CHP and District Heating - how efficient are these technologies?

CIBSE Technical Symposium, DeMontfort University, Leicester UK
6th and 7th September 2011

With the increasing demand for action on greenhouse gas reductions there is a need to compare low carbon solutions on a consistent basis. This paper defines an ‘equivalent heat efficiency’ parameter and a CO2 content of heat supply to enable Combined Heat and Power (CHP) to be compared to boilers and heat pumps. This shows that a heat pump needs to have a CoP of at least four to compete with most CHP systems with the current grid electricity efficiency of 40%. The comparison also considers CHP supplying District Heating (DH) and the impact of heat mains losses and the use of peak boilers. These theoretical calculations have been backed up by actual experience and data is provided based on monitoring results from CHP/DH schemes operated by Cofely GdF Suez and from statistics published by the Danish District Heating Association. The information from the recent Energy Saving Trust trials of condensing boilers and heat pumps is also summarised. In the future, as the electricity grid decarbonises, gas-fired CHP systems will save less CO2 and the paper discusses the ways in which CHP and DH schemes would need to evolve to maintain an environmental and economic benefit over other low carbon solutions, including through the use of large-scale heat pumps and thermal storage.