THE Window Thread (merged)

Ludi · Posted: Sun Feb 18, 2007 4:25 pm Post subject: Re: Window insulation in summer

I live in a hot climate and we don't air condition our house, only our work spaces. But it is relatively dry here, which helps fans be more efficient at cooling. If you own your home, in a hot climate you may consider not having any glazing at all on the West side, or quite small windows, or make sure any windows you have are completely shaded. We have awnings, window film, and blinds on our West windows, and my plan is to eventually replace the big cheap windows we have with smaller, double-glazed ones, or put a veranda on that side of the house.

For winter, I plan to make thermal shades for the inside of some of the windows, and a similar thing could be used during the summer especially on the hot side of the house.

thermal shade
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snax · Tar Sands Joined: Jan 20, 2007 Posts: 75

Although not as attractive as a thermal shade, rigid foam blocks cut to window size, covered with veneer on both sides and wrapped in fabric make terrific insulators at the expense of daylight. Hinged to the inside casing, they can be opened or closed tightly with relative ease.

Likewise, exterior shading can make a huge difference on heat gain in the structure. Even if it's just a bunch of bamboo rollups hanging from the eaves, keeping the sun off of the sides of the house and windows makes a noticeable impact.

Calicocat · Coal Joined: Apr 17, 2008 Posts: 1

BigTex

If you want to do something nice for yourself and your neighbors, do this:

Purchase a few sheets of radiant sheathing. It's got foil on both sides and has a quarter inch or so of foam in between. The sheets have an R-value of 7-10, in addition to the ability to reflect radiant heat.

Purchase some material that is more or less the color of a tasteful curtain. Lighter is probably better.

Cut pieces of this material to the size of your window openings so that you can place it into the window cutout (if there is one). If there is not a window cutout, make the piece a size the will cover the window with a little overhang all around and you can secure it to the window frame or wall in a variety of ways.

Now, this is the important part, cover the area that is going to face out with the fabric you purchased. From the outside, it should just look like a piece of fabric over the window, not some hillbilly peak oil mitigation strategy.

You can cover the inside part of the sheets with the fabric if you want as well, but I am thinking that there will probably be blinds or curtains covering the inserts you made.

I have tried radiant barrier materials with the reflective sides exposed on both sides, exposed on the side facing the sun and exposed on the side facing away from the sun. I haven't noticed a big difference in performance, notwithstanding what the science would suggest.

This is just an approach that will give you real additional window insulation, block the heat and the light, and not drag your neighbor's property values down too much.

Using the bubble foil mentioned above with thick cardboard in between could be used to achieve the same effect of a fitted window covering. Use aluminum tape with the bubble foil to make the edges look clean.
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Keith_McClary · Last edited by Keith_McClary on Sat May 10, 2008 1:23 am; edited 1 time in total

There is "emergency blanket" or "space blanket" from camping stores or "dollar stores". I paid $1.50 for 52" x 82" (132 x 210 cm.).

This is thin mylar with an aluminium coating.

The advantage is, you are not messing with taping 1' wide strips so it is easy to take off and re-use seasonally..

Also, the coating is so thin that you can see outside through it.

(EDIT - so you can save the aluminum foil to line your hat)

Ferretlover · Last edited by Ferretlover on Mon Aug 25, 2008 4:03 pm; edited 1 time in total

Whatever you use, I would suggest that you invite a neighbor in, or discuss it with your landlord or neighbors, so that you aren't sitting around making lists or watching tv or taking a shower when Law Enforcement breaks your door down looking for a meth lab or marijuana plot.

edited to fix spelling error.
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vandal49588

I replaced my windows with a 5.7mm thick gray reflective glass. Most homes have 2.2mm-3.1mm thick glass. I did this for little or no money since I just happened to work in a glass factory.

energytech · Coal Joined: Dec 28, 2006 Posts: 5 Location: Far North

Ok, pay attention.
Rule One -Heat always travels from Hot -to- Cold
Rule Two -Heat energy only travels three ways.
1. Conduction (through solids, metal, wood, glass, etc.)
2. Convection (through liquids, air, gases, water, oil, etc.)
3. Radiation (through space, radiant heat only heats the objects it strikes - like sunlight on your back with a dark shirt on)

All three heat transfer mechanisms are active in windows.

Radiation from the sun passes through the glass and warms surfaces in your home.

Conduction of heat through the glass warms the air in your home causing heat to convect upward on hot days and downward on cold days.

Convection, or rising warmer air and falling colder (more dense) air occurs against the inside and outside surfaces of windows and also on the gas filling inside, between multiple panes.

In a douple pane window on a hot day, (with AC on) heat from outside passes(conducts) through the exterior pane of glass and warms the molecules of gas resting against it causing them to spread apart (expand) and become lighter than air further away - but within the space. This boundry layer of gas rises because it is now slighty warmer than air in the middle of the gap. As it continues upward it takes on more heat energy and accellerates. At the top of the window it jams up against the spacer, floats over to the cooler interior glass surface and becomes more dense as it gives up heat to the cool interior pane, which causes it to fall.

This rotating motion is, in effect, a convection loop, transfering heat to the interior pane of glass from the warmer exterior pane and increasing heat transfer in the process.

Insulation works by trapping air or gasses and minimizing heat transfer by conduction and convection.

Radiation is reduced by low emissivity films that reflect long wave infrared waves. When such radiation is reflected back to the outside of the glass it reduces solar radiation input into the building. When the film is placed to face the inside it reflects the heat (long wave IR) back to the interior. These films are a fairly recent advance in window technology and provide rapid pay-backs in both warm and cold climates providing placement is correct for the environments.

Multiple panes of glass separate air films from each other making transfer by convection difficult. Optimum air gap thickness is between 1/2 to 3/4 inch... with air. A heavy nobel gas such as Aargon or Krypton improve convection protection by making it difficult for convection to take place within the gap between panes. Such gases contain large molecules which are heavy and difficult to mobilize. This means that moving them is more difficult than common air filling which is mostly nitrogen (78%) and oxygen (21%), containing much smaller molecules and easy to get moving.

Conduction through windows is best reduced by using insulated spacers such as warm edge or squiggle strip (TM) which impede heat conduction at the edges where it is greatest. Insulated spacers with Krypton gas filling and multiple panes having multiple low emissivity films make great windows no matter what the climate. When placed into insulated fiberglass frames you can have a view with comfort, low heat loss and minimal maintenance.

If you are buying new windows, go for the best available product. Buying junk window products costs more, and it doesn't save a thing. High quality lasts longer, performs to higher standards, saves more energy, improves comfort and actually has a payback. And who knows if they will be available when you really need them as energy costs continue to rise?

snax · Tar Sands Joined: Jan 20, 2007 Posts: 75

I think somebody is in the window business.

criticalmass · Posted: Mon Aug 25, 2008 1:10 pm Post subject: Re: THE Window Thread (merged)

Solar curtains can be purchased at wdrake.com or mileskimball.com. They are made from a similar material as emergency blankets and do a great job of keeping the sun out in the summer and the heat in in the winter.

Yes, they do darken a room in the daytime.

Frank · Posted: Wed Aug 27, 2008 7:34 am Post subject: Re: THE Window Thread (merged)

We generally install some shrink wrap plastic on the north facing and one or two east or west facing windows that are tree-shaded. It's cheap, fast and adds insulation value. No loss of insolation as there's no direct sunlight on those sides.