Calculate Heat Loads from the Sun for Outdoor Control Panels

I am always happy to see the sun rise each morning. But, electrical panels that are exposed to the sun are not.  Solar heat adds significant BTU’s to the overall heat load in an electrical panel.

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A customer had a VFD to control a 300HP blower motor for a dust collection system. The VFD was getting an over-temp error and shutting down the system.  He contacted EXAIR to get a Cabinet Cooler to keep the VFD cool.  We went through our normal questions to determine the heat load, i.e. the size of the cabinet, the temperature inside, the temperature outside, the maximum external temperature and the desired temperature.  As we went through the questions, he stated that the cabinet was located outside.  This is not an issue for our Cabinet Coolers as EXAIR has NEMA 4 and 4X (IP66) Cabinet Coolers.  It did stem another question; was it under cover?  He mentioned that it was not.

NEMA 4 Cabinet Cooler
NEMA 4 Cabinet Cooler

Generally in calculating cooling capacities with our Cabinet Coolers, we size the units by adding the ambient heat load and the electrical heat load. With the panel exposed to the sun, this adds another component to the total heat load.  To get an estimation on the amount of solar heat, color becomes a big factor as the darker colors will draw more heat.  Here is a good approximation to follow:

Solar heating by color
Solar heating by color

In this application, the customer had a gray panel, a common color. With an exposed surface area of 16 ft^2 (1.47 M^2), we would have to increase the heat load by 16 ft^2 * 7 Watts/ft^2 = 112 Watts.  This equates to 112 Watts * 3.41 BTU/hr/Watt = 382 BTU/hr of added heat.  (Or 112 Watts * 0.86 Kcal/hr/Watts = 96 Kcal/hr).

If an electrical panel is outside and cannot be shaded from the sun, we can still protect the sensitive components inside.  With the proper sized Cabinet Cooler, your equipment will remain running cool.  If you need help to determine the correct Cabinet Cooler, inside or out, you can either contact an Application Engineers at 800-903-9247 or fill out our Cabinet Cooler Sizing Guide.

John Ball
Application Engineer
Email: mailto:johnball@exair.com
Twitter: @EXAIR_jb

 

“The sun” image courtesy of Lima Andruška, https://creativecommons.org/licenses/by-sa/2.0

Replacing Cooling Fans with Cabinet Coolers

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Which device is causing the overheating condition?

When an electrical device mounted inside a control panel goes offline due to an overheating condition, it can be difficult to determine which component in the panel is the root cause.  There may be an intermittent heat load from a variable frequency drive that isn’t present when troubleshooting, making things appear to be OK.  Or, the overheating condition may only happen during peak operation on days with high ambient temperatures.

Fortunately, no matter the root cause, an EXAIR Cabinet Cooler can maintain temperature within the enclosure at a desired set-point, eliminating overheating conditions and lost throughput due to downtime.

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We investigate to determine what is housed inside of our customer’s electrical control panels.

When calculating heat load, EXAIR Application Engineers consider the components within the control panel.  We inquire with our customers regarding devices such as VFD’s, which may lead to temperature spikes, or fans, which actively remove heat (albeit that they often force dirt and debris into the enclosures they’re designed to be cooling).

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To accurately calculate heat load, we require the diameter of any fans installed on the enclosure.

Fans can be particularly important, because with the installation of any EXAIR Cabinet Cooler, all external fans will need to be removed, and their openings will need to be sealed (internal fans can remain in place).  So, this means we have to account for any heat the fans may already be removing from the application, even if it isn’t enough to keep the enclosure cool.

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Measure any fans used to bring ambient air into the enclosure.

In order to determine the amount of heat a fan is removing from an application, we consider the diameter of the fan, which corresponds to a typical air flow volume in CFM (cubic feet per minute).  We then consider that 1 BTU/hr. is the amount of heat required to raise the temperature of one pound of water by 1 degree Fahrenheit, and it is also the amount of heat needed to raise/lower the temperature of one cubic foot of air by 1 degree Fahrenheit in one minute.  This means that for every CFM the fan is moving, we are reducing the temperature of the air by 1°F .  To put it another way, we remove 1 BTU/hr. for every °F * every CFM the fan is moving.

As an example, a 3″ fan will move 22 CFM.  In an enclosure with a current temperature differential of 15 degrees Fahrenheit, this fan is removing 330 BTU/hr.

15°F * 22 CFM = 330°F*CFM

15°F

x 22 CFM X 1 Btu/hr = 330 Btu/hr

CFM °F

The fans holes should be covered up with sheet metal using rivets, caulk/sealant, duct tape or other ingenious methods you know of. But please cover and seal the cabinet as well as you can.

Using the Cabinet Cooler Sizing Guide and the experience of the EXAIR Application Engineers, we can accurately calculate heat load of an overheating electrical control panel.  When you need help with determining which Cabinet Cooler to use, contact an EXAIR Application Engineer.  We’re here to help.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE