Used widely throughout industry, compressed air is often called the fourth utility. In a typical industrial facility, generating compressed air consumes from 10 percent to 30 percent of the total electrical usage and efficiencies can be as low as 10 percent. A compressed air system that is managed properly can save substantial amounts of energy while reducing maintenance costs, decreasing downtime, increasing productivity, and improving overall product quality.
An analysis will identify areas for improvement. There are two types: a basic assessment and a comprehensive audit. A basic assessment can be conducted internally by trained staff, whereas an audit should be conducted by an external compressed-air expert. Although an audit provides much more detail, a basic assessment can result in energy use reductions of 25 percent or more, and lower maintenance costs. A basic assessment can also identify:
Compressed air needs are defined as the air quality and air quantity required by the tools and machinery in your plant. A thorough analysis of a compressed air system will determine the air, pressure and demand load requirements. Air quality is based on air dryness and maximum allowable limits of air contaminants for reliable production. To determine total air quantity, add up the average air requirement for each process—including factors affecting load—and the duration of each application.
Each compressed air application and process may have a different pressure rating than the next. These ratings are combined with the pressure drops from components in the system to determine the minimum required discharge pressure level. By measuring pressure at various points in the system, a pressure profile can be developed; identifying which components are producing excessive pressure drop.
Knowing demand loads is also critical in understanding and optimizing your system. This involves analyzing a plant’s load profile (compressed air requirements over a specific period). The load profile will help determine what type of control strategy is needed. A wider variation in air demand will require a more complicated control strategy.
After appropriate compressor controls are implemented (and adjusted), energy consumption and pressures should be measured again to recalculate energy use and costs. Next, take a walk through the plant to identify opportunities for reducing costs through preventive maintenance. Locate and fix leaks, along with any other problems. Once these problems are fixed, measure energy consumption again so controls can be adjusted properly.
Completion of these steps will enhance the performance of your compressed air system, however, continuous improvement is necessary in order to optimize energy savings and increase productivity. Develop a program to continually monitor the system and take required actions to increase efficiency. Also, consider implementing a leak-detection and repair program using an ultrasonic leak detector. To realize energy savings, an effective leak repair program must include a review of system pressure and controls.
After a manufacturer of fine and specialty chemicals completed a compressed air audit, it was discovered that both facility compressors were operating at lower pressures than required. In addition, higher air use was occurring during transfers—as opposed to reactions—and there were significant leaks. To solve some of these problems, a leak detection and repair (LDAR) program was established and more efficient compressors were installed.
At a cost of $2,500, the LDAR program saved 120,832 kWh or $9,100 with a simple payback of three months. The more efficient compressed air system cost $27,800 for a savings of 292,283 kWh or $21,980 with a simple payback of 15 months. Since the comprehensive, compressed air system energy-reduction strategy was implemented in 2008, the facility has saved nearly 1,240,976 kilowatt hours.
If a basic assessment reveals problems that require additional analysis to identify their causes and solutions, a more comprehensive audit is required. An experienced expert in compressed-air system efficiency should be hired. The U.S. Department of Energy also provides a guideline for selecting a compressed air expert.
Compressed Air Challenge. Compressed Air System Analysis. August 2010. (Last accessed on April 23, 2013).
Compressed Air Challenge. Improving Compressed Air System Performance: A Sourcebook for Industry. November 2003. (Last accessed on April 23, 2013).
Smith, Duane. How to Analyze Energy Consumption of Compressed Air Systems. Sustainable Plant. August 23, 2011. (Last accessed on April 23, 2013).