The system performance of a transcritical CO₂ heat pump is significantly influenced by the heat rejection pressure due to the nature of the transcritical refrigeration cycle. It has received wide attention in the scientific community. In this article, an experimental investigation of the optimal heat rejection pressure for a transcritical CO₂ heat pump water heater is presented. It is found that the optimal heat rejection pressure varies with gas-cooler outlet refrigeration temperature at different ambient temperatures. The further experimental results show that the Coefficient of Performance (COP) at the optimal heat rejection pressure decreases substantially with increasing gas-cooler outlet refrigeration temperature in a range from 25 to 45 °C. Based on the experimental data, a simple correlation of the optimal heat rejection pressure in terms of gas-cooler outlet refrigeration temperature is obtained. The analysis shows that the deviation of the correlation is within ±5%, and the predicted COP at the optimal heat rejection pressure is within 6%.

Item Type:	Refereed Article
Keywords:	carbon dioxide, transcritical cycle, heat pump, heat rejection pressure
Research Division:	Engineering
Research Group:	Mechanical engineering
Research Field:	Energy generation, conversion and storage (excl. chemical and electrical)
Objective Division:	Manufacturing
Objective Group:	Machinery and equipment
Objective Field:	Industrial machinery and equipment
UTAS Author:	Wang, X-L (Professor Xiaolin Wang)
ID Code:	85628
Year Published:	2013
Web of Science® Times Cited:	83
Deposited By:	Engineering
Deposited On:	2013-07-24
Last Modified:	2017-11-06
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