Experimental investigation of multi-ejector CO2 heat pump system with and without IHX

Abstract

Environmental degradation due to the use of synthetic refrigerants should motivate end users to request natural refrigerants to secure their businesses from unforeseen negative ecological impacts. Further, using natural refrigerants as working fluids for HVAC requirements helps achieve zero CO2 emissions from this sector. The CO2 heat pumps are energy efficient units providing simultaneous heating and cooling. Implementing performance enhancing components like ejectors and/or internal heat exchangers (IHX) is sometimes beneficial. This study experimentally evaluates the ejector performance in a multi-ejector CO2 system of 33 kW cooling capacity, with and without an IHX, at different gas cooler exit temperatures. Evaporator and gas cooler exit temperatures are varied from 4 to 10 °C and 34 to 46 °C, respectively. These temperature ranges suit the simultaneous cooling (AC) and heating demands in various buildings and food- and beverage industries. At the gas cooler exit temperature of 42 °C, the system COP is improved by 12 % with an IHX, whereas the ejector efficiency increased from 14 to 18 % without the IHX. The ejector efficiency and entrainment ratio also increased at elevated heat rejection temperatures. However, as expected, the system COP decreased. Therefore, the heating system must be adapted to avoid high gas cooler exit temperatures.