Best Practice Guide

Food and Beverage Growers and Processors

Introduction

Planning an Energy Program

Funding and Approval

Commissioning

On-the-Farm Energy Use

Lighting

Building Envelope

Central HVAC System

Boilers

Steam

Combined Heat and Power

Compressed Air

Energy Use Basics

Proper Maintenance

Proper Operations

Waste Heat Recovery

Refrigeration

Motors

Demand Response

Distributed Generation

Water Use


Fetzer Vineyard

J Vineyards and Winery

Mission Foods

S. Martinelli and Company

Sara Lee

Vineyard 29


View the Glossary

Compressed Air

Proper Maintenance

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Check and Repair Air Leaks
Leaks in a compressed air system are the number one reason for energy waste. Leaks reduce system capacity, which results in either less pressurized air available for end-uses or in wasted energy as compressors work harder to maintain adequate system pressure. A one-quarter-inch hole, for example, in a 115-pounds-per-square-inch (psi) system running 8520 hours per year would lose about 174,100 kilowatt-hours annually, at a cost of nearly $17,150.

Besides lost capacity and excessive energy costs, leaks can have adverse effects on end-use equipment. Leaks cause system pressure to drop. If pressure drops below minimum levels, tools and operations could be less efficient and equipment life could be shortened. In some cases, production lines could even be stopped.

Photo courtesy of S. Martinelli & Co.View Details.

In a typical facility, leaks range from two to 20 percent of the overall system capacity, but may climb as high as 40 percent in facilities lacking routine maintenance. In a well-maintained system, leaks should account for less than 10 percent.

Check and repair leaks before adding capacity to an existing compressed air system. Too often, new compressors are brought online in response to diminished capacity when repair of leaks might have solved the problem without capitol investment or added operating costs. Remember that the total cost of each compressor includes the capitol cost for purchase and installation as well as operating costs for energy and maintenance.

Owners and managers should develop a leak detection plan as part of routine operations and maintenance. The frequency of inspections will depend on individual facility characteristics, but should probably be no less than once per month. Heat, vibrations, or anything that causes pipes or hoses to move results in a higher incidence of leaks.

Once a plan is in place, responsibility for conducting inspections can either be contracted to a compressed air specialist, or done in-house by trained staff.

Ilustration of compressed air leaks and cost per year. Data from Compressed Air Challenge.View Details.

There are a few clear advantages to working with contractors. First, they arrive equipped with all necessary diagnostic and repair equipment, and are ready to fix leaks on-the-spot. Contractors generally fix leaks much faster than in-house staff, who may have several competing priorities and responsibilities. Second, contractors have specialized experience, and can quickly hone in on problem areas. Similarly, contractors can offer objective opinions about how the system is set-up and operated, and identify opportunities to improve energy efficiency beyond leak repair. Finally, incentive programs exist that might help finance onsite assessments of compressed air systems (energy audits) - contact your local utility or check online to find out more.

If in-house staff decide to undertake routine inspections, be sure someone is well trained using an ultrasonic leak detector. Staff should try to fix leaks as they find them, rather than simply adding these projects to a long-list of needed maintenance. As leaks are repaired, system pressure rises, which can create more leaks. The system pressure must be adjusted each time leaks are repaired. This is a constant battle - leaks will never by 100 percent fixed, and new leaks will continue to appear. Staff must remain diligent.

In addition to checking for leaks, it is a good idea to change air filters as part of routine maintenance. As dirt accumulates, the compressor must work harder to move air through the distribution lines. For every one psi increase in air pressure gained through proper changes of air filters, compressor energy use is reduced by about one-half percent.

Unregulated Uses
Adding regulators is the least expensive measure a company can take to control compressed air. It also makes a lot of (dollars and) cents - unregulated air is the second largest user of compressed air after leaks, accounting for as much as 20 percent of total system capacity.

Consider this example. A paint sprayer needs 10 cubic feet per minute (CFM) of compressed air at 25 pounds per square inch of pressure (psi). Without a regulator, air in the lines that feed the sprayer is pressurized to about 125-psi. So the sprayer receives nearly 40 CFM of air instead of 10, about four times more than necessary. These calculations are rough (actual line pressure fluctuates, and psi-requirements of different end-use tools varies), but are useful to illustrate energy wasted from unregulated uses of compressed air.

Group equipment, whenever possible, according to pressure requirements, then add regulators to distribution lines. Once installed, adjust regulators gradually over time to find the lowest system pressure possible without affecting the performance of end-use equipment. The lower the workable pressure, the more efficient the system is operating.

Remember that if things are buggy, do not adjust regulators up. Higher system pressure results in less air being generated, not more.

Business Examples

At S. Martinelli & Company juice delivered to the bottling line is pasteurized, cooled, labeled and ready for sale. The entire process - including filling and bottling machines, filters and tanks, and case packaging with positioning devices, stop gates and motorized valves -- relies on a large compressed air system as well as over a hundred motors. Realizing the potential for energy leaks along this entire system, Martinelli's initiated a compressed air audit and consequently upgraded the compressed air systems at both facilities. Upgrades included an oil-free air compressor with flow control, a compressed air pipe loop, and EPACT motors, which deliver an automatic two to three percent increase in energy efficiency. In addition to being more energy efficient, the upgraded air systems are also cleaner and quieter. The compressed air upgrade resulted in less leaks and real time cycling according to plant pressure.


Not only did the juice company obtain a $24,000 rebate for the compressed air system upgrades and replacement motors, but Martinelli's has also reduced its use of the system by 13 percent, which will continue to reward the company with lower energy costs year after year.

At Sara Lee's Sacramento bakery, a maladjusted compressor controls package and a failed pressure/flow controller caused the compressed air system to perform erratically, increasing both energy use and maintenance costs.


Sara Lee contracted Draw Professional Services, a Department of Energy (DOE) Allied Partner, to conduct a systems-level assessment of the compressed air system that included an AIRMaster+ analysis (AIRMaster+ is a free, Windows-based software tool used to analyze industrial compressed air systems; available from DOE).


Sara Lee's compressed air system consisted of one 100-hp and two 150-hp rotary screw compressors. When the pressure/flow controller failed, air demand patterns began fluctuating severely, forcing workers to operate all three compressors simultaneously just so they could meet production targets. At the same time, the compressor controls were out of adjustment, causing them to respond incorrectly to different air pressures. More than one compressor would activate, for example, when only one unit was actually needed.


On top of this, air leaks accounted for 15 to 20 percent of the entire system capacity. Even worse, the assessment discovered multiple uncontrolled open-blowing applications. Those two problems exacerbated the pressure fluctuations and wasted even more compressed air.


Draw configured the system so that the 100-hp fixed-speed compressor is now the base unit. A 100-hp variable speed drive unit serves as the trim compressor; it comes online as needed, and can vary output to match actual demand. Sara Lee was able to retire one of the old 150-hp compressors, and stored the other one as a backup. The newly optimized system performs much better, and supplies the plant with a consistent air supply at a stable pressure.


Sara Lee's compressed air project is yielding impressive energy savings while making production more reliable. Measurements indicate energy savings of 471,000 kWh and cost savings of $40,000 per year. These figures are consistent with AIRMaster+ estimates. Because two compressors can now be off-line, maintenance costs have also declined, saving another $10,000 per year, for a total annual savings of $50,000. An $11,000 rebate from the Sacramento Municipal Utility District reduced the total project costs to $27,000, for a simple payback of 6.5 months.


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.