Experimental study of an improved air-source heat pump system with a novel three-cylinder two-stage variable volume ratio rotary compressor

摘要

Traditional air source heat pumps (ASHPs) only can work above about -20 degrees C to -25 degrees C, and have limitations in terms of performance. This paper proposes a novel three-cylinder two-stage variable volume ratio (TSVVR) rotary compressor to improve the performance of the ASHP. Utilizing the variation characteristics of the compressor optimal volume ratio under the different temperatures, the compressor volume can be switched for better performance. Experiments are conducted on the improved ASHP with the TSVVR rotary compressor and the two traditional ASHPs with the single-stage and two-stage compressor using the simulation of the residential building in the environmental laboratory. The results show that the TSVVR system operates in a stable manner with the COP of 1.52 W/W at -30 degrees C, and achieves a higher COP than the traditional ASHPs. The optimal volume ratio decreases with the decrease of the evaporation temperature. The TSVVR system works in the three-cylinder mode at low temperature and directly expands the heating capacity and compression efficiency because of the increase of the low-pressure volume and suction volume. When the water temperature varies between 40 degrees C and the maximum possible temperature, the COP of the TSVVR system is 18.4-22.3% higher and 6.6-7.3% higher than the single-stage and two-stage systems, respectively; when the indoor temperature varies between 12.5 degrees C and 18 degrees C, the COP of the TSVVR system is around 18.4-23.4% and 5.2-8.8% higher than the single-stage and two-stage systems, respectively. The two-cylinder mode of the TSVVR system has a larger volume ratio than the single-stage and two-stage ASHPs and is closer to the optimal volume ratio, which is more suitable for the high temperature and low load conditions. In the three-cylinder mode, the TSVVR system has a smaller volume ratio, and the compression efficiency and system refrigerant flow rate increase, when the evaporation temperature is low. Two modes ensure that the TSVVR system always work in the efficient states, especially in the low temperature environments. (C) 2018 Elsevier Ltd and IIR. All rights reserved.