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Old 06-12-2015, 09:43 AM   #41
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Also, the outside wall is being heated on the vertical edge.
Yes, of course. In the sun, the outside wall is being evenly heated. With A/C the interior wall is being actively cooled.


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Originally Posted by austin1989us View Post
The bottom edge of the wall is cooler than the vertical side of the wall. It won't have the same effect as if the wall is being heated from the bottom (which would induce maximum convection).

True. We're dealing with this for the wall cavity:

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Old 06-12-2015, 10:07 AM   #42
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Yes, of course. In the sun, the outside wall is being evenly heated. With A/C the interior wall is being actively cooled.





True. We're dealing with this for the wall cavity:
Yes. Any idea how fast it's moving? Got an h value? What about the insulation that's there? I don't have modeling software to model this wall with.


This became a very involved discussion about the merits of putting new insulation in the walls. I understand that there are some strong opinions from those who've gone through the work of tearing out their interior walls. While I can see the benefits of getting in there, getting the old crap out, and fixing any rust; I don't see much of a benefit when it comes to heat transfer.

I'm not sure which way I'll go yet. I might be able to save a considerable amount of time and effort by not tearing down the original walls.
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Old 06-12-2015, 10:46 AM   #43
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The bus will smell better after its all out.
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Old 06-12-2015, 10:51 AM   #44
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I was just going over the initial calculations and it doesn't actually take into consideration either the inner or outer sheet metal. I suppose they fall under radiant heat transfer?

It appears we will need an infrared heat gun after all.

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I don't see much of a benefit when it comes to heat transfer.
The benefit for insulating the inner wall is this: it all adds up. For those who are interested in putting the time into having a long-term build and a well insulated space it makes sense. We can (affordably) insulate the dead space between the sheet metal while dealing with other notorious problems. We can reduce radiant and convective heat transfer in that zone to nearly zero. Then we can do the necessary step of insulating over the ribs. It's all accumulative.

I insulated between the ribs 3.75" thick and over the top of the ribs 1" for a consistent, flat insulated envelope to work with. Of course, I haven't tried the bus with only 1" XPS or spray foam over the entire inside, but from other jobs I've done in more favourable conditions I know that only 1" of XPS doesn't do a whole lot, though it's a nice addition to the outside of a building to reduce those accumulative thermal leaks. This bus I can use in the winter without a problem (our Canadian winter). The ribs and windows are still the weak point, but in its current state it does a great job while maximizing the available floor sq/ft (those oh so precious inches).

With the intention of creating a long-term livable situation... well, I just couldn't imagine NOT pulling those panels off, cleaning and insulating.

A short term metal tent? Just glue XPS over everything, then 5/8" plywood over the XPS with strategically placed screws to hold it in place while the glue dries and make sure it ain't going anywhere down the road. Another thermal bridge with the screws, but you can't win 'em all.
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Old 06-12-2015, 11:10 AM   #45
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what an awesome thread
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Old 06-12-2015, 11:13 AM   #46
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Ok.. I really need to stop thinking about this and do some work, but I can't help myself

I wonder; how do we actually properly calculate the area of the ribs?
With a solid, dimensionally simple product like a spruce 2x4 it's fairly easy. We can easily say that it is 1.5" thick and 3.5" wide.
A rib is different, though, no? It has 2 "feet" on the exterior end. Each one being 1/2"-3/4" wide, then it is ~1/8" thick metal all the way to the interior, where the surface is ~2" wide. I think the previous A.ribs was assuming a solid metal rib. Wouldn't the fact that it is hollow play a part?
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Old 06-12-2015, 11:14 AM   #47
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what an awesome thread
Yeh, no kidding! This is fun

It'd still be nice to get some IR thermometer read outs, though.
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Old 06-12-2015, 11:44 AM   #48
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I need to practice making one or two of those radiation calcs. I'm gonna be taking an engineering licensure exam this October. If I can convince my boss to let me play around with some modeling software I might build a bus model.


I'll probably be able to buy enough BTUs to keep the bus hot in the winter and cool in the summer. I'm a little concerned about sealing any potential leaks. I'm sure there will be some but I'm not sure how to stop them. I was thinking of painting on something like Herculiner or the Rustoleum bed liner inside the bus. On the outside would be pretty cool, but my wife doesn't like that idea.

Tearing out the walls at this point in time would force me to repair the rusted exterior sheet metal. I don't think I'll have time to complete all of the sheet metal work before I have to have it ready in the fall. I'll probably only be able to get one or two working days a week for the next 15 or so weeks. So, in ~20 work days I'll have to have a reasonably livable bus.
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Old 06-12-2015, 11:47 AM   #49
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Yeh, no kidding! This is fun

It'd still be nice to get some IR thermometer read outs, though.
I'm having fun with this. I haven't done heat transfer calcs since college. Idk how to convince my boss to let me get some modeling software though. He probably won't like that I'm using it for bus calculations.
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Old 06-12-2015, 12:09 PM   #50
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Forget what the wife wants. She has no clue about how the products work. Far too many of them base their decisions on looks alone.

Elastomeric paint needs to be applied to the exterior of the bus, not the inside.

Also forget bed liners. Not the right product for the job.

I have never understood why people allow a person with no knowledge on how things work, dictate and demand what they wants on nothing more than looks. It makes me sick. Take control and make some knowledgeable decisions.

If my wife knows more in a certain field, she can make the Educated decisions. If not, I'm making them because I know I'm more knowledgeable in most walks of life.

And yes, the metal work takes longer than building the rest of the bus.

Nat
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Old 06-12-2015, 12:09 PM   #51
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Holy moly.. How did I not even think of this??!! There already is so much data out there for this problem thanks to metal studs in houses! It's not 100% applicable (we aren't using drywall or exterior plywood; sheet metal radiates heat more), but I think it's worth looking at until Austin builds a computer model of the bus (which would be awesome).

IMPROVING ENERGY PERFORMANCE OF STEEL STUD WALLS

I like figure 8 in the above article: http://web.ornl.gov/sci/roofs+walls/...es/figure8.pdf
That's probably the closest representation of what is going on in my walls. Not exact, but close.


This PDF is less scientific, but has some pretty pictures
http://www.foamular.com/uploadedFile...MAL%20ONLY.pdf

Page 13 shows a good diagram of a typical bus wall.
Page 14 shows what most of us try to accomplish after removing the inner skin. (note, replace the phrase, "warm interior" with "warm or cold exterior" and it makes sense)
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Old 06-12-2015, 12:14 PM   #52
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Holy moly.. How did I not even think of this??!! There already is so much data out there for this problem thanks to metal studs in houses! It's not 100% applicable (we aren't using drywall or exterior plywood; sheet metal radiates heat more), but I think it's worth looking at until Austin builds a computer model of the bus (which would be awesome).

IMPROVING ENERGY PERFORMANCE OF STEEL STUD WALLS

I like figure 8 in the above article: http://web.ornl.gov/sci/roofs+walls/...es/figure8.pdf
That's probably the closest representation of what is going on in my walls. Not exact, but close.
Bus ribs will be much worse due to the thickness of the metal they are made from. Metal studs are made from a much lighter gauge steel.

Great starting point though.

Nat
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Old 06-12-2015, 12:19 PM   #53
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Grow some balls
I recently lost my left testicle to cancer. I find statements like that offensive.
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Old 06-12-2015, 12:20 PM   #54
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Elastomeric paint needs to be applied to the exterior of the bus, not the inside.
What elastomeric paint? Why not bedliner? And why not on the inside?
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Old 06-12-2015, 12:33 PM   #55
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I recently lost my left testicle to cancer. I find statements like that offensive.
Yep, I thought it was offensive as well. This isn't the place to educate people on how they should treat their wives. Never mind how it was offensive to women in general. I'm pretty sure it's against forum rules to post remarks of that nature here as well.
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Old 06-12-2015, 12:34 PM   #56
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What elastomeric paint?
It is a rubber like paint that is made for sealing small leaks in metal roofs.
There is even a few made just for buses like "Bus Cote". Almost every build here has used one form or another of the same product.

This is why the new members here need to go read a bunch of build threads before asking questions. All the info is there, waiting to be consumed and learned. Asking questions one at a time for each new member is a waste of every ones time, and important details get lost in the short answers given to some of these highly detailed topics.

All of your questions have been answered over and over again. In thread after thread after thread.

Pirate 4x4 calls this spoon feeding.

I only write this to help. I'm in no way trying to be mean, nasty, ignorant, ect.

Nat
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Old 06-12-2015, 12:43 PM   #57
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And why not on the inside?
Putting paint on the inside is only part of the process in dealing with interior rust. You need to scrape, wire brush, use a rust treatment, then paint. Painting on the inside will do nothing to seal leaks and prevent moisture from getting in the walls. That's an exterior job.

Elastomeric paints do a good job in reflecting the sun's heat away, since they are a blinding white colour. Their thick, rubbery nature probably also helps in that regard (slight insulating benefit). In addition, the fact that it is a thick, rubbery paint means it contributes to sealing the roof. I wouldn't trust it 100% for that purpose, but I'm confident it helps. You'll want to remove loose caulking, clean the roof, and reapply caulking to seal the roof properly. After that, many coats of elastomeric paint should keep things in good order.

Windows are also a point of water entry. You'll want to replace or re-caulk them as well... unless, again, this bus is meant to be a throw-away, short-term solution.

Nat is right about reading other build threads. You'll see discussion and great pictures that will answer all of these questions.

EDIT: I know... I'm guilty of spoon-feeding here.. For some reason, I just can't help myself today
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Old 06-12-2015, 12:43 PM   #58
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Having never done stuff like this before I don't even know the right vocabulary to use. When I search "elastomeric coating" I can find some useful threads. Didn't know that's what it was called. I figured something like bedliner would be water tight and rugged. I'd seen some of the threads about paint, but not much about water proofing.

I googled and found something called Sta-Kool 770 says it's good for metal roofs. Can it be painted over?
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Old 06-12-2015, 12:49 PM   #59
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I googled and found something called Sta-Kool says it's good for metal roofs. Can it be painted over?
Painting elastomeric paint will reduce it's effectiveness. You want it to be white.

I'd advise you to go to a local hardware store such as Ace Hardware and see what they sell. The one around here had several choices for elastomeric paints. Read the labels, see which one has the qualities you want at the price you're willing to pay.

I didn't know much about any of this stuff when I got started.. If you keep reading, you'll get new ideas. Go wander some hardware stores. Poke around an RV dealer, see what they've done. Then do the opposite
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Old 06-12-2015, 12:50 PM   #60
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Painting elastomeric paint will reduce it's effectiveness. You want it to be white.

I'd advise you to go to a local hardware store such as Ace Hardware and see what they sell. The one around here had several choices for elastomeric paints. Read the labels, see which one has the qualities you want at the price you're willing to pay.

I didn't know much about any of this stuff when I got started.. If you keep reading, you'll get new ideas. Go wander some hardware stores. Poke around an RV dealer, see what they've done. Then do the opposite
Cool beans. Thanks for the advice.
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