Study of mist-cooling for semi-enclosed spaces in Osaka, Japan

Evaporative mist cooling systems are increasingly used in Japan to cool urban spaces as a counter to the urban heat island problem. Japan has a humid climate, which reduces evaporation. The balance between cooling and undesirable wetting requires careful control and placement of misting nozzles. Spraying from varying heights in an atrium showed that a single spray nozzle with Sauter mean droplet diameter of 41 microns can provide cooling of 0.7K without wetting. Cooling effects of mists with larger droplet diameters that cause slight wetting cannot be accurately measured due to the wet bulb effect on the sensors. Simulations suggest actual air temperatures are higher than wet sensor readings. Calculations of effective temperature ET* show that increases in humidity do not overcome the increase in thermal comfort due to the temperature reductions from fine mist.