Numerical modeling of latent heat thermal energy storage integrated with heat pump for domestic hot water production

A combination of a heat pump and thermal energy storage is an efficient method to utilize variable renewable energy. Phase change materials have the potential to provide higher energy densities for thermal energy storage. Previous thermal energy storages utilizing phase change materials are either limited to sequential charge and discharge cycles or a complicated design that limits the maximum charge and responsiveness. This paper presents a novel integration of a heat pump and a thermal energy storage for a responsive simultaneous consumption and charging of the thermal energy storage up to the maximum charge. This concept is illustrated with a process model which is an essential tool in the dimensioning, design, and analysis of integrated thermal energy storage systems. The concept is demonstrated in domestic hot water with the heat pump operating either constantly, with solar energy, or with cheap electricity. For the daily demand of 138.4 kWh, heat pump outputs of 6.0, 14.0, and 22.8 kW were required with thermal energy storage capacities of 30.5, 54.6, and 130.2 kWh. This demonstrates the applicability of the concept as well as the process model for research and design of thermal energy storage with phase change materials.