Validation of a fully-mixed model for simulating gas-fired water storage tanks

An ESP-r component model for gas-fired water storage tanks was developed within the context of the simulation for building-integrated cogeneration systems. Charged by the cogeneration unit with gas back-up, the tank can be used to satisfy both domestic hot water needs and space heating. Based on the fully-mixed water assumption, the model has three control volumes representing the water and casing, the combustion chamber, and the flue gas. The experimental data used in this validation study comes from nine groups of tests, covering four commercial water heaters and three different water drawing schedules. The validation is carried out via a plant network with two components: the water tank and a boundary condition. It is found that the model can predict the mean tank temperature well. However, the fully-mixed assumption may lead to an underestimation of energy consumption by 8-15%, depending on the water drawing schedule