Using the sun to keep Australians cool

CSIRO Energy Technology (Newcastle, New South Wales, Australia; www.csiro.au) is developing a solar-powered air conditioning unit for residential use, using a desiccant-evaporative process to provide cool and dehumidified air. Thermally driven ab- or adsorption chillers are commonly used to provide cooling using heat, but these entail disadvantages: they are expensive, bulky, they produce chilled water instead of air, and they are not ideal for providing dehumidification under Australian summer ambient conditions.

Stephen White, a member of the CSIRO team, says that using solar heating for cooling is a new and important research area for Australia. "It addresses a national challenge since air conditioning and space heating are responsible for around 18% of the annual residential greenhouse gas emissions in Australia. Replacing 10% of the existing air conditioners in Australia with a low-energy consumption, solar-powered system could result in CO2 emission reductions of up to 1 million ton/yr of CO2."

The CSIRO team has tested the dehumidification performance of a desiccant wheel (300 mm dia.) made of an iron-alumino-phosphate zeolite with an AFI structure and traded under the name of FAM Z-01. Moisture removal capacity of the material is 8 g of water per kilogram of dry air with regeneration air at 80°C and 8.25% relative humidity, and an inlet air stream of 30°C and 93% relative humidity. The difference in moisture removal between 50°C and 80°C regeneration temperature was found to be less than 1-g water/kg dry air, for supply inlet temperatures between 10°C and 30°C and supply inlet relative humidity between 20 and 50%. Compared with silica gel, the performance of the FAM-Z01 material was best at the low regeneration temperatures expected in solar applications.