Performance analysis of a R134a/CO2 cascade heat pump in severe cold regions of China

Abstract

To achieve efficient and reliable heating in severe cold regions below −20 °C, this paper investigates a R134a/CO2 cascade air source heat pump (ASHP) system. Firstly, a simulation model is constructed and used for energy performance analysis. Then experiments are carried out for model verification and performance investigation. Finally, its performance is evaluated in detail with the meteorological data of Harbin under different working conditions for energy performance forecast. Simulation results show that the heating coefficient of performance (COP) increases with higher ambient temperature and lower water supply temperature. At the same time, the modeling errors on coefficient of performance (COP) are all within ±0.2%. The experimental results show that the proposed R134a/CO2 ASHP can supply water above 50 °C with high COP up to 3.07 and 1.60 when the ambient air temperature is −5 °C and −45 °C, respectively. Furthermore, under four working conditions, the heating seasonal performance factors (HSPF) are all above 2.30 and the best is 2.39 for the −25 °C nominal operating temperature and the typical working condition of civil buildings (15 °C). Both the experimental data and the simulation results show that the proposed R134a/CO2 cascade air source heat pump system can provide efficient and reliable heating in severe cold regions.