This paper elucidates the mathematical modeling of ice build-up, analysis of performance and projected economic impact of a custom-designed external-melt ice thermal energy storage (TES) that was constructed in the Philippines. Custom-designed TES evaporator coil at compressor-aided, partial storage mode with maximum design ice thickness of 2.95 in (74.93 mm) was used for the TES facility with computed maximum cooling demand of 326.2 TR (1,147 kW).
The model was developed for ice formation rates based on relevant and validated researches. The governing equations for freezing were formed to solve for the weight of water converted to ice and prevailing TES bulk water temperature. All the thermophysical properties of ice expressed as a function of bulk ice temperature with correlated compressor capacity based on actual refrigeration system operating parameters was used.
Performance and cost analyses showed that the custom-designed TES cooling coil requires an increase in initial investment by about 14.26% compared to conventional water chiller of similar capacity by only considering the addition of TES tank, excluding electrical and piping requirements of the chiller and TES systems. Benefits from time-of-use (TOU) rates, wherein electricity is cheaper at night, and coefficient of performance (COP) improvement due to lower ambient temperature at night translate to 31.88% internal rate of return (IRR) at 5-year cash flow or simple payback period of 2.55 years.