Schematic of solar desiccant cooling.
The hot desiccant material absorbs moisture from incoming ventilation air and
increases the dry-bulb temperature. This dry air stream is cooled in two
steps. First, it is sensibly cooled by heat exchange with the building
exhaust air. Then it is evaporatively cooled and partially rehumidified by
contact with a water spray. The exhaust air from the building is
evaporatively cooled to improve the performance of the heat exchanger. After
being heated by heat exchange with the incoming air, the exhaust air is
further heated by energy from the solar system and/or from an auxiliary energy
source. The hot exhaust air passes through the desiccant material and desorbs
moisture from it, thereby regenerating it for continuation of the process.
Desiccant systems have faced problems of high parasitic power and large space
requirements relative to capacity. Because of their bulkiness, the systems
may have primary application in the low capacity range (i.e., residential
systems) if and when ways can be found to reduce parasitic power requirements
to acceptable levels.
The Institute of Gas Technology (IGT) has been investigating design
modifications in a prototype 3-ton system. AiResearch is developing a
1-l/2-ton desiccant cooling system around a radial flow design. Illinois
Institute of Technology is developing a dehumidifier of a cross-flow design
that will provide more compact and efficient operation than previous designs.
Zeopower is developing a unique closed cycle desiccant system in which the
desiccant is integral with the collector.