Solar-powered systems for cooling, dehumidification and air-conditioning

Abstract

This paper describes current trends in solar-powered air conditioning, which has seen renewed interest in recent years due to the growing awareness of global warming and other environmental problems. Closed-cycle heat-powered cooling devices are based mainly on absorption chillers, a proven technology employing LiBr–water as the working fluid pair. Recent developments in gas-fired systems of this type make available double- and triple-effect chillers with considerably higher COP than their single-effect counterparts, which makes it possible to reduce the amount of solar heat required per kW of cooling. These systems require, however, high-temperature solar collectors. The principles of multi-staging absorption systems are described. An economic comparison is provided which shows the total system cost to be dominated by the solar part of the system. At current prices, the high COP, high temperature alternative is still more costly than the low temperature one. Open-cycle desiccant systems employing either solid or liquid sorbents are described. While the main thrust in research on novel closed-cycle absorption systems has been toward increasing the operating temperature in order to improve efficiency through multi-staging, open-cycle absorption and desiccant systems have been developed for use with low temperature heat sources such as flat plate solar collectors. A novel open-cycle (DER) system is described, which makes it possible to use the solar heat at relatively low temperatures, for producing both chilled water and cold, dehumidified air in variable quantities, as required by the load.