Optimal compressor discharge pressure and performance characteristics of transcritical CO2 heat pump for crude oil heating

The compressor discharge pressure is an important parameter for optimizing the performance of a transcritical CO2 heat pump system. In this study, the factors influencing the optimal compressor discharge pressure of an air source transcritical CO2 heat pump system were examined experimentally. The results showed that the optimal compressor discharge pressure is affected by the gas cooler water inlet temperature and gas cooler CO2 outlet temperature. Consequently, a correlation formula for the optimal compressor discharge pressure appropriate for a more comprehensive temperature range and higher prediction accuracy was determined based on the experimental data. Compared with the experimental results, the maximum error was less than 10%, which is minor considering the lower gas cooler CO2 outlet temperature. In addition, a control strategy for the optimal compressor discharge pressure based on the degree of superheat correction was proposed. Subsequently, under variable operating conditions, the air source transcritical CO2 heat pump crude oil heating system was continuously operated based on this control strategy. The results showed that the compressor discharge pressure agreed with the optimal compressor discharge pressure calculated using the new correlation formula. Compared with the control strategy of constant opening under a variable frequency mode, the results showed that the system could operate under the control strategy proposed in this paper, the thermodynamic perfection of the system being higher.