Experimental Verification of Mist Cooling Effect in Front of Air-Conditioning Condenser Unit, Open Space, and Bus Stop

Abstract

Mist spraying is a technique for locally lowering air temperature by spraying fine mist into the air and using the latent heat of evaporation immediately after spraying. This study focuses on the conditions under which mist spraying contributes to the increase in sensible heat release from the human body, using the ratio of air temperature decrease and humidity increase in the space where mist is sprayed. From the measurement results in front of the air-conditioning condenser unit, humidity increased by about 10 g/kg(DA), while air temperature decreased by about 10 °C. From the measurement results in an open space in a park, air temperature decreased by about 0.5 to 1 °C within 2 m of the mist spray and humidity increased by about 0.5 to 1 g/kg(DA) at the height of the mist spray, regardless of the distance from the mist spray. From the measurement results at semi-open bus stops, air temperature decreased slightly to 1 °C and humidity increased slightly to 1 g/kg(DA) under low-wind conditions. Unfortunately, the measured results of air temperature decrease in relation to humidity increase, which the human body perceives as cooler, were not available.

A Simplified Evaluation Framework for Adaptation Measures to Urban Heat Islands

“…In the case of watering the road surface, the road surface temperature decreased by about 10 °C, MRT on the adjacent sidewalks decreased by about 2.4 °C [8,11], SET* by about 0.21 × 2.4 = 0.5 °C (equation ( 21)), and WBGT by about 0.2 × 0.4 × 2.4 = 0.2 °C (equations ( 22), ( 24)). In the case of mist spray, air temperature Ta decreases by about 2.0 °C, air humidity Xa increases by about 0.8 g/kg', and the relative humidity RH increases by about 2.4 % [8,9], SET* by about 0.63 × 2.0 -0.13 × 2.4 = 0.9 °C (equations ( 18), ( 19)), and WBGT by about 0.2 × 0.6 × 2.0 + 0.1 × 2.0 = 0.4 °C (equations ( 22), ( 25)). In this case, the wet bulb temperature Tw does not change because of the constant enthalpy change.…”

“…in cooperation with Kobe City, one Japanese local government [6,7]. Then, Kobe City has begun to actively adopt them in redevelopment projects in front of its main station [8][9][10][11]. Since the advanced efforts by Kobe City are of interest at least domestically, it is necessary to develop a simple evaluation method for the effects of the implementation of these measures in order to expand their use to other regions.…”