Combined Heat and Power

 

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 water requirements. The simplest thermal load to supply is hot water. The primary applications for CHP in the commercial/institutional and residential sectors are those building types with relatively high and coincident electric and hot water demand such as colleges and universities, hospitals and nursing homes, multifamily residential buildings, and lodging. If space heating needs are incorporated, office buildings, and certain warehousing and mercantile/service applications can be economical applications for CHP. Technology development efforts targeted at heat activated cooling/refrigeration and thermally regenerated desiccants expand the application of engine-driven CHP by increasing the thermal energy loads in certain building types. Use of CHP thermal output for absorption cooling and/or desiccant dehumidification could increase the size and improve the economics of CHP systems in already strong CHP markets such as schools, multifamily residential buildings, lodging, nursing homes and hospitals. Use of these advanced technologies in other sectors such as restaurants, supermarkets and refrigerated warehouses provides a base thermal load that opens these sectors to CHP application.

Reciprocating engine CHP systems usually meet customer thermal and electric needs as in the two hypothetical examples below:

• A typical commercial application for reciprocating engine CHP is a hospital or health care facility with a 1 MW CHP system comprised of multiple 200 to 300 kW natural gas engine.

Catalog of CHP Technologies 2–2 Reciprocating IC Engines  system is designed to satisfy the baseload electric needs of the facility. Approximately 1.6 MW of thermal energy (MWth), in the form of hot water, is recovered from engine exhaust and engine cooling systems to provide space heating and domestic hot water to the facility as well as to drive absorption chillers for space conditioning during summer months. Overall efficiency of this type of CHP system can exceed 70 percent.

• A typical industrial application for engine CHP would be a food processing plant with a 2 MW natural gas engine-driven CHP system comprised of multiple 500 to 800 kW engine gensets. The system provides baseload power to the facility and approximately 2.2 MWth low pressure steam for process heating and washdown. Overall efficiency for a CHP system of this type approaches 75 percent.

2.2.2 Emergency/Standby Generators

Reciprocating engine emergency/standby generators are used in a wide variety of settings from residential homes to hospitals, scientific laboratories, data centers, telecommunication equipment, and modern naval ships. Residential systems include portable gasoline fueled spark-ignition engines or permanent installations fueled by natural gas or propane. Commercial and industrial systems more typically use diesel engines. The advantages of diesel engines in standby applications include low upfront cost, ability to store on-site fuel if required for emergency applications, and rapid start-up and ramping to full load. Because of their relatively high emissions of air pollutants, such diesel systems are generally limited in the number of hours they can operate. These systems may also be restricted by permit from providing any other services such as peak-shaving.

2.2.3 Peak Shaving

Engine generators can supply power during utility peak load periods thereby providing benefits to both the end user and the local utility company. The facility can save on peak power charges and the utility can optimize operations and minimize investments in generation, transmission, and distribution that are used only 0-200 hours/year. In a typical utility peak shaving program, a utility will ask a facility to run its on-site generator during the utility’s peak load period, and in exchange, the utility will provide the facility with monthly payments.

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