Re: [AFMUG] How to reliably cool a small enclosure in direct sunlight?

Mon, 16 Jul 2018 08:46:10 -0700

When I was building the Long-EZ, there was a debate among fiberglass airplane builders about the tolerable temperatures for ambient-temp cured fiberglass/epoxy structures. The point being that too high heat would be "very bad" for a fiberglass/epoxy airplane.

So Burt Rutan and his crew did a bunch of tests using various colors. What they found was that pure white had the lowest heat gain of any color. Black the worst. Silver was right up there with gray. Almost any tint had a significant heat gain over ambient.

I painted my EZ pure white with no tints whatsoever. It did have blue/gold trim colors, but the trim was basically just accent stripes on the fuselage and winglets.


bp
<part15sbs{at}gmail{dot}com>
On 7/16/2018 8:31 AM, Chuck McCown wrote:
Foil or shiny silver stuff seems to draw more heat than black paint for some reason. 
 
I think it is black in the infra red spectrum. 
 
Just leave a chrome plated wrench out in the sun for a few hours. 
Black wrench will be much cooler. 
You can actually pick up the black wrench but you can get a blister from picking up and holding a chrome one.
 
One of my kids still has a scar from the chrome tab of a car seat belt. 
We knew she hated to be put in the car seat, figured all the screaming was just the normal objections. 
 
Sent: Monday, July 16, 2018 9:24 AM
Subject: Re: [AFMUG] How to reliably cool a small enclosure in direct sunlight?
 
I wonder if the foil faced foam would work without having to paint and stucco.
 
Cameron
 
On Mon, Jul 16, 2018 at 10:07 AM, Chuck McCown <[email protected]> wrote:
Doesn’t look like I emailed the test results to anyone. 
We started adding foam insulation with stucco and then white paint on the exterior of lots of stuff. 
An amazing combination. 
 
Sent: Monday, July 16, 2018 9:00 AM
Subject: Re: [AFMUG] How to reliably cool a small enclosure in direct sunlight?
 
Here is one snippit about exterior insulation:
 
Infrared camera proved what I proved years ago.  The exterior insulation
does the trick.  A wall in shade is the same temperature (inside) as a wall
in sun.  Therefore, false roof does not decrease heat flux.  I spent one
whole summer testing all these assertions.  Multiple boxes with telemetry.
Paint, sun shades, vents, etc etc.  White paint and exterior insulation does
the job.  Nothing measurable came from adding a shade to that combination.

But to prove it once again, I had Jeremy use the infrared camera to measure
all the walls and ceiling in Ticaboo.  Sunny walls were no warmer than those
on the shade side.
 
Sent: Monday, July 16, 2018 8:54 AM
Subject: Re: [AFMUG] How to reliably cool a small enclosure in direct sunlight?
 
On peltier you also have to locate the power supply outside of the box. Or at least that is what I found. The heat load from the PS was always more than the peltier it powered could keep up with. Everything has a bit of inefficiency built in that shows up as heat.
 
On Mon, Jul 16, 2018 at 9:52 AM Lewis Bergman <[email protected]> wrote:
Are you saying white paint outperformed heat shields? That's awesome info. I always thought heart shields were the best.


On Fri, Jul 13, 2018, 7:43 PM <[email protected]> wrote:
I did a bunch of trials one summer testing a variety of methods including heat shields, exterior insulation, interior insulation, convection ventilation, forced ventilation, peltier effect active cooling.
 
#1 by a long shot is painting the enclosure bright white. 
 
 
Sent: Friday, July 13, 2018 6:37 PM
Subject: Re: [AFMUG] How to reliably cool a small enclosure in direct sunlight?
 

1. Add a thermostatically controlled ventilation fan

2. Put a heat shield up on the south side of the enclosure. This can be just a plate of aluminum, painted white on the sun side, and mounted to the enclosure with 1" standoffs

We have a site like yours, and just the fan keeps the temperature below 120° F (49° C). I think if we added the heat shield we could drop it another 10° F.

 

bp
<part15sbs{at}gmail{dot}com>
On 7/13/2018 4:51 PM, Sterling Jacobson wrote:

I’ve got a few side of the house enclosures exposed to direct sunlight part of the day.

 

Inside the electronics are about ready to melt. Like 90C+ CPU temps.

 

These are about 3’ x 3’ x 12 deep or something like that, so not a lot of room.

 

What are you guys using to keep these things decently cool?




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