Compressed air, despite its prevalence as a utility in industrial settings, often carries a significant cost burden and environmental impact due to its inefficient transmission of energy to machinery. However, the complete elimination of compressed air from industrial operations isn’t a feasible solution. Instead, optimizing compressed air systems offers a pathway to enhance efficiency, reduce energy consumption, and maintain operational effectiveness. Here, we explore three primary strategies for compressed air optimization, each contributing to improved performance and sustainability within industrial environments.
1. System Awareness and Training
What you don’t know can very often hurt you. Such is the case with the cost of compressed air inefficiency. Many industrial operators are unaware of the true costs and inefficiencies associated with their compressed air systems. Although common in industrial facilities, compressed air systems are generally one of the least efficient pieces of equipment with upwards of 80-90% of input energy lost to the heat of compression alone.
Implementing comprehensive training programs for employees on compressed air system operation and efficiency can yield significant benefits. By increasing awareness, employees can better understand their equipment and its energy consumption, leading to informed decision-making and proactive measures to optimize system performance.
A study by The Department of Energy focused on compressed air awareness training found that attending the training helped more than 75% of attendees initiate positive actions to reduce system waste. Such actions include replacing inefficient equipment, changing maintenance procedures, and implementing low cost/no cost measures like leak detection and repair.
The study also found that every dollar invested in compressed air training paid back at a rate of more than 80 times the initial outlay. More information on training for your staff can be found by visiting the Compressed Air Challenge website (www.compressedairchallenge.org).
2. Efficient Control Strategies
Compressor controls are designed to match air compressor delivery with compressed air demand by maintaining the compressor discharge pressure within a specified range. This discharge pressure should be set as low as possible to minimize energy use.
Effective control of air compressors, dryers and associated equipment is essential for optimizing compressed air systems. The type of control specified for a given system is largely determined by the type of compressor being used and the facility’s demand profile. If a system has a single compressor with a very steady demand, a simple control system may be appropriate. On the other hand, a complex system with multiple compressors, varying demand, and many types of end-uses will require a more sophisticated strategy.
Control strategies need to be developed using a systems approach, considering system dynamics and storage. Some basic types of individual compressor controls include:
- Start/Stop: Activates the motor based on discharge pressure; suitable for low-duty cycle applications to avoid frequent cycling and potential overheating.
- Load/Unload: Runs the motor continuously, unloading the compressor when pressure is adequate; though always consuming some power, it can be inefficient due to partial energy use without output.
- Modulating/Inlet Throttling Controls: Progressively adjusts compressor output to match flow requirements by throttling the inlet valve; best for large, industrial applications.
- Variable Displacement: Allows compressor to operate in partially loaded conditions without frequent starts/stops. Delivers more accurate and efficient pressure control than other strategies.
- Variable Frequency Drives (VFDs): Adjusts the air compressor output by changing the speed of the motor to match the demand capacity. Very effective for applications where there is constant demand but sensitive to environmental factors.
System controls orchestrate the actions of multiple individual compressors that supply air to the system. The objective of an effective automatic system control strategy is to match system demand with compressors operated at or near their maximum efficiency levels. This can be accomplished in a number of ways:
- Sequencing Controls: Utilizes a master unit to sequence compressor operation, taking individual compressor capacity on-and-offline in response to monitored system pressure (demand). This type of control system typically offers a higher efficiency because the control range around the system target pressure is tighter which typically allows for a reduction in average system pressure.
- Multi-Master (Network) Controls: Network controllers manage multiple compressors, enhancing operational responsiveness and efficiency through shared information.
- Flow Controllers: Separate supply and demand sides, allowing operation at optimal pressures and reducing demand-side pressures for efficiency.
- Air Storage and Controls: Use storage to manage demand fluctuations, reducing pressure drops and enhancing system responsiveness.
3. Equipment Sizing and Investments
Piping needs to be sized appropriately to match the capacity in any system. On many systems, the pipe connected to the air compressor is selected to match the diameter of the outlet on the machine. While it may seem intuitive to correlate pipe diameter with outlet diameter, this can lead to errors within the system, such as drops in pressure and losses in efficiency
There will come a day when it may be in the site’s best interest to consider replacing old or poorly functioning equipment with newer, more efficient versions. Older or inefficient compressed air systems often require more frequent maintenance and repairs. Upgrading to newer equipment will often significantly reduce the need for costly repairs, spare parts, and maintenance services. Newer, more reliable systems often come with improved monitoring and predictive maintenance capabilities to help reduce the risk of unplanned downtime and associated financial losses.
Like many things in life, all components of a compressed air system are interrelated; action in one area impacts performance elsewhere. Therefore, the chief tenet to keep in mind when working to optimize such systems is to focus on the efficiency of the system as a whole.
