What helps with thermal transfer or heat from the sun?

[Hooker-SKO]

So I have put an 8,000 BTU window unit AC in one of the E exit windows of this bus. Ratings say the AC should cool 250 sq feet and the bus cabin is 180 sq. feet. This AC doesn't even touch it. I've put reflectix in the windows, and even hung double layer silver tarps over the walls and windows and still not cooling. So I tarped off the back 1/3 of the bus so now we're talking about 80 sq feet. It'll cool it down after the sun goes down. Leaving the AC on all night, by about Noon, you can feel the heat radiating off the ceiling and the tarps hung on the walls with reflectix over the windows and it can't keep it. Temp slowly rises to 80 then 85 and won't cool back to 72 until well after dark again.

I realize this is all factory insulation and nothing else has been added. I did end up putting a silver tarp over the top of the bus in that back 1/3 section and it seems to help just a little. I'm just wondering does anyone else know for a fact what works as a thermal barrier so hot sun isn't transferred in this tin can? I have a feeling it would work much better if I could park in the shade, but where I'm at, there is no shade to park under.

I don't want to spend a fortune on things like painting the roof with products like Silver Seal or TropiCool, and take down the metal on the ceiling and use some type of insulation if it's not going to do any good.

Anyone have any input on what they've done that worked to where they can park in the hot sunlight and a reasonable size AC unit can keep up?

 

[mmoore6856]

we have a 40 ft dognose bluebird. we cool with a 5k unit quite easy in the 100 degree and have no shade. unfortunatly the most important step is to insulate as i have recorded 149 on the roof skin of it when it was still yelow during our build. at this point you have few easy options if you dont want to redo he inside. buy a digital temp gun at harbor freight and search for your heat as its everywhere. to start look for or make insulated tarps and cover your bus. even cheap white spraw painthelps if you can stick some 2x2 on top to help create some air space between it and your roof helps. build a wood deck to help get the heat away from your roof. try to have your tarp come down the sides as far as you can. we even put a pink foam door between the drivers seat and the back as the windshild is also a problem. so just use your temp gun and find your heat

 

[Hooker-SKO]

we have a 40 ft dognose bluebird. we cool with a 5k unit quite easy in the 100 degree and have no shade. unfortunatly the most important step is to insulate as i have recorded 149 on the roof skin of it when it was still yelow during our build. at this point you have few easy options if you dont want to redo he inside. buy a digital temp gun at harbor freight and search for your heat as its everywhere. to start look for or make insulated tarps and cover your bus. even cheap white spraw painthelps if you can stick some 2x2 on top to help create some air space between it and your roof helps. build a wood deck to help get the heat away from your roof. try to have your tarp come down the sides as far as you can. we even put a pink foam door between the drivers seat and the back as the windshild is also a problem. so just use your temp gun and find your heat

I've done exactly that with the heat gun. The heat is the glass and the ceiling. The glass is like 130 and the ceiling is around 117.
So insulation does help that much? I'm not against insulation at all. I just don't want to do all that work and the expense and it not work. Here I thought we insulated more for winter than summer but it appears the opposite. My little diesel heater took a bit to get it warmed up inside, but it did get it done and once it did, it kept it warm. That's in 18-25 degree weather.

What type of insulation did you use.

 

[Rucker]

They don't call these tin can tents for no reason.

Get one of those thermal temp measuring devices as Moore says. Find the sources of heat.

1. Reduce insolation by shading. There must be circulating air under the shade for it to work.
2. Put window covers on all sun-facing windows. I have 1" polyisocyanate, but even white styrofoam will help. Very flammable, so smart to wrap it in something to reduce contact flammability.
3. Add positive ventilation to circulate the hot air out of the bus.
3. Increase reflectance by painting the roof white.
4. Insulate the cavity between the metal roof and the interior. This will make a huge difference.
5. Thermally break all metal surfaces in contact with the roof. This means put something over the roof ribs so the metal surface can't conduct heat to the interior air. (Do this also to avoid condensation issues in the winter).

To the extent you do any of these your total heat gain inside the bus will drop. In my experience, nothing short of a minisplit brings the temp down inside my shuttlebus. The way these buses are built they just added BTUs to the A/C systems to overcome the heat.

 

[Hooker-SKO]

They don't call these tin can tents for no reason.

Get one of those thermal temp measuring devices as Moore says. Find the sources of heat.

1. Reduce insolation by shading. There must be circulating air under the shade for it to work.
2. Put window covers on all sun-facing windows. I have 1" polyisocyanate, but even white styrofoam will help. Very flammable, so smart to wrap it in something to reduce contact flammability.
3. Add positive ventilation to circulate the hot air out of the bus.
3. Increase reflectance by painting the roof white.
4. Insulate the cavity between the metal roof and the interior. This will make a huge difference.
5. Thermally break all metal surfaces in contact with the roof. This means put something over the roof ribs so the metal surface can't conduct heat to the interior air. (Do this also to avoid condensation issues in the winter).

To the extent you do any of these your total heat gain inside the bus will drop. In my experience, nothing short of a minisplit brings the temp down inside my shuttlebus. The way these buses are built they just added BTUs to the A/C systems to overcome the heat.

You listed all the things I figured I could do. I was just wondering if after all that does it work? I don't want to spend a fortune and not get cool, but obviously some of my plans have changed, IF I continue to build it. Like, I wasn't going to have a deck on top. I probably will now, or at least a cat walk and more solar to shade the roof. I was hoping someone had a magic bean for this but it doesn't appear so.

 

[Hooker-SKO]

So what types of materials is anyone having success with as far as insulating the ceiling? How about spray foam? Can anyone say for sure if it really works or are they just going to say it works because they spent $2000-$2500 to have it installed? I do certainly understand about the thermal transfer science and using things like butal tape and very little contact with the metal as possible etc. I see some of these people spend the big money on foam and then fail at their framing which really defeats the purpose almost of spending the big money to do it right. In short, just wanting to know if the spray foam is worth it? I mean, if I can use a different product that's half the cost, and spray foam is only marginally better, then I'll save my money. If it's night and day difference and works twice as well as other products that are half the cost, then I can see spending the money if that makes sense.

 

[turf]

ima fan of sprayfoam.

my bus came that way from the factory, i dont have windows either so lots of surface gets covered.
it works great imo. it takes twin 15k rooftops to cool my bus, but you'll need a sweater when they're going.

i get some wicked thermal transfer. the bus can be nice and cool, but the screws that hold up the roof panels are screwed into the hat channel. you can touch one and almost burn yourself.

i consider the thermal transfer a feature and evidence that the sprayfoam is doing its job.

the amount of heat transfer with just the screws is hardly worth the effort to solve it.

 

[rossvtaylor]

Spray foam is great. Pink foam board is great, too. For thinness, with good thermal barrier properties, I have found that the ceramic felts or ceramic papers are pretty impressive. I have a couple of rolls for my own Crown conversion and they'll get layered inside the exterior surfaces. Look up EHP Rollboard or the Ceratex products from Minseal (short for Mineral Seal), in Tucson. I've found them to be very similar, except in price...Ceratex is about half the price. They were developed specifically for creating a barrier between engine compartments (in aviation) or generator bays (in ambulances...or are they ambuli?) and it's impressive stuff. I've found no other thin product which actually makes a difference.

 

[Hooker-SKO]

Anyone else have any recommendations for roll on roofing products? I've heard of TropiCool. It appears to be a bit expensive and for success I hear it requires multiple coats. As in several, not just a couple coats. I've heard from a guy who painted the roof of his RV with Silver Seal and says it works great and also seals any minor leaks and strengthens joints where you'd have vents and such. It appears to be much cheaper but is silver in color but offers reflective properties and he swears it helps significantly and added fact of no leaks he highly recommends it. And then there's Kool Top Aluminum Roof Coating that also claims to help seal any leaks and it's much cheaper than TropiCool. Anyone have any input on these type products???

 

[La Camioneta]

https://americantarping.com/collect...ade-kit-pt300-mountain?variant=40304881893532

How well would something like this work while parked? I'll have a roof rack and no solar or rooftop a/c it would interfere with.

If you had permanent shading of your roof, how much does that cut your a/c needs? Add awnings on both sides, and you'd be completely shaded.

What's the difference in a/c performance from full-sun exposure to parking in the shade?

 

[Tin Roadtube Vagrant]

I'm counterculture on cooling the Tube. I don't mind the heat retention since I may be sitting over 2.5' of frozen lake ice. Even in cold climate the Roof is still what matters. In our previous bus with a preway diesel-fired stove the roof could exchange heat so fast (esp@night) you barely felt a thermal cline till you laid on the floor. It really is all about the roof.

 

[Rucker]

You listed all the things I figured I could do. I was just wondering if after all that does it work? I don't want to spend a fortune and not get cool, but obviously some of my plans have changed, IF I continue to build it. Like, I wasn't going to have a deck on top. I probably will now, or at least a cat walk and more solar to shade the roof. I was hoping someone had a magic bean for this but it doesn't appear so.

Correct, no magic bean.

At the end of the day the tin can only lends itself to compromises in cooling.
The more you moderate the temperature inside the bus from outside ambient temp the cost becomes exponentially greater.

You have to start with answering the question 'What will I use it for?' Being clear with yourself on that will help you define your real requirements.

For instance, my system is designed for four days' boondocking. This determined how big the battery and solar were, how much water storage, etc.

In your case, how often will you find yourself in the sun? Maybe you can do what some others have done, just plan on being outside the bus during the hottest part of the day.

Others need four-season functionality so they have basically superinsulated the interior. There are plenty of videos on spray foam interior worth watching.

 

[Hooker-SKO]

https://americantarping.com/collect...ade-kit-pt300-mountain?variant=40304881893532

How well would something like this work while parked? I'll have a roof rack and no solar or rooftop a/c it would interfere with.

If you had permanent shading of your roof, how much does that cut your a/c needs? Add awnings on both sides, and you'd be completely shaded.

What's the difference in a/c performance from full-sun exposure to parking in the shade?

I think you're right. From all the responses, it appears it's going to come down to shade. And self shading would work. Like someone mentioned, make sure there's an air gap between whatever you cover the top of the bus with. So like I'm think NOW of a roof deck and have it at least 6 inches from touch the roof, so that'll break the thermal trasfer and believe it or not, an air gap is a form of an insulator. This is one reason why newer homes now put their AC vents over or under the windows. As the air is flowing across the windows, it's making an invisible air curtain. So if a guy was to put a roof top deck over his bus for shade and had hooks on the side of the deck to hang shade down the sides while parked, it would likely do the trick. Harbor Freight has some black tarping that's not water proof, but it's for shade. I bought one to check out. It's of great quality and thickness. You can even see through it so you'd still be able to look out your windows. The other great thing about it, It appears to me it would work great as mosquito and fly netting so that you could keep the flies and skeeters out of your bus and open windows if you wanted to. They are available in different sizes. https://www.harborfreight.com/12-ft-x-20-ft-mesh-all-purposeweather-resistant-tarp-60584.html

 

[Meathead]

The stuff Hooker is talking about is essentially tennis court windscreen. It’s 90% windscreen and 90% shadescreen. If you want custom sizes and colors I recommend Ball Fabrics in DeLand, FL. I’ve done business with them for years. Check out their website for a general understanding of their products and then give them a call. There are factors to consider that you just can’t get from a website.

[emoji3522]Dave

 

[magnakansas]

buses in north africa

imagine two roof skins on your bus. the YOU have and another about 4" - 100mm higher. the second roof is mounted on standoffs, little towers, columns. this allows your own shade every where you go. and some airflow under the roof taking all the heat. these are usually metal. I have seen two others, one fiberglass and one that appeared to be kevlar honeycomb.

william

 

[Meathead]

Yep. Shade.

I’m I Houston this summer, at a campground. 27 days in August were at or above 100*F. I would not be here except for a family member undergoing radiation treatment at MD Anderson Hosp.

People are investing in these



I am NOT recommending this and I will not buy one but ppl are spending aprox $1000 for one of these systems.
I’m just posting this to illustrate a point. Seems to work.

Me. I moved to a spot under a tree [emoji3]

[emoji3522]Dave

 

[rossvtaylor]

imagine two roof skins on your bus. the YOU have and another about 4" - 100mm higher. the second roof is mounted on standoffs, little towers, columns. this allows your own shade every where you go. and some airflow under the roof taking all the heat. these are usually metal. I have seen two others, one fiberglass and one that appeared to be kevlar honeycomb.

william

Exactly - I was going to mention these exact buses, made by MCI for the Saudi government (I think). They did some of those double roofs on some MC-5s and possibly other models, later, too. Apparently some of those ended up in Texas.

 

[Hooker-SKO]

imagine two roof skins on your bus. the YOU have and another about 4" - 100mm higher. the second roof is mounted on standoffs, little towers, columns. this allows your own shade every where you go. and some airflow under the roof taking all the heat. these are usually metal. I have seen two others, one fiberglass and one that appeared to be kevlar honeycomb.

william

Sounds exactly as I'm talking about making a roof deck and keeping it about 6 inches from touching the roof to provide that air gap between the roof and bottom of the deck. I didn't want a roof deck at first, but I think I do now. Or maybe 2 rows of solar panels, 1 on each side of the roof, and a cat walk down the center with openings for the Maxx Air fans/ Emergency Exits.

Then having hooks on the sides to be able hang those black shade tarps for use when parked. These tarps have grommets sewn in at the corners and every 2 feet along the perimeter. They could either just hang down the side of the bus, or a guy could rig up poles with tethers too to work similar to an awning to provide even more shade on either side of the bus. I believe this will be my plan eventually.

 

[shorthair-SKO]

imagine two roof skins on your bus. the YOU have and another about 4" - 100mm higher. the second roof is mounted on standoffs, little towers, columns. this allows your own shade every where you go. and some airflow under the roof taking all the heat. these are usually metal. I have seen two others, one fiberglass and one that appeared to be kevlar honeycomb.

william

The added second skin 4" above the stock roof would have to be well attached or it will part company with the bus at freeway speeds and could be a considerable liability risk. But if mounted well it should help considerably.

 

[nolahusker]

That rating is based on R-19 walls and R-30 ceilings and slab-on-grade construction. You are far from that. I’m an HVAC designer and forensic engineer by trade. You’re going to need way more than that if you haven’t insulated the heck out of your bus and replaced the windows with heavy tint dual pane.