The Solar-AC FAQ : (Category) Heat-driven cooling – absorption, desiccants, Vuilleumier : (Answer) What desiccants exist and how can they produce a cooling effect?
Desiccants are materials with a high tendency to adsorb water. If a dry desiccant is exposed to the air, it will dehumidify the air, while the desiccant becomes warm. Eventually the desiccant will become saturated with water, but it can be “regenerated” by heating. The most common desiccants are silica gel, calcium chloride (CaCl2), activated carbon, zeolites, lithium chloride (LiCl) and lithium bromide (LiBr). Some desiccants can adsorb other liquids than water. Of interest are liquids which boil at temperatures somewhat below water’s freezing point: methanol, ammonia, ethanol, methylene chloride. The most obvious use of desiccants in the HVAC area is to dehumidify intake air. Systems which do this are usually set up as “desiccant wheels”. If the heat produced during adsorption is excluded from the conditioned space, this produces a form of cooling effect by removing enthalpy from the air. (Warm dry air has less potential energy in it than warm wet air; if you were to add moisture bac
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