2.2.1 Combined Heat and Power There are over 2,000 active reciprocating engine combined heat and power (CHP) installations in the U.S. providing nearly 2.3 gigawatts (GW) of power capacity . These systems are predominantly spark ignition engines fueled by natural gas and other gaseous fuels (biogas, landfill gas). Natural gas is lower in cost than petroleum based fuels and emissions control is generally more effective using gaseous fuels. Reciprocating engine CHP systems are commonly used in universities, hospitals, water treatment facilities, industrial facilities, and commercial and residential buildings. Facility capacities range from 30 kW to 30 MW, with many larger facilities comprised of multiple units. Spark ignited engines fueled by natural gas or other gaseous fuels represent 84 percent of the installed reciprocating engine CHP capacity. Thermal loads most amenable to engine-driven CHP systems in commercial/institutional buildings are space heating and hot wa