Abstract
Within the last fifteen years, the development and utilization of cool thermal energy storage for use in building air-conditioning has witnessed a dramatic increase. Originally, research in thermal storage was rooted in designing systems which would effectively shift the on-peak demand for electrical energy to off-peak hours. Recently, along with peak shifting, utilities have required that storage systems must also be energy conservative. Research is now concentrated on the optimization of the storage device in order to meet the utility's mandate. The first part of this study looks at the effects of adding propylene glycol to a static-water ice thermal storage tank, in the pursuit of increasing storage capacity. The effects of glycol addition on overall storage capacity, Carnot efficiency and on heat transfer irreversibility are all considered. The results of the first study show glycol addition to be detrimental to the storage process. The addition of glycol to the water decreases the total storage capacity due to a large decrease in the latent heat of fusion of the water in the storage solution. Carnot efficiencies, for the storage process, decrease with the lower operating temperatures. Finally, despite a fixed temperature differential of 10'F, the irreversibility developed from the heat transfer between the tank water and the refrigerant increases with lower freezing temperatures. The second part of this study presents a simplified optimization method for a pure water, ice storage process. This method minimizes the amount of required compressor work, per unit mass of ice produced, by adjusting evaporating temperatures and/or heat exchanger size. The heat transfer irreversibility is also used to exemplify the usefulness of the second law in the design of storage systems. Performance data from a laboratory test is used to evaluate the merit of the method. The method predicted compressor work within 21 % of the laboratory data.
Abraham, Michaela Marie (1993). Investigations in cool thermal storage: storage process optimization and glycol sensible storage enhancement. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -A159.