Development of a fundamentally based stratified thermal storage tank model for energy analysis calculations

Stratified thermal storage systems utilize the temperature dependence of water density to store both warm return water and cold supply water in a single tank. Manifolds and diffusers at the tank inlets minimize turbulence and mixing in the tank, resulting in a relatively small thermocline between the hot and cold layers. A discrete time step model based on previous work by Wildin and Truman (1985) was developed for implementation in an hourly energy analysis program. The model numerically solves the one-dimensional, time-dependent equation for the tank water temperatures using a Runge-Kutta method. Appropriate time scaling was required to achieve stability. Sensitivity to model and environmental parameters is discussed. The performance of the model is compared to experimental data and a finite difference model.