Thermodynamic analysis of the heat pump steam system with medium-low temperature heat source

Heat Pump Steam technology driven by electric power has an important application value in the industrial thermal field. A cascade air source heat pump steam system (CASGHP) using in thermal workshop is proposed in this paper. A numerical model is established by EES software. The thermal performances of several feasible refrigerants in the cascade system are analyzed comparatively. The influences of intermediate cooling temperature (Tintc), the injection temperature (Tinje), the evaporating temperature (Tevap), the outlet steam temperature (Tout), gas-injection ratio (βg) and specific rate of compressors pressure ratio (PRR) on system power consumption of generating a ton steam (Wper) and system COP are studied. The conclusions are as follows: When R134a is used in low temperature section of the cascade system, R245fa, R1234ze(Z) and R1336mzz(Z) used in high temperature section respectively can meet the requirements of steam generation. The COP of the CASGHP adopted R1234ze(Z) is the largest, followed by R245fa and R1336mzz(Z). There exists a maximum COP, which is 2.268, 2.286 and 2.211, respectively. When Tevap is 10 °C and Tout is 120 °C, the optimal Tintc of CASGHP with these high temperature refrigerants is 53 °C, 50 °C and 53 °C, the optimal Tinje is 79 °C, 78.5 and 85.5, the optimal βg is 0.207, 0.18 and 0.165, and the optimal PRR is 0.77, 0.71 and 0.972, respectively. The COP increases by 18.4%, 18.2% and 17.9% respectively when Tevap increases from 10 °C to 30 °C, but it decreases by 14.4%, 14.2% and 10.2% respectively when Tout increases from 100 °C to 120 °C.