Improving the start-up performance of the vapor compression cycle by recovering the lost cooling energy in the accumulator

Abstract

• The startup process of vapor compression cycle method was investigated by visualization. • A method was proposed to improve startup cooling performance. • Recovering the cooling capacity in the accumulator can improve startup performance. • The method improves the startup performance to approach the quasi-steady state. Due to the frequent on–off operation, the start-up process of the refrigeration system would not only lead to a 5%-25% reduction in average EER, but also seriously influence the thermal comfort by increasing the start-up time. The compressor suction capacity is the main factor that influences the start-up characteristics. An effective method to improve the compressor suction capacity is to enhance the liquid refrigerant evaporating speed in accumulator. Even though some effective methods have been proposed to improve the start-up performance, there are few optimizations on accumulator. In this study, a novel regeneration accumulator device was proposed, which could improve the start-up performance by recovering the lost cooling energy in the accumulator. Based on visualization experiment, it was demonstrated that by means of regeneration accumulator device, not only more refrigerant was prevented from migrating to the low-pressure parts during shutdown, but also the vaporization speed of liquid refrigerant was accelerated in the accumulator, thus, increasing the compressor suction capacity, therefore, the start-up performance was improved in the regeneration start-up (RS) mode. The experimental results showed that compared with the normal start-up (NS) mode, 54.76% of the start-up time was saved in the RS mode, and the average COP and the defined optimal start-up perfectness, which represents the degree of actual output cooling capacity approaching the optimal output cooling capacity, also increased by 13.84% and 42.64%, respectively. The performance of the RS mode was better than that of the existing valve-close start-up (VCS) mode and was closer to the quasi-steady state performance. The stability verification showed that: i) under constant evaporation temperature condition, the performance in the RS mode remained stable as the downtime increased; 2) under the variable evaporation temperature condition, the average COP in the RS mode was higher than that in the NS mode, with a peak increment of 0.21. This work has shown the great potential for regeneration accumulators to improve the start-up performance of the vapor compression cycle.