Estimating the Total Cost of Compressed Air

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:

Equation 1:

hp * 0.746 * hours * rate / (motor efficiency)

where:

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:

Equation 2:

KW * hours * rate / (motor efficiency)

where:

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:

100hp * 0.746 KW/hp * 1,000hr * $0.08/KWh / 0.95 = $6,282 per year.

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:

Equation 3:

C = 1000 * Rate * 0.746 / (PR * 60)

where:

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.

C = 1000 * $0.08/KWh * 0.746 / (4 CFM/hp * 60) = $0.25/1000ft3.

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.

Compressed Air 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.

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

 

Turn The Pressure Down & Save Money

In the past your typical industrial air compressor was rated to run at 100 psi and it was not often that this pressure was exceeded.  Lately with modern advances pressures have slowly crept up and have surpassed this threshold.  Unfortunately this has proven costly to the industrial user of compressed air.

To clarify this point, if a compressed air system is set to maintain 102 psi it will cost the plant 1% more in electric costs than if the system ran at 100 psi.  Also noteworthy is that unregulated air demands consume about 1% more flow for every psi of additional pressure.

So why is the air pressure getting so high and what can you do about it?  Here are some possible causes and solutions:

Devices that do require more than 100 psi:  It may not be the pneumatic device at all. If these devices are connected with restrictive fittings or there are excessive leaks in the system this can cause up to a 30 psi increase in line pressure just to make up for the poor piping. If this can be corrected it is possible that the pressure can be reduced.

EXAIR offers the Ultrasonic Leak Detector to facilitate tracking down hard to find system leaks and a wide variety of Air KnivesAir Amplifiers, Super Air Wipes, Air Nozzles, Line Vacs, Vacuum Generators and all of them are engineered to provide peak performance at 80 psi and make efficient use of compressed air. Though it is not uncommon for these products to provide a solution at much less pressure.

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EXAIR 9061, Ultrasonic Leak Detector

Applications that are believed to be high pressure:  Plant workers sometimes think that a higher air pressure is required than actually necessary.  This can be caused by a lack of training or perhaps the trainers are simply repeating what they have been taught in error.  It is good practice to review all locations that are using a higher pressure to determine if it is really necessary.

Loss due to undersize pipes:  If your plants compressed air supply lines are undersized for the volume demand, this can cause a significant restriction and raise the line pressure.  The EXAIR Digital Flow Meter can assist in recording how much demand is for a given point in time which will clarify usage.

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EXAIR Digital Flow Meter

 

Filter/Dryer restrictions:  If the Dryer or Filter/Separators are dirty and/or undersized the compressor operating pressure is typically raised to overcome these restrictions.  EXAIR has six sizes of Filter/Separators to ensure they are properly sized for the SCFM required by the devices that are connected to them.  Five of the models feature an automatic drain system and of course we carry the replacement filter elements and rebuild kits to keep them in top operating condition.

Temporary demands: There may be occasional peak compressed air demands in the plant that may be caused by a different or special compressed air process or machine. If the demand is greater than the supply, the pressure may be pulled down to unacceptably low levels.  In an attempt to make up for the increased demand a plant may raise the operating pressures.  The best way to cope with temporary demands is to install a receiver tank that stores compressed air that can be released when the demand calls for it.

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EXAIR 9500-60, 60 Gallon Receiver Tank

Factory default settings:  It is common for compressor manufacturers to set the air pressure at or very near the maximum pressure rating for that compressor.  There is no reason for this other than to verify that the air compressor will perform at its rated maximum pressure.  To save on air and maintenance costs the compressor should be set only as high as the maximum pressure for approved uses in the facility.

In the compressed air industry, EXAIR provides tools and products with quick payback times.

If you would like to discuss increasing the efficiency of your compressed air usage, quieter compressed air products and/or any EXAIR product,  I would enjoy hearing from you…give me a call.

Steve Harrison
Application Engineer
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Heat Recovery from an Air Compressor

On the whole most of us are quite aware of the considerable savings that can be accomplished by wise use and recovery of energy.   One way that a plant can save substantially is to capture the energy that an electric motor adds to the compressed air from the air compressor.  As much as 80% to 93% of the electrical energy used by an industrial air compressor is converted to heat.  A properly designed heat recovery system can capture anywhere between 50% to 90% of this energy and convert it to useful energy.

The heat recovered is sufficient in most cases to use in supplemental ways such as heating water and space heating, however generally there is not enough energy to produce steam directly.

IngersollRand_R-series-R110
Ingersoll Rand Rotary Screw Compressor

 

Packaged air cooled rotary screw compressor lend themselves easily to heat recovery, supplemental heating or other hot air uses very well due to their enclosed design.  Since ambient air is directed across the compressors aftercooler and lubricant cooler where the heat can be easily collected from both the compressed air and the lubricant.

Packaged coolers are normally enclosed cabinets that feature integral heat exchangers and fans.  This type of system only needs ducting and an additional fan to minimize back pressure on the air compressors cooling fan.  This arrangement can be controlled with a simple thermostat operated vent on a hinge and when the extra heat is not required it can be ducted outside the facility.

The recovered energy can be used for space heating, industrial drying, preheating aspirated air for oil burners or  other applications requiring warm air.  Typically there is approximately 50,000 Btu/Hr of energy available from each 100 SCFM of capacity (at full load).  The temperature differential is somewhere between 30°F – 40°F above the air inlet temperature and the recovery efficiency is commonly found to be 80% – 90%.

We all know the old saying there is “no free lunch” and that principle applies here.  If the supply air is not from outside the plant a drop in the static pressure could occur in the compressor cabinet thereby reducing the efficiency of the compressor.  If you choose to use outside air for makeup, you might need some return air to keep the air above freezing to avoid compressor damage.

Heat recovery is generally not utilized with water cooled compressors since an extra stage of heat exchange is required and the efficiency of recovering that heat is normally in the 50% – 60% range.

To calculate annual energy savings:

Energy Savings (Btu/Yr) = 0.80 * compressor bhp * 2,545 Btu/bhp-hour * hours of operation.

If we consider a 50 HP compressor:

.080 * 50bhp * 2,545 Btu/bhp-hour * 2080 hrs/year =  211,744,000 Btu/yr

Where 0.80 is the recoverable heat as a percentage of the units output, 2,545 is the conversion factor.

Cost savings in dollars per year = [(energy savings in Btu/yr)/Btu/fuel) x ($/unit fuel)]/primary heater efficiency.

If you would like to discuss saving money by reducing compressed air demand and/or any EXAIR product,  I would enjoy hearing from you…give me a call.

Steve Harrison
Application Engineer
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Photo courtesy of CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=32093890

 

 

Compressor Control – A Way to Match Supply to Demand

Rarely does the compressed air demand match the supply of the compressor system. To keep the generation costs down and the system efficiency as high as possible Compressor Controls are utilized to maximize the system performance, taking into account system dynamics and storage. I will touch on several methods briefly, and leave the reader to delve deeper into any type of interest.

air compressor

  • Start/Stop – Most basic control –  to turn the compressor motor on and off, in response to a pressure signal (for reciprocating and rotary type compressors)
  • Load/Unload – Keeps the motor turning continuously, but unloads the compressor when a pressure level is achieved.  When the pressure drops to a set level, the compressor reloads (for reciprocating, rotary screw, and centrifugal type)
  • Modulating – Restricts the air coming into the compressor, as a way to reduce the compressor output to a specified minimum, at which point the compressor is unloaded (for lubricant-injected rotary screw and centrifugal)
  • Dual/Auto Dual – Dual Control has the ability to select between Start/Stop and Load /Unload control modes.  Automatic Dual Control adds the feature of an over-run timer, so that the motor is stopped after a certain period of time without a demand.
  • Variable Displacement (Slide Valve, Spiral Valve or Turn Valve) – Allows for gradual reduction of the compressor displacement while keeping the inlet pressure constant (for rotary screw)
  • Variable Displacement (Step Control Valves or Poppet Valves) – Similar effect as above, but instead of a gradual reduction, the change is step like (for lubricant injected rotary types)
  • Variable Speed – Use of a variable frequency AC drive or by switched reluctance DC drive to vary the speed of the motor turning the compressor. The speed at which the motor turns effects the output of the system.

In summary – the primary functions of the Compressor Controls are to match supply to demand, save energy, and protect the compressor (from overheating, over-pressure situations, and excessive amperage draw.) Other functions include safety (protecting the plant and personnel), and provide diagnostic information, related to maintenance and operation warnings.

If you would like to talk about compressed air 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.

Brian Bergmann
Application Engineer

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More Efficient Compressed Air Use Could Lead To Energy Rebates

The use of compressed air can be found in almost any industry and is often referred to as a “fourth utility” next to water, gas and electric. The generation of compressed air accounts for approximately 1/3 of all energy costs in an industrial facility, in many cases, it’s the largest energy user in an industrial plant. With an average cost of $ 0.25 per every 1,000 SCF used, compressed air can be expensive to produce so it is very important to use this utility as efficiently as possible.

Utility companies recognize the benefit of using engineered products to reduce compressed air usage, like the ones manufactured by EXAIR, and offers rebate incentives for making a switch. Our local utility provider here in Cincinnati, Duke Energy, offers a $ 20 incentive for each replacement engineered nozzle.

 

Our Model # 1100SS 1/4″ FNPT and Model # 1101SS 1/4″ MNPT Super Air Nozzles

In their specification, the nozzle must meet a certain volumetric flow rate (SCFM) at 80 PSIG operating pressure for a given pipe size. For example, when looking at a 1/4″ nozzle, the flow rate must be less than or equal to 17 SCFM when operated at 80 PSIG. Our most popular nozzles for “general” blowoff applications would be our Model # 1100 (1/4″ FNPT) or our Model # 1101 (1/4″ MNPT) Super Air Nozzles. These nozzles require 14 SCFM @ 80 PSIG so this would be the ideal solution to reduce the air demand and take advantage of the rebate.

Here at EXAIR, much of our focus is to improve the overall efficiency of industrial compressed air operating processes and point of use compressed air operated products. If you’d like to contact one of our application engineers, we can help recommend the proper engineered solution to not only save on your compressed air usage but also assist with possible energy rebates available in your area.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

Intelligent Compressed Air: Things to Consider when Designing the Compressor Room

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One common thing that can be easily overlooked is the importance of designing an efficient compressor room. After you’ve determined your overall requirements and selected the appropriate compressor, you can begin designing the layout of your compressor room. For starters, the compressor room should be located in a central location when possible, close to the point of use. This will help to minimize pressure drop as well as reduce installation costs as less piping will be required. If this isn’t possible, try to keep the compressor room close to the larger volume applications in your facility. Otherwise you will have to use larger diameter piping in order to ensure an adequate volume of air is available.

The diameter of the distribution piping should NOT be based on the connection size of the compressors, aftercoolers, or filters. According to the Compressed Air Challenge Best Practices for Compressed Air Systems handbook, piping should be sized so that the maximum velocity in the pipe is 30 ft/sec. When the distance between the compressor room and the point of use is lengthy, consider increasing the pipe diameter to minimize the pressure drop across the system.

Inside of your compressor room you’ll have a variety of different equipment, all dependent on the demand, quality, supply, storage, and distribution of your compressed air. Keeping all of the equipment in its own room will also provide some insulation from the noise associated with compressed air generation. It is crucial that the space selected as your compressor room is sufficiently large enough to accommodate everything without becoming cramped. As a general rule of thumb, keep about 3′ of space between equipment such as the compressor, receiver tanks, aftercooler, and dryer. This helps to prevent equipment from overheating as well as offers maintenance personnel adequate space with which to perform any regularly scheduled maintenance or repairs.

Once you’ve selected your equipment, piping, and determined the location, another thing to consider is ventilation. As compressed air is generated, the compressor gives off a good amount of heat. It is important that the exhaust air is not permitted to re-circulate throughout the compressor room. The exhaust needs to be ducted so that it the warm air is not drawn in at the air intake on the compressor. Some equipment, such as refrigerated dryers, requires a substantial amount of cooling air. In these situations, an exhaust fan can be used to provide that additional airflow.

To further enhance the efficiency of your facility, the heat generated from compression can be re-purposed instead of simply exhausting into the ambient environment. This process is commonly referred to as compressed air energy recovery. Some industries require a source of heat for many of their manufacturing processes. In these scenarios, the heat energy that is produced during compression can be reused rather than having to generate another source of heated air. If the heated air can’t be used for any of your manufacturing processes, the heat can be used as a means to heat your water supply or even to heat the facility itself. This can drastically reduce your electricity or gas requirements during cooler periods.

To reduce the amount of required maintenance and ensure that your compressor is operating as efficiently as possible, the compressed air intake must also be free from particulate and harmful gases. When dust and dirt is drawn into the compressor, it can cause wear on the internal components. If the ambient environment contains a lot of dust and particulate, a pre-filter can be used to prevent any future problems. In these instances, it is important to consider the pressure drop that will be caused when designing the system.

Keeping these tips in mind will serve to make your life much easier in the long run. Once you have everything installed and set up, visit the EXAIR website or give us a call to speak with an Application Engineer. EXAIR’s Intelligent Compressed Air Products  can help you reduce compressed air consumption and increase worker safety by adhering to both OSHA 1910.242(b) and 1910.95.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

Image Courtesy of  thomasjackson1345 Creative Commons.

Monitor Your Compressed Air System With EXAIR’s Digital Flowmeters

A topic that we’ve talked about here on the EXAIR blog discusses the costs of compressed air and how to use it more efficiently. How can you determine the costs of your compressed air? The first step you’ll need to take is to quantify the flow. In order to do that you’ll need a measurement tool such as the EXAIR Digital Flowmeter.

dfm_sizes
EXAIR’s family of Digital Flowmeters

The Digital Flowmeter is available from stock for use on Schedule 40 pipe with sizes ranging from ½”-4” I.D. Sizes up to 6” for Schedule 40 and ¾”-4” for copper pipe are also available. With a digital readout display, it’s easy to accurately monitor your compressed air usage throughout the facility. Creating a baseline of your usage will allow you to understand your compressed air demand, identify costly leaks, and replace inefficient air products.

The Digital Flowmeter installs in minutes with help from a drill guide and locating fixture to assist in mounting the Digital Flowmeter to the pipe. Two flow sensing probes are inserted into the drilled holes in the pipe. The meter then seals to the pipe once tightened. There is no need to cut, weld, or do any calibration once it is installed. With blocking rings also available, installation can be permanent or temporary.

The newest addition to this product line is the Digital Flowmeter with wireless capability. Using a ZigBee® mesh network protocol, data is transmitted to an Ethernet connected gateway. This allows you to mount the Digital Flowmeter in areas that you may not be able to easily access and wirelessly monitor and graph the usage with the EXAIR Logger software. Take a peek at this video blog for a demonstration of the use of a wireless Digital Flowmeter software to compare an open pipe to an engineered Air Nozzle.

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In addition to communicating wirelessly with the gateway, the Digital Flowmeters can “piggyback” off of each other to extend their range. Each meter has a range of 100’. Using multiple Digital Flowmeters within the same ZigBee® mesh network, data can be passed from meter to meter to extend the distance over which the meters can operate. These can be installed on each major leg of your compressed air system to continuously monitor usage throughout the facility.

If you’d rather go with a hard-wired data collection method, the Digital Flowmeter is also available with a USB Data Logger. Simply remove the Data Logger from the Digital Flowmeter and connect it to the USB port of your computer. The data can then be viewed directly in the accompanying software or exported into Microsoft Excel.

dataloggerPRce_559wide
Digital Flowmeter w/ USB Data Logger installed

If you’d like to get a clear view of your compressed air usage, give us a call. An Application Engineer will be happy to work with you and get the proper Digital Flowmeters installed in your facility!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD