Dynamic performance of a solar and PCM integrated quasi two stage CO2 heat pump heating system

Integrating efficient CO 2 heat pumps with solar energy and thermal storage (PSCHP system) supports low-carbon building heating. Using MATLAB-TRNSYS and Hooke-Jeeves optimization, this study analyzes the system’s dynamic performance. The results show that the temperature interactions among system components are well coordinated throughout the heating season: the solar collector output follows solar radiation trends, while the air-source heat pump fluctuates significantly in early and late stages but stabilizes in mid-season. The PCM tank maintains thermal stability of around 58 °C during the mid season, with increased initial and final changes. The buffer tank always reflects the temperature dynamics of the heat pump. The maximum COP of the system in March was 3.21, and the minimum COP in December was 2.07. At the optimal gas injection ratio of 0.3, the heating capacity increased by 80.18 % compared with the case without gas injection. The outlet temperature of the solar collector increased by 18.36 % when the ambient temperature rose from −10 °C to 30 °C, and showed an irradiance-dependent growth of 27.85 %–30.44 % when the solar irradiance increased from 200 W/m 2 to 1000 W/m 2 under ambient temperatures of 0 °C, 10 °C, and 20 °C. After optimization, the annualized cost was reduced by 15.22 % compared with the baseline design before optimization, and the volumetric storage and discharge capacities of the PCM tank were increased by 14.3 % and 13.5 %, respectively, relative to the pre-optimization configuration.