Using Data for Compressed Air Management

Synopsis: Often the owners and operators of compressed air systems typically do not have adequate measurement data to properly manage their system.  Installation of system measurement devices can reveal surprising results that can lead managers to needed system improvements.  When management acts on these improvements significant financial savings and productivity improvements can result.

Ron Marshall, Marshall Compressed Air Consulting

In the past, when the Utilities Manager of a large textile mill proposed improvement projects, he was usually met with a blank stare by the CFO.  In previous times, they were directed to run all their compressed air production equipment flat out, at the highest pressure possible, with management hoping to achieve maximum productivity in their production areas.  When they ran out of compressed air capacity, they added more machines, and eventually they ended up with ten large turbo compressors ranging in size from 375 kW to 500 kW consuming a total of 26 Gwh per year, costing $2.2M in total.

But the machines were aging and costly to repair and the manager suspected they were not getting the best value for their energy dollar.  Should he add more compressors, buy new, or rebuild the ones he had: he didn’t know.  He was basically operating blindly because no energy or flow monitoring had been installed.  And his CFO was demanding evidence that the proposed improvements were justified.

In a timely decision, the plant management decided to implement an ISO 50001 Energy Management System.  To meet this standard all significant energy uses needed to be monitored.  Management was surprised to learn, from initial measurements, that their compressed air system was consuming about 61% of their total electrical bill.  This got the CFO’s attention and he quickly woke up to the potential opportunities available for productivity gains and cost reductions.

The facility management team set some specific goals in addressing their compressed air system:

  • To optimize the production of compressed air
  • To reduce electricity cost and energy consumption
  • To reduce CO2 emission by reducing energy consumption
  • To upgrade and modernize production machinery
Figure 1: Management was surprised to learn compressed air was the biggest energy consumer in this large textile mill.

The new data collection system for the compressed air comprised energy metering on each compressor, pressure monitoring and individual flow meters.  The collected data was aggregated to produce total electricity and compressed air consumption, with outputs sent to the energy management information system. Monitoring individual compressors proved to be a huge benefit because the performance of each unit could be easily assessed. 

Looking at the individual compressor data, and calculating key performance indicators, management could see which of the running compressors were most efficient, guiding them to correct conclusions on whether to fix or replace troublesome units. And once improvement projects were completed, the results could be tabulated and even used to calculate the return on investment.

For example, when analyzing the initial data, two air compressors in particular were identified as low performers and scheduled for inspection.  During subsequent overhauls, a number of internal defects were found and corrected.  After the work was done, as shown in Figure 2 & 3,  it was found that the efficiency of both compressors improved by about 10 percent, saving 69,000 kWh per month, totalling $70,000 per year.  Since overhaul costs were about $73,000, the payback for this measure was slightly over one year.

Figure 2: Trending the system energy and air output showed overall improvement after compressor overhauls were completed.

Another one of the facility’s compressors was identified as a very low performer but because overhaul estimates totaled $154,000, it was deemed too expensive to repair.  Since the cost of a new compressor was $186,000, the decision was made to replace the unit.  The new air compressor was found to be 16 percent more efficient than the old unit and therefore saved significant energy per unit output, resulting in an estimated 65,000 kWh per month in savings worth $66,000 per year.  Simple payback on the completed project was 3.1 years.

Figure 3: Information system data was able to show an improvement in compressor efficiency after a rebuild.

Using the data from the energy management system, the company initiated action on the newly identified problems not only reducing their electricity costs but also experiencing increased fabric output volumes due to the replacement of inefficient and outdated equipment.  The system data had shown there was improvement potential in the end use of compressed air.  Upgrade projects increased plant profitability and reduced production costs.  All of this was tracked and verified using the energy management information system.

Energy efficiency measures reduced the total consumption of compressed air and increased compressor system efficiency, resulting in 5,533,000 kWh per year in decreased energy consumption, leading to annual savings of $468,000 per year.  This calculates to a 21% savings.

The next time the Utilities Manager visited the CFO’s office he was greeted with open arms.  And to his surprise he detected a hint of a smile.

Figure 4: Tracking of key parameters showed the improvement projects saved energy and increased fabric output.

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