In the process of routine prospecting, a KAESER field sales rep contacted the production team at an aerospace manufacturer with the simple objective of sharing information on compressed air. The conversations that followed left the Facilities Manager with useful tips that they could employ whether they continued with KAESER or not. After a site visit, KAESER learned that the compressed air demand profile in this plant was typically low enough that the existing 25 hp compressor alone would maintain pressure in the plant. There was one manufacturing process, however, that consumed significantly more compressed air, which reduced system pressure to the point where the manufacturer’s “lag” compressor, a 60 hp, would turn on, load, unload, idle, and turn back off.
Those familiar with “lead/lag” systems will recognize the peculiarities of operating the smaller of two compressors as the “lead” and the larger as the “lag”, but from an efficiency and duty cycle standpoint, the Facilities Team was doing the right thing with the equipment they had available. In addition to the gross oversize of the “lag” compressor, both compressors were aging, and the plant recognized that there was likely a good business case to replacing both units. The Facilities Team at the plant also explained that in the event of a breakdown, they had no way of knowing a problem existed until pressure began to fall in the plant. They wished there was a way to remotely monitor their compressed air system, and they wanted some form of control system that would select the appropriate compressor for the current demand in the plant.
KAESER performed an Air Demand Analysis, recording flow, pressure, and power data for two weeks. Kaeser’s team of degreed engineers analyzed the data, and enabled Kaeser’s field sales team to return to the manufacturer with a comprehensive report. The Facilities Manager had in the meantime dutifully obtained quotes from other compressor providers, who both recommended similar systems with two 50 hp variable speed compressors - one to run, one to sit in redundancy.
Kaeser’s Air Demand Analysis reveals a specific power of 65.42, and establishes a baseline on which to discuss future options in equipment configuration.
KAESER recommended a system of three fixed speed 20 hp compressors. With an average flow of around 75 cfm, a single 20 hp compressor was all that was needed to maintain pressure. This single unit would run at a high duty cycle. This higher utilization rate reduces unit cycling, reducing wear and extending mean time between failures. The plant’s peak flow was measured at 145 cfm, and based on the data, this peak demand only occurred about a dozen times per week, and for less than fifteen minutes at a time. Thus, compressor “1” could satisfy the 75 cfm average demand. Compressor “2” would turn on, load, and “trim” during periods of peak demand. Compressor “3” would remain in standby for redundancy to be employed during preventative maintenance. A Sigma Air Manager 4.0 controller could be employed to rotate which compressor served as “#1” vs. “#2” vs ”#3” and ensure that service/run hours were accumulated evenly. The Facilities Manager was surprised and intrigued.
The Facilities Manager was intrigued by the very different approach, but was still interested in the benefits of a variable speed compressor. After all, the plant did experience a significant variance in demand, so why shouldn’t they employ the technology of a variable speed? This is where KAESER highlighted a key factor in applying variable speed compressors: minimum speed. The other compressor providers had quoted 50 hp variable speed compressors which each had a minimum speed in the 70-80 cfm range. This means that when compressed air consumption in the plant falls below the variable speed compressor’s minimum speed, the compressor must turn off. This, of course, will result in pressure drop, which would then prompt the compressor to turn back on again very quickly. This process might occur multiple times until demand increased or stopped completely. This type of short cycling frequently results in drive fatigue, and a significantly shorter mean time between failure for multiple components within the air compressor.
After explaining the issues inherent in a variable speed operating below minimum speed, KAESER pointed out that their own 50 hp variable speed compressor actually had a lower minimum speed at 54 cfm than the other offerings, but that this still may not be the best equipment arrangement for the user’s standpoint. In their particular region, energy costs are relatively low, and the energy consumption of a 20 hp compressor operating at an ~85% duty cycle would be very similar to that of a 50 hp variable speed compressor serving the same flow requirement anyway. KAESER recommended the fixed speed system for its lower capital and maintenance costs compared to the variable speed system.
When the Facilities Manager spoke to the other compressed air providers again, he raised his concerns with their variable speed drive compressors operating below minimum speed. The response he received was simply a new quote for a 40 hp variable speed compressor instead. This afforded a few cfm lower of a turndown rate, and a bit of capital cost savings. The Facilities Manager was not impressed.
When the order for the three 20 hp fixed speed system was placed with KAESER, the Facilities Manager shared that KAESER was the only provider who thought through the solution and stood by their recommendation despite the customer’s expressed preferences. KAESER had made independent observations, learned about compressed air consumption in the plant, and put together a recommendation that would provide the plant with clean, efficient, and reliable compressed air for years to come.
SAM 4.0 automatically controls which compressor runs lead, which runs lag, and which waits in standby. Hours are distributed evenly to improve preventative maintenance efficiency.
A closer look at how SAM 4.0 orchestrates multiple compressors to maintain pressure in the plant while consuming minimal kW. In this system, typical operation only requires one compressor, while spikes in demand necessitate additional flow from the trim compressor. Long before pressure drops below system minimums, SAM 4.0 cues a second compressor to load. That compressor runs loaded, until pressure is re-built, and SAM 4.0’s algorithm is satisfied
The Facilities Manager remarked “My guys tease me about me being right on the 20s and them being wrong on the 50s. They swore they would not work, but they are getting it done.”
The team is now able to remotely monitor the compressed air system through their SAM 4.0, which independently selects the lead, lag, and standby compressor in a manner that evens out their service hours. They are alerted of any issues that arise via email, and can easily track run hours and changes in compressed air demand via SAM’s intuitive touch-screen interface. Perhaps most impressively, SAM 4.0 can provide real time energy consumption data, including period comparisons. A recent survey of this system’s SAM 4.0 has revealed a 67% improvement in kW/100 cfm from the initial Air Demand Analysis. This energy savings alone has afforded the plant a simple return on investment period of three years in addition to their capital cost savings in selecting the KAESER proposal vs. more costly variable speed alternatives.
Data gathered on-site from SAM 4.0 indicates a specific power improvement from 65.43 kW.100 cfm to as low as 21.20 kW/100 cfm. This is a 67% energy savings!
There is a time and a place for all technologies, and the moral of this story is to pursue the best business outcome by considering capital investment, energy and service costs. This sometimes requires challenging customer expectations and preconceptions in order to explore solutions they may not have yet considered.
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