SCFM vs ACFM: What’s the Difference?

If there’s anything that confuses people about blower performance, it’s SCFM vs ACFM. This distinction can be the difference between efficient, seamless operation and expensive repairs, and extended downtime for the company. 

In this guide, Best Blower will break down these two concepts, talking about the differences between these two terms and how you can convert one to another with a few simple calculations. 

What is the Difference Between SCFM vs ACFM?

The difference between SCFM vs ACFM comes down to the different calculations that you need to make in determining blower performance based on reference conditions or the actual set of conditions where the blower will be installed.

Different conditions consist of pressure, temperature, and relative humidity; all of which can affect blower performance if they are off by even a few degrees. 

SCFM – also known as Standard Cubic Feet per Minute – is used when designating flow with basic or reference conditions. 

Many standards may be used, but the most common is 14.5 PSIA, 68°F, and 0% RH which leaves you with a density of 0.074 lbs per cubic foot of air. This calculation for SCFM is the standard used by the Compressed Air & Gas Institute (CAGI).

ACFM – also known as Actual Cubic Feet per Minute – should be used when designating the level of flow based on actual conditions in the 

SCFM must be corrected to ACFM to ensure the blower can provide enough oxygen to the rest of the system for it to function properly. 

Blower Formulations

Blower performance calculations are based on actual conditions at the inlet and outlet connections of the blower. This includes head and horsepower calculations, which means if the calculation is wrong it can impart too much or too little torque necessary to function.

It is important to ensure you know whether you need to calculate at SCFM or ACFM before purchasing a new installation. Almost every industry requires a minimum energy output and input based on the actual conditions where the blower will be housed, but SCFM can come in handy when actual conditions cannot be accurately measured.

Calculating for Actual Conditions

As an example of calculating ACFM, we can use the following calculation assuming we are working with ambient air. If another type of gas is required, you will need to make additional calculations based on the density and pressures of that gas. For now, the simplest method for example will use ambient air as a model. 

Here we can look at this calculation assuming the following:

TA = Actual temperature (°R)1
PS = Standard pressure (PSIA)
PB = Atmospheric pressure – barometer (PSIA)
PA = Actual pressure (PSIA)
RHS = Standard relative humidity
RHA = Actual relative humidity
PVS = Saturated vapor pressure of water at standard temperature (PSI)1
PVA = Saturated vapor pressure of water at actual temperature (PSI)1
TS = Standard temperature (°R) NOTE: °R =°F+460

Just one problem: we aren’t looking for SCFM, so let’s add an example of actual conditions into this calculation and see how it comes out differently. 

Let’s use the following metrics to determine the ACFM of our blower if it were put into operation in Atlanta, GA. With some quick research, we can get the actual conditions of this location and put it to the test.

Location:  Atlanta, GA
Elevation: 960 feet above sea level
SCFM:  1,000
Ambient Temperature:  80°F
Relative Humidity: 70%
Inlet Pressure Drop: 0.3 psi (due to filter and silencer)
Standard Conditions: CAGI Standards (14.5 psia, 0% RH, and 68°F)

At this stage, we know the answer works out to 1,095.86 ACFM. If the flow isn’t corrected based on actual conditions, we miss the requirement by 9.6%. We further miss the blower requirements if we calculate the Actual Temperature (TA) at 100°F. 

Now, this calculation looks a lot different suddenly. By adding the actual conditions assuming 100°F, the calculation changes and the ACFM would work out to 1,136, a wide margin away from where we started.

Best Blower: Your Choice for Blower Sales, Service, and Repair 

At Best Blower, we are among the top choices for blower sales and service, taking customer satisfaction to another level. With two locations in Virginia, we stand by our products’ quality and provide the support to build lasting relationships with all our clients. 

Our team has 33 years of experience in repairing blowers and helping industry specialists determine their needs. We strive to help you establish yourself in any market, no matter how competitive, by providing exceptional quality service and products. Click here to learn more about our experience as a distributor for Howden, the manufacturer of roots blowers.

If you have any questions about your order or want to double-check SCFM and ACFM specifications, our team can help you. Give our sales and applications team a call today or email us about your project on our Contact page today. We are happy to look at your project details and provide advice where needed.