Refrigerant charge distribution in brine-to-water heat pump using R290 as refrigerant.

This paper presents experimental results from a brine-to-water heat pump used for space heating at low temperature, with a low refrigerant charge of R290 (propane). Performance and refrigerant distribution were analysed in every test condition studied. Performance results show a declared heating capacity of 9.5 kW, obtaining a specific capacity of 48.7 kW rmkg and a seasonal coefficient of performance of 4.01. In terms of refrigerant distribution, at the nominal point, 41.5% of the refrigerant is located in the compressor, mainly dissolved in the oil, and the rest is separated almost evenly in both heat exchangers, 23.9% in the condenser and 27.8% in the evaporator; having the lines and accessories (pneumatic-ball valves) the remaining 6.8%. Due to this fact, reducing oil solubility by heating the crankcase or increasing the superheat (SH) has a positive impact on the refrigerant charge reduction, but it also affects the coefficient of performance.