Heat pump condenser and desuperheater integrated into a storage tank: Model development and comparison with measurements

This work describes the development of a simulation model for a novel storage tank system with an integrated heat pump (HP) condenser and desuperheater. The model was designed to enable both design calculations of the condenser/desuperheater and annual simulations of the system integrated into a whole heating system. For the heat exchangers heat transfer coefficients and pressure drop are calculated on both fluid sides depending on the geometry, flow conditions and thermal properties using empirical correlations available in literature. As the heat exchangers are always (desuperheater) or partly (condenser) operated by means of a free flow on the water side, a model for calculating the water mass flow rate depending on temperature and density differences was implemented. The storage model is based on a one-dimensional multi-node approach, like it is commonly used for the simulation of water storage tanks. The results of the model were compared to measurements carried out with an experimental storage tank and a HP with a capacity of about 6 kW for different modes of operation. The simulation results agree well with the measurements concerning the prediction of the behaviour of the condenser and desuperheater and the storage tank temperatures.