Design recommendations for plate heat exchangers in heat pumps using pure and mixed refrigerants

This paper aims at deriving design recommendations for plate heat exchanger (PHE) evaporators and condensers in heat pump (HP) systems using different refrigerants. A coupled HP - PHE simulation framework was used to carry out cycle and component design for a case study, with different combinations of PHE geometrical parameters, and propane, butane and propylene/butane (0.5/0.5) as refrigerants. An operating model subsequently evaluated the heat pump thermodynamic and economic performance with the different designed PHEs: the trade-off between heat transfer area and refrigerant pressure drops was therefore taken into account for both components. Only evaporator pressure drops affected the Coefficient of Performance (COP), and different refrigerants presented dissimilar slopes of degradation. Condenser design did not influence the COP, and the economic optimum corresponded to the lowest size. The evaporator design at minimum cost was instead found as a trade-off between heat transfer area and pressure drops for all the working fluids. Despite the different rates of COP drop, the three refrigerants resulted in the same optimal pressure drop at the evaporator, equal to around 5 kPa.