Pesaran and Wipke (1994) used an unglazed transpired solar collector for desiccant regeneration in a solid
desiccant cooling cycle. These types of collectors are less expensive than conventional glazed flat-plate
collectors. They found that the thermal coefficient of performance of the cooling system with unglazed
collectors was lower than that of the cooling system with glazed collectors because the former system did
not use the heat of adsorption released during the dehumidification process. The thermal COP of a desiccant
cooling system regenerated with an unglazed transpired solar collector is about 50% less than the thermal
COP of a desiccant system regenerated with a conventional gazed flat-plate collector. The collector
efficiency of the unglazed collector is about 20% higher than that of the glazed collector at a regeneration
temperature of 70°C. Although the area required for the unglazed collector array was 70% more than that
required for the glazed collector array in a 10.56 kW solar cooling system, the cost of the unglazed array
was 45% less than the cost of the glassed array. Although the use of unglazed transpired collectors seems to
make economic sense relative to use of glazed conventional collectors, some practical considerations (such
as sustaining very low emissitivity for a long period of time, the use of horizontal orientation during winter,
and lower absorber heat-exchanger effectiveness) may limit their use for desiccant regeneration.