Take a deep dive into audit costs, benefits

A lack of awareness is the primary culprit of this energy and financial cost. By understanding more about how to manage compressed air, and by realizing that at its core “air isn’t free,” many facilities can make rapid gains in avoiding inappropriate usage of air and compressed air leakages throughout the plant.

12/17/2014


Although electric motors consume the majority of electricity in manufacturing plants, compressed air systems require huge expenditures of energy and cost that are easy to overlook in a plant’s calculated cost of production. A lack of awareness is the primary culprit of this energy and financial cost. By understanding more about how to manage compressed air, and by realizing that at its core “air isn’t free,” many facilities can make rapid gains in avoiding inappropriate usage of air and compressed air leakages throughout the plant.

Many manufacturers are just beginning to grapple with improving compressed air management systems, and there are resources available to help understand ways to improve. The Detroit Edison Utility Company offers a free facility audit to identify ways to reduce energy use (although less than 20% of its customers take advantage of it). The company reports that only about 10% of the compressed air systems in operation are regularly audited and improved.

The cost of pneumatic energy

According to different estimates provided by the U.S. Dept. of Energy, the automotive industry, and pneumatic equipment distributors, the cost of air ranges from 16 cents to 30 cents per 1000 ft3. Buying electricity accounts for 76% of the cost. Equipment and maintenance also factor into the cost of air.
The manufacturing sector is learning that a piecemeal approach to machinery designs, oversized applications, leaks, mismatched supply and demand for air, and inappropriate uses of compressed air systems results in energy waste, increased operating costs, and reduced productivity. The facts behind the problem are well documented:

  • Production of 1 hp of pneumatic energy costs six times as much as 1 hp of electrical energy.
  • 23% of air cost results from leaks; another 23% comes from inappropriate uses or artificial demand.
  • Every 2 psi reduction in air pressure equates to 1% of input hp cost reduction in electricity.
  • Higher operating pressures lead to higher costs, so a 2 psi reduction in air pressure equals a 1/4 hp cost reduction in electricity ($110/year).
  • Compressor inefficiency impacts costs, as many run continuous duty when not necessary.

Figure 1: Inefficient use of compressed aire is more wide-spread than in any other energy source. All charts courtesy: Parker Automation GroupEvaluate air use

At Parker Hannifin, we’ve seen these types of inefficient compressed air usage in a wide variety of industries and facilities. Recently, we conducted 32 audits of compressed air systems and determined that the average annual cost associated with production and waste was $278,155. Further examination focused on identifying areas of improved efficiency revealed a potential annual savings of $55,354 (19.5%) with the average cost of corrective action only $18,950. The elapsed time required to realize these savings is notable too; the average time to ROI was only 127 days.
Audits of compressed air systems often focus on two main objectives:

  • Specifying correct air pressure levels by analyzing and reviewing the application of compressors, headers, and dryers to make air savings recommendations. If a system audit confirms that a plant can pressure down, it may be able to avoid purchasing additional satellite compressors.
  • Reviewing compressed air systems for leaks and incorporating leak prevention programs into regular plant operations.

If a system isn’t regulated and monitored properly, artificial demand for air is created. For instance, high-pressure air should not be specified or used unless it is absolutely necessary, and it makes sense to reduce required operating pressures wherever possible to realize savings in air costs and maintenance. In addition, specifying and using correct pressure levels for equipment improves the performance of most compressed air systems and also keeps equipment from being overworked.

Figure 2: Most of the cost of compressed air is tied up in the energy to make it, but that still leaves almost 25% of the costs in equipment and maintenence. Opportunities for savings

There are savings opportunities on the supply side of the compressed air equation. Different compressor types that supply compressed air systems operate at different efficiencies. Piston, rotary screw, and centrifugal compressors operate between 50% and 90% efficiency, depending on the application. During the equipment selection process, current and future demands on the system must be considered.

Let’s consider cylinders in this scenario. Typically, cylinders work in one direction and are usually operated at a pressure well above what is required. Operating consistently at higher pressure than necessary damages the equipment prematurely and wears on the actuators as well. In the retract direction, cylinders typically have very little load and can be retracted at half of the typical operating pressure.

Instead of running actuators at 80 psig for both extension and retraction, operating them at 60 psig extension and 40 psig retraction will still effectively perform the work required, but result in air savings of potentially several thousand dollars per actuator per year.

Vacuum applications provide another opportunity for pressuring down on air demand. Many vacuum cups that operate satisfactorily on 70 psig, for instance, at times are supplied with air at 100 psig, which is completely unnecessary. To take this example a step further, Parker offers air economizing/emergency stop vacuum solutions that enable the vacuum to be turned off over 90% of the time that the part is present.

Another source of compressed air waste is air blow off applications, which utilize pneumatics on conveyors either to blow chips or dirt off a part, or to blow the part itself off the conveyor. Frequently, they are set to blow air nonstop; to save cost, air should only be blown when the part is present. Parker offers a solution that senses the presence of the part and switches the airflow on and then off. High-efficiency nozzles and adjustable blow guns can also reduce air consumption by 50%-75% and increase impact pressure. Air blowers can also be replaced by even more efficient centrifugal blowers.

These systems can be quite powerful in terms of cost savings. To put that in terms of dollars, if the annual cost of electricity for a vacuum application is $25,000, using an air economizing solution can cut the electricity cost by 90% to about $2,000.

Best practices and design considerations

A combination of best practices and pressure-reduction solutions can mean significant savings on the plant floor. Proper sizing of system components, such as tubing, hose, connectors, and fittings, can reduce operational pressure and minimize component cost.

  • Valves: Oversizing valves can waste energy and take up valuable space in machine and system designs. There are many formulas available from air system specialists, such as Parker, that can be used to specify the right flow rating (Cv) for valves. Using valves with solenoid air pilot and low watt coil designs reduces electrical costs and burnouts. Common coils in various valve sizes lower costs for replacements and labor time.
  • Fittings: Another source of drain on air systems. Using straight fittings wherever possible, rather than 45- or 90-deg elbow fittings, minimizes pressure drops. Properly applying thread sealant helps prevent leakage and system contamination.
  • Actuators: Select higher quality, repairable models that last longer, leak less, and reduce maintenance costs. Typically, cylinders can be sized at 60 psig to provide a safety margin.
  • Regulators: Using regulators to pressure down can reduce air costs. Installing reverse flow regulators, piped between the valve and the cylinder, provides independent pressure control for extend and retract. The nonrelieving design of these regulators saves air, as well as wear, on components and mechanical devices.
  • Proactive maintenance: Plants that have neither proactive programs nor resources should implement smart air prep systems that ensure adequate airflow by servicing filtration and pressure controls. These systems include drip leg assemblies to protect equipment against water and contamination, primary and coalescing filters, and pressure drop indicators and sensors used to complement and support maintenance programs. Visual and electrical sensors detect pressure drops as filters clog. Clogged filters reduce flow, increasing both air and maintenance costs.

Identifying and repairing leaks

Beyond wasting pressure and electricity, leaks contribute to operating problems because of fluctuating system pressure that causes equipment to function less effectively, and decrease equipment service life because of extra cycling and increased run time.

Compressed air can be lost through multiple locations in the system, but the most common problem areas are faulty couplings, joints, quick disconnects, hoses or tubes, fittings, valves, and FRLs (filters, regulators, and lubricators). The rate of leakage depends on the supply pressure in the system and the size of the leak. The amount of lost air is measured in cubic feet per minute (cfm).

Using an ultrasonic acoustic detector is the most effective way to detect system leaks. These detectors locate the source of high-frequency hissing coming from leaks. Because leaks will continue to occur, a leak prevention program should be incorporated to help maintain the efficiency and cost-effectiveness of the air system.

As leaks are repaired, re-evaluation of the compressed air system should follow. Many plants need to work with air system specialists to adjust compressor controls. This often entails reducing compressor run times to match the reduced demand. These system audits and corresponding adjustments can often be achieved with minimal capital expenditures.

Realizing savings

Within operations and production teams, there is a general lack of awareness of the negative impact that inadequate air compression practices and systems have on their businesses. System audits and corresponding adjustments can generally be achieved with minimal capital expenditures, and efficient use of compressed air can be realized through better pneumatic designs and component/system selection. Aggressive best practice initiatives and maintenance programs that fix and prevent leaks in pneumatic systems can have the immediate payoff of saving energy, lowering operating costs, and providing better plant operational efficiency.

Russ Strobach is global target market manager for Parker Automation Group.



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