A Heat Pump and Thermal Storage System for Solar Heating and Cooling Based on the Reaction of Calcium Chloride and Methanol Vapor

Abstract

Thermodynamic, kinetic, heat transfer and mass transfer data are presented on the reaction of CaCl2 and CH3OH vapor to form solid-phase CaCl2•2CH3OH. These data demonstrate the suitability of the reaction for storing solar energy, and for pumping heat, either for use in space heating (at a solar coefficient of performance > 1), air conditioning, or both. CaCl2 reacts with CH3OH to form CaCl2•2CH3OH with an enthalpy and entropy of reaction 51.7 kJ (mole CH3OH)−1 and 126 J deg−1 (mole CH3OH)−1, respectively. Reaction kinetics close to equilibrium are complex, although the reaction is first order when the temperature of the reacting salt is far from equilibrium. Heat transfer through the salt appears to follow the Russel equation, and reaction rates are not limited by mass transfer in a well-designed system. In the heating mode, a solar coefficient of performance (COP) of about 1.6 should be achievable if the entire heat of CH3OH condensation is used; this could permit a substantial reduction in solar collector area for a given amount of heat delivered to the load. In the cooling mode, the COP should be about 0.6. The system should be capable of pumping heat from an ambient source of 0°C to an indoor air duct temperature above 40°C, or from an indoor chiller at 5°C to an outdoor ambient air sink. The required solar collector temperature is below 140°C, and the energy storage density is about 4 × 105 kJ m−3.