THRML HRTRISTIS OF DOUBL-LZD XTRNL WLL SYSTM WITH ROLL SRN IN OOLIN SSON H. Tanaka, M. Okumiya, H.Tanaka,.Yoon, and K. Watanabe Nikken Sekkei o.ltd., ichi, Japan Department of nvironment & rchitecture, Nagoya University, ichi, Japan Depatment of rchitecture, hubu University, ichi, Japan BSTRT The double-glazed external wall (double-skin) system is an effective passive technique that can decrease solar heat gain into the building. Detailed information concerning the thermal characteristics of the double skin is necessary to accomplish a good design for thermal comfort and energy-saving. In this paper, the -dimensional thermal characteristics of the double skin that had the openings partially installed and was partially shaded by the adjacent building were investigated by a field measurement. To that end, field measurements were conducted at a double-skin exterior wall (. m high and. m wide) installed in an atrium located in the west of an existing building, during cooling period for typical summer conditions. Maximum air change rate of natural ventilation through the bottom opening up to the top opening is about ~ (/hour), the reduction ration of total solar heat gain to compared with those of non-natural ventilation is about %. The exhaust solar heat gain is kw and is about w/m per inner glass surface area of the double-skin. The double-skin was verified its effectiveness of reducing the air-conditioning loads by field measurement during the cooling. KYWORDS Double-skin, Solar heat load, Natural ventilation, -dimentional thermal characteristics INTRODUTION The double-glazed external wall (double-skin) system is an effective passive technique that can decrease solar heat gain into the building, the system is increased to use in high-rise buildings)). xperimental and analytical studies)) on the thermal characteristics of double-skin façade have also been performed. Most of them are usually assumed to have only the air temperature distribution at vertical direction or at depth direction from outdoor to room, and are not taken into account of -dimensional thermal characteristics. But it is conceivable that a double-skin in existing building has the -dimensinal thermal distribution caused by the various reasons, for example, such that the double-skin is partially shaded by the adjacent buildings or the opening is partially installed or the shading conditions and the set point temperature of room faced to the double-skin is different among every room. Detailed information concerning the thermal characteristics of the double skin is necessary to accomplish a good design for thermal comfort and energy-saving. In this paper, a field measurements were conducted to investigated the influence of the openings and the shade conditions on -dimensinal thermal characteristics and cooling load reduction of the double-skin, which had the openings partially installed and was partially shaded by the adjacent building. MTHOD OF XPRIMNT onfiguration of the Double Skin orresponding uthor: Tel: + ---, Fax: + --- -mail address: tanakahiro@nikken.co.jp.
The double-skin is installed in an atrium located in the west façade of an existing building in Japan as shown in Fig.. Figure and show the plan and the section around the double-skin. The double skin consists of outside single-layer transparent plate glass, outer air space, a roll screen (solar shading material), inner air space and inside single-layer transparent plate glass. In summer, solar shading material located in double glazing absorbs the solar radiation. The natural ventilation are caused by a temperature rise of the solar shade, and the high temperature air is exhausted from the opening at the top. The solar heat gain into rooms and cooling loads can be reduced by this process. The double-skin is.m in height, m in wide, and.9m in depth between outside and inside glass. Both outside and inside glass are 9mm in thickness. For solar optical properties of the roll screen, absorptance, reflectance and transmittance is.,. and.9 respectively. The upper exhaust opening for stack effect is divided into south opening and north one, which area is. m and.m respectively. There is no upper opening from.m(around ) to.m(around F) as shown in Fig.. rea of the bottom opening that is.m. It is thought that the double-skin has -dimensional thermal characteristics caused by the openings partially installed and direct solar radiation partially shaded by the adjacent south building. Figure Site of double-skin Figure Façade section Figure Façade plan xperimental Procedures Field measurements were conducted during cooling period for two days from to on ugust for typical summer conditions. Measured items and points are shown in Fig. and. ir temperature of outer air space and inner air space, inside glass surface temperature faced to inner air space were measured at the height of.m,.m,.m,.m for each Zone,,,, respectively. For air flow velocity in the double-skin, the average of upward air flow velocity for seconds per one place was measured at the height of.m,.m,.m for each Zone to, respectively. To calculate the air change rate of the double skin, inlet air velocity through the bottom openings were measured at points of. The air change volume in the double-skin is assumed to equivalent the air volume through the bottom opening in this study. Schedule of xperiment Table shows the schedule of measurements, which were carried out to evaluate the influence of the roll screen and the opening conditions on thermal characteristics of the double-skin. On the first day, the opening was opened during the day and the screen was rolled down to the height of FL+m only from : to :. On the second day, we started measurements with the roll screen taken up to the top and the opening closed. fterward, the screen was rolled down to the heights of FL+.m at : and of FL+m at :, and the opening was opened at : to :.
st day nd day ondition of openig for stack effect ondition of the roll screen ondition of openig for stack effect ondition of the roll screen time 9 OPN LOSD OPN OPN to FL+m in heigth OPN LOSD OPN LOSD LOSD OPN to FL+.m in heigth to FL+m in heigth Table Schedule of experiments valuation Index To evaluate the efficiency of cooling load reduction, solar heat gain exhausted by natural ventilation q nv and solar heat gain rate exhausted by natural ventilation ν nv are used as the evaluation index. The equation of qnv andν nv are as follows: Solar heat gain exhausted by natural ventilation; qnv = cρl( th tl) V [] Solar heat gain rate exhausted by natural ventilation; q ( I ) ν = [] nv nv DS DS where c=specific heat of air.[kj/(kg K)],ρ L =the average of density of inlet air through bottom opening [kg/m ],t H := the average of air temperature at the height of FL+.m[ ],t L = the average of inlet air temperature through the bottom opening[ ],V=air flow volume through the double-skin[m /h],i DS =global solar radiation into the outer glass surface of the double skin[w/m ], DS = the sum area of the double skin[m ] RSULT ND DISSUSION Outdoor ir Temperature and Solar Radiation The maximum outdoor air dry-bulb temperature of these two days was deg. and daily range was deg. as shown in Fig.. Figure shows global solar radiation on horizontal and solar radiation into the outside glass of double-skin. The direct solar radiation was calculated by Udagawa-Kimura s equation), diffuse solar radiation is calculated by Berlage s equation. Solar radiation into the outside glass increased gradually after : to : on ugust, and maximum value was above W/m from : to :. On ugust, the solar radiation decreased gradually caused by cloudy after :. In the following, we explain about the results of measurements on ugust for typical summer conditions, which solar radiation was larger than those on ugust. Outdoor ir th th 9 Time[hours] Figure Outdoor air temperature Solar radiation [W/ m ] global solar radiation on th solar radiation into the double skin on th 9 Time[hours] Figure lobal solar radiation Time ourses of ir Temperature in the Double Skin Figure shows air temperature and glass surface temperature of zone, etc. Just after the opening was opened at :, outer air temperature at.m in heigth of zone decreased from 9 to [ ] rapidly because the high temperature air was exhausted caused by the stack effect from the opening at
the top. But air temperature at.m in height of zone didn t decrease because the high temperature air was not exhausted due to no upper opening, and was higher about [ ] than those of zone througtout : to :. The opening and the shade coditions had considerable influence on -dimensional thermal charactrsitics of double-skin. In constract to the change at FL+.m, air temperature of.m in heigth of zone rose.[ ] quickly after the openings were opened at :. This rise is thought to be due to transferring the heat accumulated in the roll screen to outer and inner air space caused by upward air flow through the bottom to the top. t the same time, the inside glass surface temperature hardly changed, so that this rise did not have the influence on thermal comfort for the occupant in the atrium. Just after the roll screen was roll down at :, globe temperature fall from. to[ ] caused by a decrease of transmitted radiation through double-skin into the atrium. Temperature opening screen opened closed closed (rolled down tofl+.m) _outer air(.m) _outer air(.m) Outdoor _glass(.m) f room air tem. at point b globe-tem. at point c Time(hours) _outer air(.m) Figure Time courses of temperature around zone opened closed(tofl+m) ir Temperature Distribution at the Vertical Direction Figure (a) and (b) show a comparison of outer air space temperature distribution at the vertical direction. ir temperature distribution of each zone,,, was very similar to those at : when the direct solar radiation was lower, but changed drastically at :. The influenced of the shade and the exhaust opening(upper opening) conditions on temperature distribution is reviewed as follows. ir temperature of zone, which was shaded by the adjacent building and had the exhaust opening, was lowest at every height among the other zones,,, and was lower [ ] and [ ] than those of. and.m in heigth of Zone, respectively. ir temperature difference ( Tdsk) between the bottom(fl+.m) and the top(fl+.m) is approximately [ ]. ir temperature difference( Tdsk) of Zone, which was partial shaded only below.m in height by adjacent building and didn t have the exhaust opening, was [ ] and was largest among those of the other zones. ir temperature of Zone at the top was also highest and was [ ]. ir temperature of Zone, which was not shaded and didn t have the exhaust opening, was higher at every height than those of the other zones. ir temperature at the top was [ ] and Tdsk was 9[ ]. vertical air temperature distribution of Zone, which was not shaded and had the exhaust opening, was very similar to those of zone below.m in height. But air temperature of Zone at the top(fl+.m) was lower [ ] than those of Zone due to the exhaust solar gain from the upper opening. Influence of the openings and the shade conditions on temperature distribution of double skin is found to be significant. Figure (c) shows inner glass surface temperature distribution. ir temprature difference between the bottom(fl+.m) and the top(fl+.m) was about [ ] at Zone, [ ] at Zone and Zone, [ ] at Zone, respectively. Figure (d) shows temperature distribution at width direction from outer
air space to glass surface. ir temperature of inner air space at.m in height was equivalent to those of glass surface. ir temperature of inner air space at.m in height was equivalent to those of outer air space at the same height. ir temperature difference between outer air space and inner air space was to [ ]. : : Outdoor outdoor (a) outer air space temperature(:) (b)outer air space temperature (:) zone : inner air space inside glass surface outer air space outdoor outdoor zone : (c) Inner glass surface temperature (:) (d) temperature at depth direction (:) Figure Temperature distribution at the vertical direction ir hange Rate through the Double Skin ir change volume(m /h) D Time(hours) Figure ir change volume ir change volume [m /h] Solar radiation was smaller xternal wind velocity is above.m/s High correlation......... ir density between air at the top and the bottom[kg/m ] Figure 9 orrelation with air change volume and air density difference Figure shows air change volume by natural ventilation through the bottom opening. ir change volume of Zone and that had the upper openings was larger than those of Zone, D and that didn t have the upper opening. For example, the percentages of ir change volume of zone to those of zone at : was about %. Figure 9 shows the correlation with air change volume and air density difference between the bottom(fl+.m) and the top(fl+.m). We confirmed that the
correlation was higher when the air density difference was more than.[kg/m ] and was lower when external velocity was large or the direct solar radiation into the double-skin was small comparatively. Reduction of Heat Rate of HV ooling System Figure shows the solar heat gain through the double skin into the atrium. ir change rate of natural ventilation of double skin was about ~ per an hour when the roll screen was roll down to the floor level from : to :. The maximum value of exhaust solar heat gain by stack effect was kw at : and was about w/m per inner glass surface area of the double-skin. The values of exhaust solar heat gain rate were from. to.. Figure shows heat gain distribution into the atrium. Heat gain difference among the measuring points was extremely large and its distribution was ranged from to w/m. ir chage rate [/h] xhaust solar heat gain [KW] xhaust solar heat gain rate air change rate xhaust solar heat gain Time[hours] Figure ir change rate and exhaust solar heat gain xhaust solar heat gain rate [%] Figure heat gain distribution into the atrium ONLUSION Field measurements were conducted to investigated the influence of the openings and the shades condition on -dimensinal thermal characteristics and cooling load reduction of the double-skin, which had the openings partially installed and was partially shaded by the adjacent building, during cooling period for two days for typical summer conditions. Our conclusions are as follows: ir temperature distribution of air space in the double skin was ranged from to [ ], and Heat gain difference among the measuring points was extremely large and its distribution was ranged from to w/m. For the performance of double-skin, maximum air change rate of natural ventilation through the exhaust opening was about ~ (/hour), the reduction rate of total solar heat gain to compared with those of non-natural ventilation was about %. The exhaust solar heat gain was kw and was about w/m per inner glass surface area of the double-skin. RFRNS. T. Pasquay () Natural ventilation in high-rise buildings with double facades, saving or waste of energy, nergy and Building, -9... Yoon, H. Komoda, Hideki Tanaka and M. Okumiya () Study on the energy conservation performance of the air-conditioning system for building combined a double skin and earth-to-air heat exchanger, The World Sustainable Building onference in Tokyo, Pro., D, -.. Jun. Taniguchi and K. Kimura (99) Numerical simulation on the air flow window integrated with roll screen, INDOOR IR, Vol., 9-.. J. von. rade () prediction tool for the temperature field of double facades, nergy and Building, 9-99.. M. Udagawa and K.Kimura (9) The estimation of direct solar radiation from global radiation (in Japanese), Transactions of the rchitectural Institute of Japan, No., -9. : Heat gain from the double skin [W/m ]