Influence of reversing methods on the performance of a reversible water-to-water heat pump

Steady state performance of a reversible water-to-water heat pump are analysed using a computer simulation. The simulation adopts a distributed parameter modelling approach. The operation of the system and its components are described based on the principles of mass and energy conservation. The heat exchanger models are designed especially to address issues related to refrigerant mixture, such as two-phase property non-linearity and temperature glide, using an element by element analysis. The use of two refrigerants, R407C and R134a, are considered. The study emphasis on the influence of the heat exchanger volume ratio on the performance of both forward and reversed modes of the cycle. In the case of mixture application, the effects of glide mismatch resulting from reversing are investigated. Three different reversing methods are examined. Two of these methods use four-way reversing valve and the third method involves redirection of heat transfer fluid between the condenser and the evaporator to implement change of mode. The third method appears to be the best reversing technique for both refrigerants considered. With all the three methods, in the reversed mode, the R407C system performs better than the R134a system over a large range of volume ratios.