Document Type : Research Paper
Authors
1
Ph.D. candidate, Department of Architecture, Faculty of Art and Architecture, Shiraz Branch, Islamic Azad University, Shiraz, Iran
2
Associate Professor, Department of Architecture, School of Architecture, College of Fine Arts, University of Tehran, Tehran, Iran.
3
Associate professor, Department of Architecture, Faculty of Art and Architecture, Shiraz Branch, Islamic Azad University, Shiraz, Iran
10.22059/jfaup.2024.363130.672895
Abstract
Objective: It is not possible to establish thermal comfort zones in extreme conditions solely through natural ventilation in hot and humid climates. Continuous use of mechanical cooling also deprives building users of access to fresh air, which threatens their health. On the other hand, the building's skin and windows play a crucial role in the heat exchange between the indoors and outdoors. Consequently, they impact the cooling loads, energy demands of the building, and the thermal comfort of the residents. This study aimed to minimize the total annual discomfort hours and solar radiation heat gain from external windows while utilizing natural ventilation in a residential building in the hot-humid climate of Asalouyeh City. The study also examined the impact of transparent and opaque wall materials, as well as window shadings, on the optimal Window-to-Wall Ratio, which aims to minimize solar gain and discomfort hours.
Method: For each common and proposed configuration of building construction and different values for WWR (10%-90%), the annual Predicted Mean Vote and the Percentage of Dissatisfied were determined at 1-hour intervals in a sitting zone of the case study building. The indices were also determined for the thermal peak day at 30-minute intervals. The obtained values were compared with the comfort range recommended by ASHRAE Standard 55 (+0.5 < PMV < -0.5, 0 < PPD < 80%). The annual total hours during which achieving thermal comfort through natural ventilation is possible were calculated. Finally, the optimal window-to-wall ratio (WWR) and opening areas in the optimal construction configuration were determined using the optimization method.
Results: showed that with a WWR of 30% (a common ratio in building construction), the total annual solar radiation heat gain decreased from 3574 kW to 270 kW with the implementation of the proposed materials. The seating area remained within the comfortable temperature range for at least 737 hours throughout the year, thanks to natural cooling. 10%, 16%, 18%, 20%, 22%, 24%, 26%, 32%, 34%, 36% for the WWR in combination with 75%, 49%, 84%, 54%, 66%, 36%, 94%, 38%, 5%, 5% for the open areas were the optimal values. The optimal properties for transparent surfaces include aluminum thermal break window frames, a 1-meter overhang, and left and right side-fin shadings for windows made from lightweight concrete cast (Conductivity: 0.3800 W/m-K, Specific Heat: 1000.00 J/kg-K, Density: 1200.00 kg/m³, Thickness: 0.002 m), and 6mm/6mm air blue double-glazed glass (SHGC: 0.15, LT: 0.15, U-Value: 2.555 W/m²-K). The conductivity, specific heat, density, and thickness of the outermost and innermost layers were 0.16 and 0.17 W/m-K, 880.00 and 900.00 J/kg-K, 2800.00 and 1390.00 kg/m³, 0.002 and 0.005 m, respectively. The study also introduced the thermal properties of non-transparent surfaces.
Conclusion: Findings showed that the glass properties (Light Transmission and Thermal transmittance or U-Value) and Solar Heat Gain Coefficient (total solar transmission) are the most important factors in determining the optimal design compared to other parameters (including thermal insulation, R-value of non-transparent surfaces, shading devices). Although minimizing WWR is recommended for hot and humid climates, this ratio can be increased by choosing the appropriate glass.
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