Harvesting Dew with Radiation Cooled Condensers to Supplement Drinking Water Supply in Semi-arid

Abstract

This paper describes the development of dew harvest systems for use in semi-arid coastal region of north-west India, chronically short of drinking water. These were developed to ameliorate drinking water problem, especially of people living near the coast where groundwater is of poor quality and surface sources scarce. Although dew is much smaller in magnitude (20-30 mm) than the rains (300 mm) it is a more reliable source. Dew occurs over a season of seven months (October to April), rain over four (June - September). Dew nights number ~ 100, rainy days 15-20. There is much greater year to year variation in rainfall than in the dew amount. A R&D program of over four years led to development of three types of systems - condenser-on-roof (CoR), condenser-on-ground (CoG) and Roof-as-Condenser (RaC). The CoR, CoGs employ condenser made of plastic film insulated on the underside. CoRs are constructed over the roof of buildings, CoGs on open ground. The RaCs use metal roof of buildings itself as condenser. The CoR and CoGs give higher output, require higher investment. The RaCs give lower output; require only a small investment in collection and storage. Examples of working installation are presented. Rain and dew seasons in the region are complementary. Although engineered specifically to harvest dew, these also harvest rain, providing varying amounts of potable water through the year. Benefits to the region, learning accrued and partnerships created in the course of work are also briefly discussed.