FEMP First Thursday Seminar
Combined Heat and Power:
An Integrated Approach to Energy Resource Optimization
Short Description
Combined Heat and Power allows you to recover waste heat from power generation to use for
additional heating, cooling, or dehumidification. This course explores CHP as an option for
Federal facilities, exploring the technology, its applications, and potential funding options.
Core Competency Areas Addressed in the Training
After completing this seminar, the learner will:
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Define CHP for on-site power generation.
Discuss potential benefits of CHP for the learner’s site or facility including
whether the site has characteristics that make CHP cost-effective.
Discuss “prime mover” and “thermally activated technologies,” including the advantages
and limitations of specific technology options.
Conduct a feasibility analysis to inform the technical feasibility and cost effectiveness of implementing a CHP project.
Learn best practices and lessons learned from CHP projects in the Federal government.
Consider the potential financing vehicles including CHP as part of
an ECM in ESPCs, UESCs, and PPAs.
Expected Results for Those Completing this Training
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Have the information to determine whether a Combined Heat and Power project is
technically and economically feasible.
Be able to consider various CHP technology options that may be selected.
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CHP Resources
Re s o u r c e s
The Department of Energy's, EERE Industrial Distributed Energy website:
http://www1.eere.energy.gov/manufacturing/distributedenergy/
The Department of Energy's Intermountain Clean Energy Application Center:
http://www.intermountaincleanenergy.org/
The Environmental Protection Agency's Combined Heat and Power Partnership:
http://www.epa.gov/chp/
COMBINED HEAT AND POWER: Effective Energy Solutions for a Sustainable Future
(2008 Oak Ridge National Laboratory publication):
http://info.ornl.gov/sites/publications/files/Pub13655.pdf
Glossary
Absorption chiller: A cooling machine that uses heat as the primary source of energy for driving an
absorption refrigeration cycle. Absorption chillers are classified as either indirect-fired, heat-recovery,
or direct-fired units.
Aftercooler: A gas-to-liquid (air-to-water) heat exchanger that removes heat from reciprocating engine
turbochargers.
Apparent power: The vector sum of real power and reactive power. Electrical generators are typically
rated in units of kilovolt-amp (kVA). This apparent or total power rating is the product of the generator
rated voltage and the rated maximum current.
Avoided cost: The incremental cost to an electric power producer to generate or purchase a unit of
electricity or capacity, or both, but which is instead provided by a third party or which is not needed due
to energy conservation and efficiency.
Backup tariff: A fee or tariff charged to a CHP system owner or operator by the electrical supplier that
provides electrical energy to the site when on-site electrical generating equipment cannot satisfy the
demand.
Base load: The level of demand, for heat or electricity, that exists for the majority of the operating
period. Demand will rarely be less than the base load.
Base-loaded design and operation: An operating mode in which the combined heat and power (CHP)
system is interconnected to the electrical grid and sized to meet the site’s base-load requirements. By
operating in this mode, part-load operation is avoided, no redundant capacity is required, and only
supplemental power in excess of the base load is purchased from the electric utility.
Bias firing (BF): An emission control technique that involves injecting more fuel to some burners
(typically the lower burners) while reducing fuel to other burners (typically the upper burners) to create
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staged combustion conditions inside a boiler. This technique decreases the excess oxygen
concentration and thereby reduces the formation of nitrogen oxides during combustion.
Boiler efficiency: A value that characterizes the amount of heat captured by the boiler or HRSG and
transferred to the water, compared to the heat input. Boiler efficiency is a function of boiler losses and
combustion losses.
Bottoming cycle: A heat-recovery scheme in which high-temperature thermal energy is produced and
first used for industrial applications such as glass processing and metal smelting furnaces. Waste heat
recovered from the industrial process is then used to drive a turbine to produce electric power.
Burner tuning (BT): An emission control technique that limits the amount of excess oxygen available for
combustion and thereby reduces formation of nitrogen oxides.
Burners out of service (BOOS): An emission control techniques that reduces the formation of nitrogen
oxides. In this technique, certain burners are removed from service by stopping fuel flow but maintaining
air flow to create staged combustion conditions inside a boiler.
Buy-back rate: The rate paid to a CHP system owner or operator by the electrical supplier for the
excess electricity generated by the CHP system.
Carnot cycle: the maximum value obtainable for any heat engine. A cycle (of expansion and
compression) of an idealized reversible heat engine that does work without loss of heat.
CHP electrical efficiency: A measure of the amount of fuel energy converted into electricity. In
numerical terms, CHP electrical efficiency is a function of the net electricity generated and the total fuel
input expressed as follows: Net electricity generated/Total fuel input.
Cogeneration: is the sequential use of fuel energy to produce more than one finished energy product,
such as electric power, steam, refrigeration, thermal drying, air heating, or a host of others.
Cogeneration technology: A technology in which conventional power generation systems have the
means to make use of the energy remaining in exhaust gases, cooling systems, or other energy waste
streams.
Combined cycle: A term referring to the combination of two or more heat-recovery schemes to extract
the most energy from the fuel. Typically, the exhaust from a gas turbine that is coupled to an electrical
generator is used to produce steam that then drives a steam turbine coupled to another electrical
generator. This increases the efficiency of electricity generation to about 50%.
Combined heat and power (CHP): The sequential production of two forms of useful energy from a
single fuel source. In most CHP applications, chemical energy in fuel is converted to both mechanical
and thermal energy. The mechanical energy is generally used to generate electricity while the thermal
energy or heat is used to produce steam, hot water, or hot air. Depending on the application, CHP is
referred to by various names including cogeneration, Building Cooling, Heating, and Power (BCHP);
Cooling, Heating, and Power for Buildings (CHPB); Combined Cooling, Heating, and Power (CCHP);
Integrated Energy Systems (IES), or Distributed Energy Resources (DER).
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Compression ignition (CI) engine: A reciprocating internal combustion engine that compresses air until
the air temperature is higher than the fuel ignition temperature. At that point in the cycle, fuel is injected
into the cylinder where it spontaneously ignites, burns, and expands against the piston. Diesel engines
are characterized as CI engines.
Demand charge: A fee or tariff charged for the use of electricity based on the maximum power
requirement, electrical demand, during a specified period of time, typically a month ($/kW).
Desiccant dehumidifier: A machine that uses heat to achieve a cooling effect by removing water vapor
from an air stream thereby decreasing the latent cooling load. Desiccant dehumidifiers use materials
known as desiccants that naturally remove moisture from humid air. As the desiccant become saturated,
it loses its ability to remove moisture and must be either replaced or recharged. Recharging a desiccant
involves increasing its temperature to expel the captured moisture.
Desiccant: A material that naturally attracts moisture from gases and liquids. As moisture is absorbed, it
collects on the surface of the desiccant and the desiccant becomes saturated. When heated, the
desiccant dries out, or regenerates, and can be used again. Some common desiccants include silica gel,
activated alumina, alumina oxide, and deliquescent absorbents such as lithium chloride (LiCl) and
calcium chloride (CaCl2).
Ebullient cooling system: A cooling system for reciprocating internal combustion engines that uses
natural circulation of a boiling coolant such as treated water to remove heat. In operation, pressurized
coolant enters the engine near the bottom where the heat causes part of the coolant to boil generating
two-phase flow. Because only part of the coolant boils, heat rejection occurs at a constant temperature
with less thermal stress to the engine. The formation of bubbles lowers the density of the coolant and
causes natural circulation to the top of the engine.
Economically dispatched: An operating approach for a CHP system that factors in the value of
purchased power and boiler fuel costs relative to CHP system fuel and maintenance costs and the ability
to use recoverable heat. By operating in this mode, it is possible to use microprocessor control systems
to perform real-time calculations of operating costs and cost savings as a basis for making operating
decisions.
Effective Electric Efficiency: the net electric output divided by the effective fuel input. Effective fuel
input is the total fuel used by the combined heat and power (CHP) system minus the fuel that would be
used by an 80 percent efficient boiler to generate the same amount of steam as produced by the CHP
system. For a discussion of effective efficiencies and calculations, please review the introduction to the
Catalog of CHP Technologies and/or the Methods for Calculating Efficiency Web page.
Electrostatic precipitator (ESP): A post-combustion emission control device used to remove
particulate matter suspended in flue gas. Separation within an ESP is accomplished by electrically
charging the particles. As the particles take on a negative charge, they migrate toward collector plates,
thereby cleaning the flue gas.
Enthalpy: a thermodynamic property: a general measure of the internally stored energy per unit of mass.
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Entropy: a thermodynamic property – the property of steam held constant in a reversible adiabatic
process.
Exit fee: A fee or tariff imposed on a customer that will no longer be supporting the payoff of the
electricity supplier’s sunk or stranded cost in generation equipment.
Fuel Source: In CHP systems, fuel sources can include natural gas, biomass, biogas, coal, waste heat,
or oil.
Flue gas desulfurization (FGD): A post-combustion emission control technique for removing sulfur
dioxide from flue gas. Wet scrubbers, dry scrubbers, and sorbent injection represent different FGD
techniques.
Flue gas recirculation (FGR): The process of injecting flue gas into a boiler along with fresh combustion
air to modify conditions within the combustion zone. The result of FGR is control of nitrogen oxide
formation by lowering the peak flame temperature and reducing the oxygen concentration.
Forced-internal recirculation (FIR): A type of burner that uses a combination of premixing, staging, and
inter-stage heat removal to control nitrogen oxide and carbon monoxide formation during combustion of
natural gas.
Fuel-induced recirculation (FIR): A nitrogen oxide reduction technique applicable to boilers that burn
gaseous fuel. Fuel-induced recirculation is similar to flue gas desulfurization except that a portion of the
flue gas is mixed with the fuel instead of combustion air. The effect of this mixture on the combustion
process is to reduce the peak flame temperature.
Gas turbine: A rotating machine that converts the chemical energy of fuel into mechanical energy. Basic
elements of a gas turbine are the compressor, combustion chamber, and turbine. In operation, fresh air
is drawn in by the compressor and forced into the combustion chamber. Inside the combustion
chamber, the compressed air mixes with the fuel, and combustion occurs. During combustion, the
chemical energy in the fuel is released to produce high-temperature combustion products that expand
through the turbine and cause rotation.
Heat exchanger: An unfired heat-recovery device that is capable of transferring heat from
gas-to-gas, gas-to-liquid, liquid-to-gas, or liquid-to-liquid.
Heat recovery: The effective capture and use of heat rejected from the power cycles. Heat recovery
turns a relatively inefficient simple cycle power generation process into a more efficient cogeneration or
combined cycle process.
Heat-recovery muffler: An unfired heat-recovery device that recovers heat from reciprocating engine
exhaust and uses the heat to generate hot water or steam.
Heat-recovery steam generator (HRSG): An unfired or supplementary-fired heat exchanger that uses
thermal energy to produce hot water or steam. The main application for unfired HRSGs is waste heat
recovery and steam production from gas turbine exhaust. Supplementary-fired HRSGs for gas turbine
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applications include gas-fired or oil-fired burners that augment the steam or hot water generating
capacity of the exhaust gas stream.
Higher heating value (HHV): The standard measure of the energy released during combustion of a fuel,
assuming the product water is in the liquid state. For natural gas fuel, the HHV is approximately 10%
higher than the lower heating value (LHV).
ICI boiler: A fired heat-recovery device for industrial, commercial, and institutional facilities that uses the
chemical energy in fuel to raise the energy content of water so that it can be used for heating and power
applications.
Inverter: An electrical device that converts direct current power to alternating current power. Most
inverters operate by cutting the direct current power into a series of blocks or square waves at a number
of different frequencies. These blocks are then electrically summed to create a voltage waveform that
approximates the required alternating current.
Isentropic efficiency: A comparison of the actual work output of a machine compared to the ideal, or
isentropic, output. It is a measure of the effectiveness of extracting work from the expansion process
and is used to determine the outlet conditions of the steam from a steam turbine.
Islanding: A safety hazard that can occur when a generating facility such as a CHP system continues to
supply power to a portion of the electrical grid after the balance of the grid has been de-energized.
Isolated design and operation: An operating mode in which the CHP system is sized to meet the site
peak with reserve allowance for short-term power transients and to operate with no connection to the
electrical grid. By operating in this mode, no electricity purchases are required.
Load-tracking: An operating mode for a CHP system that is designed to track either the site’s thermal
or electric load. By operating in this mode, supplemental power purchases, heat rejection, or
supplemental thermal energy may be required, but both electric and thermal approaches can be
designed to supply the site’s peak requirements.
Low excess air (LEA): A boiler operating condition in which the lowest possible excess air level is
provided while maintaining good combustion. Operating with LEA creates conditions within the
combustion zone that lower nitrogen oxide production.
Lower heating value (LHV): The standard measure of the energy released during combustion of a fuel,
assuming the product water is in the gaseous state. For natural gas fuel, the LHV is approximately 10%
lower than the higher heating value (HHV).
Low-NOx burner (LNB): A specially designed piece of combustion equipment that reduces nitrogen
oxide formation through careful control of the fuel-air mixture during combustion. By proper staging of
fuel and air, nitrogen oxide formation is controlled due to a lower maximum flame temperature and a
reduced oxygen concentration.
Microturbine: A small gas turbine consisting of a compressor and a turbine. An internal heat exchanger
known as a recuperator is often added to recover heat from the exhaust gases and thereby improve
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overall energy efficiency. In operation, a radial flow (centrifugal) compressor compresses the combustion
air that is then preheated in the recuperator using heat recovered from the exhaust gas stream. After the
heated air from the recuperator mixes with fuel in the combustion chamber, the hot combustion gases
expand through the turbine and cause rotation.
Molten carbonate fuel cell (MCFC): A type of fuel cell that operates at higher temperature and is more
efficient than the commercially available phosphoric acid fuel cell. The high exhaust temperature of a
MCFC can generate additional electricity in a steam turbine or in a gas turbine combined-cycle CHP
system. The MCFC is expected to target 1-20 MW stationary power applications and should be well
suited for industrial CHP applications.
Natural gas reburning (NGR): A combustion modification technique for reducing emissions of nitrogen
oxides by staging fuel rather than combustion air. In this technique, a portion of the fuel is injected
downstream of the main combustion zone. The result is reduced formation of nitrogen oxides through
lower peak flame temperatures and reduced oxygen concentrations.
Opportunity Fuels: Opportunity fuels are materials from agricultural or industrial processes that would
otherwise be wasted but could power a CHP system and are available at or in close proximity to a
CHP site.
Overfire air (OFA): Combustion air that is injected into a boiler above the normal combustion zone. This
approach is generally used in conjunction with operating the burners at a lower than normal air-to fuel
ratio to reduce the formation of nitrogen oxides. When applied, OFA is supplied above the main
combustion zone to achieve complete combustion. Overfire air is a feature often incorporated into
low-NOx burner designs.
Oxygen trim (OT): A boiler operational modification that limits the amount of excess oxygen available
for combustion.
Peak load: The peak load is the maximum demand for heat or electricity that occurs in any one hour
in a year.
Peak shaving: An operating mode for a CHP system that is designed to satisfy the site’s peak power
requirements either by operating during the site’s peak demand periods or during the utility’s peak
demand periods. By operating in this mode, the purchase of more expensive
on-peak power is avoided thereby decreasing the average price of power.
Phosphoric acid fuel cell (PAFC): A type of fuel cell that uses concentrated phosphoric acid as the
electrolyte. The relative stability of concentrated phosphoric acid is high compared to other common
acids; consequently, a PAFC is capable of operating at the high end of the acid temperature range (212
to 428°C).
Power quality: A relative term used to characterize electrical energy. Power quality is influenced by
correcting the power factor to keep the voltage and current in phase, maintaining strict voltage levels,
and minimizing harmonic distortions.
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Power-to-heat ratio: An indication of the proportion of power (electrical or mechanical energy) to heat
energy (steam or hot water) produced by a CHP system.
Prime Movers: Prime movers are the devices that convert fuels to electrical or mechanical energy.
Reliable Power: Reliable power refers to the ability to provide electric power that meets stringent
standards for minimal power interruptions.
Spark Spread: For a CHP system, spark spread is the difference between the delivered electricity price
and the total cost to generate power with CHP.
Proton exchange membrane fuel cell (PEMFC): A type of fuel cell that is of particular interest to the
automotive industry as a future power plant for electric vehicles. The PEMFC has very high power
densities and can start-up quickly and meet varying demand.
Public Utility Holding Company Act (PUHCA): Federal legislation of 1935 that prevents utility holding
companies from subsidizing unregulated business activities from profits obtained from their regulated
business activities and captive customers.
Public Utility Regulatory Policy Act (PURPA): A 1978 Federal law that requires utilities to buy electric
power from private “qualifying facilities,” at an avoided cost rate. This avoided cost rate is equivalent to
what it would have otherwise cost the utility to generate or purchase that power themselves. Utilities
must further provide customers who choose to self-generate a reasonably priced backup supply of
electricity.
Qualified Facility (QF): A utility is required under Section 210 of PURPA to purchase excess electricity
generated by a qualified facility and to provide backup power at a reasonable cost. Qualified facilities
include plants that use renewable resources or cogeneration technologies to produce electricity.
Reactive power: A measure of the amount of energy stored in an electrical circuit that performs no real
work. The energy may be stored in magnetic fields of transformers and motors or in electromotive fields
in capacitors. Reactive power, which is sometimes referred to as inductive power, is the product of the
inductive current flowing through a load, and the voltage drop across the load is expressed in units of
reactive kilovolt-amp (kVAR).
Real power: An indication of the amount of energy that performs real work. In simple resistive circuits,
real power is defined as the product of the current flowing through the circuit and the voltage across that
circuit. Real power is typically measured in units of kilowatt (kW).
Reciprocating internal combustion engine (RICE): An internal combustion engine with a crankshaft
that is turned by the movement of pistons inside cylinders.
Recuperator: A gas-to-gas heat exchanger designed to extract heat from an exhaust gas steam and
use it to increase the temperature of incoming combustion air. Recuperators rely on tubes or plates to
continuously transfer heat from the outgoing exhaust gas to the incoming combustion air. These
components are arranged to keep the two gas streams from mixing.
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Regenerator: A gas-to-gas heat exchanger in which heat is transferred indirectly as a heat storage
medium is alternately exposed to hot and cold flow streams. Periodic exposure to hot and cold flow
streams can be accomplished either by rotary or valve-switching devices. During operation, a small but
significant amount of air leakage occurs from one gas stream to the other.
Selective catalytic reduction (SCR): A post-combustion emission control technique for reducing
emissions of nitrogen oxides. In this technique, a catalyst and a reductant (ammonia gas) are used to
dissociate nitrogen oxides to nitrogen gas and water vapor.
Selective discounting: A practice whereby an electrical supplier agrees to provide electricity to a
customer at a reduced or discounted rate as an incentive to pursuing alternative electrical generating
capability.
Selective noncatalytic reduction (SNCR): A post-combustion emission control technique for reducing
emissions of nitrogen oxides. In this technique, a reducing agent of either ammonia or urea is used to
dissociate nitrogen oxides to nitrogen gas and water vapor.
Simple Cycle: refers to the conventional application of a single prime mover cycle.
Solid oxide fuel cell (SOFC): A type of fuel cell that offers the reliability of all solid ceramic construction
and is expected to have an electric efficiency of up to 50% (LHV). The high exhaust temperature of a
SOFC can be used to generate additional electricity in a steam turbine or in a gas turbine combinedcycle CHP system.
Spark ignition (SI) engine: A reciprocating internal combustion engine that uses an externally supplied
spark to ignite a compressed mixture of fuel and air. (Caution: Spark ignition should not be confused
with steam injection, which is also represented by the acronym SI.)
Staged combustion air (SCA): An emission control technique in which air is injected into a boiler at
different points or stages in the combustion process to reduce the peak flame temperature and lower the
oxygen concentration, thereby controlling the formation of nitrogen oxides. Techniques based on this
concept include BOOS, BF, OFA, and LNBs.
Staged combustion: A technique that involves mixing air and fuel at two or more locations inside a
boiler to create zones with high and low excess air levels. Combustion at either very low or very high
excess air levels results in reduced formation of nitrogen oxides.
Steam injection (SI): An emission control technique used to decrease the flame temperature and
thereby reduce the formation of nitrogen oxides during combustion.
Steam turbine: A rotating machine that converts the kinetic energy of moving steam into mechanical
energy. Steam turbines are constructed with a stationary set of blades (called nozzles) and a moving set
of adjacent blades (called buckets or rotor blades) installed within a pressure-retaining housing.
Stationary nozzles accelerate the steam to high velocity by expanding it to lower pressure while the
rotating blades change the direction of the steam flow to produce torque. Steam turbines are subdivided
into two principal turbine types, impulse and reaction, depending on the way they direct steam flow.
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Synchronizing: The process by which the sinusoidal output voltage waveform of an alternating current
electrical generator is brought precisely into line with the frequency, time, and voltage of another
electrical generator or with the main system to which it is to be connected.
Thermodynamic efficiency: A term used for expressing efficiency for devices that operate in cycles or
for individual components that operate in processes.
Three-way catalyst (TWC): A post-combustion emission control device for spark ignition engines that
uses ceramic substrates and trimetal catalyst formulations.
Tire-derived fuel (TDF): A solid fuel consisting of whole scrap tires in a chipped form.
Topping cycle: A heat-recovery scheme in which the energy in fuel is first used to generate electricity.
Waste heat from the prime mover is then recovered and used for process heating or cooling
applications.
Total CHP efficiency: A measure of the net electricity generated, the net heat supplied to the process,
and the total fuel input expressed as follows: (Net electricity generated + Net heat supplied to
process)/Total fuel input.
Trigeneration: A combined-cycle CHP system that includes cooling equipment such as an absorption
chiller.
Uplift tariff: A fee or tariff charged to a CHP system owner or operator by the distribution utility for
transmission of the CHP-produced electricity to the market. The uplift tariff could reflect costs for
distribution, ancillary services, capacity, and losses.
Waste heat-recovery boiler: An unfired heat-recovery device such as a heat-recovery steam generator
that uses heat recovered from hot exhaust gases as fuel for generating hot water or steam.
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