Best Practice Guide

Food and Beverage Growers and Processors

Compressed Air

Proper Operations

Preventing Misuse
It is the end of a long day at the widget factor, and the crew is running late. They need to prep the work area for the next shift, so Joe Genius grabs a blowgun to blast clean floors and workbenches. He also uses compressed air to dry a set of tools that accidentally got wet before putting them away. Work done, the crew leaves.

This is an example of another major energy waste - misuse of compressed air.

Remember that compressed air is a utility, often the only one produced onsite. To workers who are not concerned with costs, compressed air is always on, ample in supply, and seemingly "free". It powers tools that are more maneuverable, lighter in weight, safer to use, and easier to control than electric or mechanical counterparts. Why not use compressed air whenever it can accomplish the task at hand?

Plant managers responsible for controlling costs will think otherwise. As described earlier in this chapter, generating compressed air is tremendously inefficient and costly. A general rule of thumb is that it takes seven to eight hp of energy to generate one hp worth of air force. Compressed air should be reserved for applications requiring high-pressure or high-torque, i.e., only when other options are inadequate.

Evaluate with employees the cost and performance of pneumatic tools versus their electric or mechanical counterparts, especially for low-pressure or low-torque applications. Use a low-pressure air blower, for example, to clean parts or materials rather than compressed air. Similarly, use a broom to sweep rather than blowing a dirty floor clean, and use fans when ventilation is needed.

It can be challenging to change behaviors, especially if people are used to doing things a certain way. If using alternative equipment, like electric drills, be sure there is a sufficient supply and that workers can easily access it. New rules governing the appropriate use of compressed air might initially need to be enforced or otherwise incentivized.

Alternative Applications to Low-Pressure End Uses*

Low-Pressure End Use Potential AlternativesReasoning
Open blowing, mixingFans, blower, mixers, nozzlesOpen-blowing applications waste compressed air. For existing open-blowing applications, high efficiency nozzles could be applied, or if high-pressure air isn't needed, consider a blower or a fan. Mechanical methods of mixing typically use less energy than compressed air.
Personnel coolingFans, air conditioningUsing compressed air for personnel cooling is not only expensive, but can also be hazardous. Additional fans or HVAC upgrade should be considered instead.
Parts CleaningBrushes, blowers, vacuum pumps Low-pressure blowers, electric fans, brooms, and high-efficiency nozzles are more efficient for parts cleaning than using compressed air to accomplish such tasks.
Air motors and air pumpsElectric motors, mechanical pumpsThe tasks performed by air motors can usually be done more efficiently by an electric motor except in hazardous environments. Similarly, mechanical pumps are more efficient than air-operated double diaphragm pumps. However, in an explosive atmosphere and/or the pumping of abrasive slurries, the application of a double diaphragm pump with appropriate pressure regulating and air shut-off controls may be appropriate.

* Table courtesy of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program.

Right-Sizing, Sequencing and Controls
Matching compressor capacity to actual facility demands is important for both energy and production efficiency. Typically, compressed air systems are sized to meet maximum required loads. However, in actual use, loads can vary widely and frequently do not reach maximum capacity. The result is that installed systems tend to be oversized, and, when run at full capacity, waste significant energy.

In small systems with constant loads, right-sizing the compressor and choosing an appropriate control technology should suffice.

If loads vary, it might be cost-effective to purchase a "trim" compressor and sequence run times. In sequencing, one compressor is used for base loads; as demand for compressed air rises, the system pressure drops, triggering the trim compressor to come online and provide additional capacity. When demand drops, extra capacity is taken offline by shutting down the trim compressor.

Sequencing works well with two to three compressors, but begins to falter as more are added because of an increase in pressure bandwidth. The base compressor has about a 10-psi operating pressure band, plus about three pounds for each trim compressor. So, a system with three sequenced compressors would have a pressure band totaling 16-psi. Now consider that for every two pounds of pressure, efficiency drops or rises by 10 percent - thus, that 16-psi pressure band could equal as much as eight percent of the total system capacity. As the pressure bandwidth increases, the energy saving benefits of sequencing compressors disappears.

In larger compressed air systems, multiple compressors use controls to match capacity to actual demand. Older control systems are less accurate, and have a much wider range between pressure set points that trigger increases and decreases in compressor output (the control range). To avoid wide swings in pressure, control points are usually set at higher pressures than needed (requiring more energy to operate).

New computerized control systems narrow the control range, and let compressor output more closely match actual demand. This allows the overall system pressure to decrease (two pounds = one percent efficiency).

Besides the direct energy savings stemming from reduction in compressor output, minimizing system pressure has another important effect on the system - less energy is lost from leaks and misuses of compressed air.


Resources

Improving Compressed Air System Performance: A Sourcebook for Industry. Compressed Air Challenge and U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. The Compressed Air Challenge(CAC) is a voluntary coalition of industry, manufacturers, state research and development agencies, energy efficiency organizations, contractors, and utilities. CAC provides a number of resources online, including best practices, tips, and case studies, as well as live trainings held throughout the country. The mission of CAC is to develop and provide resources that educate industry on the opportunities to increase net profits through compressed air system optimization.

Efficiency Improvements in Industrial Compressed Air Systems. Pacific Gas & Electric Company, April 25, 1997.

Air Compressor Energy-Saving Tips. Minnesota Technical Assistance Program, University of Minnesota, 2003.

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, Compressed Air Best Practices.

Wise Rules for Industrial Energy Efficiency: A Toolkit for Estimating Energy Savings and Greenhouse Gas Emissions Reductions. U.S. Environmental Protection Agency, ENERGY STAR, September 2003.

The Compressor Guy website, archived files on Profit and Productivity Thieves and Unregulated Use.