Experimental study on the performance of a vapor injection high temperature heat pump

• The high temperature heat pump with a vapor injection was experimentally studied.
• The experimental setup of the HTHP system with vapor injection was developed.
• Injection pressure showed a large effect on heating capacity and no effect on COP.
• Major benefit of injection is reduction of refrigerant temperature at the EEV inlet.
• The condensation pressure showed a large effect on system performance.

In this study, a vapor injection technique was applied in a high temperature heat pump (HTHP) for providing hot water at temperatures up to 88 °C. A prototype HTHP system with economizer vapor injection was developed and its performance was experimentally investigated under various operating conditions. Results showed that the vapor injection pressure had a large effect on heating capacity and on refrigerant temperature at the inlet of the electronic expansion valve (EEV). As the injection pressure increased from 0.82 to 0.98 MPa, the vapor injection flow ratio increased from 7.3% to 22.61% and the heating capacity increased by 7%. The system COP did not show significant change although the COP trend showed an optimal value for the injection pressure. The refrigerant temperature at the EEV inlet showed a subcooling of more than 16 °C under all studied conditions, which improved the EEV operating reliability.