Issue link: https://www.e-digitaleditions.com/i/1380119
42 / June 2021 powderbulk.com cost $50,000 but instead cost in excess of $200,000. When asked how the compressor was sized, the salesperson replied that he just matched the size of the portable compressor that was running the site at that particular time. Clearly, this is an exaggerated case, but it illus- trates the point that insufficient data collection and analysis can lead to very bad economic consequences. What an audit looks like A compressed-air system audit usually has three stages: preaudit, field stage, and analysis. Preaudit stage. The preaudit stage is when the audit scope and objectives are defined. As mentioned previously, this is necessary so that the scope of work is specific to your compressed-air system issues and your goals are in focus throughout the entire audit. Usually, this stage is effectively done via a preaudit conference call or meeting that includes people with plant oper- ations knowledge. However, major or highly complex audits might require an on-site preaudit. Field stage. The field stage is when inspections and measurements take place. This stage includes installing sensors and data loggers and inspecting the compressor room, compressed-air distribution, and compressed-air points of use. Analysis stage. The analysis stage is when the auditing team creates a model using the collected data from the field stage to understand the system's behav- ior and how that's reflected in terms of cost. From that, an optimal solution based on the existing system is developed. Once the audit analysis is done, the auditor gen- erates an output report and presentation of their bidder to explain their recommended scope of work and how that would achieve the company's goals. Considering the variables When thinking about the scope of work for a compressed- air audit, two variables that are important to consider are the breadth of the audit's goal and the audit's depth. Breadth of the audit's goal. First, determine whether the audit should be designed to deal with one specific issue or to develop a long-term plan. For example, assume you want to incorporate a new piece of production equipment into your process, which will increase demand to a compressed-air system that you're concerned is already taxed. If that production equipment is being delivered sooner rather than later, it may make sense to limit the audit's scope so that you can understand the compressed-air system's capacity before the production equipment arrives. Depth of the audit. The second variable to consider is how deeply the audit should examine your system, which can be broken into two broad categories. The first category concerns how much of your compressed-air system the audit will encompass. For example, should you focus solely on the compressor room or on leaks? What about applications that may be using excessive amounts of air? What about the pressure drop in the pip- ing system? In most material handling systems, it pays to look at the entire system, especially when devising a long-term plan for system evolution. This would include looking at the compressed-air supply, distribution, and demand as well as the infrastructure that supports the technologies in the various areas. That infrastructure is broadly defined as procedures and people. For example, if you want to reduce your facili- ty's electricity consumption, is it better to turn off unnecessary lights or leave them on and just install more efficient light bulbs? With light bulbs, as with compressed- air systems, it's good to start with demand. If your consultant is only focused on installing a better compressor in the compressor room and not on how to use your existing compressed-air capacity more efficiently, you'll be missing one- to two-thirds of the potential savings. The second category concerns the depth of the data the audit should develop in terms of which and how much data to collect. An example of this occurred at a mine processing facility, as shown in Figure 1. When auditing that facility, a compressor was found to be oversized by a factor of five. In this particular case, the client not only spent too much money on the equipment but also ran an oversized power supply up half a mile of rugged mountain terrain. The project should have FIGURE 1 This mine's compressor building housed a compressor that was five times too big.