Arjun Srinivasan writes about window systems and their role in the energy performance of a green building
A leading newspaper reports that India ranks third in LEED green buildings with 1,883 certified projects. Canada leads the top 10 list with a total of 4,814 LEED certified and registered projects followed by China with 2,022 such projects.
Window systems and glazing have a large role to play in the energy performance of a green building. With the growing pressure on green building certifications, such as GRIHA, LEED and IGBC, uPVC (Unplasticized Polyvinyl Chloride) is a preferred choice among architects and builders.
Benefits of uPVC window systems
- Acoustic insulation: Double-glazed uPVC window systems help in noise reduction by as much as 70 per cent
- Eco-friendly: uPVC profiles are lead free, making it 100 per cent recyclable
- Economical: It is almost 30 per cent more economical compared to other alternatives such as aluminium and timber
- Low maintenance: They are easy to maintain by the use of mild cleaning agents
- Durable: They have a long service life
- Energy efficient: uPVC is energy efficient and does not allow the climatic conditions to affect the interiors
Key parameters to consider for uPVC window
U-value: The heat transfer co-efficient is often referred to as the U-value. This indicates the rate of heat flow due to conduction, convection and radiation through a window as a result of a temperature difference between the interior and exterior. It is expressed by the W/sq.m K value and determines the amount of existing thermal energy gained while it is transmitted through a building component with the size of 1sq. metre within 1 second, assuming an air temperature difference of 1K between interior and exterior surfaces. The lower the U-value drops, the more the insulation qualities of frame and glass rises.
Co-efficient of solar energy transmittance: This parameter defines the part of solar radiation striking the window at an angle close to right angles transmitted through the glass unit into the building. This defines the portion of the solar energy transmitted through a glass pane of the total sunlight striking it. It is the sum of the energy transmitted through the glazing unit and the energy absorbed by the glazing and re-emitted into the building. This is always given as a percentage value. The larger the percentage value of the solar energy transmittance, the greater the passive gains from the solar energy transmitted into the building.
Co-efficient of light transmission: The co-efficient of light transmission defines the part of visible light striking the window surface at an angle close to right angles. This indicates the portion of the total sunlight striking the glazing that is transmitted across the insulated glazing. This is always given as a percentage value. The larger the percentage value, the more light is transmitted through the glass unit into the building. Window buyers must make sure that new windows have the highest possible light transmission values.
Window to Wall Ratio (WWR): It is the ratio of total visible or window area to total wall area.
- Recommended to maintain a maximum of 40 per cent WWR
- ECBC (Energy Conservation Building Code) allows up to 60 per cent in prescriptive approach
- 40 per cent in whole building approach
- Use a combination of external shading and high-performance glass for proper solar control, daylighting and glare control
Glazing requirement for GRIHA
Window to wall ratioTotal glazed area to be less than 60 per cent
- Appropriate SHGC (Solar Heat Gain Coefficient) and U-value (measure of thermal resistance)
selection for a corresponding WWR
Daylighting requirement as per GRIHA
- Minimum 25 per cent of total living area should be day lit
- This can be achieved by having openings in the building envelope as well as using glass, which will allow the penetration of daylight and also permit solar control
The author is the Director of Ecube Windoors, one of India’s rapidly growing fenestration brands. With installation covering an area of close to 2 million sq. ft., Ecube has worked with some of the most prestigious builders in the industry, such as Prestige Group, Mahindra Lifespaces, Radiance Realty Developers, Sterling Developers, Value and Budget Housing Corporation (VBHC), KG Foundations Pvt Ltd and PSG College of Technology. Ecube Windoors, a brand of Mantralaya Impex Pvt Ltd (MIPL), boasts of a sprawling fabrication unit in Chennai that covers an area of 1, 00,000 sq.ft.