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This chapter describes the use of zeolites in solar energy storage and in solar energy heating and cooling applications. This chapter concentrates on natural zeolites, but considerable work has also been done with synthetic zeolites, especially zeolite 13X. The chapter begins with a review of energy storage applications of natural zeolites, both for short-term (day-to-night) and long-term (seasonal) storage. It then discusses the use of zeolites in heating and cooling cycles. Open cycles are considered first, where the zeolite is open to the ambient air and is used mainly for air dehumidification followed by evaporative cooling. This is followed by a discussion of closed-cycle systems, where the zeolite and the working refrigerant gas are sealed in an airtight container, which excludes all other impurity gases. The pressure in the closed-cycle systems is not ambient but is determined by the condensation and evaporation pressures of the refrigerant.
The chapter concludes with a brief description of the needs and directions for future research in this field. For this reason it describes the thermodynamic analysis of open and closed cycles, the approximations involved in the analysis, and the appropriate application of the Clausius-Clapeyron equation to determine the isosteric heat of adsorption for various gases on natural and modified or synthetic zeolites.
Solar energy is intermittent by nature. The sun shines during the day whereas the need for heat in homes is largest at night, when the ambient temperature is lowest. To overcome the time lag between supply and demand, people have used day-to-night averaging of solar energy since very early times. Throughout human history, homes in hot climates were built with thick walls of large thermal mass that warmed slowly during the day (keeping the home cool) and released the stored heat during the night. Zeolitic tuffs have been used for centuries as …