In 1938 Abbot and Costello first performed their legendary routine of “Who’s on First”. If you haven’t heard this before I only have two things to say to you – 1) I’m sorry and 2) go listen to this. This is one of the funniest routines in comedic history, and you should listen to it at least once a decade. The craziest thing about this is that in 2007 there was a MLB player from the Los Angeles Dodgers that got his first MLB hit and was standing on first base. After 69 years, Abbot and Costello’s famous act came true and Hu was on first. Chin-Lung Hu that is. It was destined to happen one day, but now we have to focus on Watts on second? That’s right— Watts on second.

When we size your electrical cabinet, we ask for a current internal temperature of the cabinet. This is critical to us being able to make this calculation. You would think this is an easy request, but surprisingly we get pushback to get this number. The best way to get this number is to simply put a thermometer in the cabinet, let it sit for a few minutes and let us know the temp. The pushback is surprising as this is the most important number to know, as this is the temperature that we are cooling. If I had a nickel for every time I am asked to just guess at a number here, I wouldn’t be rich, but I could buy a soda each month. This temperature is critical for us to know, because it tells us how much cooling is needed to overtake that heat to make your cabinet safe. But, I do understand that there are times when this is not possible. And of course there are new installations where there is not a cabinet there yet… So what do we do next or “second”… You guessed it, Watts on second.

In these instances we need to find the total watts that will be used in this electrical cabinet. How do we find this? In a perfect world there should be a list of every electrical component that is on that cabinet. Each of those components should have paperwork, and or labels on them that state the total watts used. When we have this information it is as easy as adding these watts up (not much, watts up with you?)…. Sorry, that’s the dad in me.

There are times when we don’t have the data, the label was destroyed etc. So how do we find the watts? Well now we have to digress back to math. Thankfully this is not a math that we have to Google to find a refresher course to remember how to do. We just have to remember the formula. Watt = AMP x VOLT x Efficiency rating (@95%). It really is that easy. As an example, if the current is 4 amps (4A) and the Voltage is 110V, you will multiply 4×110= 440W. This is why watts are sometimes called volt-amps. Next, we take into account a 95% efficiency rate for the electronics – meaning that 95% of the energy is used, and the 5% remaining is the heat that component gives off. This example will give us 440W x 5% = 22 total Watts for this component. We do this for each component and then add them all together for total watts. Volts and amps can be found in most operating manuals, and 99% of the time you can look up common amps and volts on Mr Google.

Once we have the total Watts of the cabinet cooler components, we simply multiply that by the 3.41 conversion rate to give us the BTU/HR needed for the internal heat load.

With this information we can finalize the calculations for the Cabinet Cooler by calculating the outside heat transfer. This is pretty easy, as we simply find the temp difference between the max external temp and the max desired internal temp. We take that temp difference and match it to this top secret table (right). We then multiply the BTU/HR by the square footage of the cabinet to find the external heat load.

SPOILER ALERT: To find the total heat load for your enclosure you add the internal and external heat loads together, and botta being, botta boom, Bob’s your uncle.

There are times when the sizing gets complicated with large heat loads. Please do not hesitate to reach out and talk to myself, or one of the other application engineers for this, or any other product.

Thank you for stopping by,

Brian Wages

Application Engineer

EXAIR LLC

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Cover photo by JayMantri , Spoiler photo by emkanicepic, both sponsored by Pixabay