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.