Human demand for energy has reached unprecedented levels. A high-efficiency chemical heat pump (CHP) that uses solar thermal as heat source called SCHP system has been studied for decades in our laboratory. The solar chemical heat pump (SCHP) system using CaSO₄∙1/2H₂O/CaSO₄ can store solar thermal energy in the form of chemical energy and release it as hot heat and cold heat. This study presents a simplified three-dimensional unsteady model of reactant bed using CaSO₄∙1/2H₂O/CaSO₄ for heat releasing step of SCHP system. The simplified model is programmed by finite difference method and enabled operation by Microsoft Excel on a personal computer instead of other complex programming languages on workstations etc. Even the simplified model can simulate the heat/mass transfer in the reactant bed under different evaporator temperatures. The simulation results of temperature distribution and overall hydration conversion are in good agreement with the experimental results. Furthermore, the effects of fins inserted in the reactant bed and fins thickness on the enhancement of the hydration conversion and the hot/cold heat power were shown at different evaporator temperatures.