Thermal comfort level is crucial in increasing space utilization, Outdoors open space design goal is to provide a comfortable environment for activities. In Taiwan, urban heat island effect is getting worse every year because over decades large amount of vegetated surfaces had been replaced by impermeable surfaces for pavement design purpose. This study proposed different types of surface design criteria to adjust urban microclimate, increasing the thermal comfort of the environment, research focus on three types of surfaces, permeable surface, impermeable surface, and grass, effect on outdoor thermal comfort, by designing a field measurement, quantify the evapotranspiration level and using Penman-Monteith equation, and PET level (Physiological Equivalent Temperature). The result showed that grass surface evapotranspiration level was at 0.04mm/day – 0.15mm/day, PET level was between 22℃~35℃, permeable surface evapotranspiration level was at 0.03mm/day – 0.13mm/day, PET level was between 28℃~36℃, impermeable surface evapotranspiration level was at 0.04mm/day – 0.12mm/day. PET level was between 27℃~37℃, higher evapotranspiration level resulted in more comfort environment.
