Defrosting performance of small parallel capillary carbon dioxide heat pump systems

A transcritical carbon dioxide air-source heat pump system has attracted the attention of researchers due to its high heating coefficient of performance. However, when operating under the frosting conditions of the evaporator, the heat supply and the coefficient of performance decrease. Presents a heat pump system using parallel capillary instead of an electronic expansion valve as a throttling component, and tests the defrosting performance. The experimental results show that the defrost efficiency of the parallel capillary heat pump system is slightly lower than that of the conventional heat pump system, but the defrosting process is relatively stable to realize the continuous heating, and the compressor is not required to be specially protected, which not only simplifies the defrosting system, but also avoids the difficulty of restarting the compressor when the heating is restored after defrosting.