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Old 03-15-2008, 12:22 PM   #1
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Insulation effectiveness tests

After many different experiments and configurations, I think I have reliable data on the performance of insulation in a typical Airstream shell configuration. Some of you may have read the thread where I tried to do four test panels at once--that data (or the analysis strategy) didn't work out. So I built the single panel test rig here:

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All the panels were identical--1-1/2" thick and 12x12". The insulation was installed as you would expect, the glass mat was placed to ensure there were no gaps in the corners and the sheets of foil were glued in place, ensuring an airtight seal and supporting the foil directly between the face sheets, with a 5/8" air gap on each side.

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The test setup was an old PC-XT running a single chip 12-bit A/D converter through the parallel port. The sensors were Kelvin devices so there was very little electronic noise--precision was 0.3 degrees F and accuracy was on the order of 0.5 degrees F. Samples were taken every two minutes.

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The charts below show the absolute temperatures of representative test runs on the left. The right hand charts in each case show how close the panel temperatures were to their environment (the inner panel to the water and the outer panel to the outside air) divided by the temperature difference between the water and the outside air.

The data was analyzed in two ways. First, how fast did the water bottle lose heat? This should provide some idea of the R-value of the insulation. However, the heat lost throught large surface area of the five other insulated walls of the box was, in total, more significant than the heat lost through the test panel, so the data show only small differences between the panels. In any event, a smaller absolute value of the slope means better insulation performance.

Second, what was the ratio of the inner and outer panel temperatures to the total temperature difference between the outside air and the water? It seems intuitive that if the inner panel is relatively warmer, then the insulation is doing a better job. What this means is that lower numbers are better (if the percentages were zero, that would mean zero heat flow through the panel--the inner panel temperature would be equal to the inner environment and the outer panel temperature would be equal to the outside air).

You have to get the full size images (click on them) to see all the lines on the charts.

When you look at the charts, it's obvious that an empty panel (air only) has worse performance all the way around--higher heat leakage and colder inside panel.

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The glass mat performance is good. Relatively warm inner panel, but the heat loss number is higher than for both of the foils. Remember, lower numbers in the right hand chart are better.

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The Home Depot foil (in visual appearance it has two layers of large bubbles between the foil) performance as well as the glass mat and had lower heat loss.

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The "Prodex" (Prodex TOTAL Insulation - Aluminum-Foam-Aluminum from Insulation4LESS.com) was a puzzle. The inner panel was relatively cold, but the heat loss was very close to that of the "HD foil." I dissassembled both of these panels to check their construction, reassembled them, and got the same data in a second test.

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The bottom line is that I still have open questions. First, it's obvious that the inner air temperature isn't the same as the water--lots of heat (relatively speaking) is going out through the walls of the box, so the air temperature is quite a bit different than the water. The next series of tests will include an inside air temperature sensor, which will give more precision to the temperature ratio test (in about a week--it usually takes one night per panel test, unless it's overcast and cold during the day).

Second, will the foils perform even better when the summer sun is heating the outer panel to 160+ degrees? I'm more interested in hot performance than cold, so that test is coming this summer.

Zep
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Old 03-15-2008, 12:46 PM   #2
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Zepp, very interesting, I am looking forward to the summer test, and thanks for the good work! Red Rover^^^
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Old 03-15-2008, 01:45 PM   #3
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I leapt at Prodex since it attenuates sound while the foil-bubble-foil is pretty much transparent to sound.

The double-bubble style foil hasn't been described other than double layer - is it twice the thickness of the Prodex or is it just the construction to achieve two shiny sides with the bubbles keying together?

The foil-bubble has a smoother surface & is 'shinier' than the Prodex so when new it does reflect heat transfer better than the crinkly duller Prodex but that will be reduced quickly if/when dust or condensation dregs appear on it.

I am looking forward to your next tests; hope you rig the heat panel tests with multiple installations of each type ie: air gap at outer shell or applied on shell with second layer gapped 1/2-inch etc... Oh, and thanks again for sharing.. .
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Old 03-15-2008, 02:58 PM   #4
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by the way, the hot water was in a one-gallon plastic milk jug. I occurs to me that some additional precision can be achieved by adding some "rails" on the bottom of the box to ensure that the jug is placed the same way every time. Back to the lab to add a sensor and the rails...

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Old 03-15-2008, 09:33 PM   #5
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Man you're killing me making me wait. I plan on insulating this summer. I have your metal pieces by the way.
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Old 03-15-2008, 09:34 PM   #6
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Zep, Iím not a scientist and didnít play one on TV, but lemme see if I am interpreting your results correctly.

Basically, you built a 6 sided box with one side of the box removable. You inserted several different insulating materials in that side, one at a time, and tested them against heat loss in cold weather. Is that about right?

The charts seem to show that the Prodex product is just a bit more efficient than the Homey D foil, which is just slightly more efficient than the pink stuff insulation. Is that about right?

Is there any real reason to believe that these materials will act radically differently in warm weather than cold? Not trying to dissuade you from running the warm weather tests, just thinking out loud.

BTW, I find it amazing that you still have an XT machine still functioning. Thatís gotta be some kinda longevity record all by itself.

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Old 03-15-2008, 09:49 PM   #7
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I want to use the spray expanding polyurethane foam. Mainly due to the sealing properties. If I say please will you do a test panel of this. Please. I will be glad to chip in for the cost.
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Old 03-15-2008, 09:53 PM   #8
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OK OK What we are looking for is a clear standout product that is cheap. Your doing a lot of hard work so the rest of us can sleep better at night. Thanks Man

Looking forward to the summer testing.
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Old 03-15-2008, 09:56 PM   #9
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On the road testing

Quote:
Originally Posted by FC7039
I want to use the spray expanding polyurethane foam. Mainly due to the sealing properties. If I say please will you do a test panel of this. Please. I will be glad to chip in for the cost.
I am wondering how expanded polyurethane holds up to the flexing of a trailer going down the road. Has it been tested. I have a local guy that is willing to install.
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Old 03-15-2008, 11:09 PM   #10
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If using sprayed-in-place polyurethane foam, be sure the AS is leveled-out well , before spraying. The foam is very rigid, and will not allow the shell to flex very much,(this is a very good thing). As to the effectivness of the foam, it is perhaps a complete order of magnitude better than almost anything else commonly available at reasonable cost. This is based on a good quality foam of around 2-2.5lbs. per cubic ft. density product. The difference between sprayed foam, and air bubbles or fibergass batting is simply amazing. If possible, run wiring inside of plastic conduit, with junction boxes at key locations, to permit later removal, or pulling-thru new wiring. The sprayed foam will also almost completly eliminate the problems of trapped condensation within the shell. Foam such as this is rated with a "K" factor, rather then "R" factors, as fiberglass is. Go for it. The foam is also FAR better as a sound barrier. It is so far ahead of anything else, there is no second place.
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Old 03-15-2008, 11:48 PM   #11
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Quote:
Originally Posted by Jim & Susan
...The charts seem to show that the Prodex product is just a bit more efficient than the Homey D foil, which is just slightly more efficient than the pink stuff insulation. Is that about right?

Is there any real reason to believe that these materials will act radically differently in warm weather than cold? Not trying to dissuade you from running the warm weather tests, just thinking out loud.

BTW, I find it amazing that you still have an XT machine still functioning. That’s gotta be some kinda longevity record all by itself.
...
I, myself, am a longevity record. I didn't think I'd see the millenium. Not age, mind you, just risky business. BTW I have 16 of these ancient "laptops" that run on 12V, 1 Amp. If you're a DOS nut and need a data logging machine, let's talk.

Yes, the materials will potentially act differently in the heat. This is only intuitive, but when the outer skin is heated by the sun and is easily 160+ degrees in the desert, radiation might predominate. In cold weather I "feel" like convection and conduction predominate. The foil insulation should have interesting properties in a radiation environment.

Your interpretation of "slightly better" is influenced by the small difference in the numbers in the data. But don't forget that the other five walls are very nearly swamping the panels' performance. That's why I'm going to do tests with a stabilized water bottle position and an internal air temperature sensor. I think those two changes will show quite a bit of difference between the different insulations. Stand by for data.

For those interested, I like the idea of an expanded foam test and will do one this week (do you all agree that using the "low expansion" canned foam at HD will suffice?). I've got two more sets of panels (thank you again, Aerowood), plus I found that I can disassemble a panel without significant damage. I mention this because when I get to the warm tests, I also want to coat the outside and inside of the outer panel with white paint to see what increasing the reflectivity and reducing the emissivity of the outer panel does to its heat transmission--this is more important in a warm weather test than in cold.

WARNING: youse guys are focusing on the insulation performance and forgetting that I'm not simulating the ribs. I'm no expert, but I would bet that the ribs transmit 30-50% of the heat through the shell, if the cavities are well insulated (less of the total if the cavities are poorly insulated). So, putting some foam tape, felt, or cork along the inside flange of the ribs before your reinstall your interior skins would be a significant contribution, even if a thin strip of this stuff only provided a small R-value. Small is bigger than zero, or so I've been told. I believe UWE or someone did this and noted it in a thread.

Zep
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Old 03-16-2008, 12:02 AM   #12
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I've been reading some of the posts about foam insulation purely out of curiosity - I know nothing about foam insulation and have no intentions of changing my insulation.

Two things I was thinking about before - rangebowdrie mentioned above.

You'd really have to be sure that you never needed to fish a wire outside of the conduit - presuming you did followed that recommendation.

Presuming that the foam will be sprayed on with the inner walls removed.. With the rigidity of the foam on the outer skin - isn't that going to cause problems? I'm trying to visualize the trailer trying to flex as it's being towed - like an Airstream is supposed to do - the outer skin has new rigidity - the inner skin is trying to flex with the floor/frame.....

I don't know - maybe I'm just over thinking it....
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Old 03-16-2008, 12:16 AM   #13
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Quote:
Originally Posted by FC7039
I want to use the spray expanding polyurethane foam. Mainly due to the sealing properties. If I say please will you do a test panel of this. Please. I will be glad to chip in for the cost.
The only problem I see with the expanding foam is removing it if there is a problem. Much more difficult than most other insulations.
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Old 03-16-2008, 12:37 AM   #14
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There will always be a certain amount of flexing of the trailer, in the AS design, they try to use the inherant rigidity of the shell to make-up for weak,flexible frames. We've all read those posts of people talking about popped rivits,doors that don't close properly, windows that don't seal,etc,etc, ad infinitum. Also Andy, at Inland RV is always speaking of the need to distribute the load properly, to lessen the twist and flexing of the units. A good spray job will go a long way towards stiffening-up the structure, and let the suspension system do it's job properly. A good foam job go'es a long way towards a real monocoque system. If Wally would have had it, he would have used it. The qualitys of insulation and sound control, are the icing on the cake.
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