Unique climate control technique.

[KevinLee]

I saw a video not long ago with an idea for keeping a box truck cool in the summer, didn’t think I would be able to do it myself at the time but things have changed and I thought I might give it a try. Of course, I can’t find the video again now. Basically, instead of just sandwiching two or three inches of insulation between the outer and inner walls, the guy framed out his walls about 4” thick and put an inch of insulation on both the inner and outer walls, leaving a 2” gap in between. Then he drilled holes in the floor inside the gap, made sure that there was air flow between the walls and the ceiling, and installed a roof vent inside the air gap in the ceiling isolated from the living space by a hatch.

It might be hard to picture if you haven’t seen the video, but anyone who has will know what I’m talking about. Has anyone seen it? Can anyone provide a link? Any opinions?

 

[tx2sturgis]

Putts built something similar with his step-van, look for post number 29 on this page:

https://vanlivingforum.com/showthread.php?tid=23928

Or the permalink for post #29 is here:

https://vanlivingforum.com/showthread.php?tid=23928&pid=291284#pid291284

The air gap is called a 'plenum' and its used to remove heat radiating (and convecting) into the living space before it can heat up the interior.

.

 

[KevinLee]

Thanks! That’s exactly what I was trying to explain. Not sure if it’s the same guy/van, but it’s the same basic idea. This one gives me a couple of new ideas, like sideways airflow through the ribs. It would be easier for me since the ribs in my van are only 1” thick. I was planning on spacing out the walls with 1X3’s, which would be easier to bore holes in. I’ll try to post here if I can make some progress on this idea.

 

[Matlock]

.... spacing out the walls with 1X3’s, which would be easier to bore holes in.

I have a total of 3" insulation on walls and ceiling of my box van with 1x8 pine planks screwed to the 1x3's I glued to the walls.

No measurable advantage of having an air space in between insulation sheets. You still need to circulate fresh air inside and warm and cool that air relative to what's going on outside. Open a window or door and that envelope you created with a hollow space will be a non-issue.

Just my 2¢ here as I too over-thought the process and decided it might be worth trying something simple and traditional first. Turns out about a 15* difference between the cab and box interiors on a 90* day. Very stuffy until I turn on a exhaust fan, of course that's where all that insulation means nothing. Same thing happens in the winter cold. Course in the cold you have to contend with inside moisture removal.

My box is 10x6x6 finished inside. Buying a larger truck with a 15 or 17 foot box with 8' ceiling would give you room to do what your thinking about and still not killing interior space.

Again, just my ol 2¢..

 

[KevinLee]

I do have a box about 14’X7.5 and about 7.5 high, so I have plenty of room for extra thick walls/ceiling. The video that originally got me thinking about this was from a guy who was camping in the desert, and staying cool was the main goal. I think his idea was that it would stay as cool in full sunlight as if it was in the shade. The idea seemed to be venting the heat that penetrates the outer walls before it gets to the interior. Ultimately, if it’s 100 degrees out, sooner or later it will be 100 degrees inside without AC or something. Where I am now it seldom gets very warm but I was surprised to find out that even sitting in direct sun on a 75 degree day it only gets up to about 85 inside without any insulation. I figure white paint and no windows for the greenhouse effect is why. We’ll see what happens when I put in the two windows I have.

 

[bullfrog]

My home built trailer is an all white box with no windows and it stays several degrees cooler most of the morning if opened up at night on 100 degree days. White plastic vent lets in some light but not much heat as it is usually out of the sun being on a wall instead of the roof.

 

[B and C]

They make vent covers to go over vents so the vent can remain open in the rain and will provide shade to the cover. Of course some light gets in but this is a good thing.

 

[rokguy]

Not so much as an insulation idea but I decided to install small round screw down hatches (from a marine store) into my wooden floor. While moving the vent hatches are (lid screwed down) blocked off so no road pollution enters the box.
When parked simple unscrew the lids combined with the roof vents open it will move air through the living area quickly.
These vents require a 4 - 5 inch hole to be cut in the floor for the surround, on mine I add flyscreens to keep out the bugs.

After a hot summers day these vent draw cold air up from the ground, pushing hot air out the roof vents.

 

[highdesertranger]

that's a great idea. I thought of doing that myself. back in the day they made screen that would screw in in place of the hatch but I haven't been able to locate those. how will you incorporate the screens. anyhow thanks for the great tip. highdesertranger

 

[MrNoodly]

I think some type of artificial shade is more effective than insulation. Block as much sunlight as possible from ever touching the vehicle.

 

[bullfrog]

I used 6" square concrete driveway grates that had a removable inset grate held in with screws. They were about 1 1/2" deep with a 4" round plastic pipe connection on the rear, I just removed the grate and laid screen under it and trimmed off the excess then used a slip on pipe cap to seal when traveling. Just glued them in as they are plastic. I do like those better as they are flush mounted.

 

[rokguy]

that's a great idea.  I thought of doing that myself.  back in the day they made screen that would screw in in place of the hatch but I haven't been able to locate those.  how will you incorporate the screens.  anyhow thanks for the great tip.  highdesertranger

highdesertranger,
I simply cut flyscreen a little oversize to the hole cut, so when you pushed the round plastic insert in the hole, it naturally tensioned the screen between it and the floor. They are simple, available everywhere, light weight and easy to replace if they get damaged.

However its best to position them where you are not likely to stand on them when open, a corner near a built in sofa or bed is ideal as you have a nice cool breeze drawing in to cool things down.
In winter I've found they have the opposite effect after driving as the heat from the drivetrain is drawn up into the box (roof vents closed) warming the place for a short while, then close em up.

NB Not recommended to drive with them open.