Pinch point variation in the gas cooler of the CO2 heat pump water heater: An experimental and simulation comparative study

Abstract

The carbon dioxide heat pump operation is strongly impacted by the presence of the pinch point within the gas cooler. The existing findings regarding the pinch point need to be verified due to the deficiencies of the simulation method. Given this, an experimental and simulation comparative study is performed. The pinch point variation characteristics and its connection with the heat pump operation are elucidated. The limitations and accuracy of the simulation model are revealed. The location and number of the pinch point are at most four scenarios. One locates at inside. Two locate at inside and cold end, respectively. One locates at cold end. One locates at hot end. The hot end pinch point is difficult to occur for actual heat pump operating conditions. As the carbon dioxide pressure rises, the pinch point temperature difference first grows slightly and then drops. The experiments demonstrated that the actual best operation of the carbon dioxide heat pump corresponds to one inside pinch point rather than two. The simulation model cannot reproduce this phenomenon well. The accuracy of the simulation model can be greatly improved in case the pinch point location is known, and it is acceptable from the perspective of meeting the engineering permissible error. This study may contribute to a better understanding of the pinch point variation. Moreover, it may play a reference role in the building and optimization of the gas cooler model.