Comparative experimental investigation of novel organic materials for direct evaporative cooling applications in hot-dry climate

Abstract

In the last decade, energy consumption for air conditioning applications has been dramatically rising as a result of the growing global population and increasing comfort demand. Consequently, direct evaporative cooling (EC) technology is emerging as an alternative to vapour compression air conditioners due to its lower environmental impacts, less energy consumption and lower operating costs. EC pad is one of the most important components of such systems and in present day, corrugated cellulose paper pads, produced through industrial processing, are mostly used. Despite such materials are efficient, production of them requires energy and advanced machinery resulting in associated costs. Therefore, new organic EC materials, which are locally available, abundant and efficient are needed for making EC applications economically and environmentally more viable. Accordingly, in this study five new natural porous materials including eucalyptus fibres (EF), ceramic pipes (CP), yellow stone (YS), dry bulrush basket (DBB) and Cyprus marble (CM) were experimentally investigated for EC applications in hot-dry climate (RH<20%). Within the study, materials were tested in a wind tunnel at different air velocities varying in the range of 0.1-1.2 m/s. According to the study results EF and CP were found as the most promising candidates with effectiveness values varying in the range of 72-33% and 68-26% for the air velocities between 0.1 -> 1.2 m/s. In contrast to the cooling effectiveness, cooling capacities showed an increasing trend with the rise of air velocity and they were found in the range of 0.13 -> 0.71 kW and 0.12 -> 0.55 kW for EF and CP respectively. Among the other investigated materials, YS was found competitive with these materials with effectiveness and cooling capacity in the range of 46%-> 22% and 0.08 -> 0.48 kW. On the other hand, DBB and CM showed relatively poor performances where effectiveness and cooling capacity obtained with them were below 35% and 0.45 kW respectively. Study results also demonstrated an inversely proportional correlation between cooling capacity and effectiveness. According to this correlation, optimal mass flow rate for system operation was found as 0.063 kg/s, which was valid for all tested materials and which was only the function of inlet air temperature and relative humidity. Such correlation will be useful for performance optimization in EC applications.