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BUILDOTECH spoke to leading window manufacturers, Fenesta Building Systems and Sohom Fenestertech Pvt. Ltd, on window design, selection and installation aspects which can help minimize heating, cooling and lighting costs

Buildotech: Design considerations while planning windows to achieve thermal efficiency.


Alexander W. Murphy President and Business Head Fenesta Building Systems

Murphy: A well designed window will not just prove to be energy efficient but it provides comfort all year round by holding in the heat during winter and keeping it out in summer. Whether it is a new house or an existing home, windows can make significant difference in the energy consumption. The best windows are ones that will minimize heat loss and maximize solar light gains. Some of the factors which define the role of energy efficient windows are U-value, solar heat gain coefficient, air leakage and condensation resistance. Aluminum windows conduct heat energy and their inadequate sealing and imperfect installation can contribute to a lot of energy loss. PVC has the lowest U value which implies it is the preferred material for energy efficient windows. UPVC windows save up to 30% energy as they are poor conductors of heat. They have excellent sealing with multiple point locks, double or even triple glazing and fusion welded joints that leave no gaps. Such superior insulation leads to reduction in energy bills as air-conditioning becomes more effective.


Patel: Windows can be a major source of heat loss in the winter and heat gain in the summer, as energy is transferred through the centres, edges and frames of windows. Therefore, eliminating or reducing these paths of heat flow through proper installation techniques and appropriate glazing can greatly improve the energy efficiency. Different types of window designs are effective as per their dimensions and construction technicalities. Location too is an important factor while planning window openings to achieve indoor thermal efficiency.

Buildotech: How can the thermal resistance of doors & windows frame can be improved?


Murphy: Thermal resistance of doors and windows can be improved by use of higher quality UPVC material and better sealing and welding at the joints. Windows with lower U Value are more energy efficient and high quality glass with required coating should be used. The thermal efficiency is also affected by how the window is installed, the type of material and technology used to fabricate the window. For instance, Fenesta windows are double-sealed and fitted with multiple point locks and welded joints. The superior engineering ensures that there are no gaps and the heat stabilizers ensure that windows retain their shape and luster in high temperatures. During installation, silicon is filled around the perimeter of the window ensuring no leakage. Fenesta uses special additives for UPVC in India.

Patel: The UPVC profiles are hollow with chambers which can be used for increasing insulating value of frames. Filling the chambers with insulation material stop and control the heat or cold conducted through frames. We suggest our customers the type of window systems best suitable to their requirement after analyzing different parameters such as the location of the openings, installation and dimension of windows.

Buildotech: Are some window styles more energy efficient?

Murphy: Yes indeed, some window styles are more efficient in terms of energy saving. The engineered design should include fusion welded joints, multi chambered profiles and multiple point locks for airtight sealing. Windows with low U-Value and low Solar Heat Gain Co-efficient (measure being dependent on the climate) are more energy efficient.

Patel: An important consideration is how the windows operate, because some operating types have lower air leakage rates than others which will improve your home’s energy efficiency. The window styles such as casement type of systems are more energy efficient as they provide complete openings and when locked it doesn’t allow air leakage due to gasket getting sealed from two sides i.e., frame and sash gives it a vacuum closing.

Buildotech: Comparison of UPVC frames with other window framing materials

Murphy: Aluminum windows (being metal) conduct heat energy. Though, wooden windows conserve more energy than aluminum windows, their poor sealing and imperfect installation lead to lot of energy loss. UPVC windows do not conduct heat and their excellent sealing with multiple point locks and fusion welded joints help conserve energy. Moreover, wooden windows use tropical hardwoods and aluminum frames use large amounts of energy in production which makes them ecologically unsound. UPVC windows use less energy at the time of production and are 100% recyclable. Also UPVC does not require emitting materials like paints and coating.

Patel: Wood is a bad conductor of heat but due to gaps in joints, these windows are not really energy efficient. Aluminum windows are good conductor of heat but again gaps in the joints make them thermally inefficient. UPVC on the other hand is a bad conductor of heat and almost airtight. Hence these windows are the most energy efficient option available.

Buildotech: Types of high performance glazing used for energy efficient windows

Murphy: As part of the research done at Fenesta UPVC Windows, the chart below shows the performance details for different types of glazing for energy efficient windows. Double glazed window offers best solutions for sound insulation, thermal insulation & safety.

Hitesh Patel Marketing In-charge Sohom Fenestertech Pvt. Ltd

Patel: One of the most important features of an energy efficient window is its glazing system. Products with “clear” glass are the least efficient, while those with Low-E are much more thermally effective. Double glazing units (DGU) are more effective for high performance of energy efficient windows as the unit is a composition of two single glasses with the gap in between filled with argon gas and aluminum spacer seal from the sides resulting in control over the heat, cold, UV radiations and also the sound.

Tinted glass are useful as they are made with the heat rejection films to reduce the amount of infrared, visible light and ultraviolet (UV) radiation entering through windows. Toughened glass is physically and thermally stronger than normal glass and is used for its strength, safety and thermal resistance. Toughened laminated glass offers greatly increased resistance to both sudden temperature changes and temperature differentials up to 200K compared with annealed glass, up to 40K.

Buildotech: What are some of the options to reduce air leaks?

Murphy: Air Leak can be minimized by proper designing with multiple point locks and fusion welded joints. Multiple chambered profiles also help the cause. The airtight sealing using silicon sealant between wall and frame prevents cold air from escaping and hot air from flowing in.

Patel: Proper precautions taken at the time of installation process such as use of EPE Foam rod set on the back part of frame profile and complete seal of the frame corners with the silicon will reduce the air leakage. Even the gaskets play major role in the seal locking system of the windows for the control over air leakages. We are using TPE (Thermo Plastic Elastomers) gaskets for all our window systems. TPE are soft on the top to give a vacuum closing between the sash and the frame and hard at the bottom for locking grip that gets inserted into the profile.

Buildotech: Latest products in energy efficient windows segment

Murphy: Fenesta has come up with various innovations to suit the climate and weather conditions in India.

• Weather Proof Windows: Tropical UPVC blend, strengthened with special additives, ensures that the windows retain their shape and luster over long periods. These windows are designed with ongoing color stability (avoid fading), additional strength and heat stabilizers.

• Monsoon Proof Windows: Sliding windows are equipped with a Rain Track, Sill and Gradient Slope to block rainwater. Rain track and gradient slope in sliding windows ensure that water coming at high speed flows out instead of coming indoors. Window sill can be fitted in casement windows ensuring that rain water flows away from the face of the buildings.

• Resistant to Strong Winds Windows: Wind speeds in India, especially northern plains are very high. These windows have broad sections reinforced with steel and further strengthened with a special Hurricane Bar ensuring strong performance.

• Noise Free windows: In these, casement systems are double-sealed, steel-reinforced and have a multiple-point locking system. There are no gaps in the frame or between the wall and the window. Result: Noise, dust and pollution cannot find routes to enter your home.

• Special Designs: Tilt and turn, bay windows, arch windows and combinations of sliding windows and casement windows joined in the same plane without any thick sight lines are all possible.

• Villa Windows: The villa window integrates traditional Indian window design of grill and mesh (popularly made out of wood) with UPVC. For the first time, sizes that span entire balconies and rise from floor to ceiling can be made in casements (windows with sash that opens outside).

Patel: Sohom has different range of products that provides new aesthetic look and improved energy efficiency such as casement, Sliding, Tilt & Turn, Lift & Slide and Bifold systems. We are using Deceuninck profiles, hardware and accessories which are A rated in energy performance ratings in UK.

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