Prime Movers
CHP prime mover, or power generation technologies, include reciprocating engines, microturbines, industrial turbines, and fuel cells. (Click on any image to enlarge.) Natural gas is the cleanest and most common fuel; propane is less common but also relatively clean. There is a growing trend toward dual-fuel systems that can combust either natural gas or diesel:
Reciprocating engines
(5 kW-7 MW)
Combustion turbines
(500 kW-25 MW)
Microturbines
(25-500 kW)
Backpressure Steam Turbines
(50 kW and up)
Fuel cells
(1 kW-10 MW)
Thermally Activated Technologies – Heat Recovery Units (HRUs)
These units capture heat from the prime mover that can then be used to drive an absorption chiller, run a desiccant dehumidifier, or make hot water or steam for heating.
Absorption Chillers
Chillers transfer recovered heat from prime movers to a heat sink through an absorbent fluid and a refrigerant. The chiller accomplishes its cooling effect by absorbing and then releasing water vapor into and out of a lithium bromide solution.
Desiccant Dehumidifiers
Desiccants use drying agents to remove water from the air being used to condition building space by exposing the desiccant material (such as silica gel, activated alumina, lithium chloride salt, and molecular sieves) to a high relative humidity air stream-allowing it to attract and retain some of the water vapor-and then to a lower relative humidity air stream, which draws the retained moisture from the desiccant. For more on desiccant technologies, visit NREL’s Distributed Thermal Energy Technologies Program site.
ORNL’s Heating and Cooling Equipment R&D site also has technical details on CHP applications.
CHP Technological Advances – Packaged CHP Systems
According to the DOE, “packaged CHP systems” integrated into commercial buildings can offer up to a 30-40 percent improvement in building efficiency over today’s best practices. CHP component manufacturers and DOE are developing pre-engineered, modular CHP systems to make it easier for building owners to connect CHP systems to power, piping, or ducting systems.
Heat Recovery Steam Generator (HRSG)
The waste heat generated by a combustion 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.
