Comparative Analysis of Thermal Energy Storage Stratification Efficiency - A New Method Combines Advantages of Previous Approaches

In solar thermal heating systems, optimal stratification within the storage tank results in lower
return temperatures of the collector and reduces auxiliary heating demand. Despite the
extensive research in the field of tank stratification, a widely accepted parameter that can be
used to quantify the stratification efficiency of a thermal storage has not emerged yet. In this
contribution, existing methods to determine stratification efficiency are analyzed from a
theoretical point of view, and a new method is shown that combines advantages of the
existing approaches. It is claimed that the new method, if applied to any storage process,
determines its stratification efficiency alone, eliminating as much as possible the bias of
storage heat losses that has sometimes been included in previous approaches. A theoretical
example illustrates the effectiveness of the new method presented