Chemical and adsorption heat pumps: Cycle efficiency and boundary temperatures

The efficiency of an ideal three-temperature (3T) cycle of a chemical heat pump (CHP) is considered. For a reversible CHP 3T cycle, the maximal efficiency can be determined using the ratio of the heat of evaporation of the working fluid and the heat of the chemical reaction or using the boundary temperatures of the cycle. The boundary temperatures of the reversible CHP cycle are not independent variables relative to each other. As they are related by the Clausius-Clapeyron equation for the equilibrium of the pure fluid and by the van't Hoff equation for the chemical reaction, the choice of one of these temperatures completely determines the two others. Comparison of the efficiencies of the CHP cycle and the cycle of an adsorption heat pump (AHP) shows that the CHP efficiency can theoretically reach the Carnot-cycle efficiency whereas the AHP efficiency is always less than the Carnot-cycle efficiency because of the generation of entropy due to the transfer of heat to (from) the adsorber at a finite temperature difference. The minimal temperature of the external heat source needed for the operation of the CHP (AHP) cycle, the minimal evaporator temperature, and the maximal condenser temperature are calculated. These temperatures are determined for CHP (AHP) applications such as heating, air conditioning, ice production, and deep freezing in different climatic zones.