|
|
|
|
The first printing press was unveiled almost 600 years ago. Shortly thereafter, the first commercial printing business was ...
Drug and alcohol addiction must be stopped. Perhaps you have read or heard this line endlessly. When a person addicted to ...
I spoke with Bob Kadane, the president of KFG Resources (TSX.V:KFG) and learned a lot about the true story behind petroleum ...
|
|
|
|
|
|
Articles » Home & Family » Home Improvement » Cutting energy losses using energy efficient window coverings
|
|
|
|
|
- Article Views: 1268
- Word Count: 1830
- Date Contributed: Feb 17, 2009
|
|
- -
|
| Cutting energy losses using energy efficient window coverings |
If your windows are worn out and aren't doing a passable job of keeping the heat inside your house in cold weather (or keeping it out in warm weather), it may be time to think about having new, energy efficient windows installed. But new windows, in particular good quality energy saving ones, can be very expensive. This means that their payback period can be quite long. For the amount of money it would cost you to replace the windows in one large room, you can achieve almost the same energy savings with some basic weather stripping and by using energy efficient window coverings to eliminate heat transfer between your home and the out of doors.
Let's first look at how windows help keep the cold out in winter, and the hot out in summer. Windows minimize heat transfer in three ways: convection, conduction, and radiation.
Windows stop or reduce the convection airflow between the inside and the outdoors, preventing heat from traveling through the window with the air. A leaky window, or one with cracks in the glass or damaged putty, allows air through these openings, so heat escapes in cold weather, and heat leaks in during the summer.
Even the thinnest sheet of glass has some insulating properties, but if there are two sheets of glass and the space between the panes is an inert gas such as argon, the panes provide extra insulating value, which reduces heat transfer through conduction. Conduction is what causes the metal handle of a pot to heat up when you boil water in the pot; so you can guess that a metal window frame, if not properly built, can allow a lot of heat through the window frame. Although you can't readily add extra glass sheets to a window, there are other methods to create extra still air spaces between the window glass and the room, which will increase insulation and cut conduction losses.
Radiation, the third kind of heat transfer, typically occurs when sunlight in the infrared spectrum travels through windows, heating the air inside, or when infrared radiation inside the room radiates out through the glass. Home energy auditors sometimes take infrared photos of a home to show where heat losses are most significant, and windows are typically one of the largest sources of heat escaping from houses in winter.
How does this knowledge about heat transfer through convection, conduction, and radiation help you reduce energy losses through your windows?
The first problem to address is convection. If your windows have cracked panes, get them repaired. If you still have the old wood-framed windows with putty holding the glass in, check the glazing for any cracked or missing putty. It's quite straightforward to pull old putty out with a putty knife and put a fresh layer of putty on in its place. If the wood of the window itself is rotten, or if the glass is hard to replace, you may not be able to put off getting new windows, but assuming you can cut the small air leaks, you'll have gone a long way towards reducing energy losses and should feel some relief in your heating and cooling bills.
You may be surprised to learn how much heat can escape from an old home in cold weather through the wood trim around a window. Just wait for a chilly day, put all the exhaust fans on in your house, and run your hand along the edges of window and exterior door trim on the inside of rooms. Anywhere you feel cold air coming in, you've got a draft that should be sealed. It probably doesn't hurt to run a thin bead of clear or white caulking around window and door frames to cut this convection heat transfer. You can also caulk exterior window frames with outdoor caulking material if there are major gaps betweent the frames and the exterior wall material.
The last thing to reduce convection heat losses is to use tape-on or Zip-Loc type energy saving window kits to close off any windows that are very leaky, or windows that definitely need replacing but that can't be replaced because of your budget (or because you are renting the place). These kits are a great way to quickly reduce your heating losses in winter: the kits normally come with several sheets of 3x5 foot clear plastic, and a roll of double sided tape. (If you have many windows to cover you should buy a 48" roll of the plastic and get the tape separately as you'll pay far less than buy buying several kits.) You measure and cut plastic rectangles a little wider than the window, run the tape around the edges of the window frame, remove the protective tape from the double sided tape, then place the cut plastic over the window, sealing along the tape line. Blow dry the plastic for five minutes, and it shrinks to form a tight, flat extra pane of 'glass' that is hardly unnoticeable. This plastic can hold its taut shape for weeks, although you may find it needs an occasional short blow dryer blast to pull up the odd wrinkle in the plastic.
The next problem you'll want to tackle is conduction - heat being drawn through the solid materials of the window. In terms of energy efficient window coverings, your goal here isn't actually to stop this conduction - you can't really change the materials the window was made of - but to add barrier layers between the window and the inside of the room to slow that conduction down. Plastic window insulation kits stop convection heat transfer by cutting drafts into the room, but they also cut conduction, by adding a layer of trapped air between the room and the window. A curtain can accomplish the same task: when closed, the curtain traps a small amount of air between the curtain and the window, so that on a cold day the air behind the curtain naturally gets cold but the air in the room stays cozy.
When you install curtains on windows to reduce conduction heat loss, you need to consider convection currents inside the living area. Hot air rises, and cool air falls, so if you install curtains you should make sure the air currents are stopped, preferably at both the top and bottom of the curtain. Otherwise, in cold weather, the cold window will cool the air between the window and the window covering, and that colder air will fall down onto the floor of the room, drawing warm air from above the window covering down in front of the glass in a continuous cycle. In summer, the process runs the other way, with the air between the curtain and the window warming from the sunlight, rising out the top opening, and drawing cool room air up towards the glass where it gets warmed.
You should block these air flows by having the curtains flush against the wall above and below, or by having the bottom touch the floor and by enclosing the curtain rod area at the top.
If you have cloth blinds that cover the entire window frame, you can put Velcro tabs along the sides of the blinds that you then press into Velcro tape along the window frame; this completely seals the air space between the window and the blind, providing an excellent insulation layer. Cloth blinds along with curtains can use a similar technique but with magnetic tape in the fabric, and metal along the window frame, so that the window covering sticks to the walls on either side of and below the opening.
Another method you can try to add an insulation barrier to conduction through the window is to buy cellular blinds, which are made in a cellular or honeycomb cross section, or other blinds that incorporate a hollow space within the blind (for example, air-foil shaped blinds). Cellular blinds when fully pulled up take up almost no space and the cells fold shut; when extended, they can add insulating value to a window from R-2 (for single-cell thickness) to R-5 (for double-cell).
Window blinds can help address the third type of heat transfer, radiation, by preventing heat from passing across the glass (into the house from sunlight in warm weather, and towards the outside from the indoor radiant heat in winter). The most effective blinds are light-colored on the outside, so that sunlight is most thoroughly reflected away from the house. Well-made window blinds can reflect enough solar energy away from a room to reduce heat transfer by up to 45%, but they do very little to the R-value of the window, so don't hold heat in winter.
Roller shades, which have a spring mechanism and roll up or down (we used to call these blinds when I was young) are an effective radiation reflector, and also provide superior R-value to reduce convection air flows around the window that lead to conduction losses through the pane or frame. Roller shades, because they sit so close to the glass, do well at reducing convection airflows, particularly if their sides and bottom are secured to the window frame (for example, by using side tracks). Unsecured shades can reduce heat exchange by as much as 28%, while secured-edge shades reduce it as much as 45%. Shades that can be reversed, with one side dark and the other light, are ideal, because you can use the light side to reflect the heat where you want it (keep it out in hot weather, inside during cold weather).
Awnings and overhangs are a good way to cut sunlight from shining into a room and warming it up in summer. Because the angle of the sun is lower in the winter months, these window coverings only block the hot sunlight you don't need, allowing the lower-angled winter sun in to help heat your rooms.
Storm windows - which were added to many older homes - can save up to 50% of the heat loss compared to single-pane windows, provided the storms are sealed against air leakage. So if you have the old wooden-framed storms gathering dust in your basement or garage, make sure to put them on each fall and take them down each spring. If you have aluminum framed storms you can usually leave them up all year long; just don't forget to close the glass during the winter.
Windows form such a small portion of the surface area of a home, yet they are one of the biggest potential energy wasters in a home being heated or air conditioned. So you should strive to do anything you can to restrict heat transfer through convection, conduction, and radiation. Just don't forget to put aside some of the cash you save on reduced utility bills, so you can replace any old, leaky windows with new, energy efficient ones when you can afford it.
Robin Green runs  www.Green-Energy-Efficient-Homes.com, a website that helps people cut their home energy use. For more on energy efficient window coverings, see Energy saving window coverings (www.green-energy-efficient-homes.com/energy-saving-window-coverings.html) on Green Energy Efficient Homes.
Article Source: UnArchived Articles
|
|
|
|
|
