Permanent Compressed Air System Metering and Monitoring
Optimal compressed air system performance, defined by efficiency, reliability and air quality, has now become the main goal when operating, installing, purchasing or designing compressed air products. Whether you are the air compressor manufacturer, distributor or end user - everyone in the compressed air industry needs to be aware and work towards these goals.
Baselines Developed by Permanent Monitoring vs. Temporary Compressed Air Audits
Rapidly rising energy costs, tough economic times and the need to reduce costs are factors impacting all businesses operations. This is driving a wave of demand for energy reduction measures and technologies. Compressed air systems, a very expensive utility, have become the first target for energy reduction measures in most industrial facilities today.
“Free” sales-based audits have become readily available, in the compressed air industry, from many organizations pushing product sales. How reliable are the results and recommendations from these free audits lasting a maximum of ten days? What is the actual value to the bottom line for an end user? These are the questions typically raised surrounding free audits. Since free doesn’t exist, what’s the catch? Do factories have another option? Yes, they do.
Airleader is heavily involved in compressed air audits, working with several utilities in the United States and in other countries around the world. For larger compressed air systems, we recommend the utility providers spend the extra incentive money to invest in a permanent monitoring system - rather than ten days of temporary metering for an audit. A permanent monitoring system can provide a very solid baseline, developed over several weeks or months. It also allows one to examine and quantify various metrics such as weekend leak rates, and different loads based on many more production day profiles. Creating a more robust baseline profile allows an audit to better identify several corrective measures such as storage, piping changes, control systems or leak repair - and precisely quantifying the ROI for each measure and prioritizing them with budgets or timelines.
An Audit Process Using Two Months of Data
We recently performed a compressed air audit at a large manufacturing facility running several large air compressors at two separate locations in the plant. Metering equipment was installed including kW meters, flow meters and pressure sensors throughout the facility. A thorough leak audit for the whole facility was also performed. The audit process took just under two months to collect the data, find the system inefficiencies and make the proper recommendations.
The compressed air audit report was presented to the client identifying substantial inefficiencies due to poor piping, improper control of the air compressors, excessive unloaded compressor times, huge amounts of air leaks, and to everyone’s surprise, the discovery that the system runs on two different pressures as the systems are separated via underground piping networks. As one can imagine, getting to the bottom of a system like this was going to be a massive undertaking. It would need to be done in stages, using a tremendous amount of instrumentation.
The first measure had to be a master controller. With the master controller, we would then be able to control the compressors and correlate the data collected to production demands and leak loads. Stage one included the master controller, large air receivers, a large energy efficient compressed air dryer and a large VFD air compressor to trim the base loaded units. Once the system was installed the savings were immediate, unloaded air compressor power went from 70% to 15% while decreasing the motor cycles - saving the motor and bearing life of the air compressors.
Metering and Monitoring of Compressed Air Flow - Click here to enlarge.
Five Months After the Audit
With proper control of the compressed air system now in hand, we began the task of identifying further measures through the data collection system and permanent metering installed. This quickly identified a leak rate >50%, which on a system consuming more than 10,000 cfm at times, is a massive volume of leaks. We identified the leak rate by correlating flow rates during down-time on Sundays and Saturday off shifts. This data was compared to the data from the kW meters (on the air compressors) which allowed us to build a proper ROI for the client. Without the permanent metering, we would have had no way of accomplishing this task. The plant, however, needed to understand the data to believe in the project.
I remember coming back to the site, five months after the audit, to do some customer training on the master controller. Just as I getting ready to leave, I was told I had to wait for their system analyst to come down. I asked the maintenance manager, “What analyst?” He responded saying the analyst was from the accounting department but he didn’t know what the analyst wanted. Soon the gentleman arrived, carrying some printed graphs from the monitoring system, similar to graph 1. He asked me, “Can I trust the data provided from your system?” I looked at the data and said, “Yes you can, why do you ask?”
The analyst was shocked that on Sundays, when the plant was closed, the flow rate was 3500 CFM and even more shocked when he realized that the plant leaks the same amount 365 days a year. The next question from the Analyst was, “How can you confirm this is the correct flow rate?” I then used the kW data, to show that yes, three air compressors were running loaded - again confirming the leak rates were correct.
Table 1: Air Compressor Performance during a full week - Click here to enlarge.
We printed the weekly performance table (table 1) and a weekend day performance table (table 2), allowing us to perform the following calculations.
Leakage = 16,789 kWh (Saturday to Friday) = 117,523 kWh / week
Total Air Demand (Saturday to Friday) = 206,666 kWh/ week
- 56.9% of compressed air is lost through leaks
- At 10 cents/kWh = leaks represent US $611,120 annually
Table 2: Air Compressor Performance during the weekend - Click here to enlarge.
Within a few weeks of our conversation, a plan was in place to install multiple flow meters and pressure sensors throughout the facility to find the losses in the vast piping network. Identifying the leak losses of 6.1 million kWh triggered the immediate installation of the sensors, which through the webserver software on the master controller, allowed the client to identify the areas of the plant that should be targeted for leak repair first. Using the tools now available to the Client, a long-term leak prevention strategy is in place by setting limits to the flow across the flow meters triggering an email or alarm if the flow (CFM) should start to climb beyond the existing “best practice” values.
Being involved in hundreds of audits of facilities, like the one described, we see the same thing repeatedly. Typically a free audit is performed and a large VFD air compressor is installed. The client carries on with production never realizing what’s going on with the system. Installing a VFD air compressor is a supply side addition, which may or may not generate savings, depending on how it is sized and applied.
A new VFD air compressor doesn’t change the demand side of the compressed air system - where the air is being used and/or wasted. The new VFD air compressor may help supply the compressed air leaks and inefficiencies at a better specific power - but it will not rectify the issues still present within the system. Opting for a more expensive, but much more detailed audit of the entire compressed air system is the only way to find these kinds of savings. Combining this type of audit with permanent metering and monitoring is a long-term sustainable solution and not just a way to purchase a new air compressor.
Permanent metering and monitoring will also provide a continuous 24/7 audit helping to sustain the savings - after compressed air system improvements are made. This provides the plant the tools to adhere to ISO 500001 energy guidelines, provide the data for utility incentives without the costs of a post-audit, as well as justify the ROI to carry out any future efficiency upgrades.
To read similar Air Compressor System Assessment articles, visit www.airbestpractices.com/system-assessments/compressor-controls.