Maldistribution in air–water heat pump evaporators. Part 1: Effects on evaporator, heat pump and system level

•The effect of evaporator maldistribution on annual operating costs is quantified.•Maldistribution is modelled with two distribution parameters.•The percentage increase of operating costs is similar in different climate zones.•Absolute cost increase is considerable in the colder climate zone.

This paper presents an approach to quantify the effect of evaporator maldistribution on operating costs of air–water heat pumps. In the proposed simulation model maldistribution is induced by two parameters describing refrigerant phase and air flow distribution. Annual operating costs are calculated based on heat pump performance at distinct operating conditions. Results show that percentage increase of operating costs is similar for the three considered climate zones, even though the effect of maldistribution on heat pump performance varies with operating conditions. Differences in terms of absolute cost increase for the climate zones arise mainly due to a varying number of operating hours. Absolute cost increase is considerable in the average and especially colder climate zone and can only partly be reduced by enlarging the evaporator.