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 Visit us on the Web Follow me on Twitter Like us on Facebook
Two basic methods to set up a compressed air operation for turning off is the ball valve and the solenoid valve. Of the two, the simplest is the ball valve. It is a quarter turn, manually operated valve that stops the flow of the compressed air when the handle is rotated 90°. It is best for operations where the compressed air is needed for a long duration, and shut off is infrequent, such as at the end of the shift.
The solenoid valve offers more flexibility. A solenoid valve is an electro-mechanical valve that uses electric current to produce a magnetic field which moves a mechanism to control the flow of air. A solenoid can be wired to simple push button station, for turning the air flow on and off – similar to the manual valve in that relies on a person to remember to turn the air off when not needed.
Another way to use a solenoid valve is to wire it in conjunction with a PLC or machine control system. Through simple programming, the solenoid can be set to turn on/off whenever certain parameters are met. An example would be to energize the solenoid to supply an air knife when a conveyor is running to blow off parts when they pass under. When the conveyor is stopped, the solenoid would close and the air would stop blowing.
The EXAIR EFC (Electronic Flow Control) is a stand alone solenoid control system. The EFC combines a photoelectric sensor with a timer control that turns the air on and off based on the presence (or lack of presence) of an object in front of the sensor. There are 8 programmable on/off modes for different process requirements. The use of the EFC provides the highest level of compressed air usage control. The air is turned on only when an object is present and turned off when the object has passed by.
By turning off the air when not needed, whether by a manual ball valve, a solenoid valve integrated into the PLC machine control or the EXAIR EFC, compressed air usage will be minimized and operation costs reduced.
If you have questions about the EFC, solenoid valves, ball valves or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.
It is important to know the cost of compressed air at your facility. Most people think that compressed air is free, but it is most certainly not. Because of the expense, compressed air is considered to be a fourth utility in manufacturing plants. In this blog, I will show you how to calculate the cost to make compressed air. Then you can use this information to determine the need for Intelligent Compressed Air® products.
There are two types of air compressors, positive displacement and dynamic. The core construction for both is an electric motor that spins a shaft. Positive displacement types use the energy from the motor and the shaft to change the volume in an area, like a piston in a reciprocating compressor or like rotors in a rotary compressor. The dynamic types use the energy from the motor and the shaft to create a velocity energy with an impeller. (You can read more about air compressors HERE). For electric motors, the power is described either in kilowatts (KW) or horsepower (hp). As a unit of conversion, there are 0.746 KW in 1 hp. The electric companies charge at a rate of kilowatt-hour (KWh). So, we can determine the energy cost to spin the electric motors. If your air compressor has a unit of horsepower, or hp, you can use Equation 1:
hp * 0.746 * hours * rate / (motor efficiency)
hp – horsepower of motor
0.746 – conversion to KW
hours – running time
rate – cost for electricity, KWh
motor efficiency – average for an electric motor is 95%.
If the air compressor motor is rated in kilowatts, or KW, then the above equation can become a little simpler, as seen in Equation 2:
KW * hours * rate / (motor efficiency)
KW – Kilowatts of motor
hours – running time
rate – cost for electricity, KWh
motor efficiency – average for an electric motor is 95%.
As an example, a manufacturing plant operates 250 day a year with 8-hour shifts. The cycle time for the air compressor is roughly 50% on and off. To calculate the hours of running time, we have 250 days at 8 hours/day with a 50% duty cycle, or 250 * 8 * 0.50 = 1,000 hours of running per year. The air compressor that they have is a 100 hp rotary screw. The electrical rate for this facility is at $0.08/KWh. With these factors, the annual cost can be calculated by Equation 1:
In both equations, you can substitute your information to see what you actually pay to make compressed air each year at your facility.
The type of air compressor can help in the amount of compressed air that can be produced by the electric motor. Generally, the production rate can be expressed in different ways, but I like to use cubic feet per minute per horsepower, or CFM/hp.
The positive displacement types have different values depending on how efficient the design. For a single-acting piston type air compressor, the amount of air is between 3.1 to 3.3 CFM/hp. So, if you have a 10 hp single-acting piston, you can produce between 31 to 33 CFM of compressed air. For a 10 hp double-acting piston type, it can produce roughly 4.7 to 5.0 CFM/hp. As you can see, the double-acting air compressor can produce more compressed air at the same horsepower.
The rotary screws are roughly 3.4 to 4.1 CFM/hp. While the dynamic type of air compressor is roughly 3.7 – 4.7 CFM/hr. If you know the type of air compressor that you have, you can calculate the amount of compressed air that you can produce per horsepower. As an average, EXAIR uses 4 CFM/hp of air compressor when speaking with customers who would like to know the general output of their compressor.
With this information, we can estimate the total cost to make compressed air as shown in Equation 3:
C = 1000 * Rate * 0.746 / (PR * 60)
C – Cost of compressed air ($ per 1000 cubic feet)
1000 – Scalar
Rate – cost of electricity (KWh)
0.746 – conversion hp to KW
PR – Production Rate (CFM/hp)
60 – conversion from minutes to hour
So, if we look at the average of 4 CFM/hp and an average electrical rate of $0.08/KWh, we can use Equation 3 to determine the average cost to make 1000 cubic feet of air.
Once you have established a cost for compressed air, then you can determine which areas to start saving money. One of the worst culprits for inefficient air use is open pipe blow-offs. This would include cheap air guns, drilled holes in pipes, and tubes. These are very inefficient for compressed air and can cost you a lot of money. I will share a comparison to a 1/8” NPT pipe to an EXAIR Mini Super Air Nozzle. (Reference below). As you can see, by just adding the EXAIR nozzle to the end of the pipe, the company was able to save $1,872 per year. That is some real savings.
Making compressed air is expensive, so why would you not use it as efficiently as you can. With the equations above, you can calculate how much you are paying. You can use this information to make informed decisions and to find the “low hanging fruit” for cost savings. As in the example above, targeting the blow-off systems in a facility is a fast and easy way to save money. If you need any help to try and find a way to be more efficient with your compressed air system, please contact an Application Engineer at EXAIR. We will be happy to assist you.
EXAIR’s Digital Flow Meter offers an easy way to measure, monitor and record compressed air consumption. The Digital display shows the current amount of compressed air flow, allowing for tracking to identify costly leaks and/or inefficient air users.
How exactly does the Digital Flow Meter work? The unit falls under the category of Thermal Mass or Thermal Dispersion type flow meters. Below shows the backside of a unit.
Thermal mass flow meters have the advantage of using a simple method of measuring flow without causing a significant pressure drop. The EXAIR units have (2) probes that are inserted through the pipe wall and into the air flow. Each of the probes has a resistance temperature detector (RTD.) One of the probes measures the temperature of the air flow. The other probe is heated to maintain a preset temperature difference from the temperature measured by the first probe. The faster the air flow, the more heat that is required to keep the second probe at the prescribed temperature. From Heat Transfer principles, the heat energy input required to maintain the preset temperature is based on the mass velocity of the air. Using basic physical properties for compressed air, the volumetric rate can be determined (SCFM), and displayed.
It is important to note that the compressed air should be filtered to remove oils, and dried to remove water, as these liquids have different physical properties from air, and will cause erroneous readings.
If you have any questions about the Digital Flow Meter or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.