Field study of energy and environmental performance of ground source heat pumps retrofitted in a cluster of UK social housing dwellings

Abstract

This paper uses an empirical field based approach to examine seasonal variation in heat pump electricity use and indoor temperatures across a cluster of 50 social housing dwellings retrofitted with ground source heat pumps (GSHP). The case study dwellings were co-located in a socially deprived housing estate in Oxford (UK). Time series monitoring data was collected on indoor, outdoor and target temperatures, heat pump electricity use (kWh), space heating and hot water operation status (on/off) in non-heating and heating seasons. Contextual data about the dwellings were gathered through heat pump surveys and energy performance certificates. Results showed 60% rise in electricity use during the heating season with statistically significant correlation observed between indoor and target temperatures, energy efficiency rating and monthly electricity use. When electricity use was normalised for outdoor temperature, lower electricity use per heating degree day (HDD) was observed in the heating season in the majority of dwellings, confirming the efficient running of the heat pumps. Mean daily indoor temperatures were found to be stable across majority of dwellings, with peak electricity use largely happening outside of the national evening peak period of 4pm-7pm. Despite there being a ‘Timer’ mode in relation to outside weather, most of the residents used the ‘Manual’ mode of operation to adjust target temperatures, possibly to overcome the low output temperatures of heat pumps. While resident training will help to enhance understanding of heating controls, smarter operation of heat pumps through automation based on optimisation of indoor and outdoor temperature, occupancy patterns, heating preferences and electricity price signals could result in further energy savings.