DHWStrat – Thermal stratification of domestic hot water storage tanks

Thermal stratification of heat storage has a high impact on the efficiency of thermal energy systems. This correlation was shown in the StorEx project for combined storage tanks, with a new test procedure for stratification efficiency that is based on the second law of thermodynamics. This procedure is now well established, but could so far not be applied to domestic hot water (DHW) storage tanks. Therefore, in the DHWstrat project, the existing procedure was extended and applied to four DHW storage tanks. The results show that a well stratified DHW storage tank concept not only achieves higher comfort and better hygienic conditions, but in combination with a heat pump saves up to 40 % electrical energy compared to another storage tank. These results underline the need to evaluate the stratification efficiency also of DHW storage tanks.