Experimental performance of a new mixed-flow two-stage regenerative indirect evaporative cooler

Abstract

Evaporative cooling can improve energy efficiency in buildings; however, the air supplied to indoor spaces may be excessively humid or not cool enough to ensure thermal comfort. To overcome this, Indirect Evaporative Coolers maintain a constant humidity ratio at the product airstream, and regenerative airflow configurations allow cooling below the inlet air’s wet bulb temperature. Such devices rely on the well-known Maisotsenko cycle and are often referred to as Dew Point Evaporative Coolers, as they can ideally reach the dew point temperature of inlet air. This work proposes a mixed-flow prototype that combines the superior thermal performance of counter-flow designs with the compact size of cross-flow systems. The heat exchanger is made of polycarbonate plates, while water distribution is optimized thanks to outlet nozzles and a wicking material placed on the wet side of such plates. The device has a volume of 0.025 m3 and supplies 40 l/s of cooled air, achieving a cooling capacity greater than 325 W under inlet air conditions of 40 ◦C and 30 % relative humidity, with a water consumption of 1.9 l/h. Experimental results demonstrate that increasing the inlet dry bulb temperature and decreasing the inlet air relative humidity significantly improve temperature drop and cooling capacity, though they have a limited effect on the thermal effectiveness. Compared to a previous one-stage prototype, the two- stage configuration increases the temperature drop and both the wet bulb and dew point effectiveness by about 50 %. However, the cooling capacity barely improves less than 17 %, due to the use of part of the product air as working air.