Energy efficiency of windows?
Last Post 10 Jul 2015 08:40 AM by BRL Inc Building Resource Limited. 7 Replies.
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richardjamesUser is Offline
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22 Dec 2014 01:19 AM
I want to choose some windows for my newly constructing house in Toronto. I have searched online and found a few like Clera windows, Landmark windows and Centennial windows. All of these companies seem to be offering a wide variety of windows, but I am looking for energy efficient windows, which can help me save energy cost as well. I have read reviews of all these companies on homestars, Ontario Window Reviews and yelp. They seem good, but I have got only a vague idea about their energy efficiency. Can someone help me with this?
Lee DodgeUser is Offline
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22 Dec 2014 11:47 AM
One place to start is the Efficient Windows Collaborative at http://efficientwindows.org/. You can look for the "window selection tool" under "selecting windows for new construction." Canadian building codes generally require high solar gain windows. One reference for the Canadian window energy rating is http://www.hpo.bc.ca/files/download/Report/Window-ER-Report-Executive-Summary.pdf.

If you want a more quantitative approach, you can use tools like BeOPT or RESFEN, the first being more accurate and the second easier to use.
Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
StuieUser is Offline
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22 Dec 2014 01:37 PM
richardjames,
  Check out http://www.strassburger.net/ they are in Barrie ON. I used their windows and doors for my lake house I am just finishing building. They are very well built and energy eff. ( I went with triple glazing) and the prices are very reasonable.
I have no affiliation with them I looked at many mfg's around the Toronto area.
Stuart
Tom WhiteUser is Offline
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08 Jun 2015 12:00 PM
There is something I don’t understand about NFRC ratings, what is the purpose of visible transmittance. Maybe i’m getting the language wrong.
http://homeimprovement5.webnode.com/colorado/
Thanks in advance.
Lee DodgeUser is Offline
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08 Jun 2015 12:21 PM
Tom-

The visible transmittance is what it sounds like, how much of the visible light spectrum makes it past the window and into the house. In theory, un-coated glass reflects 4% of visible light at normal incidence (at right angles to the surface) at each surface, so the visible transmittance is 92% for a single pane window, and for a double pane that drops down to 85%. It is desirable to have one or more of the glass surfaces to be coated to increase short-wave infrared reflectance in the case of low solar gain windows, and typically to reduce the long-wave infrared emittance to reduce heat losses. Further, it is handy to use ultraviolet blocking to reduce fabric fading. These various coatings typically reduce visible light transmission. The purpose of a window is to let you see outdoors and to add light to the indoors, and if the visible light transmission is too low, then the view outdoors and the light that makes it indoors is reduced. What good is a highly thermally efficient window if you can't see out of it, and if light does not make it inside?

Human eyes have roughly logarithmic detection sensitivity, so a light transmittance of 50% might appear to your brain as only a modest light loss much less than 50%.

Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
AltonUser is Offline
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08 Jun 2015 12:23 PM
Lee, Thanks for that excellent explanation. Very helpful. Great use of this forum.
Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
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jonrUser is Offline
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10 Jun 2015 01:24 PM
Note that if you have big windows to expose a good view, you can make them heavily tinted and still have a brighter interior than a room with small windows. You will be able to see out of any window.
BRL Inc Building Resource LimitedUser is Offline
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10 Jul 2015 08:40 AM
HI good and interesting topic which you discussing .You can improve the energy efficiency of existing windows by adding storm windows, caulking and weatherstripping, and using window treatments or coverings.
Selecting New Energy-Efficient Windows

If your home has very old and/or inefficient windows, it might be more cost-effective to replace them than to try to improve their energy efficiency. New, energy-efficient windows eventually pay for themselves through lower heating and cooling costs, and sometimes even lighting costs.

When properly selected and installed, energy-efficient windows can help minimize your heating, cooling, and lighting costs. Improving window performance in your home involves design, selection, and installation.
Design

Before selecting new windows for your home, determine what types of windows will work best and where to improve your home's energy efficiency. It's a good idea to understand the energy performance ratings of windows so you’ll know what energy performance ratings you need for your windows based on your climate and the home's design.

For labeling energy-efficient windows, ENERGY STAR® has established minimum energy performance rating criteria by climate. However, these criteria don't account for a home's design, such as window orientation.

Windows are an important element in passive solar home design, which uses solar energy at the site to provide heating, cooling, and lighting for a house. Passive solar design strategies vary by building location and regional climate, but the basic window guidelines remain the same—select, orient, and size glass to maximize solar heat gain in winter and minimize it in summer.

In heating-dominated climates, major glazing areas should generally face south to collect solar heat during the winter when the sun is low in the sky. In the summer, when the sun is high overhead, overhangs or other shading devices prevent excessive heat gain.

To be effective, south-facing windows should have a solar heat gain coefficient (SHGC) of greater than 0.6 to maximize solar heat gain during the winter, a U-factor of 0.35 or less to reduce conductive heat transfer, and a high visible transmittance (VT) for good visible light transfer. See Energy Performance Ratings to learn more about these ratings.

Windows on east-, west-, and north-facing walls should be minimized while still allowing for adequate daylight. It is difficult to control heat and light through east- and west-facing windows when the sun is low in the sky, and these windows should have a low SHGC and/or be shaded. North-facing windows collect little solar heat, so they are used only for lighting. Low-emissivity (low-e) window glazing can help control solar heat gain and loss in heating climates.

In cooling climates, particularly effective strategies include preferential use of north-facing windows and generously shaded south-facing windows. Windows with low SHGCs are more effective at reducing cooling loads.

Some types of glazing help reduce solar heat gain, lowering a window's SHGC. Low-e coatings—microscopically thin, virtually invisible metal or metallic oxide layers deposited directly on the surface of glass—control heat transfer through windows with insulated glazing. Tinted glass absorbs a large fraction of incoming solar radiation through a window, reflective coatings reduce the transmission of solar radiation, and spectrally selective coatings filter out 40% to 70% of the heat normally transmitted through insulated window glass or glazing, while allowing the full amount of light to be transmitted. Except for spectrally selective, these types of glazing also lower a window's VT. See Window Types to learn more about glazing, coatings, tints, and other options when selecting efficient windows.

If you're constructing a new home or doing some major remodeling, you should also take advantage of the opportunity to incorporate your window design and selection as an integral part of your whole-house design—an approach for building an energy-efficient home.
Selection

You'll find that you have several options to consider when selecting what type of windows you should use in your home.

When selecting windows for energy efficiency, it's important to first consider their energy performance ratings in relation to your climate and your home's design. This will help narrow your selection.

Illustration showing a cross-section of a window, with parts labeled. Double-paned glass is shown to have a low-e and/or solar control coating, a gas fill between the double panes, and a spacer at the base of the window between the panes. On the interior of the house is a strip of wood at the bottom edge of the window labeled the stop, and just in front of it is a step-like shelf labeled the stool. Beneath the stool and on top of a two by four is a thin pipe labeled the backer rod. On the exterior of the house, the illustration shows the frame of the window labeled the sash, and the shelf in front of the window labeled the sill. Weatherstripping is shown to be between the sill and sash. Beneath the sash, vertical against the house, is a strip of wood called the apron or flange, and the jamb is on the end of the sill.

A window's energy efficiency is dependent upon all of its components. Window frames conduct heat, contributing to a window's overall energy efficiency, particularly its U-factor. Glazing or glass technologies have become very sophisticated, and designers often specify different types of glazing or glass for different windows, based on orientation, climate, building design, etc.

Another 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. Traditional operating types include:

Awning. Hinged at the top and open outward. Because the sash closes by pressing against the frame, they generally have lower air leakage rates than sliding windows.
Casement. Hinged at the sides. Like awning windows, they generally have lower air leakage rates than sliding windows because the sash closes by pressing against the frame.
Fixed. Fixed panes that don't open. When installed properly they're airtight, but are not suitable in places where window ventilation is desired.
Hopper. Hinged at the bottom and open inward. Like both awning and casement, they generally have lower air leakage rates because the sash closes by pressing against the frame.
Single- and double-hung. Both sashes slide vertically in a double-hung window. Only the bottom sash slides upward in a single-hung window. These sliding windows generally have higher air leakage rates than projecting or hinged windows.
Single- and double-sliding. Both sashes slide horizontally in a double-sliding window. Only one sash slides in a single-sliding window. Like single- and double-hung windows, they generally have higher air leakage rates than projecting or hinged windows.

: Illustration of six window types. The awning window is hinged at the top and pushes outward. The hopper style is hinged at the bottom and opens inward. The sliding style has one or two windows that slide side-to-side. A fixed window does not open at all. The double-hung window shows two sashes that slide vertically over one another. The casement window is hinged at the side and opens outward.
Installation

Even the most energy-efficient window must be properly installed to ensure energy efficiency. Therefore, it's best to have a professional install your windows.

Window installation varies depending on the type of window, the construction of the house (wood, masonry, etc.), the exterior cladding (wood siding, stucco, brick, etc.), and the type (if any) of weather-restrictive barrier.

Windows should be installed according to the manufacturer’s recommendations and be properly air sealed during installation to perform correctly. To air seal the window, caulk the frame and weatherstrip the operable components.



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