With the increase of the urban population in developing country, the demand for new city is increasing in these days. According to these phenomenon, a lot of opportunity to extend urban design business abroad has been increased. Outdoor spaces are important in urban design because they accommodate daily pedestrian traffic and various outdoor activities and contribute greatly to urban livability and vitality. In these days, making outdoor spaces attractive to people has been recognized as a goal in urban planning and design. However, there is no index for understanding the outdoor thermal comfort.
In this study, an outdoor thermal comfort index, CSDH(Cold Sense Degree Hour) and HSDH(Hot Sense Degree Hour) and are proposed. CSDH and HSDH are based on PET and can be used as an annual outdoor thermal comfort index.

(1) Most researches have focused on thermal comfort of indoor environment. This research analyzed characteristics and major factors, and proposed new outdoor thermal comfort index, CSDH and HSDH. The CSDH means the degree hour of cold sense under outdoor environment for a certain city or district. While the HSDH means the degree hour of hot sense. This new index, CSDH&HSDH, use OUT_MRT to consider the effect of the solar radiation in outdoor environment, PET to express human thermal comfort as a numerical value, and the concept of accumulated temperature to express annual or monthly outdoor thermal comfort.

(2) Existing comfort range for PET has a limit for adopting all climate zones. Therefore, in this study, the PET comfort ranges are reset through preceding researches that conducted experiments of thermal comfort in their region.

(3) Lastly, the outdoor thermal comfort of 6 cities which in different climate zones were analyzed using CSDH&HSDH. It has a high usability in that it can evaluate the outdoor thermal comfort by period, time, regional range.

The results of this study will be helpful for urban designer, policy maker and construction engineers to realize the sustainable cities and outdoor environment.