How does Natural Gas Combined Heat and Power (CHP) System works?
In gas CHP the combustion turbine or reciprocating engine CHP systems burn natural gas as the fuel to turn generators to produce electricity, using heat recovery devices to capture the heat from the turbine or engine.
As with biomass CHP, this heat is converted into useful thermal energy, usually in the form of steam or hot water.
Gas CHP systems can operate with up to 90% efficiency and a commercial CHP unit turns approximately 60% of its input energy into heat and 30% into electricity.
Gas CHP has become a well-established and proven technology in the UK. Unlike biomass CHP that constantly needs to run at full capacity, gas CHP units can modulate their output between 50% and 100% to match the base heating load of a building. As a result, end-users typically see savings in the region of 20% to 30%.
How are Natural Gas Combined Heat and Power (CHP) Systems applied to a building?
Gas CHP units are designed to run long hours, ideally 16 hours a day and very often 24 hours a day. To do this the unit needs to be sized correctly to be able to supply the base heat and electrical loads.
The CHP unit will operate automatically and can modulate but ideally needs to run at full load for as long as possible to maximise efficiency and minimise wear.
If the electrical site load drops below the CHP output, then there are two possible outcomes depending on the localised conditions.
The CHP power could be exported under a pre-agreed import/export agreement (however sometimes this may not be financially beneficial) or the other consideration is to modulate the CHP electrical output, to match the site load requirements so all the site power comes from the CHP. On some occasions the site heat load falls below the CHP heat output and when this happens the heat will need to be rejected. This part of the operation may not be eligible for the financial incentives.
Gas CHP systems need to have access to a reliable gas supply; if a mains gas connection is not available, one would need to be installed. Space for the unit is needed in or next to the existing boiler plant room. The CHP unit can be integrated to sit alongside existing boilers but can be installed in a new dedicated plant room if required.
For integration alongside existing boilers, an available installation space of at least 8m2 with a minimum ceiling height of 2m and entrance of at least 0.8m wide is required.
In jurisdictions that have significantly decarbonised grid derived electricity through the mass deployment of renewable generation, electricity derived from fossil fuelled CHP’s such as gas, could lead to increased carbon emissions.