Window to wall ratio in building design
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Window-to-Wall Ratio (WWR) and Building Energy Efficiency
The window-to-wall ratio (WWR) is a key factor in building design, directly affecting energy consumption, daylight, thermal comfort, and overall sustainability. Optimizing WWR can lead to significant improvements in energy efficiency and occupant comfort across various building types and climates 12345678+2 MORE.
Optimal WWR Ranges for Different Climates and Building Types
Research consistently shows that the ideal WWR varies by climate, building orientation, and use:
- In hot summer Mediterranean climates, a WWR of 65% is recommended for southern and eastern walls, 95% for northern walls, and 30% for western walls to maximize energy savings and building intelligence 1.
- In US office buildings, reducing WWR from a baseline of 40% can slightly lower energy use and environmental impacts, but the improvements are modest (about 1%), suggesting that WWR optimization should be combined with other design strategies for best results 2.
- For public and educational buildings in hot regions, a WWR between 20% and 30% is optimal for balancing daylight and minimizing energy loads, with slightly higher ratios possible in high-altitude locations 36.
- In subtropical monsoon climates like Bangladesh, the optimal WWR for air-conditioned office buildings is 30% to 40%, which can save up to 9.4% in electricity use 8.
- For traditional dwellings and rural residences, the optimal WWR depends on orientation and local climate, but typically falls within 20% to 50% for most facades 45.
Influence of Orientation and Glazing Type
The orientation of windows and the type of glazing used are crucial in determining the best WWR:
- Southern and eastern orientations often benefit from higher WWRs due to better daylight and solar gain management, while western and northern facades may require lower ratios to reduce heat loss or unwanted solar gain 1510.
- Low-emissivity (low-E) glazing and appropriate shading devices can further enhance energy performance, especially when paired with optimal WWRs. For example, a WWR of 60% with low-E glazing maximizes energy efficiency in Algerian climates, while different glazing types may be needed for regions requiring more solar protection 10.
- In educational buildings with double-skin façades, a WWR of 40% to 60% combined with suitable shading coefficients provides the best daylight optimization 9.
Daylight, Comfort, and Occupant Satisfaction
WWR not only impacts energy use but also affects daylight availability and occupant comfort:
- Properly optimized WWR improves indoor daylight levels, reduces reliance on artificial lighting, and helps maintain comfortable indoor temperatures 469.
- However, increasing WWR beyond optimal levels can lead to higher cooling loads, glare, and occupant dissatisfaction, especially in large office buildings 2.
Life Cycle and Sustainability Considerations
A comprehensive approach to WWR optimization considers not just operational energy, but also embodied energy, material use, and life cycle costs:
- While reducing WWR can lower operational energy, the overall environmental and economic benefits are modest unless combined with other sustainable design strategies 2.
- The triple-bottom-line approach (environmental, economic, and social) highlights the need for integrated solutions beyond just adjusting WWR 2.
Conclusion
Optimizing the window-to-wall ratio is a critical aspect of sustainable building design. The best WWR depends on climate, building orientation, glazing type, and building use. Generally, a WWR between 20% and 40% is effective for energy efficiency in many climates, but higher ratios may be suitable for certain orientations or with advanced glazing. Combining WWR optimization with other design strategies, such as shading and high-performance windows, yields the greatest benefits for energy savings, occupant comfort, and overall sustainability 12456789+1 MORE.
Sources and full results
Most relevant research papers on this topic
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Optimising Window-to-Wall Ratio for Enhanced Energy Efficiency and Building Intelligence in Hot Summer Mediterranean Climates
Optimising the window-to-wall ratio in low-rise residential apartments in hot summer Mediterranean climates can significantly reduce energy consumption and enhance building intelligence.
2024·
1citation
·Hawar Tawfeeqet al.Sustainability
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2
Triple bottom line sustainability assessment of window-to-wall ratio in US office buildings
Reducing window-to-wall ratio in US office buildings leads to improvements in environmental impacts, occupant dissatisfaction, and life cycle cost, but other design strategies are needed to meet energy consumption and environmental impact reduction goals.
2020·
55citations
·R. Phillipset al.Building and Environment
4
4
An investigation of optimal window-to-wall ratio based on changes in building orientations for traditional dwellings
The optimal window-to-wall ratio for traditional dwellings in China is determined based on building orientation, daylight factor, indoor temperature, and air velocity, ensuring indoor comfort and energy consumption.
Highly Cited
2020·
72citations
·Fang'ai Chiet al.Solar Energy
5
5
The Optimum Window-to-Wall Ratio in Office Buildings for Hot‒Humid, Hot‒Dry, and Cold Climates in Iran
The optimal window-to-wall ratio for office buildings in Iran's hot, humid, hot-dry, and cold climates is 20-30% for the north facade, 20-30% for the southern facade, and 30-50% for the eastern and western facades.
2019·
50citations
·J. Shaeriet al.Environments
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6
Impact of Window to Wall Ratio on Energy Loads in Hot Regions: A Study of Building Energy Performance
The optimal window to wall ratio for energy performance and daylight in educational buildings should range from 20% to 30%, depending on orientation and climate, with slightly greater ratios in higher altitude locations.
2021·
21citations
·M. Alwetaishiet al.Energies
7
7
Optimization of Window-to-Wall Ratio for Buildings Located in Different Climates: An IDA-Indoor Climate and Energy Simulation Study
Optimal window-to-wall ratios can be achieved in various climate conditions by combining window types, orientation, and comfort conditions, with overhangs, blinds, or both.
2021·
35citations
·Sana Sayadiet al.Energies
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8
Impact assessment of window to wall ratio on energy consumption of an office building of subtropical monsoon climatic country Bangladesh
The optimal window-to-wall ratio for air-conditioned office buildings in Bangladesh is 30% to 40%, which can save 9.40% of electricity and can be incorporated into the Bangladesh National Building Code.
2020·
43citations
·Jewel Ranaet al.International Journal of Construction Management
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9
Window-to-Wall Ratio as a Mode of Daylight Optimization for an Educational Building with Opaque Double-Skin Façade
40% Window-to-Wall Ratio with shading coefficient 0.42 and 60% Window-to-Wall Ratio with shading coefficient 0.95 are optimal for daylight optimization in an opaque brick Double-Skin Façade building.
2022·
6citations
·O. C. Dewiet al.Journal of Sustainable Architecture and Civil Engineering
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10
Impact of Glazing Type, Window-to-Wall Ratio, and Orientation on Building Energy Savings Quality: A Parametric Analysis in Algerian Climatic Conditions
Optimizing window size, glazing type, and orientation can significantly enhance energy efficiency in Algerian buildings, with a 60% window-to-wall ratio and low-E glazing being most effective.
2024·
12citations
·M. Cherieret al.Case Studies in Thermal Engineering