Screening of heat pump performance improvements obtained through gradual heating using a tank system

Many industrial processes require both cooling and heating of process streams. The use of a cogeneration heat pump system enables the simultaneous production of both utilities within one single, electrically driven unit. Within this work, the addition of a tank system at the hot end of different heat pump systems was investigated.

The tank system consists of a stratified storage tank for the storage of hot water and a smaller charge tank, which allows for multiple circulations of the water through the condenser. This leads to a gradual heating of the water, leading to a higher COP compared to heating in one step. Using numerical modelling and simulation, a screening was carried out investigating the influence of different working fluids and heat pump configurations, different temperature glides in the heat sink and different temperature lifts on the performance of the heat pump system.

The largest improvement, compared to a conventional heat pump, was achieved with a one-stage heat pump with R600a, increasing the COP by 35 %.