Selection of heat storage materials for ammonia-water and lithium bromide solar-powered absorption heat pump systems

A procedure for incorporating phase-change thermal storage materials in ammonia-water and lithium bromide absorption heat pumps systems is explored. Performance evaluation of the systems is presented and results are used as a guide in selecting appropriate phase-change materials (PCMs) for the absorption heat systems. Evaluation of the system indicates that there is a minimum generator temperature for each configuration of the system, below which there is a drastic drop in the performance of the absorption heat pump system. This temperature provides the lead to the selection of appropriate PCMs for heat storage in heat pump systems, especially those powered by solar energy. Eutectics, therefore, are best suited for such operations. This paper shows that the selection of appropriate PCMs can be determined purely from theoretical thermodynamic considerations. Various heat exchange designs for the storage systems are discussed and their merits and demerits pinpointed. The study concludes that the selection and arrangement of the best design of the storage system can only be achieved by optimisation studies, though the two-fluid tube/shell heat exchanger arrangement presents several advantages over the others.