Microclimate Observation by Outdoor Thermal Indices (Case Study of Five Climates)

Abstract

Because of the differences between indoor and outdoor thermal condition, preparing some outdoor thermal indices is a way to understand and categorize the outdoor thermal sensation. The aim of these indices is not to provide thermal comfort as it is the aim of indoor indices. Instead, they are provided to analyze outdoor thermal sensation to help architects, landscape architects and urban designers in design procedure to provide the most possible tolerable thermal condition in outdoor places such as urban public spaces. This article is the result of some field studies have been done in 2010 2012 in five different climates: hot semi humid (Ahvaz, Iran), tropical (Kuala Lumpur, Malaysia), hot-arid (Kashan, Iran), moderate-arid (Tehran, Iran) and cold (Sheffield, UK) in their worst thermal period. The main question in this research is: which outdoor thermal index is appropriate for a specific climate? And how much it is accurate to evaluate outdoor thermal sensation especially in different levels of cold stress and heat stress condition? In each field study the weather data including temperature, humidity and wind speed, are collected by two portable Kestrel weather stations to show weather condition in local and microclimate levels. People's behavior in outdoor spaces is observed to understand their reaction to the different thermal conditions. A nominal observation scale is used for people’s age, health, clothes, activity and exposure time. Outdoor thermal indices that are used in this research are: Humidex, WBGT (wet bulb globe temperature), TSI (tropical summer index), Summer Outdoor Comfort Zone, WCET (wind chill equivalent temperature), THI (temperature humidity index) and UTCI (universal thermal climate index). The results show that outdoor thermal indices may have not the same explanation for the same thermal condition. Some of them are more appropriate for some specific condition while others are not. At last it would be summarized that they have acceptable sensitivity to temperature but most of them need to become more sensitive to humidity and air velocity.