Trigeneration: CCHP

Trigeneration: CCHP in Rio de Janeiro

Building installed combined cooling, heat and power (CCHP) systems using biofuels can sustainably generate electrical power. Waste heat can drive a chiller to provide building cooling. Photo by Bilfinger licensed under creative commons.

Combined Cooling Heat and Power (CCHP, or trigeneration) involves using a heat engine or a power station to simultaneously generate both electricity and useful heat. In the context of Rio de Janeiro the heat produced can be used to drive chillers to provide cooling.

In general, CCHP helps reduce greenhouse gas emissions because waste heat, an inevitable by-product of thermal electricity generating stations, can be used for useful purposes. In addition, transmission and distribution losses – an inevitable consequence of remote electricity generation – are minimised.

These assumptions need to be  closely examined In the context of Rio de Janeiro.

The majority of electrical power supplied to Rio derives from hydroelectric power plants – a form of generation which does not burn fuel and does not produce greenhouse gases. In this low carbon context, generating electricity locally by CCHP would not result in a reduction of greenhouse gas emissions unless renewable fuels were used.

Local generation of electricity by means of CCHP does have a number of advantages. It would significantly reduce transmission and distribution losses, serving to increase the resilience of the Brazilian grid and fit the strategic objectives of the Brazilian government. On the local level, building-scale CCHP in Rio would help ensure security of power supplies – which in the past have been interrupted due to environmental factors associated with the extensive transmission and distribution network.

However, for CCHP to have the potential to reduce greenhouse gas emissions, it is critical that renewable fuels must be used. For more information on renewable fuels in the context of Rio de Janeiro, see the section on Biofuels in this toolkit.

Heat Engine or Power Station?

Building installed CCHP generally consists of an internal combustion engine attached to an alternator.  Very large CCHP units (over 10 MWe) may use a gas turbine to increase efficiency.  Because multiple units are required for resilience of supply, a 10 MWe unit is likely to be one of at least three – resulting in a very large installation (30 MWe).  Such a large installation would probably be used to distribute heat over a large area, thereby increasing pipework heat losses and pump power requirements. This would partially militate against the increased efficiency of the turbine over the internal combustion engine.