An efficient CO2 air-to-water heat pump central space heating system in cold regions: A case study

CO2 air-source heat pump is expected to play an important role in low-carbon space heating due to its advantages of environment-friendly and energy-saving. However, the severe performance degradation caused by lower ambient temperature and higher inlet water temperature seriously hinders its application. Herein, this research aims to develop an efficient CO2 air-to-water heat pump (CO2-AWHP) space heating system. By increasing suction enthalpy, reducing inlet water temperature and optimizing compressor frequency, a performance-enhanced CO2-AWHP was designed and built. The test results indicated that the heating capacity and coefficient of performance (COP) of the CO2-AWHP were as high as 71.53 kW and 2.10 respectively, under the conditions of ambient temperature of −12 °C, inlet water temperature of 35 °C and outlet water temperature of 65 °C. The proposed CO2-AWHP was applied to a central space heating system in Dalian, China. The test results showed that the CO2-AWHP space heating system could meet the thermal comfort requirements. Compared with traditional space heating systems, the primary energy consumption and CO2 emissions of the CO2-AWHP could be reduced by 57.54%–69.52% and 10.74%–57.59%, respectively. From the aspects of thermal comfort, energy-saving and environmental benefits, the proposed CO2-AWHP is an alternative way for clean space heating.