Combined Heat & Power (CHP)

Combined heat and power (CHP) is also known as cogeneration, and through some configurations also trigeneration. CHP systems, including both cogeneration and trigeneration, make common use of a heat engine to produce electricity and thermal heating that can be used by utility consumers or an industrial process. Common examples of heat engines in a CHP system are reciprocating engines, external combustion engines (ECE) and internal combustion engines (ICE), or even a gas turbine.

Gas turbines and true heat engines all generate excess exhaust heat that represents waste thermal energy not converted into electrical energy. The exact efficiency claims of CHP systems and power plants remain controversial due to energy conversion metrics, but the implementation of CHP does increase the efficiency of a turbine or heat engine by capturing exhaust thermal energy and making it useful to another process.

Other process applications for captured thermal energy in CHP systems include utility or district heating, steam or hot water delivery, thermal energy input to other industrial processes, and the generation of steam to drive a steam turbine for greater power generation efficiency. Steam generation from exhaust heat is accomplished through a heat recovery steam generator (HRSG) or a large-scale heat exchanger. CHP systems that use gas turbine exhaust heat to drive a steam turbine are known as combined cycle power plants or combined cycle gas turbines (CCGT). Trigeneration refers to a CHP system that uses exhaust heat to provide cooling, air conditioning, or cooling through the Rankine cycle or the refrigeration cycle. Complex systems including multiple sources of power generation, heating or cooling are also called polygeneration systems.