Efficiency of heat pump systems with integrated latent heat storage

Heat pumps in combination with a thermal storage enable the temporal decoupling of heat generation and heat consumption. Latent heat storages offer advantages over conventional heat stores, especially for integration in heat pump systems. Due to the constant temperature conditions during charging and discharging, latent heat storages are particularly well suited for integration into the internal refrigerant circle of heat pumps, which is determined by the temperature levels of evaporation and condensation. There are different options for integrating latent heat storages into heat pump systems. On the one hand, two heating condensers can be used in conjunction with a latent heat storage. In this case, charging and discharging of the storage takes place exclusively by heat transfer between the refrigerant and the phase change material. On the other hand, a heating condenser and a latent heat storage can be integrated in parallel, with charging of the storage by direct condensation of refrigerant and discharging by heat transfer to the heating water. The concepts for integrating the latent heat storage into the heat pump system as well as the implementation of the internal heat pump cycle are presented. As a conventional reference, a heat pump system with a water-based heat storage is included in the analysis. The energy efficiency of the three heating systems with heat storage are analyzed by means of a model-based simulation. The performance of the systems during a typical charing/discharging cycle is compared with regard to the systemic impact on the COP. In order to avoid peak demand situations of the electric grid, an operating strategy with constant electric consumption during day time and reduced power demand at night time is investigated.