From the viewpoints of energy savings and environmental impacts, we have been studying on chemical heat pumps (CHPs) especially using calcium systems. In this study, the applicability of a scallop to CaO/H2O/Ca(OH)(2).CHP using hydration of calcium oxide and dehydration of calcium hydroxide as a new original material for the reaction systems was examined by thermogravimetry experiments and lab-scale CHP apparatus. As a result, the scallop CaO decomposed from scallop CaCO3 was found to work as a reactant for CaO/H2O/Ca(OH)(2).CHPs by some treatments of hydration repetition. (C) 2004 Elsevier B.V. All rights reserved.