The purpose of this study was to analyze cooling effect of airing and shading on the urban microclimate, especially focused on the Wet Bulb Globe Temperature(WBGT) in the summer of southern Korea.
To monitor the time-serial changes of Dry-bulb Temperature(DT), Globe Temperature(GT) and Relative Humidity(RH) in the wind blocking and shading conditions, Two hexahedral steel frames were established on the open grass field, the dimension of each frame was 1.5m(W)×1.5m(L)×1.5m(H). Four vertical side of one frame was covered by transparent polyethylene film to prevent wind passing through(Site A). The top side of the other frame was covered with shading curtain which intercept 95% of solar light and energy(Site B). And, Another vertical steel frame without any treatment preventing airing and sunlight was set up, which represents natural conditions(Site C).
Dry-bulb Temperature(DT), Globe Temperature(GT) was measured with Resistance Temperature Detector(RTD, Pt-100)s and standard black globes whose diameter is 150㎜. Relative Humidity(RH) was measured with electric humidity sensor GHM-15. Each sensor was located at the 1.2m hight above the grass surface.
From 4th September to 30th October in 2009, The analogue voltage measurements of every minute were converted and recorded into digital values with Labview 8.2 and Compact field point(NI-cFP-2120, RTD-122, AI-110) of National Instruments.
The data from noon to 4p.m. of four sunny days with little cloud were selected and analyzed(5, 6, 7, 18th in September).
The major findings were as follows ;
1. The average globe temperature(GT) was highest at site A showing 49.71℃ and lowest at site B showing 33.67℃. The GT of natural condition(site C) was 42.56℃ locating the midst between site A and B. The difference of GT of each site was about 7℃, which means the airing and shading has significant effect on controlling the micro climate.
2. Site A showed the highest average dry-bulb temperature(DT) of 37.46℃ which apparently differ from site B and C showing 31.87℃ and 32.01℃ respectively. The DT of B and C were nearly the same.
3. The average relative humidity(RH) was lowest at site A showing 19.16%, but site B and C had similar RH 31.63%, 32.49% respectively.
4. The average of calculated WBGT were the highest at the site A(27.78℃) and the lowest at the site B(23.61℃). The site C(25.67℃) was in the middle of the others.
As summery, compared with natural condition(site C), the wind blocking increased about 2℃ WBGT, but the shading decreased about 2℃ WBGT. So It can be apparently said that the urban open space with much shading trees, sheltering furnitures and well-delivered wind corridor can reduce useless and even harmful energy for human outdoor activity considerably in summer of Korea.