Thermal comfort of persons staying outdoors is one of the factors that would encourage outdoor activities. City residents normally spend much time indoors without enjoying the outside natural wind and sunshine .Residents wish to have outdoor spaces to enjoy walking, cycling, and other activities. Thus on a hot summer day or cold winter day, people are discouraged to spend time outdoor and get exposed to thermally uncomfortable environment.
While indoor environment can be easily changed by air conditioning, methods for making an outdoor environment comfortable are very limited. Thermal comfort in the outdoor environment is mainly related to climatology(focus on climate), thermo-physiology (heat balance of human body), and also connects the urban and landscape designers. In principle, there are three different approaches to study the human body- thermal comfort relation, a psychological, a thermo-physiological and one based on heat balance of human body. The psychological one states that thermal comfort is a condition of mind which expresses satisfaction with the thermal environment. On the other hand, thermo-physiological declares that comfort is based on the firing of thermal receptors in the skin and in the hypothalamus. Heat balance states that thermal comfort is reached when heat flows to and from the human body are balanced and skin temperature and sweat rate are within comfort range. For the assessment of outdoor thermal comfort not all of the three approaches can be