Technical Feasibility

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Technical Advantages

The technical advantages of district energy with CHP systems are compelling.  These systems are:

  • Energy efficient. When steam, hot water or chilled water arrive at a customer's building, they are ready to use. They are 100 percent efficient "at the door," compared with 80 percent or lower efficiencies when burning natural gas or fuel oil at a building. In addition, district energy systems can use the "reject heat" that results from burning fuel to produce electricity at a power plant, nearly doubling the power plant's fuel efficiency and also lowers the emissions typically associated with standard electrical generation.

  • Environmentally sound. The less energy used, the less sulfur dioxide and carbon dioxide expelled into the environment. District energy enables building owners and managers to conserve energy, improve operating efficiency and protect the environment. With district energy, building managers no longer need to burn fuels or store or use refrigerants on site, so the site is safer and more environmentally sound - and does not need unsightly smokestacks. Instead, fuel and refrigerants are used at district energy plants. These systems employ stringent emission controls - more so than individual buildings - and this provides air-quality benefits.

  • Easy to operate and maintain. District energy is worry-free heating and/or cooling delivered directly to a customer's building - ready to use. Customers do not need boilers or chillers, so there is less maintenance, monitoring and equipment permitting. And that allows occupants, rather than energy operations, to be the focus. District energy customers also eliminate the need for fuel deliveries, handling and storage so there are fewer safety and liability concerns for employees and building occupants.

  • Flexible in design.  No smoke stacks, boilers or cooling towers means greater building design flexibility. Architects can easily design or renovate buildings to be more versatile and aesthetically pleasing for both potential occupants and the community.

  • Able to capture efficiencies of scale.  District energy systems produce steam, hot water or chilled water at a central plant and then pipe that energy out to buildings in the district for space heating, domestic hot water heating and air conditioning. Individual buildings don't need their own boilers or furnaces, chillers or air conditioners. A district energy system does that work for them

End-Use requirements

End-use requirements include thermal load matching and load duration curves, which may need to be determined by a professional developer.  A back-of-the-envelope calculation of  CHP load suitability can give an end-user a good idea of whether or not it makes sense to move ahead with an official technical feasibility study.

CHP load suitability is a measure of the efficiency of usage throughout the entire year of both the electric energy and the thermal energy generated by the CHP unit. In other words, a high Load Suitability means the electricity and thermal energy are not wasted, and the CHP unit is well matched to the facility. 

Modern CHP developers "size for thermal," i.e. the system is sized to take maximum advantage of thermal energy.  Fill in the blanks below for a good indication of suitability:


CHP Load Suitability




Ratio of annual electric energy load to peak load times 8760 hours.




Ratio of annual thermal energy load to peak load time 8760 hours.

Equipment Selection

Selecting the appropriately-sized CHP equipment is the next step.  Reciprocating engines, combustion turbines, HRSGs, and steam turbines, heat recovery units, absorption chillers, desiccant dehumidifiers, hydronic heating systems, hot water loops, steam loops, thermal storage, and turbine inlet cooling systems are the most common district energy/CHP technologies.

Gas turbines have made tremendous efficiency strides in recent years.  These reliable distributed energy resources are becoming the mainstay of peak-shaving equipment.  When needed, this equipment can be started immediately, and can quickly generate full capacity without any apparent interruption of campus living conditions.  The waste heat generated by the turbine can be used to generate steam in a heat recovery steam generator (HRSG), which can power a steam turbine, heat living space, or generate cooling using steam-driven chillers.  The advantages of these types of systems are inexpensive electrical power and better reliability since the user may be independent from the grid.  These systems can be started even if the grid has failed.

Two successful applications of these types of systems are at Princeton University and the Massachusetts Institute of Technology.   Each school deploys a gas turbine for electrical generation to meet the majority of the campus's needs.  The exhaust heat from these turbines drives an HRSG.  The steam from the HRSG provides heating for campus living spaces and cooling through steam-driven chillers.  Frequently, summer peak-time operation of electrical chillers is expensive.  Producing steam on-site enables the use of steam-driven chillers.  Operating steam-driven chillers acts to peak shave the user's high demand operations, saving money.  The electricity generated by the gas turbine also may be used to operate conventional electric chillers.  Since the user generates this electricity, the price may be lower than that of the local utility and does not have a peak or demand charge associated with it.



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