Performance of CO2 air-to-water heat pumps for small domestic buildings in the UK

The current study presents the performance analysis of a domestic high-temperature CO2 air-to-water heat pump (AWHP) coupled with a thermal energy storage system for a 2-bedroom house in the UK. TRNSYS simulation model incorporating the heat pump with the house and storage tank was developed to investigate their interactions. Data collected from experiments carried out on a commercially available 4.5 kW transcritical CO2 AWHP was used to build the heat pump model. Single storage tank of varying capacity under the same operating conditions were implemented on the model to assess their impact on the performance of the heat pump. Simulation results indicated that a tank size of 300 L was the most suitable one for a 2-bedroom house in the UK with heat load of around 7797 kWh. Environmental effect and cost analysis were undertaken by calculating the carbon emissions and annual fuel expenses for both the heat pump and natural gas boiler, simulated under the same working boundaries. While the utilisation of heat pump showed a reduction of CO2 emission by 44% compared to gas boiler, and the operating cost at present tariffs was higher for heat pumps by 38%.