Comparative performance evaluation of positive displacement compressors in variable-speed refrigeration applications

Abstract This paper presents the results of investigations into the performance of positive-displacement refrigeration compressors for variable-speed capacity control applications. Compressors tested include an open-type reciprocating, a semi-hermetic reciprocating and an open-type rotary vane. All three compressors were tested under constant and variable head-pressure operating conditions. The results indicate that all three compressors were designed for maximum efficiency at nominal speed. At constant head-pressure only the open-type compressor exhibited an improvement in the COP at reduced speeds. With variable head-pressure-control all three compressors showed an increase in the COP with a reduction in speed. The results of an energy analysis carried out based on the experimental results and weather conditions for two locations representing temperate and warm weather conditions showed that all three compressors when operated at variable speed offer energy savings compared to their fixed-speed counterparts. The analysis has shown the open-type reciprocating compressor to be the most efficient system offering 12% savings when operating in a temperate climate and 24% savings when operating in a warm climate.