An Analytic Model of Stratification for Liquid-Based Solar Systems

Abstract

Accurate modelling of solar air or liquid heating, cooling, or domestic hot water systems with storage generally requires an accounting of the stratification within such storage. Overall system performance may be significantly affected by the storage temperature distribution. Most current stratification models utilize a finite difference scheme for solution to the general equations. An analytic method to determine the temperature distribution has been derived for liquid storage within a solar system. In liquid storage, it is assumed incoming fluid enters at the location with the temperature closest to its own. Hence, the solution requires the possibility of a region within storage where there is no forced flow. In addition, ther may be collector loop flow, load loop flow, or both concurrently. Each of these cases has different boundary conditions, and each must be solved separately. Comparisons of the resulting calculations with system data for the Colorado State University Solar House I show good agreement. This suggests that inclusion of an analytic stratification model within a system simulation may be useful by allowing direct calculation of temperatures in stratified storage.