Tag: CFM

Estimating the Cost of Compressed Air Systems Leaks

Published on by exaircorpLeave a comment

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

 

 

 

 

 

Intelligent Compressed Air: SCFM, ACFM, ICFM, CFM – What do these terms mean?

Published on by Tyler Daniel2 Comments
3791199712_0e936e421a_o
An old Ingersoll-Rand air compressor

Air compressors have come a long way over the years. When sizing a new system, a few terms are commonly used: CFM, SCFM, ACFM, and ICFM. The term CFM, simply put, stands for Cubic Feet per Minute. This term can often be confusing and impossible to define for just one condition. One definition will not satisfy the conditions that will be experienced in many of your applications due to a number of variables (altitude, temperature, pressure, etc.). Air by nature is a compressible fluid. The properties of this fluid are constantly changing due to the ambient conditions of the surrounding environment.

This makes it difficult to describe the volumetric flow rate of the compressed air. Imagine you have a cubic foot of air, at standard conditions (14.696 psia, 60°F, 0% Relative Humidity), right in front of you. Then, you take that same cubic foot, pressurize it to 100 psig and place it inside of a pipe. You still have one cubic foot, but it is taking up significantly less volume. You have probably heard the terms SCFM, ACFM, and ICFM when used to define the total capacity of a compressor system. Understanding these terms, and using them correctly, will allow you to properly size your system and understand your total compressed air consumption.

SCFM is used as a reference to the standard conditions for flow rate. This term is used to create an “apples to apples” comparison when discussing compressed air volume as the conditions will change. EXAIR publishes the consumption of all products in SCFM for this reason. You will always notice that an inlet pressure is specified as well. This allows us to say that, at standard conditions and at a given inlet pressure, the product will consume a given amount of compressed air. It would be nearly impossible, not to mention impractical, to publish the ACFM of any product due to the wide range of environmental conditions possible.

ACFM stands for Actual Cubic Feet per Minute. If the conditions in the environment are “standard”, then the ACFM and SCFM will be the same. In most cases, however, that is not the case. The formula for converting SCFM to ACFM is as follows:

ACFM = SCFM [Pstd / (Pact – Psat Φ)](Tact / Tstd)

Where:

ACFM = Actual Cubic Feet per Minute
SCFM = Standard Cubic Feet per Minute
Pstd = standard absolute air pressure (psia)
Pact = absolute pressure at the actual level (psia)
Psat = saturation pressure at the actual temperature (psi)
Φ = Actual relative humidity
Tact = Actual ambient air temperature (oR)
Tstd = Standard temperature (oR)

Let’s run through an example of a compressor operating at a “non-standard” condition:

Elevation – 5000 ft.

Temperature – 80°F (80+460=540) – 540°R

Saturation Pressure – .5069psia

Relative humidity – 80%

demand – 100 SCFM

ACFM = (100 SCFM) [(14.7 psia)/((12.23psia) – (0.5069 psia)(80/100))] ((540°R)/(520°R))

=129.1 ACFM

In this example, the actual flow is greater. To determine the total ACFM consumption of any of our products with your system, take the published total consumption of the product and plug in the values for your compressed air system along with the standard variables.

The last term that you’ll see floating around to describe compressed air flow is ICFM (Inlet Cubic Feet per Minute). This term describes the conditions at the inlet of the compressor, in front of the filter, dryer, blower, etc. Because several definitions for Standard Air exist, some compressor manufacturers have adopted this simpler unit of measure when sizing a compressor system. This volume is used to determine the impeller design, nozzle diameter, and casing size for the most efficient compressor system to be used. Because the ICFM is measured before the air has passed through the filter and other components, you must account for a pressure drop.

The inlet pressure is determined by taking the barometric pressure and subtracting a reasonable loss for the inlet air filter and piping. According to the Compressed Air Handbook by the Compressed Air and Gas Institute, a typical value for filter and piping loss is 0.3 psig. The need to determine inlet pressure becomes especially critical when considering applications in high-altitudes. A change in altitude of more than a few hundred feet can greatly reduce the overall capacity of the compressor. Because of this pressure loss, it is important to assess the consumption of your compressor system in ACFM. To convert ICFM to ACFM use the following formula:

ICFM = ACFM (Pact / Pf) (Tf / Tact)

Where:

ICFM = Inlet Cubic Feet Per Minute

Pf  = Pressure after filter or inlet equipment (psia)

Tf = Temperature after filter or inlet equipment (°R)

For this example, let’s say that we’re in Denver, Colorado. The barometric pressure, as of today, is 14.85 psi with current ambient temperature at 71°F. The compressor system in this example does not have any blower or device installed before the inlet, so there will be no temperature differential after filter or inlet equipment. The ICFM rating for the system is 1,000 ICFM.

ACFM = 1,000 (14.85/14.55)(530.67/530.67)

ACFM = 1,020

In order to maintain the 1,000 ICFM rating of the system, the ACFM is 1,020, about a 2% increase.

If you’re looking into a new project utilizing EXAIR equipment and need help determining how much compressed air you’ll need, give us a call. An Application Engineer will be able to assess the application, determine the overall consumption, and help recommend a suitably sized air compressor.

Tyler Daniel
Application Engineer

E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

 

Compressor photo courtesy of David Pearcy via Creative Commons license.

Actual vs. Standard flows

Published on by John BallLeave a comment

Have you ever noticed that when a flow rate like SCFM, SLPM, or NM3/hr is reported, there is a pressure associated with it? There is a reason for this. The “S” in SCFM and SLPM, is for Standard, and the “N” in NM3/hr is for Normal. It is the amount of air being used at atmospheric pressure and temperature. To further explain it, if you take a segment of air out of a compressed air line and place it next to you at ambient temperature and pressure, it will expand to a larger volume. 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, the more pressure is applied to the balloon, and the volume decreases. 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 back to the surface, the balloon will expand back to the original size.

Pressure
Pressure

Being that the flow rate for nozzles, knives, etc., are rated at a standard or normal condition, why do we require a pressure rating? It should be at the atmospheric pressure and temperature. Well, this is where it gets tricky. Just like the air-filled balloon, the deeper you go (higher pressures), the less volume is in the balloon. So, when we have different pressures, we are trying to find the actual volume of air being used because that is what you are paying for. Also, this is where the term ACFM (lpm or M3/hr) comes into play. The “A” in ACFM is for Actual (the volume of air at the actual pressure and temperature). Pneumatic devices use this type of flow (ACFM), but for the ease of understanding, they convert it to a SCFM, SLPM, or NM^3/hr at a pressure. If we assume ambient temperatures because most of our products are used there, then the correlation between Actual and Standard is Qa = Qs * Pa/(P +Pa) .

Imperial Units                                    SI units

Qa          Actual flow (ACFM)                         Actual flow (M^3/hr)

Qs           Standard flow (SCFM)                    Normal flow (NM^3/hr)

P             Gage Pressure (psig)                      Gage Pressure (barg)

Pa           Absolute Pressure (psia)                Absolute Pressure (bara)

 

The reason for this explanation is because some competitors like to use a lower pressure to rate their products. As an example, two air nozzles are rated for 70 SCFM (119 NM^3/hr). One nozzle is cataloged at 60 psig (4.1 barg) and the other is cataloged at 80 psig (5.5 barg). By comparison, they look like they use the same amount of compressed air, but actually they do not. Under the actual condition (using the formula above), we have the following:

Imperial Units                                                                    SI Units

@60 psig                                                                              @4.1 barg

Qa = 70 SCFM * 14.7 psia/(60 psig + 14.7 psia)     Qa = 119 NM^3/hr * 1 bara/(4.1 barg + 1 bara)

= 13.8 ACFM (actual amount of air used)                 = 23.3 M^3/hr (actual amount of air used)

 

@80 psig                                                                              @5.5barg

Qa = 70 SCFM * 14.7 psia/(80 psig + 14.7 psia)     Qa = 119 NM^3/hr * 1 bara/(5.5 barg + 1 bara)

= 10.9 ACFM (actual amount of air used)                = 18.3 M^3/hr (actual amount of air used)

 

Even though it seems like they use the same amount of compressed air, you are actually using 27% more air with the nozzle reported at 60 psig than the one that was reported at 80 psig. Always remember that if you want to compare air usage, always do it at the same pressure and temperature. If you need help, you can always contact our application engineers here at EXAIR.

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

 

Image courtesy of UpUpa4me. Creative Comment License

3 Common Mistakes in Your Compressed Air System

Published on by Dave WoernerLeave a comment

Every day I speak with engineers who are having trouble using compressed air products. A common problem they have is not providing an adequate air supply to their unit. I go through a basic troubleshooting technique to ensure that their pressure and flow rate is adequate. I ask them to install tee on the inlet to the compressed air product in order to install a pressure gauge right at the inlet to the pipe. This allows us to know exactly what pressure we are supplying to the product. Customers are always surprised how the gauge on the compressor or the regulator may read 120 PSIG, but the gage on the inlet to the compressed air product is significantly less.

Last year, my colleague, Russell Bowman, made an excellent video showing how the inlet pressure at the knife will have a significant impact on the performance of the Super Air Knife.  In the video, he changes the length and ID of the compressed air supply to illustrate the difference a proper supply line will have on the performance of a compressed air products.

Not providing adequate air supply is commonly caused by these three mistakes, when plumbing compressed air systems.

1. Incorrectly Sized Piping – This can be the single biggest problem. A lack of planning before installing a compressed air product. Not all compressed air systems are created equal. Though a 1/4″ shop air hose may work for a number our products, some of our products require a larger air line because they require more volume of air to be effective. We often speak with customers an illustrate this problem by stating small air lines are like trying to feed a fire hose with a garden hose – there simply is not enough volume to create the pressure necessary to reach the fire, or solve the application in our scenarios. We publish the flow rates for all of our products and make inlet pipe size recommendation in the installation and maintenance guide furnish with the products so you may avoid this common problem. We also have air data tables in our Knowledge Base or  you may consult an application engineer who will be happy to make the proper recommendation.

2. Quick Disconnects – These handy connectors are great when operating a brad nailer, or a small blow gun, but the small through diameter can severely limit the flow rate into a long air knife, large diameter air operated conveyor, or big vortex tubes.  Due to this fact it is strongly advised to use threaded fittings or over-sized quick disconnects.

3. Adding extra hose or pipe – Extra hose is never a bad thing, right? No, an extra 30 feet of air hose can significantly drop the pressure of a compressed air system. 20 feet of ½ Pipe can flow 70 CFM with a 5 PSI pressure drop.  50 feet of ½” pipe will only flow 42 SCFM with the same 5 PSIG pressure drop. Keep your hose or pipe lengths to a minimum to improve the volume of air you can deliver to a compressed air product.

Dave Woerner
Application Engineer
DaveWoerner@EXAIR.com
@EXAIR_DW