Auditing a Compressed-Air System: A Practical Energy-Assessment Method

Compressed-air systems are vital for many industrial processes, but they can also be significant consumers of energy. Effective management of these systems requires regular audits to identify inefficiencies and opportunities for improvement. This article outlines a practical method for auditing a compressed-air system, focusing on steps that can help plant engineers, maintenance managers, and energy managers optimise their systems.

Load Profile Logging

The first step in auditing a compressed-air system is to log the load profile. This involves monitoring the system's demand over time to identify patterns and peak usage periods. Typically, this is done using data loggers or SCADA systems that can record air consumption, compressor status, and other relevant parameters. By analysing the load profile, managers can determine if the system is oversized, undersized, or if there are periods of low demand where the system could be optimised or even shut down temporarily.

Leak Survey

Leaks are a common source of inefficiency in compressed-air systems. A thorough leak survey is essential to identify and quantify these losses. This can be done using ultrasonic detectors, which can pinpoint the location of leaks even when they are not audible to the human ear. In most plants, it is not uncommon to find leaks that account for 20-30% of the total air consumption. Addressing these leaks can result in significant energy savings and improved system performance.

Pressure Profile

Monitoring the pressure profile throughout the system is another critical aspect of the audit. This involves measuring the pressure at various points in the distribution network, from the compressor outlet to the end-use points. Ideally, the pressure should be consistent and within the range specified by the equipment. However, in practice, pressure drops can occur due to restrictions in the piping, excessive length of distribution lines, or poorly maintained equipment. By identifying and addressing these issues, managers can ensure that the system operates efficiently and that end-users receive the required pressure.

kW/m3 Baseline

Establishing a baseline for the system's energy efficiency is essential for assessing its performance and identifying areas for improvement. This typically involves calculating the specific power consumption (kW/m3) of the system, which is the ratio of the total power input to the system's air output. A typical range for this value in industrial applications is 0.15-0.25 kW/m3, but this can vary depending on the specific equipment and operating conditions. By comparing the actual kW/m3 value to the baseline, managers can determine if the system is operating efficiently or if there are opportunities for energy savings.

End-Use Mapping

Understanding the end-use of compressed air in the plant is crucial for optimising the system. This involves mapping out the various applications and processes that use compressed air, and assessing their requirements in terms of pressure, volume, and quality. By doing this, managers can identify opportunities to improve the efficiency of these applications, such as by using more efficient equipment, reducing pressure requirements where possible, or implementing demand-side management strategies. This can help to reduce overall air consumption and improve the system's energy efficiency.

Building an Action List

The final step in the audit process is to compile an action list based on the findings. This list should include specific actions to address the issues identified during the audit, along with estimates of the potential energy and cost savings. For example, if the audit reveals significant leaks, the action list might include recommendations to repair or replace the affected components, along with an estimate of the energy savings that could be achieved. Similarly, if the audit identifies opportunities to improve end-use efficiency, the action list might include recommendations to implement these changes, along with an estimate of the potential savings.

By following this step-by-step method, plant engineers, maintenance managers, and energy managers can conduct a thorough audit of their compressed-air systems and identify opportunities for improvement. This can help to optimise the system's performance, reduce energy consumption, and improve overall efficiency.

Planning a compressed-air upgrade? Talk to SIND's engineers.