Tag: SCFM

Standard Temperature and Pressure: What is STP?

Published on by John BallLeave a comment

When it comes to volumetric flow rates, you probably noticed the prefix of an “S” for SCFM and SLPM, or an “N” for NM3/hr.  The “S” prefix is for Standard conditions, and the “N” prefix is for Normal conditions.  For practical reasons, they are the same thing.  What does this mean? 

Let’s look at the Ideal Gas Law in Equation 1:

Equation 1:

PV = nRT 

P – Pressure

V – Volume

n – No. of moles

R – Ideal Gas constant

T – temperature

Since air is compressible, it will react in different ways.  If we keep the volume the same and lower the temperature, the gas pressure will go down.  If we keep the temperature the same and decrease the volume, the gas pressure will go up.  If we go to a higher elevation, the number of moles is reduced, which will lower the gas pressure.  With the different degrees of changes, it is difficult to compare.  So, organizations decided to place a standard on these conditions to help compare results.  The definition is referred to as STP, or Standard Temperature and Pressure. 

In most cases, the Standard Temperature and Pressure is set at 20oC and 1 atm (1.013 bar).  If we transition all pneumatic units to this condition, we can then compare the results for each product.  We can determine which units actually use less compressed air or have higher forces.  Or if we decide to use a different STP, we can do that as well as long as we use the same temperature and pressure. 

I like to think of it like an air-filled balloon floating on top of the water.  This would be the “Standard” or “Normal” condition.  As you take the balloon into deeper water, more pressure is applied to the balloon, and the volume will decrease.  This is because air is compressible.  The balloon still has the same amount of air by weight (as the volume decreases, the density increases).  If you return to the surface, the balloon will expand back to the original size.  When doing comparisons, we need to be in the same condition, or for the balloon example, it will look like the balloon will need less air at lower depths than at the surface.   

The reason for this explanation is that some competitors like to use lower pressures to rate their products.  As an example, Competitor A rates their nozzles at 5 bar (72.5 psig).  EXAIR uses 5.5 bar (80 psig) for most of our products.  By comparison, we cannot say if one unit uses more or less compressed air unless we set them at the same conditions.  The best place to compare is at a Standard Temperature and Pressure, or STP.   I go into more detail in my blog about air flows with “CFM, ICFM, ACFM, SCFM: Volumetric Flow Rates Explained”.  EXAIR offers Super Air Knives, Super Air Nozzles, and Super Air Amplifiers to efficiently blow compressed air.  So, when a company states a compressed air flow, verify the pressure and temperature at which they recorded that information.  It will help you to be more in tune with what you are getting (allow for an apples to apples comparison). If you need any help in doing comparisons, an Application Engineer at EXAIR will be happy to assist you. 

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo:  balloon helium air flying bright by stux.  Pixabay license

How To Calculate Your Return On Investment From Using Engineered Compressed Air Products

Published on by Russ BowmanLeave a comment

There’s an old saying that goes “If it isn’t broken, don’t fix it.” Best case, this means it may not be necessary to repair, refurbish, or replace something just because there’s a newer offering on the market. Worst case, it’s used to justify continued use of something when the aforementioned repair, refurbishment, or replacement will result in quantifiable benefits. THAT makes THIS quote all the more applicable:

“The most dangerous phrase in the English language is: We’ve always done it this way. It raises the question, ‘Are we doing this because we always have, or because it’s the right thing to do?’”
-Grace Hopper, Rear Admiral USN & computer pioneer

If you consider “not spending any more than you have to on compressed air” to be “the right thing to do”, then this blog’s for you. Read on, and we’ll calculate not only how much you might save by using engineered compressed air products in place of what you’re using now, but how soon that amount you save will equal how much you spent on those products…that’s called Return On Investment, or ROI. Let’s work through an example:

A popular air gun fitted with a cross-drilled nozzle for OSHA compliance uses 34 SCFM @80psig. These are commonly replaced by our Model 1210 Soft Grip Safety Air Guns fitted with our Super Air Nozzles, which consume only 14 SCFM @80psig. It’s not likely that the trigger on an Air Gun used for blowing, cleaning, drying, etc., will be pulled continuously, but we can assume that two hours of “trigger time” per day (for an eight-hour shift) is reasonable. Here’s how to calculate annual savings:

(34-14 SCFM) X 60 min/hr X 2 hrs/day X 5 days/wk X 50 wks/yr=600,000 Standard Cubic Feet saved

Model 1210 Soft Grip Safety Air is fitted with an EXAIR Super Air Nozzle. We can also supply it with a Rigid Extension and Chip Shield (right).

Now, we need to determine the cost of your compressed air. The calculation for that, per the U.S. Department of Energy, is as follows:

Cost ($) = {bhp X 0.746 X # of operating hours X $/kWh X % time X % full load bhp}/motor efficiency

Where:
bhp = motor full load horsepower
0.746 = conversion from hp to kW
% time = percentage of run time at this operating level
% full load bhp = brake horsepower as percentage of full load bhp at this operating level
Motor efficiency = motor efficiency at this operating level

For simplicity, you could also get a fairly accurate answer by applying an “industry standard” thumb rule which states that a typical industrial air compressor generates ~4 SCFM per HP. If you know your electricity cost ($/kWh), you can calculate the cost of compressed air generation as follows. To keep most of the digits to the left of the decimal point, it’s commonly calculated as $ per 1,000 Standard Cubic Feet:

$/kWh X 0.746 hp/kW ÷ 4 hp/SCFM ÷ 60 min/hr X 1,000 = $ per 1,000 SCF

For EXTRA simplicity, you can use ANOTHER thumb rule, also endorsed by the Department of Energy, which states that compressed air costs about $0.25 per 1,000 SCF. It uses the above formula, and a typical estimate for electricity cost of $0.08 per kWh which my buddy Brian Farno did the math and provided a detailed explanation on that one here. So:

600,000 SCF X $0.25/1,000 SCF = $150.00 saved by switching to the EXAIR Safety Air Gun

Given the cost (current 2023 List Price) of $115.00 for the Model 1210 Soft Grip Safety Air Gun, we can calculate Return On Investment as a function of time…how long it takes before you end up saving the amount you spent:

$115.00 saved ÷ $150.00 spent X 12 months in a year = 9.2 months

At EXAIR (if you hadn’t figured it out already), we LOVE to do the math, but if you don’t (no judgment), we’ve got calculators on our website for that. Just fill in a few blanks, and get your answer. If there’s anything I can help with, though, give me a call.

Russ Bowman, CCASS

Application Engineer
Visit us on the Web
Follow me on Twitter
Like us on Facebook

What’s with the “S” in SCFM

Published on by bdwagesLeave a comment
Photo by Joeclub_Ake, Licensed by Pixabay

So many times, when reviewing the air requirements for our products, I am met with psi. “I have 100 psi running to this Super Air Knife, but it has almost no air flow”. PSIG and SCFM work hand in hand, and both are critical in optimal performance of our products. These two measurements are related, but they are not immediate family. PSI is more about power, whereas SCFM is more about flow and consistency. When they both combine, force is the outcome. We need both PSI and SCFM to produce force and for products to perform. It seems that most have a solid grasp on PSIG, but the SCFM tends to cause some confusion. Mostly the “S” in the SCFM.

Once we redirect the conversation to SCFM, we almost always find the heart of the issue. But SCFM can be confusing and many times is mistakenly interchanged with CFM. CFM is the easiest to explain, so let’s start there.

Photo by tookapic, licensed by Pixabay

CFM is Cubic Feet per Minute of airflow. This is exactly as it sounds, 1 CFM = 1 12″x12″x12″ box full of air moving through the product (Air Knife, Nozzle, Vortex Tube, Air Wipe and so on) per minute. To visualize this, take a look at your office (or visualize one). Let’s say it is 12x12x8 feet, like the sample to the right. That is 1152 cubic feet of air inside that office. If we used a 48″ Super Air Knife, running at 80 psig, it will consume 139.2 standard cubic feet of air per minute, or in other words, it will use all of the air in that office in 8.27 minutes. Assuming that air was not replaced, the Super Air Knife would starve and not have any airflow even though your gauge may still show 80 PSIG. So, when we break it down to this simple form and example, CFM is pretty easy to comprehend.

Photo by Paulbr75, licensed by Pixabay

Now the confusing part: what is the S in SCFM? The S simply stands for Standard. I know, this is shocking, but what is “Standard”? Standard represents values that are a baseline of measurement, even though few of us reside or work in these “ideal” surroundings. Air volume can be altered by several things, the most common are atmospheric pressure, temperature, and relative humidity.

Some genius somewhere decided that the best place to measure for a Standard CFM at sea level. I imagine they chose Key West Florida, on the beach, which sits around 14.7 psia atmospheric pressure. Then, to be precise they measured this when the thermostat read 68°F, and the hygrometer showed 0% relative humidity. Outside of creating a lab with these settings, that beach, on that day, at that precise time, is where you can get a true CFM of air equal to the Standard.

To summarize the “S” or Standard conditions are 14.7 psi atmospheric pressure, 68°F, and 0% relative humidity.

Photo by Vectors Licensed by Pixabay

Since most of us will never work in that exact environment, SCFM is “mostly” accurate. This is the reference point that we all can use, and has become the “Standard” across the globe. As you can imagine, it would be impossible for companies such as mine to publish or calculate every Actual CFM (ACFM). But we can do this…

ACFM is just what is says – the exact CFM that you will use based upon your elevation (atmospheric Pressure), your temp, and your relative humidity. I have a peer that wrote a recent blog that goes into depth on this topic as well as ACFM and ICFM (Inlet) and how to calculate each of these. You can see that blog here.

Thank you again for stopping by to find out more about the S in SCFM. If you have any questions about this, or anthing else related to our products, please do not hesitate to reach out.

Thank you for stopping by,

Brian Wages

Application Engineer

EXAIR Corporation
Visit us on the Web
Follow me on Twitter

Cover photo by PIRO4D, and licensed by Pixabay

Webinar Replay: SCFM, ACFM, ICFM, CFM – Why So Many Terms For Air Flows?

Published on by Tyler DanielLeave a comment

EXAIR’s latest addition to the Fall Webinar series was a discussion on the topic of volumetric air flow terms: SCFM, ACFM, ICFM, and CFM. In the compressed air world, these terms are used often to quantify the performance of a compressor or the point-of-use equipment on the supply side of your system. Since conditions will vary from one site location to another, it’s important that we understand how certain variables can change the performance of your system. The webinar is available to view on demand on the EXAIR.com.

The term SCFM (Standard Cubic Feet Per Minute) is used to allow us to make an apples to apples comparison across different equipment. The performance is rate at a set of “standard” conditions to remove any potential variables from the equation. CAGI, or the Compressed Air and Gas Institute, uses the standard conditions of: 14.5 psia, 0% relative humidity (RH), and 68°F. This allows us to compare different devices without needing to make any sort of adjustments.

Variables such as elevation (barometric pressure), relative humidity, and temperature all change the performance and must be considered.

With elevation, we’re looking at the atmospheric or barometric pressure at the location of operation. One way to illustrate this to consider a balloon. If you inflated a balloon at sea-level, or 14.5 psia, then carry that same balloon up to the top of Mt. Everest what would happen? Using Boyle’s Law (P1 x V1 = P2 x V2), we’re able to calculate the exact volume of the balloon. At the peak of Mt. Everest, pressure is significantly lower at roughly 4.5 psi. The balloon when taken to the peak at 4.5 psi would become 3.2x it’s original size as the pressure acting on the outside of the balloon decreases.

Relative humidity tells us how much moisture content is contained within a specific volume of air. Water molecules cannot be compressed, so when the air is compressed this water takes up the same volume. The water condenses in the inter-coolers and after-coolers or is removed via drains and dryers downstream. So, 1 cubic foot of air coming into the compressor weigh more than 1 cubic foot of air out due to this water vapor loss.

As temperature increases, so does air pressure as the molecules in the air speed up and come into contact with one another and the walls of its container at a more rapid pace. Air can also hold a greater volume of moisture at higher temperatures. So, the balance between RH and temperature is an important consideration when determining actual performance, or ACFM.

In the webinar, we walked through two different examples to highlight the changes in these variables and how it impacts the performance of a compressed air system. If you were unable to attend live, the webinar is available to view on demand on the EXAIR website. We have this latest webinar posted there on the website along with all prior webinars as well! There, we talk about topics ranging from compressed air system optimization, static electricity, OSHA Compliance, and more! Check out the available webinars on the Resources tab of the EXAIR.com page today for all the knowledge you’ll need about your compressed air system and processes.

Tyler Daniel, CCASS

Application Engineer

E-mail: TylerDaniel@EXAIR.com

Twitter: @EXAIR_TD