Extended standard effective temperature index for water-misting environment

Abstract Because the mist droplets in water-misting environments adhere to human body surfaces and cause evaporative heat loss (mist wettedness), it is difficult to effectively assess the thermal environment using basic environmental parameters (air temperature, radiant temperature, air speed, and humidity) only. Therefore, the present study proposes an environmental index considering the additional heat loss caused by mist wettedness. Heat loss by mist wettedness was applied to a two-node model (2NM) as a method of extending the existing standard effective temperature (SET*) into the water-misting environment. The modified 2NM predicted the overall skin temperature in the water-misting environment with an error of 0.15 °C. The general thermal and water-misting environments are compared using the extended SET* (SET**); the SET** without mist wettedness was calculated with a difference of 0.22 °C compared to the existing SET*. As a result of the proposed environmental index, the existing SET* decreased by 1.2 °C by water-misting in a hot outdoor environment. However, according to the SET** results, the water-misting environment has a cooling effect of 3.1 °C lower than that of the existing SET*. The results show that evaluating the water-misting environment with only basic environmental parameters can underestimate the cooling effect of the water-misting spray device. Additionally, it is expected that the cooling effect of the water-misting environment can be properly assessed using the proposed environmental index.