Effect of heat-saving measures on the CO₂ savings attributable to micro-combined heat and power (μCHP) systems in UK dwellings

This paper considers the relationship between heat-saving and micro-combined heat and power (µCHP) technological interventions for reducing the carbon footprint of existing domestic dwellings within the UK housing stock. The relationship between the annual heat requirement of individual dwellings and the CO₂ savings attributable to different µCHP systems is investigated (by means of predictive modelling based on heat and power demand datasets recorded on a 1-min time base for nine dwellings). An assessment is made of the effects of various heat-saving measures upon the annual CO₂ savings predictions for candidate µCHP system implementations, when applied to 'domestic building variants' (as defined within the Carbon Vision TARBASE research programme). The increasing application of heat-saving interventions serves to reduce the CO₂ savings solely attributable to a µCHP system. The magnitude of this effect is a function of the µCHP system's electrical efficiency and electrical power output. For example, a 1 kW prime mover of 10% electrical efficiency is predicted to reduce annual CO₂ emissions by 72 kg CO₂ for a dwelling with an annual heat requirement of 11.9 MWh, but if the identified set of heat-saving measures is implemented first the demand falls to 5.0 MWh and the µCHP system will actually result in an emissions increase of 100 kg CO₂ p.a. By comparison, relative savings of 467 and 294 kg CO₂ p.a. are predicted if this dwelling is fitted with a 1 kW prime mover of 30% electrical efficiency. Still greater savings are predicted for higher power output systems of high efficiency, but a relatively large proportion of the generated electricity (44-75% depending on the heat and electrical demand of the dwelling) must then be exported. © 2007 Elsevier Ltd. All rights reserved.