Refrigerant charge optimisation for propane heat pump water heaters.

Hydrocarbons can be interesting refrigerants in domestic facilities such as heat pumps for domestic hot water production called heat pump water heaters (HPWH). However, due to flammability and submission to severe regulations, the use of hydrocarbons requires improvements in design and optimisation of components to reduce the refrigerant charge. This paper first reviews the regulations applied to hydrocarbon technologies then discusses possibilities of charge reduction for a R290 HPWH. Mainly by selecting condensers with high thermal efficiency and low internal volume, the charge may be reduced to extremely low levels. Using the same base of refrigerating system, three types of condensers were tested: tank-wrapped D-tube, roll-bond and microchannel heat exchangers. The D-tube has a low compactness. Microchannels are penalised by the diameter of their distributors. The best performance is obtained by the roll-bond HPWH with a charge of 224 g: COP of 3.17 and heating time under 7 h. [ABSTRACT FROM AUTHOR]