Solar Radiation and Electrical Enclosures

Before I get started, I should mention that I’m quite fond of the sun. Now, I don’t spend a lot of my time working on a “bronze god” kind of tan, nor do I own the proper equipment that would have allowed me to observe, in first-person, the recent transit of the planet Venus (I did see quite a few amazing photos and videos on the internet, though). I did make it a point to be outside during the last solar eclipse that was visible in the Midwest. It was a perfect day for it too…a bright clear day in May 1994, my girlfriend & I had a lunch date, and we were lucky enough to get a table on the patio. Her father had a pair of welding goggles that she was able to borrow a lens from, and our server got us free dessert for letting her look at the eclipse through them. That’s one of a gazillion fond date memories I have with the girl that agreed to be my wife, two years later. Solar eclipse AND free dessert…it’s actually near the top of that list…

If I’m spending any time at all in the sun, though, I don’t take chances, because, as fond as I am of the sun, I am equally un-fond of sunburn. Which brings me to my topic today: solar radiation.

We are right in the middle of a very busy Cabinet Cooler season at EXAIR. Most of the applications we’re getting calls on are for indoor installations, but more than a few callers are in need of cooling for an outdoor electrical enclosure. A prime consideration in determining the total heat load for these is the heat absorption due to solar radiation, or “sun load.”

First and foremost, if you have an electrical cabinet outdoors, you can eliminate sun load by simply preventing the sun’s rays from shining on it. If you can mount it to a north wall, or get it under an awning, that’s ideal. And it’s all you have to do.

If you can’t control the mounting location, and your enclosure has to be exposed to direct sunlight, then you’re most likely going to need a significantly higher amount of cooling. Just this morning, I helped a caller determine the heat load on a small outdoor enclosure in the deep South…before accounting for sun load, they were looking at a total heat load of 450 BTU/hr, which our smallest Cabinet Cooler System is more than capable of handling. Adding in sun load, though, their mid-day/midsummer heat load was over 2,500 BTU/hr, which would require a system that consumed more compressed air. We encourage using as little air as possible; they’re looking at what it would take to put an awning on it.

If you have any say in it, the color/finish of the cabinet’s exterior makes a big difference, too. A polished aluminum, or white painted, surface will absorb less than 20% of the solar radiation as a black cabinet. And if it’s grey, the lighter the better.

Like I said, it’s a busy Cabinet Cooler season here, but we always have time for, and welcome, the next caller. Don’t forget, you’ll receive a free AC Sensor with any Cabinet Cooler purchase through then end of July…for anyone who loses track of the calendar (like I do), that’s next week. Anyway, we look forward to seeing how we can help. Give us a call!

Russ Bowman
Application Engineer
EXAIR Corporation
(513)671-3322 local
(800)923-9247 toll free
(513)671-3363 fax

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