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P.J. Littlefair, Summertime solar performance of windows with shading devices, BRE Bookshop for BRE Trust, Garston, (2005). ]. Meteorological parameters influence the human energy balance include air temperature, air humidity, wind speed and short- and longwave radiation. It is necessary to determine these parameters at a human-biometeorologically significant height of 0.5m above ground, corresponding to the average height of a standing child' centre of gravity. Large differences between air temperature and Tmrt (and PET) arise in winter days with high wind speed and in summer at calm and sunny conditions [3]. In these cases extreme cold or heat stress can be experienced. Examples of the resulting PET values at different seasonal, shading and wind conditions are shown in Table 1. Table 1: Examples of PET values at different weather conditions (Hoppe 1999) Examples
Ta (℃)
Tmrt (℃)
WS (m-1)
VP (hPa)
PET (℃)
Typical room (indoor)
21
21
0.1
12
21
Winter, sunny
-5
15
0.5
2
-1
Winter, shade
-5
-5
5
2
-13
Summer, sunny
30
60
1
21
43
Summer, shade
30
30
1
21
29
Ta : Air temperature; Tmrt: mean radiant temperature; WS: wind speed; VP: vapour pressure In this study, the author uses solar radiation, PET, to characterize the thermal comfort conditions and to evaluate the human bioclimatological comfort sensations, respectively, with different transparency of canopy. Software (Ecotect, RayMan) One of the recently used radiation and bioclimate models is RayMan, developed in the Meteorological Institute, University of Freiburg. It is well-suited to calculate radiation fluxes, thus all our calculations for Tmrt and PET were performed with this model. Table 2 : Parameters of each case 5 m 3.6 m 2.2 m Transparency
Solar heat gain coefficient
Case A
0%
0.1
Case B
50%
0.5
Case C
90%
0.9 Fig. 2 : Section through canopy and intermediate area in nursery school Intermediate space canopy space The RayMan model, developed according to guidelines of the German Engineering Society [3], calculates the radiation flux within urban structures on the basis of parameters such as air temperature, air humidity, degree of cloud cover, time of day and year, albedo of the surrounding surfaces and their solid-angle proportions[4,5]. The main advantage of the RayMan is that it facilitates the reliable determination of the microclimatological modifications of different urban environments, since the model considers the radiation modification effects of the complex surface structure (buildings, trees) very precisely[6]. Beside the meteorological parameters the model requires input data on surface morphological conditions of the study area and on personal parameters. PET index shows that it will be problematic on sunny day (22 July) in summer. Outdoor physiological equivalent temperature reaches 45.3˚C at noon with 90% transparency canopy (28.2˚C for ambient temperature), which belongs to the 'Very hot' thermal category between 11am and 15:00pm. It shows direct solar radiation plays an critical role in increasing thermal temperature. However, the vulnerable level of comfort can be reduced by adding shading, which can be lowered around 33.4˚C and 28.5 ˚C respectively with 50% and 0% transparency of canopy as shown in Fig. 3 and Fig.4. Conclusion PET index shows that it will be problematic on sunny day (22 July) in summer. Outdoor physiological equivalent temperature reaches 45.3˚C at noon with 90% transparency canopy (28.2˚C for ambient temperature), which belongs to the 'Very hot' thermal category between 11am and 15:00pm. It shows direct solar radiation plays a critical role in increasing thermal temperature. However, the vulnerable level of comfort can be reduced by adding shading, which can be lowered around 33.4˚C and 28.5 ˚C respectively with 50% and 0% transparency of canopy. Thermal comfort is also enhanced by increasing wind speed theoretically. Therefore, it can be said shading is important parameters to control outdoor comfort. However, in overcast day, no direct solar radiation but only diffuse light, the shading of canopy does not work much. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MEST) (No. 20050049406) and (No. 20110028794). References
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