Calculating Heat Loads to Cool Electronic Cabinets

With the hot summer months upon us, elevated temperatures can cause shutdowns and interference with electrical systems.  For every 10 deg. C rise above the operational temperature, the life of an electrical component is cut in half.  With Freon-based coolers, higher ambient conditions make them less effective; and opening the electrical panel to have a fan blow inside creates a dangerous hazard as well as blowing hot, humid, dirty air inside the panel.  To reduce loss in production and premature equipment failures, it is important to keep the electrical mechanisms cool.  The EXAIR Cabinet Cooler Systems are designed to do just that.

To find the correct type and size, we need some information about your electrical panel.  EXAIR makes it easy with the Cabinet Cooler Sizing Guide.  This sheet goes over the important details to find heat loads, proper NEMA type, and options for easy installation. The EXAIR Cabinet Coolers range from 275 BTU/hr (69 Kcal/hr) to 5,600 BTU/hr (1,411 Kcal/hr) in cooling capacities.  And with the filled-out form, we can make sure that the correct model is recommended.  In this blog, I will cover a section of the sizing guide, the heat loads.

To properly cool, we need to calculate how much heat is being generated.  Heat loads come from three main areas; internal, external and solar.  Here are some methods to find the information needed for heat load calculations.

Internal Heat Load:  The internal load is the heat generated from inside the electrical panel.  This heat is produced from the inefficiencies of the electrical devices.  There are three ways that we can figure the internal heat load.

Step A: The simplest way is by hanging a piece of metal like a washer inside the panel for about 15 minutes.  We can get an average temperature inside.  The best place for the washer will be toward the top half of the panel, as heat rises.  In the sizing guide, you can mark the temperature next to “Internal temperature now”.

Step B:  if you know the electrical components inside that generate heat, a list can be made with volt/amp ratings, or watts.  This is very useful for new panels.  The major devices would be VFD (Variable Frequency Drives), power supplies, UPS, transformers, thyristors, etc.  We can calculate the inefficiency of the electrical components which will give us the internal heat load.

Step C:  If you know the amount of power going into the panel, and the amount of power leaving the panel, the difference will tell us the amount of power that remains for the electrical components.  We can take a 5% average as the heat loss.

External Heat Load:  The external heat load is attributed to the environment surrounding the electrical panels.  This is a standard temperature reading in oF or oC.  Only with Step A above, we will need to know the external temperature at the time that you measured the internal heat measurement.  This needs to be placed in “External Temperature Now”.  The difference to the internal temperature will give us the heat load per square feet (square meter).  Reference chart below.  We will also need to know the highest external temperature that the panel will see.  So, during the hottest day of the hottest month, the EXAIR Cabinet Cooler will still be able to keep your electronics cool and operational.

Solar Heat Load:  The solar heat is only needed if the panel is located outside without cover and exposed to sunlight.  For this type of heat load, we will need to know the color of the electrical panel.  Lighter colors will not absorb as much heat as darker colors.

Because there is so much information that is critical for proper sizing, the Cabinet Cooler Sizing Guide is the best tool to use to facilitate the calculations.  I gave examples above to find different ways to get the proper information.  Electrical shutdowns are expensive and annoying.  If you have interruptions from high internal temperatures, EXAIR Cabinet Coolers are a great solution.  They can be installed quickly and easily.  With no moving parts or costly preventative maintenance needed, they can run for decades in keeping your electronics cool.  For our U.S. and Canadian customers, you will receive an AC Sensor for free, a $58.00 value, as a promotional item from now until the end of August 2020 with qualified purchases.  How can you not give them a try?  If you have any questions about Cabinet Coolers or the Sizing Guide, you can contact an Application Engineer at EXAIR.  We will be happy to help.

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

Factors When Sizing a Cabinet Cooler System

Heat can cause real problems for electrical and electronic components, in a hurry…we all know that.  Fortunately, we can also specify the right Cabinet Cooler System for you in a hurry too.  And since we keep them all in stock, we can get it to you in a hurry as well.

You can access our Cabinet Cooler Sizing Guide online, here.  You can fill in the blanks and submit it, or you can call in your data.  We do it over the phone all the time, and it only takes a minute.  Here’s what we’re going to ask for, and why:

NEMA 4 Cabinet Cooler
  • Enclosure dimensions.  We need the length, width, and height of your enclosure to calculate the heat transfer surface, and the volume of the enclosure.
  • Current Internal Air Temperature.  How hot is it inside your enclosure?  This is the starting point for figuring out the internal heat load…how much heat the components inside the box is generating.  This needs to be the air temperature – don’t use a heat gun, or you’re going to give me the surface temperature of something that may or may not be close to what I need.  Just put a thermometer in there for a few minutes.
  • Current External Air Temperature.  How hot is it in the area where the enclosure is located?  We’re going to compare this to the internal air temperature…the difference between the two is actually proportional to the heat load.  Also, if there’s anything cooling the enclosure right now (like circulating fans; more on those in a minute,) this reading is key to figuring out how much heat they’re removing.
  • Maximum External Air Temperature.  How hot does it get in the area on, say, the hottest day of summer?  We’ll need this to calculate the external heat load…how much heat the enclosure picks up from its surroundings.
  • Maximum Internal Temperature Desired.  Most electrical and electronic component manufacturers publish a maximum operating temperature of 104F (40C) – it’s kind of an “industry standard.”  Based on this, a lot of us in the enclosure cooling business set our products’ thermostats to 95F (35C) – if we’re maintaining the air temperature a decent amount cooler than the components are allowed to get, history and practice has shown that we’re going to provide more than adequate protection.  If your enclosure houses something with more sensitive temperature limitations, though, we can work with that too…that’s the only time you’re going to want to put something other than 95F (35C) in this field.
  • Cabinet Rating.  This is all about the environment…we offer three levels of protection, per NEMA standards:
    •  NEMA 12 – oil tight, dust tight, indoor duty.
    • NEMA 4 – oil tight, dust tight, splash resistant, indoor/outdoor duty.
    • NEMA 4X – oil tight, dust tight, splash resistant, corrosion resistant, indoor outdoor duty.

                     The NEMA rating does not affect the cooling capacity at all.

  • Other:  If the enclosure is mounted to the side of a machine, or a wall in the plant, you really don’t need to put anything here.  If it’s outside and exposed to direct sunlight, tell us what the surface finish (i.e., polished metal, painted grey, etc.) is so that we can account for solar loading too.  If anything else is unusual or peculiar about the application, let us know that too.
  • My Cabinet Is…Not Vented, Vented, Wall Mounted, Free Standing, Fan(s).  We’ll use what you tell us here to verify heat transfer surface (a wall mounted cabinet’s back surface isn’t a radiating surface, for example.)  Also, I mentioned fan cooling before, so without further ado…
  • Fan diameter or SCFM.  If there are fans circulating air into (and/or out of) the enclosure, they’re providing a finite amount of cooling right now.  Proper installation of a Cabinet Cooler System is going to require their removal.  Running a Cabinet Cooler System on a vented enclosure is just like running your air conditioner with the windows open.  So, if we know the size (or the SCFM…sometimes there’s a label on those fans, and we LOVE those folks who do that) then we can use that, and the temperatures you gave us above, to take the fan cooling into account.

Once we have all this information, it’s down to the math. Like I said, we do this all the time (especially during “Cabinet Cooler Season”) – give me a call.  Your heat problem isn’t waiting; why should you?

Jordan Shouse
Application Engineer
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Let’s Size A Cabinet Cooler System!

I can’t remember the last time I put an exclamation point in the title of my blog, but it was probably the last time I got to talk about doing math. Or write about heat transfer.  Insert your favorite engineer joke here…I’m sure I have it coming.

We’re in the dog days of summer (in the Northern Hemisphere) for sure…or, as we call it, “Cabinet Cooler Season.”  If you’re having heat related problems with a control panel, give us a call; we can help.  If you’d like to know what we’re going to talk about, read on.

Heat can cause real problems for electrical and electronic components, in a hurry…we all know that.  Fortunately, we can also specify the right Cabinet Cooler System for you in a hurry too.  And since we keep them all in stock, we can get it to you in a hurry as well.

You can access our Cabinet Cooler Sizing Guide online, here.  You can fill in the blanks and submit it, or you can call in your data.  We do it over the phone all the time, and it only takes a minute.  Here’s what we’re going to ask for, and why:

Enclosure dimensions.  We need the length, width, and height of your enclosure to calculate the heat transfer surface, and the volume of the enclosure.

Current Internal Air Temperature.  How hot is it inside your enclosure?  This is the starting point for figuring out the internal heat load…how much heat the components inside the box is generating.  This needs to be the air temperature – don’t use a heat gun, or you’re going to give me the surface temperature of something that may or may not be close to what I need.  Just put a thermometer in there for a few minutes.

Current External Air Temperature.  How hot is it in the area where the enclosure is located?  We’re going to compare this to the internal air temperature…the difference between the two is actually proportional to the heat load.  Also, if there’s anything cooling the enclosure right now (like circulating fans; more on those in a minute,) this reading is key to figuring out how much heat they’re removing.

Maximum External Air Temperature.  How hot does it get in the area on, say, the hottest day of summer?  We’ll need this to calculate the external heat load…how much heat the enclosure picks up from its surroundings.

Maximum Internal Temperature Desired.  Most electrical and electronic component manufacturers publish a maximum operating temperature of 104F (40C) – it’s kind of an “industry standard.”  Based on this, a lot of us in the enclosure cooling business set our products’ thermostats to 95F (35C) – if we’re maintaining the air temperature a decent amount cooler than the components are allowed to get, history and practice has shown that we’re going to provide more than adequate protection.  If your enclosure houses something with more sensitive temperature limitations, though, we can work with that too…that’s the only time you’re going to want to put something other than 95F (35C) in this field.

Cabinet Rating.  This is all about the environment…we offer three levels of protection, per NEMA standards:

NEMA 12 – oil tight, dust tight, indoor duty.

NEMA 4 – oil tight, dust tight, splash resistant, indoor/outdoor duty.

NEMA 4X – oil tight, dust tight, splash resistant, corrosion resistant, indoor outdoor duty.

The NEMA rating does not affect the cooling capacity at all.

Other:  If the enclosure is mounted to the side of a machine, or a wall in the plant, you really don’t need to put anything here.  If it’s outside and exposed to direct sunlight, tell us what the surface finish (i.e., polished metal, painted grey, etc.) is so that we can account for solar loading too.  If anything else is unusual or peculiar about the application, let us know that too.

My Cabinet Is…Not Vented, Vented, Wall Mounted, Free Standing, Fan(s).  We’ll use what you tell us here to verify heat transfer surface (a wall mounted cabinet’s back surface isn’t a radiative surface, for example.)  Also, I mentioned fan cooling before, so without further ado…

Fan diameter or SCFM.  If there are fans circulating air into (and/or out of) the enclosure, they’re providing a finite amount of cooling right now.  Proper installation of a Cabinet Cooler System is going to require their removal.  Running a Cabinet Cooler System on a vented enclosure is just like running your air conditioner with the windows open.  So, if we know the size (or the SCFM…sometimes there’s a label on those fans, and we LOVE those folks who do that) then we can use that, and the temperatures you gave us above, to take the fan cooling into account.

Once we have all this information, it’s down to the math. Like I said, we do this all the time (especially during “Cabinet Cooler Season”) – give me a call.  Your heat problem isn’t waiting; why should you?

Before I go…here’s a nice little video, walking you through the Cabinet Cooler Sizing Guide.  Yes, I just made you read the book before watching the movie…feel free to tell me which one you liked better.

Russ Bowman
Application Engineer
EXAIR Corporation
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