Cooling, Heating, and Power Systems
Conventional electricity generation is inherently inefficient, using only about a third of the fuel's potential energy. In building applications where heating or cooling is needed as well, the total efficiency of separate thermal and power systems is still only about 45 percent, despite the higher efficiencies of thermal conversion equipment.
Combined heating and power (CHP) systems are significantly more efficient. CHP technologies produce both electricity and thermal energy from a single energy source. These systems recover heat that normally would be wasted in an electricity generator, then use it to produce one or more of the following: steam, hot water, space heating, humidity control, or cooling. By using a CHP system, the fuel that would otherwise be used to produce heat or steam in a separate unit is saved.
In conventional conversion of fuel to electricity, two thirds of the energy input is lost to the environment as heat. By recycling and using this waste heat, CHP systems achieve efficiencies of 60 to 80 percent—a dramatic improvement over the average 33 percent efficiency of conventional fossil-fueled power plants. These higher efficiencies have an added bonus: reducing air emissions of nitrous oxides, sulfur dioxide, mercury, particulate matter, and carbon dioxide. CHP systems produce much less air pollution than conventional technologies.
CHP systems are not new. In the early 1900s, many manufacturing plants operated CHP facilities. However, as a result of improvements in the cost and reliability of electricity generated by the separate electric power industry, as well as increasing regulation, the electric generation capacity at most CHP facilities was abandoned in favor of more convenient purchased electricity. A few industries, such as pulp and paper and petroleum refining, continued to operate their CHP facilities, in part driven by high steam loads and the availability of by-product fuels.
Recent technological advances have resulted in the development of a range of efficient and versatile systems for industrial and other applications. Improvements in electricity generation technologies—in particular advanced combustion turbines and engines—have allowed for new configurations that reduce size yet increase output.
Many of the gas-fueled technologies used for distributed power generation can also be used for CHP. Pursue the following links to learn more about CHP technologies:
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Gas-Fired Distributed Energy Resource Technology Characterizations—NREL, October 2003 (PDF 2.4 MB). Download Adobe Reader. See the beginning of every chapter for information on the CHP applications of each gas-fired power-generating technology.
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CHP technology status—Extensive information on the performance, cost, markets, and prospects for CHP technologies. Provided by DOE's Distributed Energy Program.