Combined Heat and Power

Combined Heat and Power, or CHP as it is more commonly referred to, is the simultaneous generation of usable heat and power (usually electricity) in a single process. In other words, it utilizes the heat produced in electricity generation rather than releasing it wastefully into the atmosphere. CHP is also sometimes referred to as co-generation.

CHP offers energy and environmental benefits over electric-only and thermal-only systems in both central and distributed power generation applications. CHP systems have the potential for a wide range of applications and their higher efficiencies result in lower emissions than separate heat and power generation system. The advantages of CHP broadly include the following:

• The simultaneous production of useful thermal and electrical energy in CHP systems lead to increased fuel efficiency.
• CHP units can be strategically located at the point of energy use. Such onsite generation avoids the transmission and distribution losses associated with electricity purchased via the grid from central stations.
• CHP is versatile and can be coupled with existing and planned technologies for many different applications in the industrial, commercial, and residential sectors.

CHP Engine

In conventional power generation, much of the total energy input is wasted. CHP generation plants, (sometimes referred to as 'total energy plants'), where the heat produced in the electricity generation process is put to good use, can reach efficiencies in excess of 85%. CHP can provide a secure and highly efficient method of generating electricity and heat at the point of use, typically yielding energy cost savings of 35%.

CHP systems consist of a number of individual components - prime mover (heat engine), generator, heat recovery, and electrical interconnection - configured into an integrated whole. The type of equipment that drives the overall system (i.e., the prime mover) typically identifies the CHP system. Prime movers for CHP systems include reciprocating engines, combustion or gas turbines, steam turbines, micro turbines, and fuel cells.

These prime movers are capable of burning a variety of fuels, including natural gas, coal, oil and alternative fuels to produce shaft power or mechanical energy. Although mechanical energy from the prime mover is most often used to drive a generator to produce electricity, it can also be used to drive rotating equipment such as compressors, pumps, and fans.

The electrical power can be supplied at low voltage or medium voltage to suit the customer's distribution system. Thermal energy from the system can be used in direct process applications or indirectly to produce steam, hot water, hot air for drying, or chilled water for process cooling.

Conventionally CHP applications have been divided into two broad categories, based on design output: small scale (less than 1MW) and large scale (greater than 1MW). However, recent technological advances have introduced the third "Micro-CHP" category (less than 250kW).

Micro CHP

Micro-CHP (mCHP) is a mass produced small scale CHP unit that is suitable for domestic and small business applications. Micro-CHP units vary in size up to 250kW and use a number of different technologies: internal combustion engines; internal combustion engines; external combustion engines; micro turbines; and fuel cells. Many of these technologies are still under development with efficiencies always improving.

The disadvantage of CHP systems in that in order for it to be both viable and efficient the demand for both electricity and heat must be simultaneous. This may be a problem in summer months when the demand for heating would be reduced, but in this circumstance hot water fired absorption chillers can be used to provide chilled water to HVAC applications. This spreads a buildings heat demand throughout the year.

Professional maintenance and backup is essential for reliable operation of CHP units. Taking this cost into consideration, simple payback for a well designed system in typically 3-4 years. Both small and large scale systems are based on tried and tested internal combustion engine technology, where experienced suppliers can offer guaranteed availability and savings. If capital cost is an issue, leading suppliers can offer ESCo and shared saving finance options.

CHP units are traditionally powered by fossil fuels such as natural gas, LPG or diesel. However renewable CHP units are now available which consume biogas, landfill gas, bio-diesel or various concentrations of vegetable oils.

Edina are proud to be members of the Combined Heat and Power Association in the UK and Ireland

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