Transient Distribution of Refrigerant and Oil in A Residential Heat Pump Water Heater System

This paper presents an experimental investigation of transient refrigerant and oil migration in a residential heat pump water heater (HPWH) system. In the experiments, R134a is paired with POE 22 oil. The Quick Closing Valve Technique (QCVT) is employed to localize the refrigerant and oil into each section of the system. The Remove and Weigh Technique (RWT) is then applied to measure the trapped refrigerant mass in the sections, with an uncertainty about 0.17% of the total refrigerant charge. The retained oil mass in each section, except for the compressor, is determined by the Mix and Sample Technique (MST), of which the uncertainty is about 0.15% of the total oil charge. Five experiments are conducted to cover a full heating-up of five hours. The experimental data shows that the most of refrigerant is in the heat exchangers. The inventory of the refrigerant generally decreases in the evaporator and increases in the condenser during the heating-up. The measurements also indicate that most of the oil stays in the compressor. The retention of the oil generally increases in the evaporator and it first decreases then increases in the condenser