NEW METHODS FOR EVALUATING THE PERFORMANCE OF METAL HYDRIDE HEAT-PUMPS

The cycles of metal-hydride heat-pumps have three operating modes-heat upgrading, heat amplifying, and refrigeration. Carnot analyses of the se cycles show that in the case of the heat-upgrading mode a prerequis ite of high efficiency is that the reaction enthalpy for the high-pres sure hydride must be lower than that for the low-pressure hydride (ie Delta H-H < Delta H-L). In the case of the heat-amplifying and refrige rating modes the reaction enthalpy for the high-pressure hydride must be greater than, or equal to, that for the low-pressure hydride (ie De lta H-H greater than or equal to Delta H-L). The coefficient of perfor mance (COP) has been shown to be inadequate by itself for evaluation o f a metal-hydride heat-pump cycle; therefore three evaluation criteria are put forward for a comprehensive assessment-namely actual COP, all oy output and temperature output. In the present study the effects of some parameters on these criteria are discussed. Relative to other con ventional cycles, the COP values of metal-hydride heat-pumps are low, and further research is needed to improve their performance.