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

Abstract

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 Tevapis 10 °C and Toutis 120 °C, the optimal Tintcof CASGHP with these high temperature refrigerants is 53 °C, 50 °C and 53 °C, the optimal Tinjeis 79 °C, 78.5 and 85.5, the optimal βgis 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 Tevapincreases from 10 °C to 30 °C, but it decreases by 14.4%, 14.2% and 10.2% respectively when Toutincreases from 100 °C to 120 °C.

Keywords

• Low-grade heat source
• Cascade heat pump
• Steam generator
• Thermodynamic analysis