Performance analysis of a two-stage vapor compression heat pump based on intercooling effect

Abstract

The two-stage compression technology based on intercooling effect effectively improves the low-temperature adaptability of vapor compression heat pump systems. When a two-stage compression system is applied to address a spectrum of low-temperature operating conditions, obvious variations in the capacity ratio and interrelationship between the two compressors will take place, which may result in an instability of system control and compressor burnout during actual equipment operation. Therefore, to refine the control strategy and enhance the practicality of the two-stage compression system, this study mainly focuses on the investigation of the subcooling (SC) parameter and the desuperheating (SH) parameter during the injection process. Both simulation models and experimental testing platform of a two-stage compression heat pump system with a subcooler structure are conducted to explore the effects of intercooling effect under variable operating conditions on various system performance parameters. The results show that as the injection ratio Rinj increases, the changes of SC and SH, ΔTSC and ΔTSH show a parallelogram-like variation, and the turning point of the variation trend is around Rinj = 0.14, stabilized at about 21.55 °C; ΔTSH first increased slowly from 0 °C to 6.04 °C and then rapidly increased to 33.55 °C; the system heat production Qhot and COP were closely related to the change of SC, but not sensitive to the change of SH. Besides, the optimal intermediate pressure calculation equations are determined for different evaporation temperatures, condensing temperatures and cylinder capacity ratios. This study may offer valuable guidance for improving the throttling valve and compressor capacity control strategies in two-stage compression systems.

Keywords

• Two-stage compression
• Injection parameter
• Subcooling parameter
• Desuperheating parameter