The Basics of Calculating Heat Load for Cooling Electrical Cabinets

Is your electrical cabinet overheating and causing expensive shut downs? As spring and summer approach, did your enclosures have seasonal overheating problems last year? Is your electrical cabinets AC Unit failing and breaking down? Then it may be time to consider EXAIR Cabinet Coolers Systems. These systems are compressed air powered cooling units designed to keep your cabinet cool in hot environments. Major benefits include no moving parts to wear out, UL listed to maintain the NEMA integrity of your enclosure (also CE compliant), they are simple and quick to install and they reliably turn on and off as needed (perfect for solving seasonal overheating).

Just one question then; how do you pick which Cabinet Cooler is best for your application? It’s time to bust out ye ole trusty calculator and crunch some numbers. Keep in mind that the following calculations use baselines of an Inlet air pressure of 100 psig (6.9 bar), compressed air temperature of 70F (22C), and a desired internal temp of 95F (35C). Changes in these values will change the outcome, but rest assured a Cabinet Cooler system will generally operate just fine with changes to these baselines.

How the EXAIR Cabinet Cooler System Works


Before we dig right into the math, keep in mind you can submit the following parameters to EXAIR and we will do the math for you. You can use our online Cabinet Cooler Sizing Guide and receive a recommendation within 24 hours.

There are two areas where we want to find the amount of heat that is being generated in the environment; this would be the internal heat and the external heat. First, calculate the square feet exposed to the air while ignoring the top. This is just a simple surface are calculation that ignores one side.

(Height x Width x 2) + (Height x Depth x 2) + (Depth x Width) = Surface Area Exposed

Next, determine the maximum temperature differential between the maximum surrounding temperature (max external temp) and the desired Internal temperature. Majority of cases the industrial standard for optimal operation of electronics will work, this value is 95F (35C).


Max External Temp – Max Internal Temp Desired = Delta T of External Temp

Now that we have the difference between how hot the outside can get and the max, we want the inside to be, we can look at the Temperature Conversion Table which is below and also provided in EXAIR’s Cabinet Cooler System catalog section for you. If your Temperature Differential falls between two values on the table simply plug the values into the interpolation formula.

Once you have the conversion factor for either Btu/hr/ft2, multiply the Surface Area Exposed by the conversion factor to get the amount of heat being generated for the max external temperature. Keep this value as it will be used later.

Surface Area Exposed x Conversion Factor = External Heat Load

Now we will be looking at the heat generated by the internal components. If you already know the entire Watts lost for the internal components simply take the total sum and multiply by the conversion factor to get the heat generated. This conversion factor will be 3.41 which converts Watts to Btu/hr. If you do not know your watts lost simply use the current external temperature and the current internal temperature to find out. Calculating the Internal Heat Load is the same process as calculating your External Heat Load just using different numbers. Don’t forget if the value for your Delta T does not fall on the Temperature conversion chart use simple Interpolation.

Current Internal Temp – Current External Temp = Delta T of Internal Temperature
Surface Area Exposed x Conversion Factor = Internal Heat Load

Having determined both the Internal Heat Load and the External Heat Load simply add them together to get your Total Heat Load. At This point if fans are present or solar loading is present add in those cooling and heating values as well. Now, with the Total Heat Load match the value to the closet cooling capacity in the NEMA rating and kit that you want. If the external temperature is between 125F to 200F you will be looking at our High Temperature models denoted by an “HT” at the start of the part number.

From right to left: Small NEMA 12, Large NEMA 12, Large NEMA 4X

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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How to Calculate the Cost of Leaks

Leaks are a hidden nuisance in a compressed air system that can cause thousands of dollars in electricity per year. These leaks on average can account for up to 30% of the operation cost of a compressed air system. A leak will usually occur at connection joints, unions, valves, and fittings. This not only is a huge waste of energy but it can also cause a system to lose pressure along with lowering the life span of the compressor since it will have to run more often to make up for the loss of air from the leak.

There are two common ways to calculate how much compressed air a system is losing due to leaks. The first way is to turn off all of the point of use compressed air devices; once this has been complete turn on the air compressor and record the average time that it takes the compressor to cycle on and off. With the average cycle time you can calculate out the total percentage of leakage using the following formula.

The second method is to calculate out the percentage lost using a pressure gauge downstream from a receiver tank. This method requires one to know the total volume in the system to accurately estimate the leakage from the system. Once the compressor turns on wait until the system reaches the normal operating pressure for the process and record how long it takes to drop to a lower operating pressure of your choosing. Once this has been completed you can use the following formula to calculate out the total percentage of leakage.

The total percentage of the compressor that is lost should be under 10% if the system is properly maintained.

Once the total percentage of leakage has been calculated you can start to look at the cost of a single leak assuming that the leak is equivalent to a 1/16” diameter hole. This means that at 80 psig the leak is going to expel 3.8 SCFM. The average industrial air compressor can produce 4 SCFM using 1 horsepower of energy. Adding in the average energy cost of $0.25 per 1000 SCF generated one can calculate out the price per hour the leak is costing using the following calculation.

If you base the cost per year for a typical 8000 hr. of operating time per year you are looking at $480 per year for one 1/16” hole leak. As you can see the more leaks in the system the more costly it gets. If you know how much SCFM your system is consuming in leaks then that value can be plugged into the equitation instead of the assumed 3.8 SCFM.

If you’d like to discuss how EXAIR products can help identify and locate costly leaks in your compressed air system, please contact one of our application engineers at 800-903-9247.

Cody Biehle
Application Engineer
EXAIR Corporation
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Webinar by EXAIR: Use This, Not That – Four Common Ways to Save Compressed Air in Your Plant

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Not much in life is free anymore. So, make sure and take advantage of EXAIR’s upcoming FREE webinar at 2:00 PM ET on 10/17/2019. Not only are we providing it for free, but in this webinar we’ll be discussing how you can save money by reducing your compressed air consumption. Something for free, that will help save you money? Almost unheard of these days!!! Hosted by one of our highly-trained Application Engineers, Jordan Shouse, you’ll learn about four common ways that you can easily save air in your facility.

Compressed air is often referred to as the fourth utility in industry. When used improperly, compressed air is extremely expensive. Homemade devices such as open-ended and drilled pipes, inefficient air nozzles, leaks, etc. all contribute to increased energy costs. In addition to being wasteful, these devices are not safe and compliant with OSHA standards and regulations. By using an Intelligent Compressed Air Product, you’ll be both saving money and creating a safer environment for your operators.

In this webinar, you’ll gain an understanding of the places in your facility that are wasting the most compressed air. We’ll educate you on the various engineered solutions available from EXAIR to help eliminate unnecessary compressed air usage. You’ll gain the knowledge necessary to determine the best solution based on the application, sound level, compressed air usage, and compliance with OSHA safety requirements. You’ll also learn about the various solutions available to help understand and optimize your compressed air system. You can’t begin implementing a plan to reduce air consumption until you fully understand the usage in your own facility and processes. EXAIR’s line of Optimization products are ideal to help you gain a baseline measurement and begin implementing new products and processes that’ll only help add to your bottom line.

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After the conclusion of the webinar will be a brief Q&A session where you can ask any questions you have about any of the topics covered. Unable to attend the webinar live? Don’t let that stop you from registering! Afterwards, each registrant will receive a link via e-mail where they’ll be able to access the full webinar at any time. Make sure and take advantage of this opportunity to gain some knowledge about the usage of your compressed air. You’ll be glad you did!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Estimating the Cost of Compressed Air Systems Leaks

Leaks in a compressed air system can waste thousands of dollars of electricity per year. In fact, in many plants, the leakage can account for up to 30% of the total operational cost of the compressor. Some of the most common areas where you might find a leak would be at connection joints like valves, unions, couplings, fittings, etc. This not only wastes energy but it can also cause the compressed air system to lose pressure which reduces the end use product’s performance, like an air operated actuator being unable to close a valve, for instance.

One way to estimate how much leakage a system has is to turn off all of the point-of-use devices / pneumatic tools, then start the compressor and record the average time it takes for the compressor to cycle on and off. The total percentage of leakage can be calculated as follows:

Percentage = [(T x 100) / (T + t)]

T = on time in minutes
t = off time in minutes

The percentage of compressor capacity that is lost should be under 10% for a system that is properly maintained.

Another method to calculate the amount of leakage in a system is by using a downstream pressure gauge from a receiver tank. You would need to know the total volume in the system at this point though to accurately estimate the leakage. As the compressor starts to cycle on,  you want to allow the system to reach the nominal operating pressure for the process and record the length of time it takes for the pressure to drop to a lower level. As stated above, any leakage more than 10% shows that improvements could be made in the system.

Formula:

(V x (P1 – P2) / T x 14.7) x 1.25

V= Volumetric Flow (CFM)
P1 = Operating Pressure (PSIG)
P2 =  Lower Pressure (PSIG)
T = Time (minutes)
14.7 = Atmospheric Pressure
1.25 = correction factor to figure the amount of leakage as the pressure drops in the system

Now that we’ve covered how to estimate the amount of leakage there might be in a system, we can now look at the cost of a leak. For this example, we will consider a leak point to be the equivalent to a 1/16″ diameter hole.

A 1/16″ diameter hole is going to flow close to 3.8 SCFM @ 80 PSIG supply pressure. An industrial sized air compressor uses about 1 horsepower of energy to make roughly 4 SCFM of compressed air. Many plants know their actual energy costs but if not, a reasonable average to use is $0.25/1,000 SCF generated.

Calculation :

3.8 SCFM (consumed) x 60 minutes x $ 0.25 divided by 1,000 SCF

= $ 0.06 per hour
= $ 0.48 per 8 hour work shift
= $ 2.40 per 5-day work week
= $ 124.80 per year (based on 52 weeks)

As you can see, that’s a lot of money and energy being lost to just one small leak. More than likely, this wouldn’t be the only leak in the system so it wouldn’t take long for the cost to quickly add up for several leaks of this size.

If you’d like to discuss how EXAIR products can help identify and locate costly leaks in your compressed air system, please contact one of our application engineers at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN