DHW Tanks - 40 % Savings by Better Stratification
Abstract
An existing method for determining the thermal stratification of combi-storage tanks, based on the second law of thermodynamics, i.e. on the entropy balance of the storage system, was adapted for measuring domestic hot water storage tanks. The updated method uses tapping profiles from EN 16147 to test the stratification efficiency of different sized storage tanks, matching the size of the collector array to the tapping profiles when using solar thermal systems. The resulting test procedure was applied to several tanks and the results were evaluated. It is shown that the efficiency of the storage tanks and their influence on the operation mode of the charging varies considerably. A very well stratified storage tank concept not only achieved higher comfort and created better hygienic conditions, but in combination with a heat pump saved up to 40 % electrical energy compared to another storage tank. These results underline the need for an evaluation of the stratification efficiency of domestic hot water storage tanks, which can be done with the method presented here.