Enhancing the efficiency of evaporative cooling pads for livestock barns and greenhouses by moisture adsorption

Abstract

High levels of relative humidity negatively affect the efficiency of the evaporative cooling pads installed in livestock barns and greenhouses. Consequently, the productivity decreases causing economic losses. Therefore, this project aims at prototyping innovative dehumidifying/desiccant segments to be installed on the conventional cooling pads enabling them to provide suitable microclimate conditions, especially temperature and relative humidity, for animals and plants. The hypothesis is that desiccant segments adsorb air moisture before introducing the air into the pads; consequently, the treated air is then able to absorb more moisture from the cooling pads, i.e. the cooling pads evaporate more water in the treated air, where water evaporation requires heat energy which is absorbed from the treated air which results in decreasing the treated air temperature. Theoretical and experimental investigations were conducted, where 211 laboratory experiments were performed for testing this hypothesis. The theoretical investigations (calculations and designs) were conducted using the results of the lab experiments. This study presents a methodology for testing desiccant materials and assessing their suitability as filling for the desiccant segments. The water adsorption capacity was 125, 158, 257, 132, 142 g H2O/kg desiccant, and the water adsorption rate was 17, 22, 36, 18, 20 g H2O/(kg desiccant h) for ARTSorbTM, PROSorbTM, Silica Gel, Silica Gel Macro-porous, and the mixture of all 4 desiccants, respectively. Model calculations showed that the required amount of desiccant per unit area of pads is 70 kg/m2. The thickness of the desiccant segments is 10 cm, with a total pressure drop of 0.6 kPa under the toughest conditions of air velocity of 2.5 m/s and 2 mm bead size. The desiccant segments require 0.18 kW extra energy per m2 of pads to overcome the extra pressure drop, i.e. 63.5 kWh/m2 and month which is the energy required by the extractor fans and costs 12.7 € / m2 month approximately. The results show potential for developing a desiccant system to improving the efficiency of cooling pads for livestock barns and greenhouses.