators may need information to diagnose problem and determine if the
system is operating properly.
The result of this step is to determine the best CHP system configuration and operating
conditions to meet the demands of the building, which are economic.
4.2 Design of Biodiesel Fueled CHP System
A biodiesel fueled CHP system was designed, installed, operated and evaluated according
the design guide described above.
4.2.1 Load Profiles
The thermal and electrical load profiles from the Intelligent Workplace (IW) were
developed from a combination of metered and name plate data. A decision was made
early on that the CHP system would be designed to meet the peak loads of the IW to
demonstrate a facility that could be powered entirely by renewable fuels. Using data on
existing HVAC, lighting, and plug loads a peak electrical demand of approximately 20
kWe was determined.
Metered data for the double effect steam absorption chiller was available, which showed
the peak demand as 16 kWt in the form of saturated steam at 87 psig (6 bar) with a flow
rate of 65 lb/hr (29 kg/hr).
Furthermore, metered data for the heating system showed a peak heating demand of
approximately 40 kWt at 40oC (104oF), which can change rapidly as he IW does not have
87
a lot of thermal mass, therefore outdoor temperature changes are felt in the building
relatively quickly. The heating season typically lasts from early October to late March.
The heating system was fed by the steam grid which operated at about 7 psig (0.5 bar)
during the winter. Note, the main steam supply pressure is 150 psig (10 bar) during the
winter, but this is stepped down inside the buildings on campus as appropriate.
An additional load that was identified is regenerating the desiccant dehumidification
wheel in the ventilation system. Desiccant regeneration, like the chiller is also a seasonal
load, however it is steadier than the chiller load. The metered data of the ventilation
system showed a required temperature for regenerating the desiccant of approximately
195oF (95oC) with a peak demand of about 20 kWt.
4.2.2 Fuel Selection
Local fuels that were available included natural gas and biodiesel fuel. As this was a
demonstration facility, it was decided that using a renewable fuel was the most important
design consideration when selecting a fuel. Another group on the Carnegie Mellon
University campus had just commercialized a biodiesel refining process. This new
commercial entity agreed to donate the fuel for this system, which also made it the most
economic fuel choice by default.
Distribution of the biodiesel was not as simple as natural gas, which has a pipe line
infrastructure in Pittsburgh, PA. Provision for filling fuel storage tanks had to be made,
which were addressed during the detailed design and layout phase.
88
4.2.3 Energy Grids
Carnegie Mellon’s campus has many energy grids including; electric, steam, and chilled
water. These grids are connected to every building on campus; the steam and chilled
water are generated at a central plant.
The local utility, Duquesne Light, was contacted to determine what their requirements
were for installing a utility paralleled engine generator with a capacity of between 20 and
30 kWe. Due to the configuration of the Carnegie Mellon campus, electricity enters the
campus at two points. Therefore, it is unlikely that the 20 to 30 kWe system would be
noticed in a campus system that draws between two and five megawatts of electricity
from Duquesne Light. Based on this information, Duquesne Light set no requirements for
grid protection on this system. It was assumed that if there was a grid outage and the
generator was operating it would immediately be over loaded by the huge electrical
demand from the campus, which would cause the engine generator to shut down.
Additional protections were put in place as this is a demonstration facility, which will be
discussed further during auxiliary equipment.
The campus chilled water and steam grids are operated year round by Carnegie Mellon’s
facilities management service. The university agreed to allow the CHP system to
interface with the campus thermal grids to allow for importing and exporting of steam
and chilled water. The chilled water operates year round at approximately 45oF (7oC).
The steam grid also operates year round to prevent thermal expansion and contraction;
89
however the pressures vary from about 15 psig (1 bar) in the summer to 150 psig (10 bar)
during the winter. The fall and spring pressures are approximately 40 psig (3 bar).
Another smaller grid was available in the building: a hot water grid. This grid is not
campus wide, but was considered as a possible outlet for thermal energy. The building
hot water grid has an operating range of 26oC to 40oC (78oF to 105oF).
4.2.4 Prime Movers
Three options were available, microturbines, Diesel engines, and fuel cells. Fuel cells
were eliminated quickly as the cost was too high, approximately 100 times the cost of the
microturbine and Diesel engines per kWe. The smallest microturbine available at the time
was a 30 kWe unit, which corresponds to approximately 90 kWt at 530oF (270oC), much
too large for this system.
Diesel generator sets are available from many manufacturers that would provide about 20
kWt of high temperature exhaust. A 32 kWe Diesel engine generator was selected from
John Deere. John Deere was ultimately selected for two reasons, it was locally supported
and John Deere showed interest in the work. Next, as this is a prime power setup, as
opposed to a backup power setup, the engine would not be operated at full power (32
kWe) for an extended period of time. An 80% power rating is reasonable for prime power
applications or 25 kWe. Assuming that Diesel engines are about 33% electrically
efficient, it was assumed that a Diesel engine operating at 25 kWe would produce
approximately 25 kWt exhaust and coolant heat each. Based on this reasoning, a Diesel
engine generator set was selected. Because of the high steam pressure and temperature
90
required by the two stage absorption chiller the amount of available exhaust energy was
closer to 18 kWt, and therefore diminished the operation of the heat recovery system.
Specification sheets from engine manufacturers typically don’t include part load values
or exact values for CHP systems. Conservative estimates are recommended.
4.2.5 Auxiliary and Heat Recovery Equipment
Sizing the heat recovery is where the first major difficulty arose for this system
configuration, as there are no commercially available steam generators in the 10-30 kWt
size range. The smallest steam generator available for exhaust heat recovery was a 200
kWt unit from Vaporphase, Inc. The consequence of using a steam generator of this size
is that the heat up time is very long, approximately nine hours from cold start to steady
state, not including heating up the pipes. However, as a proof of concept, this was
deemed an acceptable configuration. A high pressure hot water system would be
recommended for a new system that would also include the purchase of an absorption
chiller.
Next, the remaining thermal energy stream from the engine coolant needs to be handled.
A plate and frame heat exchanger was selected to recover this energy and transfer it to
water that is utilized in the IW’s heating system. The configuration of the IW’s existing
heating system allowed for the dual use of the hot water pipes for space heating in the
winter and regenerating desiccant in the summer as the loads are not simultaneously
active. It should be noted that this is not a common system configuration. Many buildings
use what is called a four pipe heating system in which hot and cold water is available to
the heating and cooling system as many buildings have to heat and cool at the same time,
91
especially during the spring and fall. The passive design of the IW allows for the use of
what is incorrectly assumed to be an inferior two pipe system. The IW does not require
heating and cooling at the same time, and therefore an entire set of pipes can be
eliminated as shown in Figure 30 below.
Intelligent Workplace
Chilled
Water
Supply
Mullions
Radiant Panels
Fan Coils
Chilled
Water
Return
Hot Water
Supply
Regeneration Air
Desiccant
Regeneration
Wheel Heat
Exchanger
Hot Water
Return
Outside Air
Figure 30: IW Heating and Cooling System Flow Diagram\
The coolant energy has a use during the summer for regenerating the desiccant and in the
winter for space heating, however there are no reliable loads in the spring and fall.
Therefore, a remotely mounted radiator is used to dump excess coolant energy to the
atmosphere as there must always be an outlet for the coolant energy to prevent the engine
from over heating. An alternative to this would have been to purchase a single effect
absorption chiller to generate additional chilled water that could be exported to the
92
chilled water grid, or to make a connection with the domestic hot water system of the
building.
Finally, the electrical energy needs to be sent to the power grid. The advantage of
connecting power to the utility grid is that it allows operational freedom to produce the
reject heat in the quantity required. If a CHP system does not have the flexibility to
export electricity, the prime mover must always match the electrical demand other wise
the electrical circuits will overload. As electrical and thermal demands don’t necessarily
coincide, too much waste heat could be generated, or not enough. The requirements of
the utility paralleling gear (Automatic Transfer Switch / Soft Load Controller ATS/SLC)
are up to the local utility. Typically for very small systems, less than 100 kWe, the
utility’s requirements are minimal. However, as this is a demonstration facility, a much
more complex ATS/SLC was selected, which could provide additional operational
flexibility and realism for larger systems.
Based on all of this information several flow diagrams were generated and frequently
revised as details emerged on equipment, pipe sizes, and sensor and actuator
requirements.
Due to the scattered nature of this CHP installation, the heat recovery equipment had to
be placed in a relatively distant location from the absorption chiller. Therefore, piping
losses (thermal and pressure) had to be considered as the piping distance is about 220 feet
(67 meters) including a 70 foot (21 meter) vertical rise. A pressure drop of 5 psi (0.3 bar)
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and a thermal loss of 2.5 kWt were calculated based on these estimates as shown in
Appendix D. Therefore, a minimum of 18.5 kWt was needed to drive the absorption
chiller. It was decided to add a little padding to this number and set the requirements to
20 kWt.
4.2.6 Operations
A specific operational strategy was not selected for this project as one of the research
goals of this project is to compare operational strategies. The control system and
infrastructure in place for this system allow the system to thermal load follow, electrical
load follow, base load, and peak load. There is an extra cost associated with this decision,
but as a demonstration facility cost was not a driving factor.
4.2.7 Evaluation
The fuel type, prime mover, and auxiliary equipment were selected relatively quickly for
this application as there were a lot of constraints on equipment selection between the
existing chiller and ventilation systems, the energy grids, and the demands of the building.
The long term evaluation of all facets of this system was the primary focus of this project,
and is outlined in section 3. The evaluation of this system was meant to satisfy CHP
system designers, builders, operators, owners, and regulators as well as educational
entities. Therefore, there is a great emphasis on data acquisition and dissemination. Over
200 data points are continuously measured and available on the web.
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4.2.8 Submittals
Flow diagrams, material and energy balances, equipment descriptions, operating
descriptions, process and instrumentation diagrams, preliminary layout, and cost
estimates for equipment were all created and submitted to an engineering firm for
detailed evaluation and the creation of construction drawings.
The engineering firm created a detailed flow diagram, and a layout which had to balance
educational/scientific goals. The detailed flow diagram and the layout went through
several iterations as the educational and scientific goals weren’t always understood by the
engineering firm. Code requirements often clashed with scientific requirements, however
eventually a compromise was met. Upon completion of the construction drawings, bids
were sought and awarded for placing and connecting the equipment, installing
instrumentation and controls, and commissioning the system. Details on the construction
process can be viewed on the project website:
http://www.cmu.edu/iwess/components/biodiesel_engine/installation/index.html
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5.0 TRNSYS Modeling
An overall TRNSYS model has been programmed by Flore Marion to simulate the
performance of individual and combined systems in various operational modes. Many of
the IWESS components have been modeled using TRNSYS in order to develop generic
models for future building HVAC design. These models include the absorption chiller,
the engine generator with heat recovery, and the ventilation system. The purpose of the
model is to estimate what fraction of the thermal requirements of the IW can be met by
the biodiesel CHP system in various operational modes and what portion of the thermal
output must rejected to the surroundings.
5.1 IWESS Model
The IWESS model is built out of three main components, the biodiesel fueled CHP
system, the double effect absorption chiller, and the enthalpy recovery ventilation system.
Each of these systems has had a previously developed empirical model, which was
implemented in TRNSYS. Empirical models had to be used as computational models
were to calculation intensive. The model uses three measured data files which include the
heating, cooling, and regeneration loads of the IW. The outputs include the electrical
generation, fuel demand, and the necessary flows and temperatures of the thermal streams.
5.1.1 Biodiesel Fueled Engine Generator with Heat Recovery
Modeling
The design of the engine generator with heat recovery model has been completed and
tested at 6, 12, 18 and 25 kWe. The first model used manufacturer’s specifications as
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inputs [34]. The model has been validated using measured data, which as shown in
section 3.1.3 very closely matches the specifications of the manufacturer. The look up
tables developed for this engine generator are shown in Appendix E. Using the look up
table a simple TRNSYS module for the CHP system was developed that equates fuel
flow to electricity generation, hot water generation via the coolant heat exchanger, and
steam production via the steam generator.
Fuel
CHP
Module
Hot Water Flow and Temperature
High Pressure Steam Flow and Pressure
Electrical Power
Figure 31: CHP system input / output module
5.1.2 Double Effect Steam Driven Absorption Chiller
A complex Engineering Equation Solver (EES) model was developed for the absorption
chiller sub-system. However, this model was to computationally intensive for TRNSYS
to run so a table look up model was developed and implemented in TRNSYS.
The TRNSYS absorption chiller model is based on empirical data collected during the
operation of the chiller over various loads [35]. The operating data has been distilled to a
simple relationship, which equates cooling capacity with heat input.
Figure 32 shows the input and output of the chiller model.
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High Pressure
Steam Flow
and Pressure
Absorption
Chiller
Module
Cooling
Demand
Figure 32: Double effect absorption chiller input / output module
5.1.3 Ventilation Unit with enthalpy recovery and solid desiccant
wheel.
The ventilation system has also been modeled in TRNSYS, and is also quite complex.
For the purposes of the integrated system model, empirical data for the regeneration
demand from the ventilation system were used to create a table look up model that relates
regeneration demand to a demand of hot water from the CHP system [36]. Figure 33
shows the simple input / output module for the ventilation system.
Hot Water
Flow and
Temperature
Ventilation
Module
Regeneration
Demand
Figure 33: Ventilation system input / output module
5.1.4 Computational Model Issues
While it is possible to use computational models rather than empirical models there are
several drawbacks. First and foremost, the performance of the systems and how they
interact with each other in every time step must be calculated. Building a computational
model was carried out; however the system was so complex that it had to be run in small
simulation time increments (about two weeks) with a time step of five minutes to get
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accurate results. While, this is sufficient for scientific purposes it is ineffective as a
design tool.
To illustrate some of the computations necessary the following is the process by which
cooling is delivered.
1. A cooling demand is set by the building load file.
2. The chiller then calls for steam by calculating how much steam is required to
meet the new cooling demand.
3. Steam is drawn from the steam generator, which calls on the engine to adjust its
output to provide the correct amount of heat to the steam generator based on its
heat transfer characteristics.
4. Next the engine calculates the amount of fuel necessary to meet the new demand.
Simultaneously the coolant loop is operating which also has various thermal demands,
and calculates how much heat should be recovered and rejected. On top of that an over all
control strategy is running that decides which form of heat is more important, coolant or
exhaust.
Figure 34 shows the combined computational model for the CHP system with all of the
components needed to operate the system including the pipes and valves themselves.
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Figure 34: Combined TRNSYS Model
5.1.5 Combined IWESS Model
To resolve the performance issues of the computational model it was decided to use the
look up tables and simplify the entire program so that a full year simulation could be run
in a relatively short amount of time.
To simplify the entire program the following steps were taken:
1. The engine generator with coolant heat recovery were merged into a single
component based on a look up table.
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2. The ventilation system was reduced to a table look up model that relates the
regeneration load to the coolant heat demand on the engine.
3. The chiller system was also reduced to a cooling load file setting a thermal
demand on the steam generator, which was fed the engine outputs of exhaust
temperature and flow rate.
These steps resulted in the model shown in Figure 35, which is much easier to understand
and operate. Furthermore, the simplified model can now be run for a full year.
Figure 35: Combined/Simplified IWESS TRNSYS Model
The model shown in Figure 35 operates in the following way. Three empirical load files
for heating, cooling, and regeneration demands are shown on the left side of Figure 35.
These load files are fed into the controller, where the user sets an operational mode, base
load, thermal load follow, or regeneration load follow. The controller outputs a control
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signal to the engine component, which then outputs the proper temperatures, pressures,
and flows generated by the CHP system.
The model allows the user to adjust a number of different system characteristics with
relative ease.
1. The engine component uses two data files that are based on the look up tables
shown in Appendix F that can be easily replaced if operational changes are
desired.
2. The controller can operate in different modes by double clicking the controller
and selecting a different mode.
-Mode 0: Operate at 100% (25 kWe)
-Mode 1: Thermal Load Follow (Cooling, Heating)
-Mode 2: Regeneration Load Follow
3. The load files (heating, cooling, regeneration) can be altered by double clicking
on the icons and linking a new load file, which can be based on measured or
simulated data from a model.
Three simulations were conducted using the integrated TRNSYS models for the 25 kWe
model. The first simulation is a peak design operation simulation which has the engine
running at its highest efficiency point, 25 kWe. The excess steam and electricity will be
102
exported to the CMU campus grid, and the excess coolant energy will be rejected to
atmosphere.
The second operational mode is a thermal load follow mode where the engine’s output
changes to match heating and cooling demands. Excess electricity will be exported to the
grid, and electricity shortfalls will be made up by the grid. Excess coolant energy will be
dumped to atmosphere via the remote radiator, and regeneration energy short falls will be
made up by the natural gas burner in the ventilation system.
The third operational mode is also thermal load follow mode where the engine’s output
change to match the regeneration demand of the desiccant regeneration load. Similarly
heating, cooling, and electrical surpluses and short falls will be made up by the grid.
5.1.6 IWESS Simulations
The following runs show the results of the IWESS simulation runs for three modes, 1)
design operation at 25 kWe, 2) following the heating and cooling loads, and 3) following
the regeneration load. The results shown are the statistics generated for; number of hours
loads are not met, total net energy exported or imported, and average efficiency. Note,
hourly electrical data was not available as the data acquisition system stopped collecting
data periodically, however the meters themselves continued to collect data which
includes the annual totals, but not individual hours. Therefore, hours of electrical load not
met and an electrical load follow mode are not possible at this time.
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5.1.6.1 Mode Zero: Design Operation
The IWESS system operating at a constant 25 kWe with a constant 18 kWt exhaust
energy output and 18 kWe coolant energy. The output of the engine is compared to the
demand of the IW for heating, cooling, dehumidification, and electricity. The excess
electrical and exhaust energy (in the form of steam) is exported to the rest of campus,
while the coolant energy is rejected to the atmosphere with a radiator.
Mode Zero Results: Design Operation at 25 kWe
Annual Net Energy Export
1,015,470 MJ
Annual Net Thermal Energy Export
706,442
MJ
Annual Net Electrical Energy Export
309,028
MJ
Hours of Operation
8,760
Hours
Heating Hours Not Met
351
Hours
Cooling Hours Not Met
191
Hours
Regeneration Hours Not Met
265
Hours
Total Energy Used
1,791,999 MJ
Total Fuel Consumption
19,921
Gallons
Total Fuel Energy Consumption
2,712,360 MJ
Average Annual Efficiency
66%
Table 12: IWESS Design Operation Simulation Results
The base load operation has an overall CHP efficiency of 66%. The lower CHP
efficiency is due to the heat rejected by the coolant system as it does not have the ability
to be exported. If additional uses for coolant energy could be found, the over all
efficiency would increase towards 80%.
5.1.6.2 Mode One: Thermal Load Follow
The IWESS system is operating at a variable output matching the thermal load (cooling
or heating) of the IW.
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Mode One Results: Thermal Load Follow
Annual Net Energy Import
104,613
MJ
Annual Net Thermal Energy Export
31,827
MJ
Annual Net Electrical Energy Import
136,440
MJ
Hours of Operation
5,158.5
Hours
Heating Hours Not Met
2,773
Hours
Cooling Hours Not Met
2,986
Hours
Regeneration Hours Not Met
3,184
Hours
Total Energy Used
834,821
MJ
Total Fuel Consumption
9,025
Gallons
Total Fuel Energy Consumption
1,228,845 MJ
Average Annual Efficiency
68%
Table 13: IWESS Thermal Load Follow Simulation Results
A substantial increase in the number of hours of cooling and heating was not achieved.
There are two reasons for this; first the controller is only adjusted every 30 minutes due
to the limitations of the software. The controller is setup to supply either heating or
cooling, not both at the same time. If the IW’s load changes from heating to cooling in
the same 30 minute period, the controller will only cover the larger load, and not cover
both. It is unusual that the number of heating hours not met does not increase
substantially as well, however the data clearly shows that the heating load is typically
larger than the cooling load when both are present.
These loads are typically small, for example on 13 November at 9:00 in the morning
there is a 142.3 kJ cooling load in the IW. At 9:30 there is a 64.4 kJ heating load and a
32.2 kJ cooling load. At 10:00 there is a 176.7 kJ heating load and no cooling load. These
loads are tiny, yet the statistical analysis still shows that the cooling load for 9:30 was not
met. In the future it may be possible to have a finer resolution of both measured data and
simulation results to reduce these statistical analysis problems.
105
The analysis of this data would lead to the conclusion that the IW’s control system is not
fined tuned enough to prevent this fast transition from heating to cooling as is intended in
the design. The loads that are causing this issue are very small and probably do not need
to be addressed by the HVAC system, but that intelligence currently does not exist in the
IW’s HVAC control system. An alternative solution to adjusting the control system is
increasing the thermal mass of the IW by using phase change materials, which would
help moderate the changing thermal demands due to the IW’s light weight construction.
The second reason for the increase in unmet hours of heating, cooling, and regeneration is
due because the control system does not allow the engine to run when it is operating
below 25% capacity. The engine is not operating for 3,574.5 hours, and any small heating,
cooling, or regeneration load during those hours is not met. Furthermore, just like the
mode zero operation, there are 807 hours of peak operation that can’t be met with this
system.
Overall this operational mode is an improvement in efficiency due to rejecting less
coolant energy; however, the quantity of hours the heating and cooling load is not met
would not be acceptable.
5.1.6.3 Mode Two: Regeneration Load Follow
This operational mode only uses the desiccant regeneration load to set the demand on the
engine. The coolant energy is used to meet the regeneration load and the exhaust and
electrical outputs are used in the IW or exported to the campus grids if the demand in the
IW is low enough.
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Mode Two Results: Regeneration Load Follow
Annual Net Energy Export
390,334,042 MJ
Annual Net Thermal Energy Import
389,883,120 MJ
Annual Net Electrical Energy Import
450,922
MJ
Hours of Operation
1,042.0
Hours
Heating Hours Not Met
5,486
Hours
Cooling Hours Not Met
2,927
Hours
Regeneration Hours Not Met
7,136
Hours
Total Energy Used
71,217
MJ
Total Fuel Consumption
800
Gallons
Total Fuel Energy Consumption
108,900
MJ
Average Annual Efficiency
65%
Table 14: IWESS Regeneration Load Follow Simulation Results
This mode is not very effective for operation of the IWESS system. The number of hours
of cooling, heating, and dehumidification not met is very large. Counter intuitively the
number of hours not met for dehumidification rose dramatically. This is because the
regeneration load is typically small (less than 7 kWt) and the limitations set on the engine
controller does not allow the system to operate at electrical loads below 6 kWe due to low
efficiency and therefore it is incapable of producing less than 7 kWt. Therefore, during all
the low load conditions, the engine is off, which is shown in the table with only 1,042 run
hours. In the other operational modes the system focused on meeting the peak thermal
demands so there was usually enough coolant heat in the system to meet the minimal
regeneration loads with the consequence of dumping some to atmosphere.
The CHP efficiency is reduced most likely because the engine consistently operates at a
lower rating, which reduces the over all efficiency even though very little heat is rejected
to the atmosphere. To compensate for this low rating, a thermal storage system may be
included that allows the engine to run at peak efficiency for short periods of time.
107
5.1.6.4 IWESS Simulation Discussion
As previously stated, CHP systems operate most efficiently at a steady state, and high
performance buildings reduce loads to the point where systems can be turned off. When
using a thermal load follow approach in a high performance building, the CHP systems
load will drop to the point at which it is no longer desirable to operate the system.
Therefore, it is recommended to have both a electrical and thermal grid in order to
maximize the effectiveness of the CHP system when it is used in a high performance
building.
5.2 BAPP Model
A hypothetical system based on the 25 kWe system has been created that operates at
200kWe for the Building As Power Plant (BAPP) concept. A 200 kWe system was used
as this is the correct size for the peak electrical power of the BAPP. A 200 kWe Diesel
engine specification sheet was also available to compare with the 25 kWe Diesel engine
during the scale up shown in Appendix G. As discussed in the design guide, there are
many ways to size a CHP system for a building, and 200 kWe unit was selected as an
example. Finally, the BAPP design is still under development and as such subject to
change. Therefore, a modified version of the IW load file multiplied by a factor of 10 was
used for this simulation as reliable hourly thermal loads are not available at this time for
the BAPP.
5.2.1 Engine Modification
The engine specifications used for this system had to be adjusted to suit a CHP system.
Larger engines in the U.S. use an intercooler in the turbocharger to cool the incoming
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fresh air to increase its density and produce more power, therefore, meeting tougher EPA
standards, which are based only on electrical power production per gram of various types
of pollution (CO, NOX, SOX, and PM2.5). This heat is currently dumped to the space
surrounding the engine using an air-to-air heat exchanger. Instead of dumping this heat to
the air, it will be combined with the water jacket coolant system like the 25 kWe engine.
To estimate the effect of combining the turbocharger heat rejection and the engine block
heat rejection, the following steps are taken.
Given:
-Engine block heat rejection = 83.7 kWt
-Coolant (50/50 propylene glycol) flow rate = 265 liters/min
-Coolant outlet temperature = 95oC
-Air charge heat rejection = 40.4 kWt
Calculations:
-Determine engine coolant inlet temperature


Qengine  m cTout  Tin 

Tin  Tout 
Q

mc
 
Tin  95 oC 
83.7kW 
 95 oC  5.3 oC  89.7 oC
 kJ 
 kg 
4.417    3.559

 sec 
 kg  C 
 
 
 
-Combine water jacket and air charge reject heats and determine new flow rates.
109





Q coolant  Q engine  Q turbocharg er  83.7kWt  40.4kWt  124.1kWt
Q coolant  m coolant cTout  Tin 


Q
m coolant 
cTout  Tin 

m coolant 
124.1kWt
 kg 
 liter 
 6.58   394.7 
 kJ 
 sec 
 min 
o
o
3.559 
 95 C  89.7 C 
 kg  C 
 
 
The next step is to determine the part load heat transfer rates given what is known about
the 25kWe engine.
Power Level
Coolant Heat Transfer
6 kWe
6.4 kWt
12 kWe
9.9 kWt
18 kWe
13.1 kWt
25 kWe
18.1 kWt
Table 15: IWESS 25 kWe CHP Coolant Heat Exchanger Results vs. Power Level
Assuming similar proportions as shown above, below are the estimated heat transfer rates
for the 200 kWe engine.
Power Level
Coolant Heat Transfer
50 kWe
43.9 kWt
100 kWe
67.9 kWt
150 kWe
89.8 kWt
200 kWe
124.1 kWt
Table 16: Estimated BAPP 200 kWe CHP Coolant Heat Exchanger Results vs. Power Level
Similarly, air flow rates are estimated the same way based on the 25kWe engine data.
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Power Level
Air Flow Rate
6 kWe
138 kg/hr
12 kWe
144 kg/hr
18 kWe
153 kg/hr
25 kWe
165 kg/hr
Table 17: IWESS 25kWe CHP Air Flow Rate vs. Power Level
Power Level
Air Flow Rate
50 kWe
878 kg/hr
100 kWe
916 kg/hr
150 kWe
974 kg/hr
200 kWe
1050 kg/hr
Table 18: Estimated BAPP 200 kWe CHP Air Flow Rate vs. Power Level
Using the estimated information in the tables above and the 200 kWe engine generator
specification sheet, look up tables for the 200 kWe engine were created shown in
Appendix H, a similar TRNSYS simulation files was created for the 200 kWe system.
Figure 36: BAPP TRNSYS Simulation
The scaled up version of this model for the Building As Power Plant (BAPP) is nearly
identical to the IWESS model, however, the load and engine data files were altered using
to use a larger engine.
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5.2.2 BAPP Simulations
The following runs show the effect of operating an IWESS style system for BAPP using
a 200 kWe engine generator instead of a 25 kWe engine generator. A 200 kWe engine
generator was selected as this is the peak power demand of the BAPP.
5.2.2.1 Mode Zero: Design Operation
The BAPP CHP system is operating at a constant 200 kWe with a constant 111 kWt
exhaust energy output and 124 kWt coolant energy. The output of the engine generator is
compared to the demand of the IW for heating, cooling, dehumidification, and electricity.
The excess electrical and exhaust energy (in the form of steam) is exported to the rest of
campus, while the coolant energy is rejected to the atmosphere with a radiator.
Mode Zero Results: Design Operation at 200 kWe
Annual Net Energy Export
38,543
MJ
Annual Net Thermal Energy Import
3,165,375 MJ
Annual Net Electrical Energy Export
3,203,918 MJ
Hours of Operation
8,760
Hours
Heating Hours Not Met
3,531
Hours
Cooling Hours Not Met
2,050
Hours
Regeneration Hours Not Met
2,956
Hours
Total Energy Used
13,006,500 MJ
Total Fuel Consumption
119,965
Gallons
Total Fuel Energy Consumption
16,333,612 MJ
Average Annual Efficiency
80%
Table 19: BAPP Design Operation Simulation Results
The base load operation shows a high efficiency, however the simulation results show
that there was a substantial shortfall of thermal energy for the building, although there
was a lot of excess electricity to make up for it so the BAPP using this operational
method is a net energy exporter. A true BAPP should at the very least have a net export
of all forms of energy, and probably export all forms of energy for every hour. The high
112
efficiency is probably due to the fact that the engine is operating constantly at its most
efficient load, 200 kWe, and the fact that there is a large thermal load, which is using up
most of the coolant energy so little energy is rejected to atmosphere.
5.2.2.2 Mode One: Thermal Load Follow
The BAPP CHP system is operating at a variable output matching the thermal load
(cooling or heating) of the IW.
Mode One Results: Thermal Load Follow
Annual Net Energy Import
2,363,485 MJ
Annual Net Thermal Energy Import
2,058,830 MJ
Annual Net Electrical Energy Import
304,655
MJ
Hours of Operation
5,165
Hours
Heating Hours Not Met
5,817
Hours
Cooling Hours Not Met
2,981
Hours
Regeneration Hours Not Met
3,450
Hours
Total Energy Used
5,663,109 MJ
Total Fuel Consumption
54,107
Gallons
Total Fuel Energy Consumption
7,366,797 MJ
Average Annual Efficiency
77%
Table 20: BAPP Thermal Load Follow Simulation Results
Similar to the IWESS thermal load follow simulation the number of hours the loads are
not met is very high, however in addition to the issues stated in section 5.3.1.2, the 200
kWe system is under sized for the thermal load, therefore more hours are not met. On the
other hand, as the CHP system is smaller relative to the load it rejects less heat, therefore
operating at a higher efficiency.
5.2.2.3 Mode Two: Regeneration Load Follow
This operational mode only uses the desiccant regeneration load to set the demand on the
engine generator. The coolant energy is used to meet the regeneration load and the
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exhaust and electrical outputs are used in the BAPP or exported to the campus grids if the
excess is available.
Mode Two Results: Regeneration Load Follow
Annual Net Energy Import
7,008,961 MJ
Annual Net Thermal Energy Import
4,146,361 MJ
Annual Net Electrical Energy Import
2,862,600 MJ
Hours of Operation
1,042
Hours
Heating Hours Not Met
5,653
Hours
Cooling Hours Not Met
2,942
Hours
Regeneration Hours Not Met
7,283
Hours
Total Energy Used
504,924
MJ
Total Fuel Consumption
4,706
Gallons
Total Fuel Energy Consumption
640,713
MJ
Average Annual Efficiency
79%
Table 21: BAPP Regeneration Load Follow Simulation Results
Similar to the IWESS regeneration load follow simulation, the BAPP regeneration load
follow system has relatively few hours of operation. It also has a high efficiency as the
majority of the heat is captured.
5.2.2.4 BAPP Simulation Discussion
It appears that the selected CHP system for this application is too small to fulfill the role
of Building As Power Plant as there is insufficient thermal output for heating, cooling,
and regeneration even in the base load operation. Furthermore, according to Dr. Volker
Hartkopf, there should always be an excess of electricity, steam, and chilled water
generated by the BAPP CHP system to truly meet the goals of the BAPP concept.
Another prime mover should probably be selected to meet the estimated loads. That said,
the BAPP load files are estimates, and there have been several design revision in the last
five years that may not be included in the latest EnergyPlus file that was created in 2003.
114
In order to meet the varying loads of the BAPP, a modular CHP system approach might
be attempted. As the load is frequently below 50 kWe (25% of engine rating); several
smaller engine generators may be linked to operate together. For example, if eight 25
kWe engine generators were combined, then the CHP system could efficiency operate a
power level as low as 6 kWe, or 3% of the 200 kWe engine generator total rating. This
would probably also entail using several smaller absorption chillers and ventilation
systems rather than single large units.
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5.3 Data Center CHP Operation
Data center load profiles are completely different than commercial buildings. The
computational equipment inside the data centers dominates the building’s power and
cooling demands. An average electrical load for a data center is approximately 250 watts
per square foot (2.7 kW/m2), and that load is nearly directly translated into an equivalent
cooling load [37]. Furthermore, the load is nearly constant day and night as well as
seasonally for most locations as the envelope load and occupant load is typically less than
2 watts per square foot, which is negligible compared to the equipment load [37].
Therefore, the CHP system can be operated at a near constant set point. Finally, typically
there is no heating load or latent cooling load (dehumidification) for data centers so all
the thermal energy should be routed to absorption cooling [37].
Using this information, a CHP system is applied to a hypothetical data center with a peak
electrical load of 200 kWe, which translates into a 200 kWt cooling load. At 250 Watts
per square foot, this translates to an 800 square foot building, which is small for a data
center however this concept can easily be scaled up. The only change would be the
proportions of the heat and electricity generated which is discussed at length in section
2.2.
As there is no latent cooling load requiring dehumidification, it makes sense to use the
coolant energy from the Diesel engine to drive a single effect absorption chiller.
Furthermore, the outlet temperature from the double effect absorption chiller is
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approximately 160oC, which can be used in single effect chiller as well as a single effect
chiller can operate with a COP of 0.7 at temperature as low as 70oC [17].
The double effect absorption chiller receives a heat input of 95.6 kWt at a temperature of
485oC and an outlet temperature of 160oC [38]. With a COP of 1.1, this translates into
105.2 kWt of cooling. Next, the exhaust is cooled down further to 80oC, which translates
into an additional 23.5 kWt. 80oC is assumed reasonable as the exhaust can’t be cooled
all the way down to the desorber inlet temperature of the 70oC. A single effect chiller
with a COP of 0.7 would generate 16.5 kWt of cooling.
Finally, 124.1 kWt of coolant energy is available in the coolant system from the engine
block and the turbocharger. Again using the same single effect chiller with a COP of 0.7,
86.9 kWt of cooling is generated.
The total cooling potential of the combination single and double effect absorption chiller
is estimated to be 208.6 kWt, which is nearly the precise load of the building. This
demonstrates what a great match CHP systems are for data centers.
All totaled, 200 kWe of electricity and 209 kWe of cooling is delivered using 524 kWc of
fuel energy to yield a combined efficiency of 78%.
Unfortunately, it is unlikely that the reject heat from the absorption chillers will find a
substantial use. Most stand-alone data centers have a low occupancy rate so a large
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domestic hot water load is unlikely in contrast to the IWESS and BAPP systems
described above. It may be possible to use this heat for thawing of sidewalks and parking
lots where a winter climate is present. In the case that a data center can be part of a
community, many potential uses such as heating swimming pools, preheating domestic
hot water, etc. exist. Furthermore, if a data center is part of a larger office complex
additional systems integration strategies may be available.
The primary energy for operating the CHP system at 200 kWe would require about 52
kg/hr of biodiesel fuel or about 17,092 GJ per year. On the other hand, 200 kWe of grid
electricity would require 19,710 GJ of coal per year plus the electricity for cooling, which
is 200 kWt of cooling with a COP of 3.2 translates into 62.5 kWe or 6,159 GJ per year or
a total of 25,869 GJ per year. The CHP system uses about one third less primary energy
than the utility system, to provide adequate power and cooling.
Furthermore, data centers, like most mission critical systems, require back up power.
Therefore, the first cost increase for a CHP system is the slight cost increase associated
with switching the vapor compression chillers to absorption chillers and the necessary
heat recovery equipment and controls. Keep in mind, it is best to direct fire absorption
chillers when possible so the only systems integration cost should be exhaust ducting and
coolant piping, controls (sensors, dampers, valves, etc.), and insulation between the
engine and the chillers.
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6.0 Systems Integration
This final chapter is devoted to the development of an integrated example system that
includes power generation; chilled water, heated water, conditioned dehumidified air, and
domestic hot water producer. This system is designed around the existing IWESS
components of the engine generator, heat recovery, absorption chiller, ventilation system,
and auxiliary equipment.
The purpose of this example is to show potential designers and user of such a system the
opportunities for simplifying the overall system. Users typically want a finished product,
not parts to be assembled. For example, computer users typically buy a finished computer
from manufacturer or store. While there typically is some assembly required such as
connecting a power cord, monitor and other peripherals, the assembly requires no tools
and can be accomplished quickly.
The CHP system installed at CMU is more closely related to building a computer from
individual components such as a mother board, CPU, hard drive, power supply, etc. This
job requires a lot more know how, and possibly some specialized tools. Furthermore, the
IW’s CHP system, along with many other building components, have the added difficulty
of speaking different languages (like mixing MAC and PC components) and different
fittings or connectors that don’t match. The interface between these systems often
requires customized solutions, which are time and cost intensive.
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To alleviate these issues, similar to a Dell or HP, the parts are selected by a manufacturer
that work well with each other and are packaged in such a way that the connections are
made quickly. This concept is not limited to computers; Freightliner & Paccar do not
make the engines and axles in their trucks. These parts are purchased from Cummins and
Caterpillar, two previously mentioned engine generator manufacturers and integrated into
the overall system. Also, if a significant volume of units are sold, suppliers may change
specifications to suit a large customer’s requests.
6.1 Individual Systems Integration
The first step to integrating separate sub-systems is to understand how the systems are
related. There are five major IWESS components; the CHP sub-system, the absorption
chiller sub-system, the ventilation sub-system, the domestic hot water sub-system, and
the energy grids. Each of these sub-systems is made up of smaller components.
The CHP sub-system shown in Figure 37, has five major pieces including the engine
generator, the ATS/SLC, the exhaust heat recovery unit, the coolant heat recovery unit
and the supervisory controls. The engine generator is then made up of four additional
components; the Diesel engine, the generator, the radiator, and the engine controls all of
which were made by four different manufacturers and integrated by a fifth company.
As there is a large market for backup power generation, the engine generator is available
fully integrated from many dealers. The remainder of the parts are shipped separately and
are integrated onsite, which is labor intensive.
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Control
Data
Automatic
Transfer
Switch /
Soft Load
Controller
Electricity
Control
Data
Intelligen
Controls
Engine
Generator
Air
ALC Controls
Radiator
Coolant
Heat
Recovery
Fuel Hot Air
Hot
Water
Loop
Pneumatic
Controls
Exhaust
Heat
Recovery /
Steam
Generator
Compressed
Air
Steam
Hot Exhaust
Condensate
Figure 37: CHP Major Component Diagram
The absorption chiller components shown in Figure 38 are all designed and built by
Broad and shipped as a single unit. However, an absorption chiller will not operate as a
stand alone system because it requires a heat input and a heat rejection output. The Broad
chiller incorporates a cooling tower for rejecting heat. The original heat input system was
an electric boiler not shown in Figure 38 as it has been replaced by the CHP system.
Control
Data
Chilled Water
Loop
Broad Controls
Absorption
Chiller
Electricity
High Pressure
Steam
Cooling
Tower
Warm,
Humid Air
Treated
Water Air
Figure 38: Absorption Chiller Major Component Diagram
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Finally, the ventilation sub-system shown in Figure 39 has five main components, four of
which are made by one supplier. The control sub-system was outsourced yet integrated
by the main manufacturer. The ventilation sub-system is the only component within
IWESS that is able to operate without the addition of auxiliary equipment.
ALC Controls
Exhaust
Air
Enthalpy
Recovery
Module
Desiccant
Module
Heat
Pump
Module
Control
Data
Dehumidified
Supply Air
Regen Burner
Return
Natural
Air
Gas Electricity
Outside
Air
Regeneration
Air Exhaust
Figure 39: Ventilation System Major Component Diagram
The second step is to understand the quantity and quality, temperature, of the heat being
dealt with in the thermal energy cascade of Figure 40. The concept of the energy cascade
is to use the highest form of fuel or energy to create the highest quality product: from
electricity, to chilled water, to dehumidified air, to domestic hot water, and to hot water
for space heating. Using an engine generator poses an additional challenge as two sources
of energy (exhaust and coolant) are being generated simultaneously; therefore they must
be handled simultaneously.
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Fuel Energy
Engine
Generator
Electricity
Chilled Water Return
Absorption
Chiller
Exhaust
Chilled Water Supply
To DHW Preheat (See bottom)
City Water / Preheated DHW
Exhaust Heat
Recovery (DHW)
Coolant
Domestic Hot Water
Hot Water Return
Exhaust Heat
Recovery (SH)
Hot Water Supply
Outside Air
Regeneration Heat
Exchanger
Regeneration Air
Hot Water Return
Coolant Heat
Exchanger
Domestic Hot
Water Preheat
Hot Water Supply
City Water
Preheated DHW
Figure 40: CCHP/V Energy Cascade
After the qualities of the heat sources are understood, T-Q diagrams need to be developed
to understand the heat transfer processes and select proper heat transfer equipment. The
energy cascade shown in Figure 40 is not the only possible configuration, but this is the
one that was chosen for the IWESS system. Alternatives such as using high temperature
exhaust to generate steam to drive a turbine or using low temperature exhaust to melt
snow gives an idea of the possible range of applications.
The third step to integrate separate systems is to understand the inputs and outputs of
each system in the forms of energy, material and data. As described in section 3 and
shown in Table 22; the CHP system, the chiller system, and the ventilation system are
well understood.
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Existing IWESS Configuration Inputs / Outputs
CHP System
Absorption Chiller System
Ventilation System
Inputs
Outputs
Inputs
Outputs
Inputs
Outputs
Fuel
Fuel (Natural Dehumidified
Electricity
Electricity
Exhaust
(Biodiesel)
Gas)
Air
High Pressure
Outside and
Regeneration
Air
Exhaust
Condensate
Steam
Return Air
Exhaust Air
High Pressure
Chilled Water
Chilled Water
Regeneration
Condensate
Exhaust Air
Steam
Return
Supply
Air
Hot Water
Hot Water
Makeup Water
Steam (Cooling
Electricity
Return
Supply
(Cooling Tower)
Tower)
Compressed
Air
Table 22: IWESS Input / Output Table
The three IWESS systems shown in Figures 37 through 39 are integrated into a system as
shown in Figure 41. The integrated system takes advantage of some of the waste heat
sources from the CHP to drive the absorption chiller and the desiccant regeneration
processes. The advantage of this system configuration over the stand alone systems is that
there is now a demand for both low and high temperature heat during the summer
increasing the operation time of the CHP system, and increasing the year round energy
efficiency.
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Control
Data
Control
Data
Intelligen
Controls
Automatic
Transfer
Switch /
Soft Load
Controller
ALC Controls
Engine
Generator
Electricity
Air
Radiator
Coolant
Heat
Recovery
Fuel Hot Air
Dehumidified
Supply Air
Hot
Exhaust
Pump
Desiccant
Module
Enthalpy
Recovery
Module
Exhaust
Air
High
Pressure
Steam
Absorption
Chiller
Heat
Pump
Module
Electricity
Natural
Gas
Electricity
Regeneration
Air Exhaust
Regeneration
Air Supply
Cooling
Tower
Chilled Water
Loop
Air
Regen Burner
Regen Coil
Outside
Return
Air
Air
Control
Data
Broad Controls
Hot
Water
Loop
ALC Controls
Control
Data
Pneumatic
Controls
Exhaust
Heat
Recovery /
Steam
Generator
Terminal
Heating
Units
Pump
City
Water
Domestic
Hot Water
Natural
Gas
Treated
Water
Exhaust
Warm,
Humid Air
Pump
Terminal
Cooling
Units
DHW
Electricity
Figure 41: Major Component Piece-wise Systems Integration
Figure 41 is a very complex setup with many components outlined in Table 23.
System
Major
Components
ATS / SLC
Minor
Components
Radiator
Engine Generator
CHP System
Controllers
ATS / SLC
Intelligen
Controls
Coolant Heat
Exchanger
ALC Controls
Steam Generator
Pneumatic
Controls
Absorption
Chiller
Absorption Chiller
Cooling Tower
Ventilation
System
Enthalpy Recovery
Wheel
Heat Pump
Desiccant Wheel
Regeneration
Burner
Regeneration Coil
Domestic Hot
DHW Storage Tank
Water
Table 23: IWESS Component List
Broad Controls
ALC Controls
DHW Controller
Heat
Rejection
Radiator
Exhaust
Cooling
Tower Steam
Regeneration
Exhaust Air
Exhaust
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6.2 Packaged Systems Integration
This section describes how the three individual systems might be packaged so they can
work together more effectively. As discussed in section 3, the potential for further
systems integration and reduction of components and subsystems to reduce first and
operation cost and simplify the operation of the combined system are now applied to the
IWESS system in Figure 42.
Supervisory Controller
Electricity
Regeneration
Air Exhaust
Regeneration
Air Supply
Engine
Exhaust
Engine
Exhaust
Regen Coil
Automatic
Transfer
Exhaust
Engine
Switch /
Heat
Generator
Soft Load
Recovery
Controller
Electricity
Coolant
Heat
Recovery
Absorption
Chiller
Radiator
Domestic
Hot Water
Preheat
Air Fuel
Enthalpy
Recovery
Module
Heating
Coil
Cooling
Coil
Desiccant
Module
City Outside Return
Water Air
Air
Hot Air
Pump
Chilled Water
Loop
Dehumidified
Supply Air
Pump
Domestic
Hot Water
DHW
Pump
Hot Water
Loop
Terminal
Heating
Units
Terminal
Cooling
Units
Figure 42: Packaged CCHP/V System
126
System
CHP System
Absorption
Chiller
Ventilation
System
Major Components
ATS / SLC
Engine Generator
Coolant Heat
Exchanger
Exhaust Heat
Recovery
Minor
Components
Radiator
Heat Rejection
Radiator
Exhaust
Supervisory
Controller
Absorption Chiller
Enthalpy Recovery
Wheel
Desiccant Wheel
Controllers
Regeneration
Coil
Heating Coil
Cooling Coil
Regeneration
Exhaust Air
Domestic
Hot Water
DHW Storage Tank
Table 24: Packaged System Component List
Comparing Figure 41 and Table 23 with Figure 42 and Table 24 the system has been
greatly simplified with the removal of:

1 major component (heat pump)

2 minor components (regeneration burner and cooling tower)

7 control systems with their respective interfaces

2 heat rejections
Additions to Figure 42 include:

3 minor components (heating coil, cooling coil, and DHW preheat heat
exchanger)

1 supervisory controller that handles all control features with one interface
To further aid the understanding of the packaged system Figures 35 and 36 were created
to describe the operation of the packaged system in summer and winter modes.
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Exhaust
Exhaust Heat
Recovery
DHW Preheat
Pump
Building Domestic
Hot Water Storage
City
Water
Absorption
Chiller
Pump
Building Chilled
Water Grid
Air
Engine
Fuel
Building
Electric Grid
Generator
ATS/SLC
Utility Grid
Return Air
Radiator
Exhaust Air
Outside Air
Coolant Heat
Exchanger
Passive
Energy
Wheel
Preconditioned
Air
Chilled
Water
Coil
Saturated Air
Exhaust
Air
Pump
Active
Desiccant
Wheel
Dry Air
Supply Air
Regeneration
Air
Regeneration
Heat
Exchanger
Outside Air
Figure 43: CCHP/V Summer Operation Flow Diagram
Figure 43 shows the summer operation setup of the packaged system. Electricity from the
engine generator is routed through the ATS/SLC and then passed on to the building or
utility grid. The exhaust heat recovery first goes to direct fire the double effect absorption
chiller as it needs the highest quality of heat. The exhaust is then used further to heat
domestic hot water. Both the chiller and domestic hot water systems can be bypassed if
there is no demand for heat. The low quality heat from the absorption chiller can be used
to preheat the incoming city water that will be used for domestic hot water. Part of the
chilled water from the absorption chiller is routed to the chilled water coil to provide
cooling and dehumidification for ventilation air. The coolant energy is used to heat
regeneration air for the desiccant dehumidification wheel or it can be rejected to
atmosphere.
128
Winter Energy
Cascade
Exhaust
Exhaust Heat
Recovery (SH)
Pump
Air
Engine
Hot Water
Return
Hot Water
Supply
City Water
Exhaust Heat
Recovery (DHW)
Fuel
Pump
Building Domestic
Hot Water Storage
Building
Electric Grid
Generator
ATS/SLC
Utility Grid
Pump
Return Air
Radiator
Exhaust Air
Outside Air
Coolant Heat
Exchanger
Passive
Energy
Wheel
Preconditioned
Air
Hot
Water
Coil
Supply Air
Pump
Figure 44: CCHP/V Winter Operation Flow Diagram
Figure 44 shows the operation of CCHP/V system in the winter months. Similar to the
summer operation, the exhaust is first used in the domestic hot water system and then is
routed to the space heating system. The coolant energy is also used in the same heating
system. The ventilation system uses a heating coil to heat the ventilation air to its set
point after the enthalpy recovery wheel.
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7.0 Contributions, Conclusions, and Future Work
7.1 Contributions
1. This dissertation includes the complete account of the preliminary design, detailed
design, installation, commissioning, test and evaluation of a biodiesel fueled CHP
system.
The partial load data is particularly important when applying CHP systems to high
performance buildings and developing an operating strategy. Typically, prime
mover manufacturers do not publish part load data as they believe this will reduce
their competitive advantage. However, part load data is necessary for designers of
CHP systems to make intelligent choices when selecting a prime mover.
The distillation of the 25 kWe operating data, as well as the method used for
estimating the part load data of the 200 kWe engine data may shed some light on
the part load of other engines, however it will not be as accurate as actual
measured data. This inaccuracy may lead to over or under sizing systems, further
discouraging the use of CHP systems.
2. A generic preliminary CHP design guide was developed to help novice CHP
designers determine what they need to know in general, and what type of
questions need to be asked.
130
There is currently a shortage of trained engineers who understand energy systems.
Therefore, it is important to provide documentation for new-comers to the field so
that they can start making a contribution right away rather than after years of
training. (The current energy problems this country and the world face will
provide employment for anyone who understands the potential solutions for many
years to come).
3. To further assist engineers in designing CHP systems to fit buildings, a generic
TRNSYS CHP model has been developed.
The model includes building load inputs from cooling, heating, and
dehumidification data files. These data files can come from either measured data
or simulation data. Using an empirical table lookup model based on the CHP
system operation; power level, fuel consumption, and temperatures and flow rates
for the exhaust and coolant streams are output.
Within the look table are the prime mover (engine generator) and the heat
recovery systems (steam generator and coolant heat exchanger). The model
controller allows for design operation of the CHP system as well as thermal load
follow (heating and cooling), and desiccant regeneration load follow.
4. An example of systems integration is explored for integrating an engine generator
with heat recovery, a double effect absorption chiller, and a ventilation system
131
with a solid desiccant wheel. There are a number of possible equipment
combinations for prime movers, heat recovery, and heat utilization.
While this dissertation just introduces the topic, it is hoped that other researchers
and equipment manufacturers will begin to design packaged systems that can
provide energy for approximately 75% of the building stock that is currently not
available to the CHP industry due to the small size of these buildings.
7.2 Conclusions
1. The CHP system operates most efficiently at its design load and when the system
can be tied to electric and thermal grids, which allow excess energy to be used by
other buildings. The 25 kWe CHP system was able to reach an average thermal
efficiency of 76% at its design electrical load. During intermediate seasons, the
coolant energy had to be rejected or the engine had to be operated at a lower
electrical load, therefore reducing efficiency to around 65%, which was reflected
in the TRNSYS simulations. Additional hot water loads for the coolant energy
should be developed, such as providing domestic hot water or exporting the hot
water to neighboring buildings.
2. The operation and evaluation of the CHP system has led to the discovery of many
issues that effect equipment selection. Operating CHP systems that have a coolant
loop tied to space heating by radiant systems introduces a problematic control
problem. The radiant heating system requires relatively low temperature water
(30-40oC), and the engine ideally operates at a higher temperature (80-90oC). The
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installed IWESS CHP system needs an improved flow control system to maintain
higher coolant temperatures with its coolant heat exchanger. CHP system
designers need to be aware of this issue in order to operate the system efficiently.
A turbocharged Diesel engine may be a desirable prime mover selection; however
engineers need to be aware that backup power systems need to be modified to
prepare for part load operation. Furthermore, engine generator manufacturers
should be prepared to offer alternative turbochargers for CHP system designers
based on the operating profile of the CHP system.
3. Soy based biodiesel fuel was tested in the CHP system and compared to
petroleum based low sulfur Diesel fuel. Other than an increase in fuel
consumption due to the lower energy density of biodiesel fuel, the CHP system
performed similarly.
4. Design operation at peak connected with electrical and thermal grids is best for
maximizing efficiency. At the moment college campuses with electrical and
thermal grids appear to be the best fit for this technology as there is always a
demand for electricity, heating, cooling, and ventilation; the campus is always
occupied between classrooms, offices and dormitories. As the technology in
installed in more locations, the first and operating cost will be reduced, opening
additional markets.
133
5. The results from the IW and BAPP simulations lead to the conclusion that
additional thermal loads for the engine coolant must be sought. As CMU does not
have a campus hot water grid, two options are available to the mechanical systems
designers for the BAPP:
•add a single effect absorption chiller to the system so that the medium
quality coolant energy can be used to create chilled water for the campus
grid.
•integrate the BAPP hot water systems with neighboring buildings operated
in parallel with the steam grid.
Then first option is likely better as there is a chilled water grid so the entire
campus load is available whereas option two only offers heat to the immediately
adjacent buildings. If there is a sufficient budget available during the installation,
both should be included and tested.
7.3 Future Work
There are three main categories of future work. First, fully automating and integrating the
biodiesel fueled CHP system with the IW’s daily operation. Second, provide design
support for the next CHP system on the Carnegie Mellon campus, most likely the BAPP.
Third, a path to commercialization for packaged CHP systems needs to be developed.
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The automation and integration of the CHP system should be pursued in the next
development phase. Integrating the operation of the CHP system with inputs from the IW
including start up, power level, and shut down commands is necessary to show that this
CHP system can operate without direct user intervention. Additional tasks for the existing
CHP system include:

The modeling of the current configuration of the CHP system, the absorption
chiller and the ventilation systems. The model and the physical system should be
upgraded to include domestic hot water provision, replacing the heat pump in the
ventilation system with hot and chilled water coils, and adding a single effect
chiller to recover exhaust heat. This represents the largest equipment cost savings
and heat utilization gain in the CCHP/V system.

Fuel injection has been delayed approximately 15 degrees past top dead center in
the engine, which is causing late combustion. This was done intentionally to
reduce the combustion temperature and thus reducing NOX formation to meet
EPA regulation. Altering the engine timing should be explored when using
biodiesel fuels as the improved emissions may allow the engine to meet EPA
regulations with better combustion timing.

The TRNSYS model does not allow for down time for maintenance. Statistics of
annual energy demands for the IW should be analyzed to determine the best time
frame of year for maintenance, when loads are near zero.

Additional operational testing of the CHP system using a thermal load follow and
base load mode should be conducted. The engine will consume approximately
600 gallons of fuel per week.
135

Additional emissions testing to fully characterize emissions including particulates
from various types of biodiesel fuel. Furthermore, the effect of engine timing on
emissions should be investigated as the engine does not currently operate at it
most efficient point.

The long term effects of biodiesel fuel and continuous on the engine should be
explored and a maintenance program should be developed. There is a large body
of work already written for this topic, however it is typically meant for engines in
transportation applications. This testing will require a substantial fuel budget, but
facilities managers will be interested in the maintenance cycle of such systems.
For example, it is widely accepted that biodiesel fueled engines require less
frequent oil changes due to the increased lubricity of the biodiesel. In order to not
void the engine’s warranty, engine manufacturers will have to provide a reliable
maintenance program.
The next likely CHP project on the Carnegie Mellon campus is the Building As Power
Plant project. The following is a list of tasks and issues that should be resolved to aide in
the design and long term operation of the BAPP.

As the simulation model of the BAPP is updated and design decisions are made,
the scaled up IWESS simulation file should be used to test various mechanical
system configurations and operational strategies in greater detail.

Another addition to the TRNSYS model would be the ability to use multiple
engines using a modular approach to meeting the BAPP’s loads. Instead of using
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one 200 kWe engine, eight 25 kWe engine may be used or other combinations. A
modular CHP system allows for lower part load operation and/or higher
efficiency.

A problem that will have to be tackled in the future if the BAPP concept is widely
accepted will be what happens with multiple BAPP facilities on a campus. The
current operational concept is based on few high performance buildings that
provide excess energy to other buildings that simultaneously heat and cool. Most
likely, modular CHP systems will be required as a campus filled with high
performance buildings and CHP systems will mimic the same issues of a single
CHP system in a single high performance building.

A TRNSYS prime mover component design guide should be written so that prime
mover manufacturers can create component models for CHP system designers to
use in their simulations. It is not realistic for university researchers to install and
evaluate every type of prime mover and develop a component model. Prime
mover manufacturers will have detailed operating data for their products, which
could then be used to create TRNSYS components.
Finally, the CBPD should work to commercialize CHP systems by reducing the first costs
by a factor of 10 to 20. Figure 45 shows the complete cost break down by activity for the
design, procurement, installation, startup and commissioning of the CHP system for the
IW, which has a total cost of $675,781.47. That is $27,000 per kWe or if heat is included,
$11,000 per kW. The majority of the costs came from the complex installation process in
a building that did not easily accommodate the space requirements of this system.
137
Furthermore, as this is a first of a kind system, extra equipment, instrumentation and
controls were added to evaluate the system.
There is a lot of piping required to connect the engine generator with the steam generator
and the coolant heat exchanger. A significant part of the installation cost shown in Figure
45 can be attributed to long piping runs connecting the engine generator outputs to the
steam generator and the coolant heat exchanger. The remainder of the installation cost
includes electrical wiring for instrumentation and connecting the coolant heat exchanger
and steam generator outputs to the chiller, the IW, and the campus grids.
Biodiesel Fueled Engine Generator with Heat Recovery Cost Breakdown
Facilities, $18,692.72, 3%
Instrumentation & Controls,
$90,818.85, 13%
Engineering, $48,014.38, 7%
Installation, $397,613.00,
60%
Capital Equipment,
$117,756.00, 17%
Other, $2,886.52, 0%
Installation
Other
Capital Equipment
Engineering
Instrumentation & Controls
Facilities
Figure 45: Cost Breakdown of CHP System
138
The cost of piping would still be necessary if the system were packaged and skid
mounted, but the runs could be much more compact than what is currently installed and
could be standardized. An installer would not have to work out connections between
separate components. Shorter pipe runs mean fewer pump and heat losses. Finally, fewer
connections to work out will reduce installation and engineering time, which are
expensive.
Another issue arises when combining many systems into a complex machine, the
operation of the system will become more complex. Research into user interfaces and
trouble shooting from the maintenance technician’s and facilities manager’s points of
view should be investigated as ultimately they are the ones that must live with this system
on a daily basis.
The user interface and information gathered for the installed 25 kWe CHP system was
designed for the benefit of researchers. It likely that the quantity of information available
in the 25 kWe CHP would discourage maintenance technicians as they do not have the
time to sift through the large volumes of data generated by richly instrumented CHP
systems. Key data points should be identified that will benefit the users of the system.
Furthermore, having fewer data points will reduce the first cost of the CHP system.
Through standardization, systems integration and economies of scale a goal of reducing
first costs by a factor of 10 to 20 might well be realized.
139
References
1 Short-Term Energy and Summer Fuels Outlook. U.S. Department of Energy, Energy Information Agency.
http://www.eia.doe.gov/steo.
2 Electricity Flow, 2007 Energy Information Agency Annual Energy Review 2007, www.eia.doe.gov/
3 “The Market and Technical Potential for Combined Heat and Power in the Commercial/Institutional
Sector”. Prepared for U.S. Department of Energy, Energy Information Administration. Prepared by
ONSITE SYCOM Energy Corporation. January 2000.
4 “Market Potential for Advanced Thermally Activated BCHP in Five National Account Sectors”. Prepared
for Oak Ridge National Laboratory. Prepared by Energy and Environmental Analysis, Inc. May 2003.
5 “Market Potential for Advanced Thermally Activated BCHP in Five National Account Sectors”. Prepared
for Oak Ridge National Laboratory. Prepared by Energy and Environmental Analysis, Inc. May 2003.
6 Diamond, Richard C. “An Overview of the U.S. Building Stock”. Lawrence Berkley National Laboratory.
January 2001.
7 Power Scorecard. Pace University, Pace Law School Energy Project.
http://www.powerscorecard.org/tech_detail.cfm?resource_id=2
8 Casten, Thomas R. “Turning Off The Heat: Why America Must Double Energy Efficiency to Save
Money and Reduce Global Warming”. Prometheus Books, Amherst New York, 1998.
9 Ribarov L. A. and Liscinsky D. S., Microgrid Viability for Small-Scale Cooling, Heating, and Power,
Journal of Energy Resources Technology -- March 2007 -- Volume 129, Issue 1, pp. 71-78.
10 Fumo N., Mago P. J., and Chamra L. M., Evaluation of Cooling, Heating, and Power (CHP) Systems
Based on Building Energy-Rating, Energy Sustainability 2007, June 2007, Long Beach, California USA.
11 Douglas M. E., Wagner T. C., Sahm M. K., and Wepfer W. J., Economic Optimization of a Combined
Heating and Power System for an Office Building, Energy Sustainability 2007, June 2007, Long Beach,
California USA.
12 Tucker C. T., Rethinking the Benefits of CHP, ASME Power, April 2005, Chicago, Illinois USA.
13 Betz, Fred, Chris Damm, David Archer, and Brian Goodwin. “Biodiesel Fueled Engine Generator with
Heat Recovery”. Proceedings of the 2008 ASME Energy Sustainability Conference. Jacksonville, FL
August 2008. ES2008-54131.
14 U.S. Department of Energy, Oak Ridge National Laboratory, and Energy and Environmental Analysis,
Inc. Combined Heat and Power Installation Database. http://www.eea-inc.com/chpdata/
15 Discussion with Dr. Marc Portnoff. Director, Center for Advanced Fuel Technology, Carnegie Mellon
University.
16 Hennepin Energy Recovery Center (HERC):
http://www.co.hennepin.mn.us/portal/site/HCInternet/menuitem.3f94db53874f9b6f68ce1e10b1466498/?vg
nextoid=aad2c95fa29fc010VgnVCM1000000f094689RCRD
17 Herold, Keith E., Reinhard Radermacher, and Sanford A. Klein. “Absorption Chillers and Heat Pumps”.
CRC Press. 1996.
140
18 U.S. Department of Energy, Energy Efficiency and Renewable Energy. “Appliances and Commerical
Equipment Standards: Commercial Unitary Air Conditioners and Heat Pumps”.
http://www.eere.energy.gov/buildings/appliance_standards/commercial/ac_hp.html
19 Zhai, Chaoqin, David H. Archer, and John C. Fisher. “Integration Of The Active Desiccant Wheel In
CHP System Design ”. Proceedings of the 2008 ASME Energy Sustainability Conference. Jacksonville, FL
August 2008. ES2008-54190.
20 Capstone Company Website. www.microturbine.com
21 Schmitt Enertec CHP Brochure/Specification Sheets. Provided by Jim Sayre of Kraft Power.
22 PureComfortTM Brochure. United Technologies Company – Power.
23 Ingersoll Rand Company Website. www.ingersollrand.com
24 U.S. Department of Energy. Energy Efficiency and Renewable Energy. “Distributed Energy Program:
Distributed Energy Case Study Database”. http://www.sentech.org/CaseStudy/
25 Unison Solutions, Inc. Site Visit to Sun Prairie, Wisconsin Waste Water Treatment Plant. March 12 th
2002.
26 Jaaskelainen, Hannu E. and James S. Wallace. Operating Experience with a 240 kW Microturbine
Combined Heating, Cooling, and Power System. Proceedings of the 2008 ASME Energy Sustainability
Conference. Jacksonville, FL August 2008. ES2008-54314.
27 Guider, T. P. Characterization of Engine Performance with Biodiesel Fuels. Masters Thesis, Lehigh
University. December 2008.
28 Department of Energy, Office of Energy Efficiency and Renewable Energy. 2004 Biodiesel Handling
and Use Guidelines.
29 National Biodiesel Board Published Biodiesel Emissions.
www.biodiesel.org/pdf_files/fuelfactsheets/emissions.PDF
30 Brown, Jack. Producing Biodiesel from Brassica Crops in the Pacific Northwest. National Biodiesel
Conference, San Diego, CA. February 6, 2006.
31 Yin, H. 2006, "An Absorption Chiller in a Micro BCHPApplication: Model Based Design and
Performance Analysis." PhD Thesis, Carnegie Mellon University, School of Architecture, 6 September.
32 Bell, Arthur A. “HVAC Equations, Data, and Rules of Thumb”. McGraw-Hill Professional; 1 edition,
June 2, 2000.
33 Zhai, C., 2008, Performance Modeling of Desiccant Wheel Design and Operation, PhD Thesis, Carnegie
Mellon University.
34 Marion, Flore A., Sophie V. Masson, Frederik J. Betz, and David H. Archer. “Cogeneration System
Performance Modeling” Proceedings of the 2008 ASME Energy Sustainability Conference. Jacksonville,
FL August 2008. ES2008-54256.
35 Masson, Sophie, Ming Qu, and David Archer. "Performance Modeling of A Solar Driven Absorption
Cooling System for Carnegie Mellon University’s Intelligent Workplace”. Proceedings of International
Conference of Enhanced Building Operation, 2006, Shenzhen, China.
141
36 Sophie Masson, Elisabeth Aslanian. “TRNSYS Model of Hybrid Ventilation System”. Internal Report.
Carnegie Mellon University – CBPD.
37 Phone Discussion with Peter Rumsey of Rumsey Engineers regarding data center loads, 11:45 AM,
April 8th, 2009.
38 John Deere 200 kWe specifications sheet for a 6.8L Diesel Engine, Model 6068HF485
142