Whole Building Design Guide
Biodiesel Fueled Cogeneration Systems for a Building
Fred Betz, PhD.
David Archer, PhD.
Center for Building Performance and Diagnostics
School of Architecture
College of Fine Arts
Carnegie Mellon University
Pittsburgh, Pennsylvania
May 29, 2009
Table of Contents
Whole Building Design Guide ............................................................................................ 1
Biodiesel Fueled Cogeneration Systems for a Building ..................................................... 1
Table of Contents ................................................................................................................ 2
List of Figures ..................................................................................................................... 4
List of Tables ...................................................................................................................... 5
Nomenclature ...................................................................................................................... 6
1.0 Preliminary Design Guide............................................................................................. 7
1.1 Generic Design Steps ................................................................................................ 7
1.1.1 Loads .................................................................................................................. 7
1.1.2 Fuel Selection..................................................................................................... 8
1.1.3 Energy Grids ...................................................................................................... 8
1.1.4 Prime Movers ..................................................................................................... 9
1.1.5 Auxiliary and Heat Recovery Equipment .......................................................... 9
1.1.6 Operating Strategy ........................................................................................... 10
1.1.7 CHP System Evaluation ................................................................................... 11
2.0 Design of Biodiesel Fueled CHP System ................................................................... 12
2.1 Load Profiles ........................................................................................................... 12
2.2 Fuel Selection.......................................................................................................... 12
2.3 Energy Grids ........................................................................................................... 13
2.4 Prime Movers .......................................................................................................... 13
2.5 Auxiliary and Heat Recovery Equipment ............................................................... 14
2.6 Operations ............................................................................................................... 15
2.7 Evaluation ............................................................................................................... 16
2.8 Submittals ............................................................................................................... 16
Appendix A: Background ................................................................................................. 18
A.1 Fuels ....................................................................................................................... 18
A.2 Energy Grids .......................................................................................................... 19
A.3 Prime Movers ......................................................................................................... 20
A.3.1 Central Power Plants ....................................................................................... 20
A.3.2 Boilers and Steam Turbines ............................................................................ 20
A.3.3 Gas Turbine ..................................................................................................... 20
A.3.4 Internal Combustion Engines .......................................................................... 20
A.3.5 Fuel Cells ........................................................................................................ 21
A.3.6 Prime Mover Summary ................................................................................... 21
A.4 Heat Loads ............................................................................................................. 21
A.4.1 Space Heating ................................................................................................. 22
A.4.2 Absorption Cooling ......................................................................................... 22
A.4.3 Desiccant Regeneration................................................................................... 22
A.4.4 Other Heat Loads ............................................................................................ 23
A.4.5 Storage ............................................................................................................ 23
A.4.6 Heat Loads Summary ...................................................................................... 23
Appendix B: Biodiesel Fueled CHP system ..................................................................... 24
B.1.1 System Components ........................................................................................ 24
B.1.2 Input / Output .................................................................................................. 31
2
B.1.3 Operating Description and Results .................................................................. 32
B.1.3.1 Engine: Measured Data versus Manufacturer’s Specifications................ 34
B.1.3.1 Pressure – Time – Crank Angle Measurements ....................................... 35
B.1.3.2 Turbocharger Analysis ............................................................................. 37
B.1.3.3 Combustion Gas and Emissions Analysis ................................................ 38
B.1.3.4 Heat Recovery Analysis ........................................................................... 41
Appendix C ....................................................................................................................... 44
Appendix D: Steam System Schematics ........................................................................... 45
References ......................................................................................................................... 46
3
List of Figures
Figure 1: IW Heating and Cooling System Flow Diagram\ ............................................. 14
Figure 2: Basic CHP Flow Diagram ................................................................................. 24
Figure 3: CHP System Components ................................................................................. 25
Figure 4: Baldor Engine Generator ................................................................................... 25
Figure 5: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kWe......... 26
Figure 6: Assembled Components: Engine Generator (Left), Steam Generator (Right) .. 27
Figure 7: Steam - Hot Water Converter ............................................................................ 28
Figure 8: Coolant Heat Exchanger with Piping before Insulation .................................... 29
Figure 9: Remote Mounted Radiator ................................................................................ 29
Figure 10: Engine Generator Onboard Interface .............................................................. 30
Figure 11: Engine Generator Onboard Interface .............................................................. 30
Figure 12: Automated Logic CHP User Interface for the Heat Recovery/Rejection System
........................................................................................................................................... 32
Figure 13: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
........................................................................................................................................... 36
Figure 14: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
........................................................................................................................................... 37
Figure 15: Turbocharger Compressor Map [] ................................................................... 38
Figure 16: Summer Operation of the Steam Generator T-Q Diagram.............................. 42
Figure 17: T-Q Diagram for Coolant Heat Exchanger at 25 kWe .................................... 43
4
List of Tables
Table 1: Typical U.S. Commercial Building Loads ........................................................... 8
Table 2: Prime Mover Performance Summary ................................................................... 9
Table 3: Prime Mover Performance Summary ................................................................. 21
Table 4: Averaged Summer Diesel Commissioning and Experimental CHP Results ...... 33
Table 5: Averaged Winter Diesel Commissioning and Experimental CHP Results ........ 33
Table 6: Averaged Winter Biodiesel Experimental Results ............................................. 33
Table 7: Diesel Engine Generator Measured Data vs. Manufacturer Specifications ....... 34
Table 8: Biodiesel Engine Generator Data vs. Manufacturer Specifications ................... 35
Table 9: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel ................. 38
Table 10: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel ...................... 39
5
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
6
1.0 Preliminary Design Guide
This guide provides a generic approach to the preliminary design of a cogeneration
system that will provide power, cooling, heating, and ventilation to a building. A specific
example of design 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.
1.1 Generic Design Steps
The general procedure for designing a CHP system is to:
 determine the electrical and thermal loads of the building, load profiles and the
required flow rates and temperatures of cooling and heating streams.
 determine which fuel types are locally available, how they are distributed, and
their cost.
 determine what energy grids for power, natural gas, steam, chilled water, etc. are
available, what their operating conditions and costs are, and if it is possible to
interface with them.
 select a prime mover that best fits the load profile and load proportions.
 select auxiliary and heat recovery equipment to match the prime mover and the
fluids used to transfer energy.
 choose an operating strategy (thermal or electrical load follow, base load
operation, etc.)
 evaluate design options on the basis of capital, operating, and environmental cost.
As these steps are carried out the following documents should be created:
 a flow diagram.
 material and energy balances.
 equipment descriptions.
 operating descriptions.
 a process and instrumentation diagram.
 a preliminary layout of equipment
 cost estimates for the equipment and its installation
These documents provide the basis for equipment procurement, detailed design,
installation, and operation of a cogeneration system for a building.
1.1.1 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 1.
7
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.
Table 1: Typical U.S. Commercial Building Loads
Other
7.8
Table 1 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 1 gives annual energy demands; however, to properly size and evaluate a CHP
system, peak and base loads and annual hourly load profiles are required.
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; metered data is best. Over sizing systems will lead to
inefficiency. 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.
1.1.2 Fuel Selection
There are many fuels available for the operation of CHP systems including: natural gas,
petroleum products (gasoline, Diesel fuel, 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. 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.
1.1.3 Energy Grids
The availability of energy grids is an important consideration in the design of a CHP
system for a building. Energy grids can come in many forms; electrical, natural gas,
steam, chilled water, 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 that 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.
8
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 the possibility to level the
load on the CHP system by accepting or providing power or thermal energy so that it 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.
1.1.4 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 2 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, prime mover options may be eliminated or
identified 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 2: 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
1.1.5 Auxiliary and Heat Recovery Equipment
The fifth step in the design process is to select auxiliary heat recovery equipment that
makes use of exhaust gas, coolant flow or steam to meet the desired loads. This
equipment may include:
 heat exchangers
 absorption chillers (single and double effect)
 dehumidifiers
 thermal storage arrangements
Appendix A further 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
in Appendix B. T-Q diagrams should be constructed for each exchange of thermal energy
9
in the system. It may be necessary to contact several manufacturers to determine the best
match for the selected prime mover output and building load.
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
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.
1.1.6 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 the peak or at the 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; 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 for which it is
designed and importing or exporting thermal and electrical energy as required. 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 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 excess amounts of thermal and electrical
energy will have to be exported to an energy grid or rejected when loads are below peak
values. Rejecting energy decreases over all efficiency, but extra equipment, boilers and
chillers, will not be required to meet peaks.
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.
10
1.1.7 CHP System Evaluation
Evaluation serves multiple purposes. If multiple CHP system options exist the designer
must weigh and select among these options on an engineering, economic, and
environmental bases.
The CHP system designer must also evaluate 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. 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 economic demands of building operation.
11
2.0 Design of Biodiesel Fueled CHP System
A biodiesel fueled CHP system was designed, installed, operated and evaluated according
the design guide described above.
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 a renewable fuel and could
export excess energy to neighboring buildings. 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). The heating load changes rapidly as the IW has a
low 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 operates at about 7 psig (0.5 bar)
during the winter. The main steam supply pressure is 150 psig (10 bar) during the winter;
this pressure is reduced inside the buildings on campus as appropriate.
Regenerating the desiccant dehumidification wheel in the ventilation system is an
additional heat load in the IW. Desiccant regeneration, like the chiller operation 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.
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 an important
design consideration. Another group on the Carnegie Mellon University campus has
commercialized a biodiesel fuel refining process. This new commercial entity agreed to
donate the fuel for this system, which also made it the most economic fuel choice.
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 was addressed during the detailed system design and equipment layout.
12
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 their requirements for
installing a utility paralleled engine generator with a capacity of between 20 and 30 kWe.
Electricity enters the Carnegie Mellon 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 2 and
5 megawatts of electricity from Duquesne Light. Based on this information, Duquesne
Light set no requirements for grid protection on this system. A grid outage would
immediately over load the engine generator and cause it to shut down. Additional
protections were provided in this 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;
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).
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 required by the two
stage absorption chiller the amount of exhaust energy used was closer to 18 kWt, and
therefore diminished the heat recovered from the exhaust. Specification sheets from
13
engine manufacturers typically don’t include part load values or exact values for CHP
systems. Conservative estimates are recommended.
2.5 Auxiliary and Heat Recovery Equipment
Sizing the heat recovery equipment is where the first major difficulty arose for this
system configuration, as there are no commercially available steam generators in the 1030 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 thermal energy from the engine coolant needs to be recovered. A plate and
frame heat exchanger was selected to transfer this energy 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, 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 1
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 1: IW Heating and Cooling System Flow Diagram\
14
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
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. 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 determined by 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)
and a thermal loss of 2.5 kWt were calculated based on these estimates as shown in
Appendix C. Therefore, a minimum of 18.5 kWt was needed to drive the absorption
chiller. It was decided to add a safety factor to this number and to set the requirements to
20 kWt.
2.6 Operations
A specific operational strategy was not designated 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 operate in various modes:
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. The extra costs come from additional controls programming as well as having
actuators modulate their position rather than having two position valves.
15
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 made available on the web.
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 balanced
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. For example, to accurately measure fuel consumption,
a weigh tank is typically used, however code requirements indicate that tanks must be
fastened to the floor. Therefore, the fuel tanks are fastened to the floor, and extra piping
provisions were made to bypass the main fuel system so a separate fuel tank on a weigh
scale could be used. 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
16
3.0 Conclusions, Recommendations, Future Work
17
Appendix A: Background
Section two covers background information for each of step of the design guide.
A.1 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. [1]. The reason for this is that the fuel is readily available
with a nationwide distribution network, the cost per unit of energy is relatively 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.
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
18
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 [2]. 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,
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 [3].
A.2 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
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.
19
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.
A.3 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.
A.3.1 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
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 [Error!
Bookmark not defined.]. 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.
A.3.2 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.
A.3.3 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% [Error! Bookmark not defined.].
This difference is primarily based on the use of a regenerator to preheat incoming air or
the use of a combined cycle process that captures waste heat to generate steam and drive
an additional turbine. Distributed Generation systems typical operate around 15-25%
electrical efficiency.
A.3.4 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
20
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%.
A.3.5 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.
A.3.6 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
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 3.
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 3: 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
A.4 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 [4]. 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 [4].
21
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
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.
A.4.1 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.
A.4.2 Absorption Cooling
A heat pump is a technology that enables the transfer of heat from a low temperature to a
high temperature [5]. Heat pumps can be mechanical driven using electricity and a motor
or by heat. Absorption chillers are heat driven heat pumps [5].
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 [5]. 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 [5]. The higher the number of chiller stages, the
higher the overall efficiency [5]. However, the control system becomes more expensive
and there is an increased cost per unit of cooling. A typical single effect chiller will have
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 [6]. 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.
A.4.3 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 [7].
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 [7].
22
A.4.4 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
into additional usages of reject heat; however the ones stated above are currently
employed.
A.4.5 Storage
As discussed in section A.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.
A.4.6 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
season; it is up to the CHP system designer to use the given building and site loads to find
the proper balance.
23
Appendix B: Biodiesel Fueled CHP system
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.
B.1.1 System Components
There are four major components in the biodiesel CHP system shown in Figure 2:
 engine generator,
 steam generator,
 coolant heat exchanger, and
 automatic transfer switch (ATS) / soft load controller (SLC)
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 2: Basic CHP Flow Diagram
Expanding upon Figure 2, Figure 3 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.
24
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 3: CHP System Components
The engine generator is a standard engine generator assembled by Baldor Electric
Company shown in Figure 4. 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 4: Baldor Engine Generator
The engine generator is connected to the grid via an ASCO 7000 automatic transfer
switch (ATS) and soft load controller (SLC) shown in Figure 5. The ATS/SLC allows the
engine generator system to deliver excess power to the grid during operation, while
25
allowing the grid to power the mechanical room when the system is off. 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 5: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kWe.
The steam generator made by Vaporphase, Inc. shown in Figure 6 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 to the campus steam grid.
26
Figure 6: Assembled Components: Engine Generator (Left), Steam Generator (Right)
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 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/or 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 7.
27
Figure 7: Steam - Hot Water Converter
The coolant heat exchanger shown in Figure 8 is a standard plate and frame heat
exchanger made by ITT, Inc. The heat exchanger operates in parallel with a standard
engine generator radiator, which has been moved outside of the mechanical room shown
in Figure 9.
28
Figure 8: Coolant Heat Exchanger with Piping before Insulation
Figure 9: Remote Mounted Radiator
29
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 10: Engine Generator Onboard Interface
Figure 11: 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 protects both the grid and 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.
30
The steam generator has its own stand alone pneumatic control system that has three
principal tasks. First, it supplies condensate to the steam generator so that it does not run
dry. Hot exhaust gases can warp the coils if the heat is not dissipated by steam generation.
It calls for makeup water based on the output of a low level alarm and if makeup water is
not available, it bypasses the exhaust gases 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 to maintain the pressure. The purpose of this control function is
to prevent a sudden drop in steam pressure, which causes swelling and carry over of the
liquid contained in the generator.
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 routing and control of the steam flow 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 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 D.
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.
B.1.2 Input / Output
The Inputs for this system include:
 fuel (Diesel or biodiesel)
31



air (fresh air for combustion)
condensate
hot water return
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 12.
Figure 12: Automated Logic CHP User Interface for the Heat Recovery/Rejection System
B.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
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.
32
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.
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 4: 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 5: Averaged Winter Diesel Commissioning and Experimental CHP Results
CHP
Efficiency
49%
61%
70%
74%
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 6: Averaged Winter Biodiesel Experimental Results
CHP
Efficiency
54%
65%
68%
76%
Exhaust Heat
Recovered (kWt)
4
9
13
18
The results shown in Tables 4 through 6 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.
33
B.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 7: Diesel Engine Generator Measured Data vs. Manufacturer Specifications
Table 7 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 8 shows similar
results to Table 7 for biodiesel fuel.
34
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
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)
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)
Steady increase in flow rate with power (6 kW = 64
CFM, 12kW = 68 CFM, 18kW = 74 CFM)
Verified with weigh tank measurement
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 8: Biodiesel Engine Generator Data vs. Manufacturer Specifications
As shown in Tables 7 and 8, 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
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.
B.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 13.
35
Figure 13: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
Figure 13 shows the pressure vs. crank angle curve, and shows injection combustion
taking place around top dead center (TDC).
36
Figure 14: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel
As can be observed in Figure 14, the wave forms shifts soon after start up 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.
B.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 15, 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.
37
Figure 15: Turbocharger Compressor Map [8]
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 turbocharger was designed.
CHP system designers should be aware of this fact and request a turbocharger that will
operate more effectively in the appropriate range.
B.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 9: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel
38
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 10: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel
The data in Tables 9 and 10 agree with published results [9, 10, 11] with significant
reductions in CO, and UHC. However, typically soy based biodiesel has resulted in 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
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.
moles _ O2  moles _ N 2 17.75  17.753.76
AFR 

 84.5
mole _ Fuel
1
Determine quantity of excess air.

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
39
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 9 on a dry basis.
Calculated Percentage of CO2 = 8.4%
Calculated Percentage of O2 = 9.4%
Both the CO2 and O2 emissions are consistent with the measured data in Table 9.
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
40
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 
 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 
 kg  mol 
1,868,999.5 kJ 
Q  28.4   1.065  10 5 

 sec 
 sec 
 kg  mol 

 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.
B.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
41
describing the operation of heat exchangers by showing the stream temperatures versus
heat transfer between them. The required area for heat transfer between the streams, A,
can be calculated from the following function:
dq
A
,
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 16: Summer Operation of the Steam Generator T-Q Diagram
Figure 16 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
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%.
42
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 16 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 17 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 17.
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.
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 17: 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.
43
Appendix C
Insert in PDF version.
44
Appendix D: Steam System Schematics
Insert pages in PDF version
45
References
1 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/
2 Discussion with Dr. Marc Portnoff. Director, Center for Advanced Fuel Technology, Carnegie Mellon
University.
3 Hennepin Energy Recovery Center (HERC):
http://www.co.hennepin.mn.us/portal/site/HCInternet/menuitem.3f94db53874f9b6f68ce1e10b1466498/?vg
nextoid=aad2c95fa29fc010VgnVCM1000000f094689RCRD
4 Casten, Thomas R. “Turning Off The Heat: Why American Must Double Energy Efficiency to Save
Money and Reduce Global Warming”. Prometheus Books, Amherst, New Yok, 1998.
5 Herold, Keith E., Reinhard Radermacher, and Sanford A. Klein. “Absorption Chillers and Heat Pumps”.
CRC Press. 1996.
6 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
7 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.
8 Guider, T. P. Characterization of Engine Performance with Biodiesel Fuels. Masters Thesis, Lehigh
University. December 2008.
9 Department of Energy, Office of Energy Efficiency and Renewable Energy. 2004 Biodiesel Handling and
Use Guidelines.
10 National Biodiesel Board Published Biodiesel Emissions.
www.biodiesel.org/pdf_files/fuelfactsheets/emissions.PDF
11 Brown, Jack. Producing Biodiesel from Brassica Crops in the Pacific Northwest. National Biodiesel
Conference, San Diego, CA. February 6, 2006.
46