Experimental study on optimal air volume of transcritical CO2 heat pump systems

In order to explore the influence of air volume on the performance of transcritical CO2cycle system at fixed compressor speed, and to determine the optimal air volume under the maximum COP, a transcritical CO2heat pump system test bench is built. The influence of indoor and outdoor air volume on the heating performance of the system is studied, and the method to determine the optimal air volume is summarized. The results show that under the heating mode of the transcritical CO2heat pump system, when the indoor air volume is fixed, with the increase of the outdoor air volume, the exhaust pressure and the indoor air outlet temperature show a trend of rising first and then maintaining a stable state. The heating COP of the system has an optimal value with the increase of outdoor air volume. In order to accurately predict the optimal outdoor air volume, the optimal exhaust pressure deviation σ and the parameter change rate δ are introduced as the basis for judging the optimal air volume. When σ=0.48% and δ=1.4%, the system is at the optimal outdoor air volume, that is, the corresponding system operates at the maximum COP. Through experimental verification, the error of the optimal outdoor air volume prediction value is within 5%, and the method has high accuracy.