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Ken Moore

Heat Load Calculations what do you use?

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When you do the calculations for an enclosure, what do you use for the heat source values. Some vendors give a BTU/Hr for their devices, but many do not. I have used various estimations over the years, but was wondering what other folks did. On some panels, I use the power inputs, and the conversion efficiencies to determine estimated heat generation, but I never liked that method. What do you use to determine if an enclosure needs a fan or air conditioner for heat removal?

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Some of the enclosure vendors have good software that can do some of the calculations for you, like Rittal has software called Rittal Therm that can give an approx value of heat dissipated by device, and it is reasonably accurate. Most of the larger devices, (drives transformers ect) have numbers available somewhere if they are from a reputable supplier. One of the lines we sell for VFD's has nothing in their books, but when we asked tech support they sent over a pdf with heat loss #s by part number. Was very helpful. It is nice too to have documentation to help show a customer why the 1'x2' drive he ordered needs a 36x48x16 or larger enclosure or an expensive cooling unit.

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Hoffman has a thermal calculator on its Thermal Management website. I've found most manufacturers list the heat output of their devices in Watts, not BTU/Hr. You'll usually find this in their spec sheets as "Watts Loss." But whether or not you'll need air conditioning is determined by these factors: 1. The surface area and volume of the enclosure. 2. How much of that surface area is exposed to the air (so for a wall-mounted panel, you'd need to subtract the area of the back face from the total surface area) 3. The insulation value of the panel. 4. The max. temperature outside the panel 5. The max. allowable temperature inside the panel Also, it matters where the panel is located, if it's in direct sunlight, and even what color it is. Obviously if it's outside a darker-colored panel is going to absorb more heat.

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