Cooling and heating performances of a CO₂ heat pump with the variations of operating conditions

Since operating conditions are significantly different for heating and cooling mode operations in a CO₂ heat pump system, it is difficult to optimize the performance of the CO₂ cycle. In addition, the performance of a CO₂ heat pump is very sensitive to outdoor temperature and gascooler pressure. In this study, the cooling and heating performances of a variable speed CO₂ heat pump with a twin-rotary compressor were measured and analyzed with the variations of EEV opening and compressor frequency. As a result, the cooling and heating COPs were 2.3 and 3.0, respectively, when the EEV opening was 22%. When the optimal EEV openings for heating and cooling were 28% and 16%, the cooling and heating COPs increased by 3.3% and 3.9%, respectively, over the COPs at the EEV opening of 22%. Beside, the heating performance was more sensitive to EEV opening than the cooling performance. As the compressor speed decreased by 5 Hz, the cooling COP increased by 2%, while the heating COP decreased by 8%.