壁内中空層の自然換気による日射熱排除効果 : 第3報-中空層壁体モデルの気象ばく露実験結果 [in Japanese] Natural Ventilation of Wall Air Cavity for Solar Heat Gain Reduction : Part 3-Behavior of Cavity Wall Models exposed to Weather [in Japanese]
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It was indicated from the indoor model experiment (Part 1) that the cavity in a wall is satisfactorily ventilated by the buoyant force of the air, when the cavity thickness is sufficient and appropriate openings are prepared on the top and bottom of the cavity. In the present part, the effect of the ventilation to evacuate solar irradiation to outside and to reduce cooling load by it is examined by exposing models of a cavity wall to the weather. The structure of the two model walls is shown in figure 1. Each model consists mainly of a massive concrete plate. The front surface of it is the experimental surface of the heat penetration into a building. In front of this surface, a metal plate was arranged to form an air cavity between them. Slit shape openings were arranged on the top and bottom of the air cavity. The back side of the model should be the interior surface of a building, if the model was a part of a real building. In this study, this surface was thermally insulated to simplify the model. Around 60 temperature measuring points were arranged in each of the models. The models were set on the roof of a low laboratory in the campus of Toyohashi University of Technology. The thickness of the air cavities were fixed to 70mm, and the slit widths were altered from 0 to 40mm. The daily average temperatures of the central point of the concrete plate were higher than the outdoor air temperature by 7.2, 6.4 and 4.5℃, respectively for the slit widths 0, 10 and 40mm. The temperature amplitudes at the points were 8.8, 8.2 and 7.6℃, respectively. The both of the average temperature and the temperature amplitude decreased as the slit width enlarged. The temperature changes at various points in the models are shown in figure 5 to 7. The time to time heat flow on the experimental surface was analytically attained using the measured temperature change in the concrete plate. Then the heat transmission across the cavity was separated into radiative- and convective-transmission. The absorbed heat into the concrete plates through a day was 768W・h/sq.m for slit 0mm, and was 645W・h/sq.m for slit 40mm. The average air velocities were estimated from the measured air temperature in the cavities by balancing the buoyant force with the dynamic and frictional losses. At noon, the calculated average air velocity was ca. 0.1m/s for slit 10mm, and was ca. 0.3m/s for slit 40mm. These velocities correspond reasonably well with the measured air velocities, which were attained in the experiment with the indoor cavity model (see Part 1). The heat, which was evacuated by the ventilation, is calculated by multiplying the temperature rise through the flow-in and out of the cavities with the estimated air velocities. The heat evacuation rate through a day time was 369W・h/sq.m for slit width 10mm. This rate increased to 871W・h/sq.m, when the slit width was enlarged to 40mm. The increment in the air velocity by the widening the slit was 3 folds, but the increment in the heat evacuation was depressed to 2.
- Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan
Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan 12(34), 91-99, 1987
The Society of Heating, Air-Conditioning & Sanitary Engineers of Japan