Enhanced Hybrid Dry Cooler for Solar Cooling - Self Cleaning Surface Modifications
Abstract
Due to the increasing use of air conditioning in residential buildings and its associated electric energy consumption, the alternative of using solar thermally driven cooling processes is investigated at Fraunhofer UMSICHT. In this work, the use of hydrophobic, self cleaning surfaces in compact hybrid dry coolers for small capacity solar cooling applications is presented. Hybrid dry coolers are usually operated in dry mode, but if the ambient temperature rises over a minimum ambient air temperature, sprayed with water to maintain the capacity. It is necessary to apply a hydrophobic and self cleaning/easy-to-clean modification to avoid scaling and fouling on the lamellae, because untreated tap water shall be used to limit the operating costs. Different structuring methods and coatings are chosen on the basis of a literature and market research, applied on sample sheets and tested within a stress test, where tap water spraying phases are alternating with dry phases. The surface properties before and after the stressing cycles are determined by advancing and receding angle measurements and optical examination. First results are presented and discussed in this paper.