Numerical model development for tank temperature stratification and performance prediction of a R-290 heat pump water heater device

The climate crisis is pushing further boundaries in the field of industrial technology. Especially the world of simulations is becoming more and more important as, in the design phase of a product, it allows a sharp decrease in raw material in the production of prototypes. An additional advantage is the decrease in time in the product realization phase, thus allowing a strong reduction in costs. The study objective is to develop a mathematical model that predicts temperature stratification in a heat pump water heater tank, using a low-GWP refrigerant gas such as R290, also known as propane. The mathematical model implements a series of equations that replicate the physics of the problem; specifically, the algorithm development steps are an initial discretization of the tank, the implementation of the physics regarding heat transfer and the subsequent buoyancy-driven convection generated, the implementation of EN 16147 standard, and a final coupling with the model simulating heat pump operation. Simulation results confirm how the model manages to replicate very accurately the temperature profiles that are generated in the three simulated phases of the standard, i.e., the first phase of heating, the second phase of thermal degradation, and the third phase of water draw offs due to the user's demand for domestic hot water.