Experimental study on performance of double-mode refrigeration system

Abstract

To ensure energy-saving and environment-friendly operation of multifunctional cold storage refrigeration systems, an experimental platform for a double-mode refrigeration system (DMRS) has been built, which can realize both a single-compression refrigeration cycle (SRC) and a cascade refrigeration cycle with a single refrigerant (CRC). The variable-frequency characteristics and control strategy of two modes were experimentally studied. The results show that with an increase in the low-temperature stage compressor frequency, there exist an optimal COP and optimal compressor frequency, the optimum frequency increases with a decrease in evaporation temperature and condensation temperature. When the condensation temperatures are 45, 40, and 35 °C, the evaporation temperature switching values of the refrigeration capacity are 2.5, −1.2, and −4.1 °C, respectively, and the evaporation temperature switching values of the COP are −10.6, −15.0, and −19.1 °C, respectively; and a control strategy of mode switching and compressor frequency adjustment is summed. When the system is running between two modes, the compression ratio is below 6, the discharge temperature is below 100 °C, and as the evaporation temperature increases from −35 °C to 10 °C, the COP of the system at 45 °C, 40 °C and 35 °C varies from 0.98 to 3.54, 1.20 to 4.27 and 1.42 to 5.20 respectively.