Theoretical analysis of the impacts of refrigerant leakage on the performance of a flash tank vapor injection heat pump

Abstract

Refrigerant leakage is a common phenomenon for refrigeration units. In this study, we established a dynamic model of gas phase leakage from a flash tank vapor injection heat pump(VIHP). Gas leakage from a micro-slit located on the discharge pipe is assumed. R32 and R290 were selected as refrigerant, and the calculation results mainly based on R32. With indoor temperature at 18 °C and outdoor temperature at -20 °C, we found that when the leaked refrigerant amounted to 12% of the initial charge, the discharge temperature exceeded 130 °C, reaching the safety limit of the compressor. As the leakage progressed, the mass flow rate of vapor injection increased, while the COP and the heating capacity decreased. When the critical point of leakage was reached, the COP decreased by 27.7% and the heating capacity by 30.4%. A comparison was made between the impacts of refrigerant leakage on system performance in flash tank vapor injection heat pumps and normal heat pumps. If there was no initial liquid storage in the flash tank, the vapor injection heat pump failed when the leakage ratio reached 8.3%, much earlier than the 12% threshold for normal heat pump. Parametric analyses were carried out with varying indoor temperature, outdoor temperature, and initial liquid storage. If R290 was employed as refrigerant, the failure mode would change from discharge temperature excess to heating capacity deficiency. We conclude that vapor injection heat pump is more sensitive to refrigerant leakage than normal heat pump, and R32 system is more sensitive than R290 system.