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The performance of the CO2 trans-critical system is affected significantly not only by optimal system pressure but also by instantaneous ambient temperatures. This paper presents the results of a study carried out to elucidate the influence of the source and sink temperatures on the experimental research of a CO2 trans-critical refrigeration and heat pump system which used a new dual expansion valve and a balance CO2 liquid receiver adjustment device. The unit had been fully tested along a multistate experimental study, at various evaporating temperatures and different gas cooler outlet pressures. The results showed that: the source and sink temperatures rose from 15°C to 25°C, trans-critical CO2 systems COPH average increase of 4.4% each 5°C, but COP decrease of 6.8%. The influence of the source temperature on the chilled water outlet temperature which is less than the sink temperature. The effect of the source or sink temperature on the cooling water outlet temperature to average every 5°C to change the range of from 0.7°C to 1.9°C.

This work present the experimental evaluation of the energy performance of trans-critical CO2 refrigeration and heat pump systems. The optimal gas cooler pressure and the optimal COP have been analysed from a thermodynamic point of view. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler outlet pressures (75 to 120bar). It is concluded that: With the the internal heat exchanger (IHX) system compressor power is relatively low, when the high side pressure is over 100bar, and the evaporation temperature is below 0°C. The COP of the system without IHX is slightly higher than the system with the IHX, it is increase about 3% to 5%, when the evaporation temperature is over 5°C.