Upper-limit of performance improvement by using (quasi) two-stage vapor compression

Abstract

Both quasi two-stage and two-stage compressions are important ways for improving the energy efficiency of the vapor compression heat pump system, especially for high compression ratio conditions. Many experiments and simulations have been conducted to investigate the performance improvement of two-stage or quasi two-stage systems. In most occasions, positive results were obtained. However, the performance improvements reported by different studies vary significantly. Actually, the results obtained by different researchers are barely comparable, because operating conditions, refrigerants, cycles, and economizers heavily affect the performance of (quasi) two-stage system, which hinders the potential evaluation in cycle-selection period and perfectness assessment of developed (quasi) two-stage systems. In this study, a general analytical expression for the (quasi) two-stage vapor compression system is proposed, by which the upper-limit of performance improvement of (quasi) two-stage systems using different refrigerants under different operating conditions can be calculated quickly. Based on that, the potential of adopting (quasi) two-stage cycle and the maturation of the developed prototypes can be easily identified by comparing the test performance with the upper-limit improvement.