April 23, 2018
Many industrial plants and facilities employ compressed air systems. In order to determine which compressed air system is the right one for your workplace, you must first identify the air quality and quantity required by the end uses in your plant. According to the U. S. Department of Energy (DOE), careful assessment of these needs and an understanding of the difference between air quality and air quantity will ensure proper configuring of a compressed air system. Additionally, DOE recommends incorporating pressure and demand load requirements into your system analysis.
The air dryness and contaminant level required by plant end uses determine air quality. To analyze your compressed air system or determine your facility’s need for one, the department has advised learning the actual dryness level needed, along with the maximum containment level allowable for reliable production. Over-treating air beyond these levels will waste money and energy.
Air quantity, the required compressed air system volume, can be determined by summing the requirements of a facility’s compressed air applications and process operations (taking load factors into account) and the duration of such volumes by those applications. The total air requirement is not the sum of the maximum requirements for each tool and process, but the sum of the average air consumption of each.
When analyzing a compressed air system, pressure requirements must be taken into consideration alongside air quality and quantity. The minimum required discharge pressure level must include the different pressure ratings of compressed air applications and processes, along with the pressure drops from system components. Low or fluctuating pressure at end uses, DOE reports, is frequently misdiagnosed as inadequate discharge pressure.
Pressure drop is a term used to characterize the reduction in air pressure from the compressor discharge to the actual point of system end use. Because pressure drops occur as compressed air travels through the treatment and distribution system areas, excessive pressure drops can result in poor compressed air performance and excessive energy consumption. When employing a compressed air system, a facility should also establish a pressure profile. A pressure profile is a series of measurements of compressed air pressure at various system points, permitting identification of system components responsible for excessive drops in pressure.
In addition to air quality, quantity, and pressure requirements, the department recommends analyzing an industrial plant’s load profile, or its compressed air requirements over time. Air demands vary over time, and these variances are a major factor in system design. Plants with wide fluctuations in air demand requires systems that operate efficiently under part-load. In such cases, multiple compressors with sequencing controls have provided better operations from an economic standpoint. Conversely, plants with flatter load profiles have been able to utilize simpler control strategies.
Alongside DOE’s guidelines, the Compressed Air Challenge, an organization that works to optimize performances of compressed air systems, provides, in its Fundamentals of Compressed Air one-day training session, a seven step action plan to analyze and improve an individual facility’s system:
- Develop a basic block diagram of your compressed air system.
- Measure your baseline (kW, pressure profile, demand profile, and leak load) and calculate energy use and costs.
- Work with your compressed air system specialist to implement an appropriate compressor control strategy.
- Once controls are adjusted, re-measure to get more accurate readings of kW and pressures and to determine leak load. Recalculate energy use and costs.
- Walk through to check for obvious preventative maintenance items and other opportunities to reduce costs and improve performance.
- Identify and fix leaks and correct inappropriate uses—know costs, re-measure, and adjust controls as done previously.
- Begin implementation of continuous improvement programs.