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#1
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polyiso vs styrofoam
Duane C. Johnson wrote:
daestrom wrote: If there's 'no air gap' then the emissivity of the foil becomes pretty much irrelevant. I agree. Nick, can you give us citations pro or con? Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5", with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr, Hc is the conduction- convective coefficient, EeffHr is the radiation coefficient ~ 0.00686Eeff[(Tm+460)/100]^3, and Tm is the mean temp of the air space... For extrapolation from Table 2 to air spaces less than 0.5 inches (as in insulating window glass), assume Hc = 0.159(L+0.0016Tm)/L, where L is the air space thickness in inches and Hc is heat transfer through the air space only. So, the surface conductance is the sum of its radiation conductance EeffHr and Hc, which becomes a lot larger than EffHr as L decreases. For instance, with Eeff = 0.05 (1 foil) at 50 F, EffHr = 0.0455 (R22 :-), but Hc = 0.159(L+0.08)/L, ie 0.17 (R5.8) for L = 1", 0.29 (R3.5) for 0.1", 1.43 (R0.7) for 0.01", and 12.9 (R0.08) for L = 0.001". L Hc EffHr U = Hc+EffHr R = 1/U 1" 0.17 0.0455 0.2155 4.6 0.1" 0.29 0.0455 0.3317 3.0 (surprisingly large) 0.01" 1.43 0.0455 1.4755 0.7 0.001" 12.90 0.0455 12.9455 0.1 Each foil can count, on double-foil foamboard, but 2 facing foils with an air gap only reduce the combined emissivity from 0.05 to 0.03 (1/Eff = 1/E1+1/E2-1) OTOH, 2 foils may retain inert gas longer than 1 foil. Notes b and c say Values apply for ideal conditions, ie air spaces of uniform thickness bounded by plane, smooth, parallel surfaces with no air leakage from the space... Thermal resistance values of multiple air spaces must be based on careful estimates of mean temp differences for each space. A single resistance value cannot account for multiple air spaces; each space requires a separate resitance calculation that applies only for the established boundary conditions. Resistance of horizontal spaces with heat flow downward are sustantially independent of temp diff [and large, eg R8.17 for e = 0.05 with 3.5" and a 50 F mean and 30 F temp diff.] Nick |
#2
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polyiso vs styrofoam
Fibregalss is not a great insulation. However air is a
good insulaltion when you stop it from transmitting heat by convection. Fibreglass woll makes "trapped air" a good insulation. The foil people state an air gap is needed to reflect the radiant heat. If in contact it is still a metal to conduct the heat very well. "Duane C. Johnson" wrote in message ... I understand there is an associated R value associated with air gaps. However, I would have assumed that the R value of of conventional insulation, say fiber glass, would have been better than that of an air gap. At least for gaps that were greater than the separation of the fibers. What I understood was that the foil on foil backed insulation had a different function. It was to "Reflect" infra red radiation. This reflector can be behind sheet rock which is able to transmit the infra red back to the source. Duane -- Home of the $35 Solar Tracker Receiver http://www.redrok.com/led3xassm.htm[*] Powered by \ \ \ //| Thermonuclear Solar Energy from the Sun / | Energy (the SUN) \ \ \ / / | Red Rock Energy \ \ / / | Duane C. Johnson Designer \ \ / \ / | 1825 Florence St Heliostat,Control,& Mounts | White Bear Lake, Minnesota === \ / \ | USA 55110-3364 === \ | (651)426-4766 use Courier New Font \ | (my email: address) \ | http://www.redrok.com (Web site) === |
#3
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polyiso vs styrofoam
Duane C. Johnson wrote:
I understand there is an associated R value associated with air gaps. Sure... However, I would have assumed that the R value of conventional insulation, say fiber glass, would have been better than that of an air gap. Add the air gap's R-value to the insulation's R-value. What I understood was that the foil on foil backed insulation had a different function. It was to "Reflect" infra red radiation. This reflector can be behind sheet rock which is able to transmit the infra red back to the source. It could do that, with an air gap bgetween the foil and the sheet rock, but the foil won't do much if it touches the sheet rock, except to act as a vapor barrier. Nick |
#4
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polyiso vs styrofoam
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#5
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polyiso vs styrofoam
Jeff Thies wrote:
Add the air gap's R-value to the insulation's R-value. As long as we're talking about insulation, I've been trying to figure out the radiation from the insulation and am not getting far. From a EffHr 0.0455 (for that .05 foil Eff) That's a radiation conductance. Thermal resistance R = 1/C, where C = Hc + EeffHr. Which you add to the convection conductance, which typically brings the combined R-value of the foil down to something between 1 and 10. It appears to me that the max effective R value would be 22... For the foil radiation alone. But you have to add the convective conductance Hc for the foil to its radiation conductance EeffHr. Then take the reciprocal, then add the insulation's R-value. It would seem that the radiation from the insulation would mean these high R blankets would have diminishing returns. No. Add the insulation's R-value to the foil's R-value... It also seems that a foil barrier on the ambient side of the insulation would be very valuable. It's valuable on either side, but people don't like foil walls, and the foil would weather badly outdoors, and wind would raise its convection loss. Nick |
#6
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polyiso vs styrofoam
"Jeff Thies" wrote in message nk.net... wrote: Duane C. Johnson wrote: I understand there is an associated R value associated with air gaps. Sure... However, I would have assumed that the R value of conventional insulation, say fiber glass, would have been better than that of an air gap. Add the air gap's R-value to the insulation's R-value. As long as we're talking about insulation, I've been trying to figure out the radiation from the insulation and am not getting far. From a EffHr 0.0455 (for that .05 foil Eff) and: Thermal resistance R = 1/C, where C = Hc + EeffHr. It appears to me that the max effective R value would be 22, and that for an infinitely thick blanket with a foil outer barrier. It would seem that the radiation from the insulation would mean these high R blankets would have diminishing returns. Well, the law of diminishing returns certainly applies to any insulation project. But you can certainly insulate with higher effective R values than 22. Don't see what you're getting at there. One foot thick fibreglass can give you about R-38, irrespective of the coatings or any 'facing' such as drywall or OSB over it. Remember, a higher R-value *behind* the foil surface makes the foil surface temperature closer to the ambient temperature. And that reduces radiant losses as well. It also seems that a foil barrier on the ambient side of the insulation would be very valuable. But things are not done this way, what have I misunderstood? As far as a foil barrier on the ambient side, it isn't really all that valuable in most circumstances. Yes, it would certainly reduce the heat gain from direct sunlight, and reduce radiant heat loss. But if you look at how much heat is lost to the environment due to simple convection, you will realize that even if radiant heat losses were cut to zero, it wouldn't reduce the total heat losses by a significant percentage in most cases. You won't get a lot of improvement for the 'buck'. And a lot of folks don't like the idea of living in an aluminum foil sided house. Radiant losses can be a big issue if the temperature difference is large and/or you've already taken steps to reduce the other forms of heat loss (conduction/convection). Or if your goal is to reduce absorption from the sun. daestrom |
#7
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polyiso vs styrofoam
I'm not on usenet and don't know how to post there, but I read your =
posts frequently... If you can read usenet posts, you can probably post yourself... Might be worth learning how. OK. Looks like I got it figured out. Now as far as window insulation goes, what about packing peanuts between the panes? Dennis |
#8
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polyiso vs styrofoam
Dennis wrote:
If you can read usenet posts, you can probably post yourself... Might be worth learning how. OK. Looks like I got it figured out. Congratulations! Now as far as window insulation goes, what about packing peanuts between the panes? Sounds rather permanent. The Zomeworks Beadwall system moved small styrofoam beads into and out of a window cavity with a vacuum cleaner. It worked well, but the beads required lots of storage space and they wouldn't flow well through fittings, so each window cavity required a separate store and vacuum cleaner. And the multiple vacs required an electrical sequencer to avoid blowing fuses. "Replacement foam insulation" (filling the space between two glazings with soap bubble foam at night) seems more practical. It's being applied to greenhouses now. In one system, a shop vac pushes air through a 100'x2" pipe with some holes in a 10% detergent solution near the ground, making bubbles rise to the top of a 100' long quonset-shaped greenhouse. When the bubbles reach the top, the vac automatically turns off until they recede, then starts again for a few seconds every hour or so to replenish them during the night. The bubble system turns off at dawn and a small blower inflates the space between the 2 plastic glazings with air. Nick |
#9
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polyiso vs styrofoam
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#10
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polyiso vs styrofoam
Anthony Matonak wrote:
... I've heard reports that there were other issues with the beadwall system. For instance, the foam beads would break down over time. Not exactly. They tended to clump if never cycled. IIRC, cycling once a month would fix that. "Replacement foam insulation" (filling the space between two glazings with soap bubble foam at night) seems more practical. ... I question it's usefullness in a house. For instance, how clear and streak free are the windows when the foam goes away? Moreso than my $500 500 ft^2 cloudy plastic film sunspace :-) How do you insure that the window cavities are sealed well enough that they don't ever leak in some hard to detect fashion and cause damage to the structure? I'd probably make the "windows" with 2 layers of 0.020" clear polycarbonate from a 48" roll, over plastic 2x4s, with lots of silicone caulk. ... how do you design the windows so that they can open? You don't. A few plain windows might do that. How about this for a possible solution. There are double pane windows being sold now that have window shades or blinds inbetween the panes. Mostly, this means that they never get dusty and you won't find the cat has hung himself from them. Air is a pretty good insulator except when there is some kind of circulation going on. Even tiny circulations. A cellular shade could be produced using thin mylar or paper such that it folds up into a small space at the top or bottom of the window cavity and yet can unfold to fill the entire space with small air-filled pockets. It could be... One or more layers of aluminum coatings could be added as well to help cut down on radiant loss. Good idea. Scheme 18.7 on page 168 of Bill Shurcliff's 1980 Brick House book "Thermal Shutters and Shades" describes 5 sheets of metallized Mylar with springy spacers that unfold when it's rolled down. Scheme 18.8 on page 170 describes an interesting self-inflating Mylar shade. Alas, these are no longer being made. Perhaps they can be recreated with an iron or a $118 -RS1 hot roller for plastic film seam-sealing from Hillas at (800) 952 7274. Symphony "energy track" shades with tracks on each side to reduce air leaks are fairly expensive and low performing. They (877) 966-3689 say their room darkening shade has a R-value of 3.2, when used with an R1.8 window :-) This increases to R4.8 with side tracks. A 3'x6' shade costs $170 with the tracks. Tiny cold soap bubbles can have the same R-value as fiberglass. A 6" window might transmit 80% of the sun during the day and become an R20 wall at night. Nick |
#11
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polyiso vs styrofoam
Now as far as window insulation goes, what about packing peanuts
between the panes? Sounds rather permanent. I was considering this as a seasonal plan. Fill the space between a double sash window and storm window on the north wall with packing peanuts in the fall and remove in spring. I could then throw them away or keep them for next season. There is also the stationary half of my patio door, (hinged french door), that has a cavity of 35" x 78" x 4". Cost: $0.00, if using used packing peanuts that currently go to landfill. Convincing wife to agree, priceless. Dennis |
#12
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polyiso vs styrofoam
Dennis wrote:
.... I was considering this as a seasonal plan. Fill the space between a double sash window and storm window on the north wall with packing peanuts in the fall and remove in spring. I could then throw them away or keep them for next season. There is also the stationary half of my patio door, (hinged french door), that has a cavity of 35" x 78" x 4". Cost: $0.00, if using used packing peanuts that currently go to landfill. Convincing wife to agree, priceless. I think there might also be fire issues with packing peanuts. Not like they are going to spontaneously combust but if they ever did catch a spark they would burn intensely and produce lots of toxic smoke. Anthony |
#13
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polyiso vs styrofoam
Anthony Matonak wrote
I think there might also be fire issues with packing peanuts. Not like they are going to spontaneously combust but if they ever did catch a spark they would burn intensely and produce lots of toxic smoke. How is this any different than the foam board that completely surrounds my house now? Isn't glass fire resistant? How will this spark get into the cavity? My carpeting is completely exposed and far more susceptible to catching a spark, which would yield large amounts of poisionous gas, than a window space filled with packing peanuts. I was mostly curious to see if anyone actually tried this and what the result was. I think I will give it a try in one window unless someone knows of any real concerns that could damage my home. Dennis |
#14
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polyiso vs styrofoam
Anthony Matonak wrote
I think there might also be fire issues with packing peanuts. Not like they are going to spontaneously combust but if they ever did catch a spark they would burn intensely and produce lots of toxic smoke. How is this any different than the foam board that completely surrounds my house now? Isn't glass fire resistant? How will this spark get into the cavity? My carpeting is completely exposed and far more susceptible to catching a spark, which would yield large amounts of poisionous gas, than a window space filled with packing peanuts. I was mostly curious to see if anyone actually tried this and what the result was. I think I will give it a try in one window unless someone knows of any real concerns that could damage my home. Dennis |
#16
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polyiso vs styrofoam
Jeff Thies wrote:
Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5", with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr, From your calculations of a typical EeffHr (radiation coefficient) of .04555 this would give a maximum effective R value of 22 no matter how thick the insulation. Thicker would get you closer to it but there are diminishing returns. No. Add Hc to EeffHr and take the reciprocal to find the R above, for the foil only. THEN ADD THAT TO THE R-VALUE OF THE INSULATION ITSELF. Nick |
#17
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polyiso vs styrofoam
Thanks Nick,
That was an old draft and I didn't mean to send it, you had answered this days ago... Cheers, Jeff Table 2 on page 22.2 of the 1993 ASHRAE HOF covers air gaps down to 0.5", with a footnote a: ... Thermal resistance R = 1/C, where C = Hc + EeffHr, From your calculations of a typical EeffHr (radiation coefficient) of .04555 this would give a maximum effective R value of 22 no matter how thick the insulation. Thicker would get you closer to it but there are diminishing returns. No. Add Hc to EeffHr and take the reciprocal to find the R above, for the foil only. THEN ADD THAT TO THE R-VALUE OF THE INSULATION ITSELF. Nick |
#18
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polyiso vs styrofoam
Dennis wrote:
I'm not on usenet and don't know how to post there, but I read your = posts frequently... If you can read usenet posts, you can probably post yourself... Might be worth learning how. OK. Looks like I got it figured out. Now as far as window insulation goes, what about packing peanuts between the panes? Dennis Bad Idea! The glass will shatter for sure when the elephants get in there. |
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