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I built an outdoor enclosure which contains electronic devices (cable modem, router, battery backup, MCU, etc) for a long-distance internet connection. The enclosure is made of insulated metal panels (approx R-15 insulation value).

Volume of enclosed space is approx. 3 cubic feet.

I currently have a squirrel-cage blower pushing hot air out the top, with a cool-air vent at the bottom on the opposite side, to generate cross-component air flow.

However, when the sun hits this enclosure from about 10am until 2pm, it's heating up to 105+F. (Outdoor ambient is about 85F, 50% RH)

The outside of the enclosure, which is painted dark green to blend with surroundings, is too hot to touch after 10am.

I am looking for suggestions to cool this enclosure to 80F or less, while hopefully keeping costs at $50 USD or less.

I realize miniature thermoelectric coolers exist, but they are cost-prohibitive, starting at around $1,000 USD.

There is a 110VAC, 20A circuit available in the enclosure.

I can't paint the unit white, due to aesthetics etc.

One possibility is to install a sun shield board a few feet from the enclosure to block direct sunlight.

I've also considered building a thermoelectric air conditioner, but I'm not sure how to calculate the BTU output to determine size needed for this space.

Any suggestions appreciated!

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    \$\begingroup\$ any reason that you couldn't just cover the box with some non-metal material? A piece of plastic with an air gap will set you back just a few dollars and will keep the case from absorbing broad spectrum energy \$\endgroup\$
    – b degnan
    Jun 12, 2016 at 19:03
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    \$\begingroup\$ You could paint the enclosure white, but it would probably be more effective to add some very loose thin fabric of whatever colour you want to scatter the direct sunlight. \$\endgroup\$ Jun 12, 2016 at 19:04
  • \$\begingroup\$ Put it inside out of the sun's full glare. Adding a few more metres to a long-distance internet connections shouldn't be a hassle. Or bury it. \$\endgroup\$
    – Andy aka
    Jun 12, 2016 at 19:10
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    \$\begingroup\$ If outdoor ambient is 85, no way are you getting to 80 inside unless you basically refrigerate the interior. I propose two things, build the largest shade you can, shading as much of the area around the box as possible, as well as the box itself, and increase the airflow as much as possible by adding extra blowers. Finally, settle for a peak temp of more like 90F inside. \$\endgroup\$
    – user57037
    Jun 12, 2016 at 19:43
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    \$\begingroup\$ Apply some shade, by all means, and consider parking some thermally massive items inside the case; the peak noon temperatures may be scary, but what are daily averages like? Bricks are inexpensive. \$\endgroup\$
    – Whit3rd
    Jun 13, 2016 at 7:28

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I would try 3 solutions, possibly 4:

1) Implement a rigid sun shade as described by user113791.

2) Add pvc pipe to intake vent so it is pulling in the coolest air possible, at ground level or below, or from the garage which usually has cool air at ground level.

3) Add extra insulated fan protected from rain that blows air onto the enclosure as broadly as possible to cool off the metal enclosure.

4) Add an internal fan to blow air on just the crucial components-those that are damaged by extensive heat.

These 4 steps combined are low cost and should push the temperature down by a useful amount. Refrigeration would cost so much you might as well move the enclosure indoors.

NOTES:
A) If temperature drops below freezing or dew points become high then condensation of moisture on crucial parts is possible. As long as power is ON and some internal fans run, self-heating should keep moisture from forming internally.

B) Under freezing conditions the external fans should be cut off. You can do this with an insulated switch or install thermal cut-offs that open at 45deg F or below. You do not want the fans to be blowing snow around or have power when they freeze and cannot rotate.

C) Make sure the intake vent cannot pull in rain, heavy moisture or snow. This would corrode exposed contacts and circuit boards over time.

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  • \$\begingroup\$ Thanks Sparky! I am testing a rigid shade to see if there is noticeable temperature reduction. \$\endgroup\$ Jun 13, 2016 at 2:35
  • \$\begingroup\$ Air intake is already at ground level. No basements nearby ... nearest building is about 1000 ft away. #4 is a good idea too. Also I have a remote 110vac relay installed to control fan power. \$\endgroup\$ Jun 13, 2016 at 2:37
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Given your fairly restricted circumstances (aesthetics, budget), your best ROI might be to add a matching color sun shade (if it must also be green. Else paint it a more reflective and UV longevity color) and position it relative to the solar patterns of the hottest 6 months of the year so that you get the actual protection you are needing. One other suggestion, make sure the sun shade does not force rain right onto/into your enclosure and make sure it doesn't become a sail- you might cut a few slits into the protective sun shade to allow wind to pass through. My initial two cents.

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  • \$\begingroup\$ I am testing a sun shield to see if this provides an adequate temperature drop. If not I will have to pursue other means. \$\endgroup\$ Jun 13, 2016 at 2:32
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Think about to bury the electronic enclosure into the ground. 1 or 2 meters deep you will get friendly temperatures nearly independent to the sun. Of course you need a really water tight enclosure.

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