The Performance Potential of Domestic Heat Pumps in a Temperate Oceanic Climate

Abstract

Domestic purpose heat pumps are commonly rated based on a manufacturer specified single coefficient of performance (COP). The performance of heat pumps however is known to vary widely for different seasons and for varying climate conditions. This study is part of an in-depth analysis of nZEB homes through the nZEB101 project funded by the Sustainable Energy Authority of Ireland (SEAI). In advance of undertaking a large-scale monitoring project, preliminary studies of nZEB technologies are being undertaken. This paper outlines a simplified method for calculation of the heat pump’s seasonal performance factor over six heating seasons in a modelled nZEB dwelling in Ireland using real hourly weather data. The study has found that while seasonal performance factor (SPF) values of 4.5 (as often claimed by manufacturers) are achievable, favourable operating conditions are required to achieve these high values. In a new building where underfloor heating and modern convective radiators are installed, the primary energy associated with the space heating is approximately 40% that of a natural gas boiler. The total CO2 emissions are also 47% less. However, in a retrofit nZEB building where existing radiators (which require higher outlet temperatures of approximately 65 ℃) are used, the difference in CO2 emissions from a heat pump and gas boiler is almost negligible in a nation where the grid’s emission factor is 437 gCO2/kwh (Irish electricity 2019). The potential for heat pumps can be improved further by decarbonising the grid and improving grid and plant production efficiencies.