Computer simulation of stratified heat storage

Abstract

A one-dimensional, explicit, finite difference model of a single tank for stratified thermal storage has been developed and tested on published experimental data. The model covers through-flow conditions for charging or discharging the thermal storage tank and conduction and turbulent mixing within the water. It was demonstrated that careful design of the algorithm and choice of the time-step are necessary to avoid computational errors, which create apparent mixing in the through-flow calculation. In order to handle variable flow rates, a ‘conceptual buffer-tank’ algorithm was developed which makes the procedure flexible and useful. Turbulent mixing across the thermocline is simulated through thermal eddy conductivity factors which have been determined from published experimental data. The complete computational model is simple and efficient enough to interface with a larger program simulating an entire air-conditioning system, which includes chillers, building loads, weather, etc. At the same time, the model reproduces hydraulic model test data better than a recent one-dimensional model found in the literature.