Research On CO₂Two-stage Compression Refrigeration And Heat Pump System Of Tandem Style

Cooling、heating and hot water supply in the civil construction is the commonneeds of our society. The application of heat pump and heat recovery system not onlymeet this demand, but also to adapt to the world society for energy saving andenvironmental protection requirements. However, the existing heat recovery systemshave problems such as heating and refrigerating capacity limited by each other, lessfunctions, lower operating efficiency. This paper presents a series of CO₂two-stagecompression refrigeration and heat pump cycle system of tandem style. The system cannot only recover condensation heat, but also supply cooling and hot water at the sametime according to the needs of users, solves the problem of cold and heat restrictingeach other of the existing heat recovery system.Based on the system coefficient of performance as the goal, this article analyzedthe outlet temperature of the heat exchanger、evaporation temperature、compressordischarge pressure, middle pressure, superheat, subcooling and flow coefficientinfluence the cycle performance of CO₂two-stage compression refrigeration and heatpump systems of tandem style. Research shows that: in the total heat recovery,evaporation temperature, hot water heat exchanger outlet temperature of CO₂has asignificant effect on the cycle of COP, and the superheat degree, gas-liquid separatorrefrigerant subcooling effect on COP is smaller; hot water heat exchanger outlettemperature of CO₂depends on as compressor discharge pressure increased, whetherCOP got its peak; it also determines whether there is an optimal value of intermediatepressure.When the water outlet of the heat exchanger CO₂temperature falls below thecharacteristic temperature, according to user needs to change the system vapour supply, circulation system will feature the exhaust pressure point, when system pressurebelow the characteristics of exhaust pressure, the circulation efficiency by improvingvapour supply of the system is greater than the total heat recovery; when the exhaustpressure is greater than the characteristics exhaust pressure, improve vapour supply, thecycle efficiency is less than the total heat recovery. Similarly, when the hot water outletof the heat exchanger CO₂temperature is lower than the temperature characteristics,there also exists a characteristics intermediate pressure point. The characteristicspressure influenced by the evaporation temperature, hot water outlet of the heatexchanger CO₂temperature and compressor pressure corresponding to the effect.System cycle parameter selection needs to consider the factors above, so that the systemcan run in cycle of high coefficient of performance. And meet the needs of users.