High performance windows

Windows are possibly the most complex elements in a home. Windows are connection between our inside and outside worlds and importantly, they let in natural light, heat and fresh air.
Choosing energy efficient windows will make your home more comfortable, can reduce energy costs and helps to create a brighter, cleaner and healthier home environment. Modern materials enable us to create efficient buildings. Windows can have an enormous effects on heating and cooling a house. Experts say that up to 40 percent of a home’s heating energy can be lost through windows. Choosing high-performing windows and placing them appropriately can reduce energy costs significantly and improve thermal comfort. There are large range of window systems available, from single to triple - glazed units with aluminium, timber, upvc, composite and other frames, low-e coatings and more.
Measure a window’s performance
One of the first thing to know about windows is that their performance do not depend solely on the number of glazing layers( single,double or triple), but also on whether the glass is tinted or coated, plus the type of frame, climate and the window’s orientation. A pane of clear glass is a great conductor that lets heat move easily in and out of a home. The whole-window U value(UW) measures how readily a window conducts heat and includes the frame as well as its glass. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value. The other important factor influencing whole-window performance is its Solar Heat Grain Coefficient(SHGCW). A window’s SHGC measures how readily radiant heat is transmitted through glass and frame, with the SHGC being the fraction of solar radiation directly transmitted, plus that which is absorbed and subsequently released inward. The lower a window’s overall SHGC, the less solar heat it transmits.
Modern technology allows us to reduce the U-value enormously(by as much as 80 percent or even more)compared with single-glazed windows. And likewise, if you want to reduce solar heat grain, you can do so by 70 or 80 percent without seriously reducing the amount of light, although at some point you do begin to reduce the light the window let in.
Types of glazing units
Single, double and triple-glazing
Double-glazed windows use insulating glass units( IGUS) with two panes of glass separated by a hermetically sealed space. Vacuum windows do exist, but most often double-glazed units are filled with an inert gas, often argon, which helps the window perform more efficiently by further limiting heat transfer compared with air. Double-glazed windows are far superior to single-glazed windows for insulating your home. If you are wondering whether the added cost of improved glazing is worthwhile, consider that compared to single-glazing, a double-glazed window could cut your heat loss in half. As soon as you have a double-glazing units as the starting point, much more is possible because the outer layer can be optimised for solar control - high or low, depending on climate and orientation - while the inner layer forms a buffer to isolate the outer layer from the room inside. This can be achieved without reducing light transmission to unacceptably low levels.
Triple-glazed windows are also available. And while more expensive, they can significantly improve a building’s performance, particularly in very cold climates such as in alpine regions.
Frames
A high-performance window is a complex package made of appropriate high-performance glass inside a high-performance frame. Frames are quite important because of their ability to exert a disproportionate influence on the whole window. If your framing material is a good conductor, it will let heat in during summer and let heat escape during winter. Aluminium frames are very good conductors(aluminium is 160 times as conductive as glass) and dark coloured frames in full sun can become hot to touch. Examples of frames with good insulating qualities include timber frames (though these require regular maintenance), aluminium frames with thermal breaks, composite frames that have aluminium on the outside and timber on the inside, and uPVC frames.
Films
Tinted glass is coloured glass that acts like sunglasses to reduce the amount of heat and light entering your home. Low- e glazing has a very thin factory-applied coating that blocks radiant heat transfer in both directions. Low-e coatings can also be turned to pass most, some, or very little solar radiation, depending on the needs of climate and orientation. Reflective galss has a mirror-like coating that reflects heat and light away from the window.