The reaction of CH/sub 3/OH vapor with solid (pellet) CaCl/sub 2/ to form the solid phase compound CaCll/sub 2/ . 2CH/sub 3/OH can be used as the basis of a combined solar heat pump/thermal energy storage system. Such a system is capable of storing heat indefinitely at ambient temperature, and can be used for space and domestic hot water heating, and for air conditioning with forced air (dry) heat rejection. It combines all features required of a residential or commercial space conditioning system except for solar collection. A detailed thermal analysis shows that the coefficient of performance for heating is greater than 1.5, and for cooling, greater than 0.5. This has been confirmed by direct experimental measurement on an engineering development test unit (EDTU). The experimental rate of CH/sub 3/OH absorption is a strong function of the absorber-evaporator temperature difference. The minimum practical hourly rate, 0.10 moles CH/sub 3/OH per mole CaCl/sub 2/, was observed with the salt-bed heat transfer fluid at 40/sup 0/C and the CH/sub 3/OH evaporator at -15/sup 0/C. a detailed performance and economic analysis was carried out for a system operated in Washington, DC. With 25 square meters of evacuated tube solar collectors, the CaCl/sub 2/-CH/submore » 3/OH chemical heat pump should be capable of meeting over 90% of the cooling load, 80% of the heating load, and 70% of the domestic hot water load with nonpurchased energy in a typical well-insulated single family residence, thus saving about $600 per year. In small-scale production, the installed cost of the system, including solar collectors and backup, is estimated to be about $10,000 greater than a conventional heating and cooling system, and a much lower cost should be possible in the longer term. « less