Modeling and simulation of the transcritical CO2 heat pump system

• A CO2 transcritical system model without imposing excessive constraints is developed.
• Complex geometry of the gas cooler and evaporator have been taken into account.
• The proposed model gives very good agreement with the experimental data.
• Effects of the operating conditions for gas cooler/evaporator are reported.
• Increasing the inlet dry bulb temperature or relative humidity improves the COP.

In this study, a CO2 transcritical cycle model without imposing any excessive constraints such as fixed discharge pressure and suction pressure is developed. The detailed geometrical variation of the gas cooler and the evaporator have been taken into account. The model is validated with the experimental measurements. Parametric influences on the CO2 system with regard to the effect of dry bulb temperature, relative humidity, inlet water temperature, compressor speed, and the capillary tube length are reported. The COP increases with the dry bulb temperature or the inlet relative humidity of the evaporator. Despite the refrigerant mass flowrate may be increased with the inlet water temperature, the COP declines considerably with it. Increasing the compressor speed leads to a higher heating capacity and to a much lower COP. Unlike those of the conventional sub-critical refrigerant, the COP of the transcritical CO2 cycle does not reveal a maximum value against the capillary tube length.