Windows
After passive design and insulation, choosing the best windows and glazing for your climate is one of the most cost effective investments you can make to keep your home comfortable and quiet year round. See.... Glazing Overview Link.
Much of the heat gained or lost in your home is through windows and doors. The glass type, frame construction, type of window system and its airtightness all affect the performance of your home.
Glass is a good heat conductor and also allows radiant heat from the sun to pass through freely. While this can be used to your advantage with careful passive design, it can be a big liability if overlooked. To avoid heat loss or heat gain it is important to use high performance windows, appropriately shaded or insulated with heavy drapes and pelmets.
Increased comfort levels and improved window energy performance can be achieved by installing the appropriate glass type.
Correct selection of glass type can:
Think quality - not quantity
Other important things to consider:
Design windows with easy access for opening, closing and cleaning. Windows should not be able to be opened any more than 100mm by a young child.
FADING
Exposure to sunlight causes many modern interior furnishings to fade. The wavelengths most responsible for fading are the ultraviolet, violet and blue wavelengths.
Appropriate glazing will block some of these wavelengths and reduce fading although it will not prevent it completely.
CONDENSATION
Energy efficient windows have surface temperature closer to the adjacent air temperature, which decreases condesation and thus mold and fungus growth.
Most double glazed units are sealed, with a desiccant in the perforated spacer bar to eliminate condensation.
Open windows can also promote condensation and mould growth when warm, moist air meets colder air inside or outside the house.
LIFECYCLE COSTING
The correct choice of energy efficient windows will reduce both heating and cooling costs. The size of air conditioning unit will also be reduced because the load on the system is reduced .
This all ads up to less money spent and less negative impact on the environment.
WINDOWS AND GLAZING
Since windows transfer radiant and conducted heat it is best to carefully choose the size and location of all windows. Too many windows create an energy liability. Heat gain and loss from day to night must be considered and a balance struck.
It is most important when placing windows that allow for the enjoyment of views, that energy efficiency is not forgotten.
HEAT LOSS THROUGH WINDOWS
Properly designed window treatments can help to reduce heat loss through windows. Insulated curtains or tightly fitted and sealed pelmets can keep warm air from coming in contact with the window and cooling.
Tightly fitting Roman type blinds and insulated shutters may also be effective as long as they form a sealed air space next to the window. There are many other ways to reduce heat loss through glazing.
HEAT GAIN THROUGH WINDOWS
In summer, external shading can reduce the outside temperature and reduce heat flow through the window.
The main role of external shading is to prevent direct or indirect solar radiation from passing through the windows.
Solar heat gain can help create a warm home in winter but in summer it is desirable to minimise solar heat gain. Solar heat gain can be controlled through appropriate orientation and shading and/or appropriate glazing decisions.
THERMAL MASS
The thermal mass of a building must be considered when choosing windows and determining their placement. Windows with southern exposure are needed in high mass buildings to take advantage of passive heating and cooling.
Windows that minimise heat loss at night and reduce heat flow into the builiding during hot weather are most efficient in low mass buildings.
Where passive design principles are compromised because of site or design restrictions, the use of energy-efficient windows is an essential alternative method for achieving thermal comfort and energy efficiency.
In all cases the performance of the windows is only as good as the installation. Proper seals within the unit itself as well as the frame around it will ensure maximum benefit. They must be airtight.
LIGHT TRANSMITTANCE
Natural light is always preferred over artificial for many reasons. It has a direct affect on mood, health and appearance. Plants, which also enhance surrounding, do better in nautural light.It is also cheaper than electric lighting.
There are different types of glass and film available that provide a wide range of options for all settings. They can be chosen to give the maximum lighttransmittance, minimum glare and allow or prevent passive heating heating as desired.
In areas where windows are not the best source of natural light, skylights are an option that are available in many new designs that are more efficient and functional.
VENTILATION
Although all open windows provide ventilation, there are windows that are better suited to provided the type of ventilation needed based on climate and location.
Opening all the windows on one side of the house (single sided ventilation) is not very effective. The air needs an entry and exit on opposite sides of the house to create maximum air movement. Cross ventilation should be considered when placing the windows in your home. In a multi level home opening a window on both the lower and upper level provides an entry for cool air to enter at the lower level and move warm air out at the upper level. Cross ventilation is about five times as effective as single-sided ventilation at encouraging air movement through the house.
Keep your individual site and climate conditions in mind when deciding on window style and placement.