Influence Factors on COP of Air Source Heat Pump Cascade Circulation System for Spray Glaze Drying

Under the guidance of the country’s “double carbon” goals, carbon dioxide air source heat pumps with natural working medium are receiving more and more attention in the field of clean energy. A thermodynamic model of R134a/CO₂ cascade heat pump system was proposed. The thermophysical parameters of working fluid are obtained by using the REFPROP software. The effects of environmental temperature, water supply temperature, low-temperature evaporation temperature,intermediate condensation temperature, high-temperature condensation temperature and intermediate heat transfer temperature difference on COP of the heat pump system are analyzed by using MATLAB software programming. The results indicate that COP of the cascade heat pump system is 52.53% higher than that of conventional heat pump system at heating temperature of 70 ℃. The low temperature stage of the cascade cycle system has matching optimum intermediate condensation temperature under the given evaporation temperature condition. When the intermediate condensation temperature is 25 ℃, the maximum COP is 4.68. The COP values of the system with high-temperature condensation temperatures of 50 ℃ and 70 ℃ are 3.92 and 2.93, respectively.