Performances of modern domestic hot-water stores

Several designs of domestic hot-water (DHW) store, including those with immersed heat-exchangers (HXs), are commercially available. So there is a need for a method that accurately assesses their effectivenesses. In this study, the behaviours of a novel stratified, and two standard, stores were analyzed. The TRNSYS simulation software was enhanced to simulate the functioning of those stores. The resulting mathematical model was validated using measurements obtained from experiments, which required a realistic daily DHW draw-off for testing the DHW systems. Evaluation of a user-related effectivenesses (URE) for each of the three tanks tested showed that the inner configurations of: (i) the tank and (ii) the immersed HX can significantly affect the store's performance. The stratified store was up to 32% more effective than the commonly employed commercially-available store.DHW store Immersed heat-exchanger Store' s performance Experimental analysis

Influence of the domestic hot-water daily draw-off profile on the performance of a hot-water store

An enhanced TRNSYS simulation model, NEM, of the behaviour of a domestic hot-water (DHW) store, with an immersed heat-exchanger (HX), has been developed and validated. This model simulates the dynamic heat-depletion and recovery processes in the immersed HX and predicts the transient temperature-patterns for various DHW draw-off versus time profiles. Realistic daily profiles (RDPs), based on field studies, were developed to provide representative draw-off patterns for the testing of thermal stores and simulation studies. The effects of these RDPs and five other existing profiles on the store's performance are analysed using the enhanced model. The simulation results indicate the importance of the HX's recovery, as well as the number, type and time of occurrence of the draw-offs in the profile, on the thermal store's performance. It is concluded that RDP profiles should be used in the performance testing of thermal stores to obtain results that reflect conditions experienced in the field.DHW store Computer modelling Immersed heat-exchanger Draw-off profiles Heat-recovery effects