Argon/Krypton Gas insulation
redsavvy
16 years ago
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skydawggy
16 years agolast modified: 9 years agocalbay03
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how to measure insulating efficiency of windows????
Comments (18)Hi ERLA - ltns! jaansu, I am guessing that you have clear glass over clear glass IGU in your windows. The temperature measurements that you gave are not unreasonable for that configuration. As a general guideline, dual pane clear glass windows will have a center-of-glass temperature of around 43 when the outside temperature is 0° with no wind or solar interference. Adding LowE coating and argon fill will increase that temp up to about 57° (when zero outside). These are center-of-glass measurements, and can vary when measuring the glass outside of the center or when measuring various compnents of the window sash / frame. Your windows are 17 years old. I would guess that they don't have a LowE coating or argon fill. Even today, only about half of windows being produced have a LowE coating - which surprises many people who assume that the coating and gas infill are "standard" features in all windows. There isn't much that you can do about raising the indoor temperature of your windows. I would recommend that you ensure that the windows are tightly sealed and that the weather-stripping is in good repair. You can also add the interior shrink-film plastic which will help limit both air infiltration and will add an insulating airspace between the glass and the plastic which may help the temp climb a little....or some folks cover their windows with exterior plastic during the winter for the same reasons. Hopefully, doing a few little things can help. I am not a big fan of either insulating curtains or shades since they tend to block interior heat from the windows which can lead to excessive condensation and potential moisture-related problems particularly in a cold environment. And a bit off topic, but since it showed up on the thread... U-value does equal 1/R and by strange coincidence R-value does indeed equal 1/U  but there is no vast conspiracy of window companies (and NFRC by extension) deciding to list U-value rather than R-value in order to "hide" poor energy performance  actually there are very sound reasons for using U versus R when dealing with windows. And, as a matter of fact, R-value can be (and sometimes is) used by window sales folks to "hide" the true performance of a window. Windows performance is presented in U-factor simply because it is a more accurate way of describing window performance. While U-factor can be converted to R-value because it is a more intuitive number and it is easier for many people to "see" the overall performance, if an energy rater (for example) wants to determine the overall performance of the window and wall system the energy rater must convert back into U-value for the calculations. R-value is a measure of resistance to conductive heat loss "thru" a material or group of materials. U-value is a measure of heat transfer "across" a group of materials. Windows are an "across" product. The primary disadvantage of using R-value for a window is that what is often given is the center-of-glass reading, which while technically correct, can be misleading when dealing with the overall energy performance of the unit (which I alluded to earlier in this post). U-factor, as listed in the NFRC directory and on the window label of units certified thru the NFRC, is the actual overall energy performance of the window system and not a number related to the best-performing portion of the unit. No one is hiding anything - it is simply a more accurate number....See More72' X 46' Triple pane Krypton Garden Window?
Comments (6)The last number I heard was that krypton is currently about 600 times the cost of argon. Using krypton in a large window can become very expensive. In order to achieve the maximum effectiveness of krypton you need a narrow airspace between the glass - roughly 1/4" or so. How big is the largest individual sash in this garden window? In a really large window, a very narrow airspace can become a problem because there may not be enough room between the lites to avoid them touching during changes in barometric pressure - this may be worse in a triple than in a double. Depending on your environment and on the level of energy performance that you desire, using argon (double or triple) in a wider airspace can result in very similar energy performance numbers, compared with using krypton, often for a good bit less money. And a wider airspace (1/2" or so) is better in a larger unit. Ultimately though, the gas infill is a good deal less important than is using the right LowE coating on the glass. With the LowE coating you can control the level of solar heat gain thru the window (from a lot to almost none) and keep "regular" heat inside your home in winter and outside in summer....See MoreRunning some numbers on heat transfer with windows - low E, Argon
Comments (2)swampwiz, Think of your home as a set of interconnecting elements that function in harmony (or not in some cases) to give you the environment that you desire. While there is certainly value in looking at the different elements individually, as Calbay noted in his post, and I agree, "...it is unclear how to apply it as a decision tool. There are too many unknowns." Also, I would suggest that since your premise is window performance, starting out by discussing "constant: BTU = .00024 KW-hr", "cost for power:", Coefficient Of Performance of an air source heat pump, etc. detracts from the basic idea of measuring or comparing window performance. These are variables that don't directly affect window performance, at least not as I read your intent. I am not suggesting that you don't need that additional information, but I am suggesting that you need to establish a baseline (in this case basic window performance) before you begin adding variables that are affected by, or affect that baseline. In your post you added variation, including at least one unsupported assumption, before you introduced measured or calculated window performance. In your post you suggested comparing a 10 sqft window with U-factor variations of .5, .3. and .25. The formula for calculating Btu from U value is Btu = U x # hours x ft² x Delta T (temperature difference - which I am going to assume 50° for these examples). So, if Btu = .50 x 1 hr x 10 ft² x 50° then Btu = 250 If Btu = .30 x 1 hr x 10 ft² x 50° Btu = 150 and If Btu = .25 x 1 hr x 10 ft² x 50° Btu = 125 These are really simple examples of the difference in Btu loss and window performance rating, it is possible to interpolate the value of improved performance when our only variable (so far) is the U-value (or U-factor) difference which is based on clear/clear (.050), clear/LowE (.030), clear/argon/LowE (.025). But your house isn't confined to windows. It has walls and things as well. Assuming for the sake of simple math that a house has 1000 sqft of exposed wall (125 linear feet x 8') and that 15% of the wall area is windows - we can calculate overall wall performance by changing window performance. By definition, while R-value defines thermal resistance of a material, U-value measures thermal transfer thru a material. The formula for computing U-value is: Btu / (hr x degrees F x sqft) and the formula for computing R-value is: (hr x degrees F x sqft) / Btu and the formula for computing heat transfer is: (BTU/hr) = (area / R) * ÄT With ÄT again representing the temperature difference between what is inside and what is outside the house. Using the formula U=1/R, we can convert U.50 to R2, U.30 to R3.33, and U.25 to R4. However, this time we will assume a less severe environment so that ÄT = 25° If ÄT = 25°, then (10 sqft / R 2) = 5 * 25° = 125 BTU/hr loss or gain If ÄT = 25°, then (10 sqft / R 3.33) = 3 * 25° = 75 BTU/hr If ÄT = 25°, then (10 sqft / R 4) = 2.5 * 25° = 62.5 BTU/hr Keeping in mind that the Btu losses or gains are based on one square foot for one hour and the example has 150 square feet if windows. Combined they equal: 125 Btu x 150 sqft = 18750 Btu 75 Btu x 150 sqft = 11250 Btu 62.5 Btu x 150 sqft = 9375 Btu I am also assuming a typical 2x4 wall with R-13 fiberglass insulation. The overall wall insulation value excluding windows will calculate out to a bit below R-10, but I am also assuming R-10 for simplicity (and laziness on my part). Wall = R10 or U.1 Window = U.5 Window = 15% of wall Wall area = 850 sqft and window area = 150 sqft Wall = 850 sqft x U.1 = 85 Window = 150 sqft x U.50 = 75 85 + 75 = 160/1000sqft = U.16 or overall wall R value including windows of 6.25. Wall = R10 or U.1 Window = U.3 Window = 15% of wall Wall area = 850 sqft and window area = 150 sqft Wall = 850 sqft x U.1 = 85 Window = 150 sqft x U.30 = 50 85 + 50 = 135/1000sqft = U.135 or overall wall R value including windows of 7.41. Wall = R10 or U.1 Window = U.25 Window = 15% of wall Wall area = 850 sqft and window area = 150 sqft Wall = 850 sqft x U.1 = 85 Window = 150 sqft x U.25 = 37.5 85 + 37.5 = 122.5/1000sqft = U.123 or overall wall R value including windows of 8.1. And assuming that I didnt make any errors in my arithmetic, Improving window performance from U.5 to U.3 results in an overall wall performance improvement of 18.56% in this example Improving window performance from U.3 to U.25 results in an overall wall performance improvement of 9.31% in this example And improving window performance from U.5 to U.25 results in an overall wall performance improvement of 28.46% in this example And finally, in my opinion, now would be time to begin discussing "constant: BTU = .00024 KW-hr", "cost for power:", Coefficient Of Performance of an air source heat pump, and any other variables that are affected by window performance rather versus effect window performance. And as a final, final aside, Btu actually = .0002931 Kwh, and there are large portions of the country, primarily California and New York and parts of New England, that have already exceeded the $.12 Kwh....See MoreDoes this mean Low E and Argon??
Comments (5)I believe it is, but I also have always found Pella literature and catalogs confusing. What are the U or R value numbers on some of the windows, that will tell a lot. Numbers around an R-value of about 0.3 +/- indicate low-e. No low-e would be about 0.5. Virtually every window manufacturer uses an argon fill in a low-e window, so that should almost be a given. Of course, if you have internal shades in your Pella, the operating knob passes through the glass pane and the argon gas can't be sealed in, those would not have argon....See Moreantonio_2008
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