A theoretical analysis of the daily performance of a new water tank with multiple outlets in solar water heating system

A variable-volume tank featured with multiple outlets is lately proposed to cater for the varying needs of tank volume. Compared with conventional tank, the new tank can help shorten the thermal response time and improve the solar charging performance. In this paper, a mathematical model is developed to simulate the solar charging and discharging performances of the new tank. The model, based on the one-dimensional multi-node approach, considers the adaptive selection of the operative outlet port. The model shows good agreement of the tank temperature development against the computational fluid dynamics simulation and experimental results. Using the model, a parametric study was conducted to analyse the effects of heat demand, initial tank temperature and solar insolation. The results show improved heat supply and reduced heat loss achieved by the new tank. It also demonstrates that the performance of the new tank is less affected by the heat load, initial tank temperature and solar insolation, which contributes to a robust heating system.