Thermoeconomic performance of a CO2 heat pump for space and water heating of a 4-bedroom house in the South of England

Abstract

Heat pumps are considered a key technology for the decarbonisation of space and water heating in domestic dwellings in the UK. Heat pumps that employ high-temperature working fluids such as CO2 have the potential to be used in retrofit applications. This paper presents the characteristics of a CO2 heat pump developed at Brunel University of London and the simulation results of its application to provide space and domestic hot water heating in a well-insulated four-bedroom semi-detached house with four occupants. The heating system is assumed to employ water thermal energy storage. Analysis has shown that storage volumes between 200 L and 300 L can satisfy the space temperature control requirements of the domestic dwelling if a heat pump capacity of 4.5 kW at 7°C ambient temperature and 60°C water flow temperature is employed. A comparison of the heat pump with a gas boiler reveals that with current gas and electricity prices, running costs for the heat pump can be 91% higher and CO2 emissions 40% lower than those of the gas boiler. Further design and control optimisation of the heat pump is expected to reduce both its running costs and CO2 emissions. Practical application: This paper examines the practical application of a 4.5 kW heat pump with water thermal energy storage for domestic heating. The system operates efficiently at 7°C ambient and 60°C water flow temperatures, and can be retrofitted in two-thirds of UK homes without upgrading radiators. For a four-bedroom house, 200–300 L thermal storage volumes are optimal. While running costs are 91% higher than a gas boiler, the heat pump reduces CO2 emissions by 40%, offering a more sustainable heating solution.