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Old 03-16-2008, 07:26 AM   #15
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(Yes, the materials will potentially act differently in the heat.)
I used to make calculations on heat transfer in electronic equipment for reliability figures and I don't remember any differences in heat transfer formula or K factors in transfer for convection or contact or radiation. Is this something new? Forgive me but I am getting old.
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Old 03-16-2008, 08:09 AM   #16
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rangebowdrie, What kind if foam insulation is an order of magnitude better than most others? I am trying to find the best insulation to use on a walk-in cooler and the R values i get over bat fiberglass is only twice as good for most foam type.
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Old 03-16-2008, 08:32 AM   #17
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This is great information and resurch. I hope this continues. I thought an interesting test would be to have a rally where we would invite a number of trailers with different insulations. We'd all sit in the sun and compare notes and temps. Windows, doors, thru holes,etc. all might have an effect on the inside heat transfer. I sure enjoy Airstrem people they love to do and think.
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Old 03-16-2008, 09:56 AM   #18
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Kudos Zep for running this experiment. Even though I have a late model AS, I love watching you guys and gals use your gifts to bring the older ones back to life. Obviously, the results of this experiment will aid many here.

Forgive my stupidity, but I am trying to understand. I was wondering if the different outside temperatures during the various tests might bias the results a little. If the slope (rate of water bottle cooling) is the measure of insulation performance, then I would think each test needs to be done at the same constant outside temperature. For example if you test material A when it is 32F outside, then test it again when it is minus 200F outside, I don’t believe your slope calculation will be the same. But, I may be wrong, just askin’.

I was curious what the outside temperatures were in Fahrenheit during the experiments. I converted temperatures on the charts from Kelvin to Fahrenheit, but the conversions don’t make sense. What am I missing? NEVER MIND, I SEE ITS F * 10.

I was also wondering if reducing the surface area of the non-aluminum box sides might cause the data to correlate more to the aluminum side. Perhaps a prism design or a rectangular box instead of a square box would help?

Again Zep, I applaud your effort and hope you don’t take my questioning in the wrong way. Sometimes I’m not the sharpest knife in the drawer. I understand completely if you respond “Kiss my butt Sky, go do your own experiment”.

Thanks
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Old 03-16-2008, 10:06 AM   #19
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Spray foam

I have used Great Stuff to seal around my root vents. After several attempts to seal them up only for them to continue to leak, this worked wonders. I have also replaced some of the front cap panels. Though I have them sealed and no leak as of now, I am not confident that leaks won't appear as soon as the trailer flexes a little while being towed.

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With Zep's help, if the insulation is not too bad, then this may be my way to go.

My plan, keep in mind these are only thoughts, not reality, is to buy a larger container, about a gallon, and while my inside panels are off, run conduit for wires, tape all the windows and other openings and spray the whole interior. This insulation is closed cell. So even if after many travels, should a seam open, the leak should not have anywhere to go. Since there are ribs to use as a depth gauge. I think trimming, though maybe a hassle, is doable.
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Old 03-16-2008, 10:18 AM   #20
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Quote:
Originally Posted by Sky
...I was wondering if the different outside temperatures during the various tests might bias the results a little. If the slope (rate of water bottle cooling) is the measure of insulation performance, then I would think each test needs to be done at the same constant outside temperature. ...
Theoretically, heat transfer depends only on the difference in temperature, which I take into account. The heat loss units are [degrees of water temperature loss]/[average temperature difference]/[time] which are the units in the box on the left hand chart. In engineering terms, this is the way you "normalize" data. Unfortunately, over large temperature differences this is not a linear function, eg, convection or radiation might predominate at higher differences, but for the purposes of this test, delta temperatures between 60 and 100 degrees are probably linear.

Quote:
I was curious what the outside temperatures were in Fahrenheit during the experiments. I converted temperatures on the charts from Kelvin to Fahrenheit, but the conversions don’t make sense. What am I missing?
The temperatures in the left charts are in degrees Fahrenheit times 10 (a function of the sensor and the A/D converter). I could have made separate columns in Excel and divided by 10 so that the charts were in degrees, but I'm lazy.

Quote:
I was also wondering if reducing the surface area of the non-aluminum box sides might cause the data to correlate more to the aluminum side. Perhaps a prism design or a rectangular box instead of a square box would help?
The box fits the hot water bottle pretty well. The big issue is, should there be a fan inside? This will be a much more important issue when we get to the hot weather test, since the air will stratify inside the bigger 4-panel test box. Why is it an issue? Because you can't guarantee that each panel gets exactly the same breeze and convection is a huge thermal issue.

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This is my happy response to everyone and everything! Always. Then go drink beer. Together.


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Old 03-16-2008, 10:26 AM   #21
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Quote:
Originally Posted by FrenchBern
...I don't remember any differences in heat transfer formula or K factors in transfer for convection or contact or radiation. Is this something new? Forgive me but I am getting old.
No, no changes. It's just that thermal properties of materials, when reduced to a simple R-value, assume a standard method of installation. For example, the foil insulations recommend an air space on both sides, becuase they are better at reflection than conduction. On the other hand, glass mat requires a snug installation between drywall and exterior siding in order to prevent convection (when installed vertically--in the attic and horizontal, convection isn't an issue). I think we Airstreamers tend to use materials in a non-standard way sometimes, so thinking about the issues that raises may help us get better insulation performance.

Not to get too technical, but black body radiation is a Kelvin function. We live in a world around 520 degrees above absolute zero, so when the temperature changes 50 degrees, it's really not that much one way or the other when you compute black body radiation. That being said, you know you can feel the radiated heat coming off a hot Airstream shell in the summer. So intuitively I'm thinking that the foil may do better when the sun is burning down on the shell.

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Old 03-16-2008, 11:08 AM   #22
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Frenchbern, in your application, for a walk-in cooler, foam will not give an order of magnitude better performance than fiberglass. The performance of fiberglass batting, when measured under controled laboratory conditions, is not all that bad, hence, the manufactures high rating numbers. The problem, is that under actual real world conditions,it is impossible to achieve these ratings. The primary culprits are air leaks, which carry moisture, and the internal condensation in an AS, which adds more moisture. This moisture wicks thru-out the fiberglass strands,drastically reducing its insulative ability. Also it is almost impossible to install batting perfectly,ie.,no compression, no voids,perfect fits,etc.,and we still have the problem of the air inside the structure,into which we place the batting. In contrast, poured/sprayed foam, is a Freon/inert gas expanded product,in which no air is present. When poured/sprayed, it not only seals the structure from any air leaks, it also displaces the air in the structure. Also, the foam is of a closed-cell nature, which inhibits/slows down the molecular motion that carrys heat. Because of this, and a number of other more esoteric considerations,foam will live-up to it's ratings in actual field useage. Hope some of this helps you. As a footnote, a well polished AS will reflect more of the sun's heat, and stay cooler inside, then a dull finished one.
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Old 03-16-2008, 12:09 PM   #23
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Quote:
Originally Posted by Zeppelinium
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
Hi Zep; Your theory on the heat loss through the ribs is close to 100% on the money. I did not carry out any sophisticated tests, however I like to tell you what I have observed this past winter with my Argosy sitting in the yard.

Bear in mind that my trailer was insulated with bubble foil. Each panel between the ribs was outlined with 1/2" X2" foam strips attached to the outer skins with 3M 5200. Each panel had a additional supporting strip in the middle of the panel. Bubble foil was cut oversize so that the foil could be wrapped to wards inside wall, along the cross section of each rib. Excess foil was then trimmed about 3/16" above the face of the rib. Slight compression of the bubble foil was purposely done so that the cut high ends of the foil could be compressed as the inner wall skins were installed.

Walking out into the yard one day around lunchtime after 2" snowfall on the previous day, I have noticed a very strange occurrence. Unfortunately my wife was away with my camera and I was unable to take any pictures. Top section of my roof was covered with 2" of snow, but at each rib at about
1 1/4" width, over each rib there was no trace of snow. It looked as someone has cut straight wall passes in the snow. The passes did not have sloped sides, they were very vertical as they were cut clean. Returning an hour later they were slightly wider. With bright sun shining all day the snow did not melt more than 1/2" further from the rib lines by the nightfall . The next day, higher temps melted it all away. When my wife is done with curtains I will perform some temp differentials tests between inside and outside and record the findings. Thanks, "Boatdoc"
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Old 03-16-2008, 01:03 PM   #24
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Quote:
Originally Posted by rangebowdrie
... As a footnote, a well polished AS will reflect more of the sun's heat, and stay cooler inside, then a dull finished one.
See this post about polished aluminum:
http://www.airforums.com/forums/452880-post35.html

I observed in this earlier (and inconclusive) insulation test that "...in two minutes [in the sun], that the mill finish is 20 degrees hotter than the polished finish. The sun angle was pretty low and it was a moderate day here today, so I think it will be even hotter on a hot day in July."

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Old 03-16-2008, 01:39 PM   #25
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In the 70's when in the army I & a couple of freinds were customizing our vans. Granted vans and trailers is an apple to orange comparisons, but a couple of interesting developments happended.

I used fiberglass insulation, one friend used the early spray foam and a third (disaster) tried glueing thin/flexible styrofoam board onto the body.

The immediate things that were noticed was the glued van squeaked like stadium full of mice when it was on the road. The foam pieces also broke loose due to body movement and expansion (we think??). It had a bad sweating problem until the foam loosened up.

The sprayed in foam had better success but eventually had pieces break loose behind the panels. It did have some squeaking but not on near the level of the first van.

Both foam vans had minor sweating problems. It was also a very humid summer in North Carolina.

My fiberglass insulation had no sweating and roade quiet. The glass was put on wtih spray glue to hold it until the panels were in.

Now we don't (at least I hope not!) ride in our trailers so sqeaking is probably not an issue. Sweating had more to do with the technique of applications. I do wonder if spray foam will fracture and get loose. It may not matter if it does as it is still held in place and contained in the walls.

Just some food for thought. We ended up pulling the panels from two of the vans and went to fiberglass in all of them.

My van was called the camel (33 gallon gas tank). One time when starting it, a big puff of smoke came out of the tail pipe and one of my soldiers commented "Smokin Camel" The name stuck. The Van was on it's 4th owner last time I saw it which was two years ago...not bad for a 79 Chevy 3/4 ton. As it was such a long lasting vehicle I named my AS after it.
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Old 03-16-2008, 02:04 PM   #26
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Zep,

It seems to me that you need some way to test the insulation combinations for both conductive and radiat heat loss. Also you might want to factor in something for the direction of the heat loss (through floor, walls and roof). One of the reasons that I feel foil insulation is such a good choice is that a very large percentage of heat loss through the walls and roof of any structure are supposedly radiant heat loss. If I recall the numbers correctly something like 90+ percent of the heat loss up is radiant. Of course when you talk about heat gain duing the summer a major component will also be radiant as long as the AS is not in the shade. Perhaps you could use something like a heat lamp inside your box to simulate a radiant source a bit better.

As a side note this whole issue of insulation types is also related to the type of heat that we chose to use in our Airstreams. I want to use direct radiant heating in large part because it gets the heat energy directly to the occupants (by radiant transfer) without relying on first heating the air inside the trailer and then the occupants (by conductive transfer). Of course when matched with foil insulation that blocks radiant heat loss this seams like a very nicely matched combination.

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Old 03-16-2008, 02:17 PM   #27
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It's to bad that foam has had such a bad reputation, due in large part because of the prevelance and general useage of the cheap squirt-can stuff they sell at various stores for home use. The industrial two-part product is so much better that there is little to compare between them. Not like apples/oranges, but more like strawberrys/limes. The squirt stuff "kicks-off" due to reaction with air, the real stuff "kicks-off" due to internal chemical reaction. In all cases, surfaces to be applied to, need to be clean and dirt/grease/oil free.
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Old 03-16-2008, 02:51 PM   #28
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Range, we had a pretty lively discussion of the two part foam stuff you're talking about around a year ago. I'll see if I can find that thread and post a link to it here. I was ready to use it, but changed my mind after we talked it out in that thread.

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