Energy Efficient Windows
Beautiful windows are possibly the most complex and interesting elements in the fabric of our homes.
They provide light and fresh air, and offer views that connect our interior living spaces with the great outdoors. However, ordinary windows can also represent a major source of unwanted heat gain in summer and significant heat loss in winter.
Today, remarkable new framing and glazing materials have changed the energy performance of windows in a radical way.
Energy efficient windows will make your home more comfortable, dramatically reduce your energy costs and help to create a brighter, cleaner, healthier environment.
Climates
Heating
The priority in a heating climate is to retain heat in the home and maximise the use of 'free' solar energy in winter. Heat transfer takes three forms: radiant heat transfer, conducted heat transfer and heat transfer by infiltration of outside air.
In a heating climate (alpine and cool temperate) the best results are obtained from windows that insulate well (low U-value) and admit plenty of free solar energy (high solar heat gain coefficient). In a cold region, large west-facing windows may contribute to short-term overheating in summer, but glazing with a low solar heat gain coefficient must be used with caution on the west because of the energy penalty it causes over the rest of the year.
Mixed
The priority in a mixed climate is to keep heat out of the home, except during a relatively mild winter season, when 'free' solar heat gain and retention of warmth in the house become important. Heat gain or loss takes three forms: radiant heat transfer, conductive heat transfer and heat transfer via air infiltration. Ideally, mixed climates call for strong solar control on east and west windows, but deliberate use of free sunlight admitted by northerly windows. This means different glazing solutions.
In a MIXED CLIMATE (temperate) the best results are obtained from windows that insulate well (low U-value), admit plenty of free solar energy (high solar heat gain coefficient) on the north during cooler months, but limit solar heat gain from the east and west (low solar heat gain coefficient). Ideally, northerly windows should be protected by correctly sized eaves. This will provide protection from summertime heat and glare while still allowing sun penetration in winter.
Cooling
The priority in a cooling climate is to keep unwanted heat out of the home. In order of decreasing importance, unwanted heat gain takes three forms: radiant heat gain, conducted heat gain and infiltration of hot outside air.
In a cooling climate (tropical, subtropical or hot arid) the best results are obtained from windows that limit solar heat gain on all orientations (low solar heat gain coefficient). Although the first two climates are frequently humid while the last one is not, they can all subject the home to the risk of overheating at any time of the year. Good insulation (a low U-value) is also beneficial, especially if the home is air-conditioned.