| Summary: | 博士 === 國立成功大學 === 建築學系碩博士班 === 95 === The energy shortage is a major crisis we face today, thus, improving natural ventilation to reduce the energy load caused by the use of air conditioning system is very important. However, the high-density distribution of buildings in urban areas, or the poor design for openings of buildings both have greatly reduced the efficacy of natural ventilation. Also, the indoor air quality in Taiwan has significantly worsened, and the problems of poor ventilation and efficiency are yet to be solved.
This study focused on the individual problems for natural ventilation of two modes of a single residential space, which one is with a single-sided opening and the other is with corresponding-sided openings, to probe into the effect of installing horizontal and vertical wind deflectors. The experimental method used CFD numerical method to compute the indoor steady-state air flow, temperature field simulation, and accompanies full-scale experiments results to verify the validity of the simulation, which results were also used as references for simulating boundary conditions. Different external environmental conditions (wind speed or direction) were set in this study, and the Air Change per Hour (ACH), concentration of carbon dioxide, vertical distribution of temperature, and DR (draft rating) for different horizontal wind deflector depths and vertical wind deflector angles were computed. Based on the results, optimal structural scale ranges and usage of wind deflectors were recommended.
The results showed that:
1. Installing horizontal deflector at single-sided opening mode
For horizontal wind deflector over 9cm can effectively improve the ACH on single-sided ventilation, and the efficiency increases as the wind deflector depth increases. The result is significant when the external wind speed is low (0.3m/s). When the wind deflector depth is 144cm, the ACH (Qnormalize) is the largest, achieving 166~230%, however, DR is very high as well. When the external wind speed is below 2m/s, the wind deflector depth needs to be below 36cm, to meet the DR standard of ASHRAE (DR≦20%) completely. When the wind deflector depth is 4cm, it not only is unable to improve the ACH, but under high wind speed (1~2m/s), ACH would be decreased by 5~13%. Based on the all variables, the optimal wind deflector depth is 18~48cm.
2. Installing vertical wind deflector at corresponding-sided opening mode
Under external wind speed of (0.5~2m/s), when the wind direction is parallel to the window, installing vertical wind deflector can averagely improve ACH by 260%. The more efficient wind deflector angle is at 45° (with average increase of 289%), while angle of 67.5° has poorer result (with average increase of 235%). When the wind direction 45° from the building wall, the wind deflector angle of (P＝0°~22.5°) is conducive to an even indoor air flow speed, and wind deflector angle of (P＝67.5°) can reduce DR. Based on the all variables, a table of the optimal wind deflector angle was recommended according to the wind direction.
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