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

Calculating and Choosing the Right Cabinet Coolers

“I need one of your Cabinet Coolers for my control panel, the dimensions are 24″ H x 30″ W x 16″ D, what do you recommend?”. This is a very common inquiry we receive when discussing our Cabinet Cooler Systems for the first time with a potential customer. While it would be nice if it was a simple as using just the dimensions, there is more that goes in to making the proper selection.

Following explains how to go about calculating and choosing a Cabinet Cooler System. If, at any time, you prefer EXAIR to calculate and assist with your choice – contact our Application Engineering department and we will be happy to get you up and running.

Our Cabinet Coolers are sized by cooling capacity in Btu/hr., which range from our lowest of 275, up to our largest Dual System providing 5,600 Btu/hr. Now if you know the Watts loss , we can convert this over to Btu/hr. (Watts X 3.41 = Btu/hr.). If you are unsure, we need to determine the current heat load of the cabinet by using the dimensions, current temperatures (internal and external) and worst case external temperature and the desired temperature you are looking to maintain inside the enclosure. To simplify this process, we offer our Cabinet Cooler Sizing Guide.

Sizing Guide
EXAIR’s Cabinet Cooler Sizing Guide

The current internal and external temperature will determine one of your ΔT’s (temperature differential), which is used to determine a multiplier from the table below. We then take your maximum external temperature and your desired internal temperature to give us another ΔT and multiplier. Use the sq. ft. of the cabinet and multiplying it by the temperature conversion multipliers. Add these sums together to determine the total heat load in Btu/Hr. This value will help you to choose the proper Cabinet Cooler system to solve your heat problem.

Temp Conversion Table

Now that we have the heat load properly calculated, we need to know the NEMA class of the enclosure. We offer NEMA 12 for general use where there aren’t any corrosives or liquids present, NEMA 4 for wet or damp environments and NEMA 4X for wet, corrosive applications.

We offer Thermostatically Controlled Systems with available voltages of 120VAC, 240 VAC or 24VDC. This is the most efficient means of operation as the unit only operates when the internal desired temperature is exceeded. In addition, we also offer Continuous Operating Systems, providing constant cooling and positive pressure into the cabinet. Each system  includes a filter separator for the supply line to keep water and dirt from entering the cabinet as well as duct tubing.

Of course, if you need any additional assistance, you can always contact one of our application engineers. If you can provide a little bit of information, we can do the calculating and get you on your way.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN