Optimization of thermal cooling Parameters applied to rock Storage systems

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This study presents a mathematical model for thermal energy storage in low energy buildings. The cooling system which uses rock bed for storing night cooling to be used later for daytime air conditioning is presented. The work initially focuses on the mathematical descriptions of the thermal cooling applied to rock storage system. A numerical method of solution is outlined and the results are compared with measured data at the outlet of the bed both using the measured inlet temperature. A good agreement of trend is observed. The results show two effects of the cooling system on the air temperature, which are damping and time delay of the peaking. The differences are examined through sensitivity analyses for both the convective heat transfer coefficient and mass flow rate. A parametric study for heat storage with materials and bed size is given. A genetic algorithm (GA) is used as a tool to identify the thermal cooling system parameters related to the mathematical model, including the radius of the sphere (rocks), mass flow rate, convective heat transfer coefficient and length of the rock bed. The simulation results have shown an improvement on the performance of the model with identified parameters compared to the performance before parameter optimization. In general, the model with optimal parameters has shown robustness to predict the performance of the cooling system by reducing the input (air) temperature as much as possible at the time when the temperature is hottest.


PhD Thesis