Wet compression versus dry compression in heat pumps working with pure refrigerants or non-azeotropic binary mixtures for different heating applications

Wet compression versus dry compression in heat pumps working with pure refrigerants or non-azeotropic binary mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures at different concentrations are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants were analysed for three different heating applications found in practice: the heating of swimming pool water, heating air for interior space heating, and the heating of water for domestic use. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better heating COPʹs when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T–s curves consistently produce higher heating COPʹs when wet compression is used. However, their heating capacities decrease while the compressor displacement rates increase. It was concluded that in general dry compression is more favourable than wet compression. From the few exceptions that do exist, some manage to produce very high COPhʹs while retaining competitive heating capacities. A by-product of this study is that from the vast amount of refrigerant mixtures analysed valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.