Companies looking to optimize their operational energy savings should actively target their compressed air system → From repairing leaks to adjusting control protocols, you can find plenty of ways to save with little to no upfront cost. And with a larger investment, you’ll see major savings within a relatively short payback period.
So why are there so many old, leaky systems still out there? In part, it’s because a lot of people don’t understand how much energy they’re actually wasting, and how easy it is to make improvements.
The following discussion is a brief overview of the best opportunities to save energy in a compressed air system, as well as strategies to identify them.
While it’s easy to understand the capacity of a compressed air system, it’s most important to understand the actual use of compressed air in the plant. We have audited many systems where large air compressors are running, and we find little or no use for compressed air within the facility.
Our number one strategic approach to improving any compressed air system is to measure it whenever possible with a flow meter. We believe in fact that every compressed air system should be installed with a flow meter permanently. This isn’t just a great strategy for ongoing system management, but the absolute best way to quantify system waste such as leaks.
2. Education of the facility or process managers.
There is so much resource information available relative to compressed air efficiency that teaching clients about self-auditing their systems in terms of pressure, flow and understanding correct system design is the quickest route towards proper system management and improved efficiency.
3. Close examination of the system capacitance (tanks) and distribution system (piping).
Not all air compressors are made the same. While they may look the same on the outside, our industry uses many different air compressor capacity control methodologies, and each of them has a different requirement for system capacitance.
We find most compressed air systems lacking in this regard — particularly when it comes to load/unload air compressors that have been incorporated into compressed air system design by the general rule of thumb:1 gallon of storage for every 1 scfm of air. In fact, to achieve efficient operation they should have between 5-10 gallons of storage per scfm.
We challenge our clients to look back into the compressor manuals, where this information is qualified. This is important not just for energy efficiency, but for compressor reliability and compressed air quality.
4. Better piping.
Compressed air piping systems are in my experience the number one system inefficiency. Every day I see air compressors running up to 125 psig, when production requirements rarely call for anything above 80 psig — a clear waste of 22% of the energy for these systems. And often there’s nothing we can do about it, because so much pressure is being lost due to friction in piping that is undersized or poorly designed.
We have found that clients are more willing to purchase a higher pressure air compressor than they are to install a new distribution system. But our most successful compressed air system retrofits have all included changing the piping. Generally we turn off, turn down or eliminate compressors when we take this approach.
We recommend to any client that they have available a pressure-loss-due-to-friction chart, and that they understand how much air they use. This simple approach will have a dramatic impact on system design efficiency, as well as a positive effect on production machine repeatability and end product quality control.
5.Variable speed drive compressors are great!
Installing one can greatly improve system efficiency. They are not, however, the answer to compressed air system efficiency. Quite simply a poorly designed system with a lot of leaks is still a poorly designed system with a lot of leaks, even with a new variable speed air compressor. Measure the system, improve the system — and then the choice for correct compressed air equipment becomes more obvious.
We are strong proponents of compressed air system maintenance programs – It surprises us how many compressor users have never seen the daily inspection chapter of the operation manual. The most basic of compressor maintenance points are filters (air inlet, oil and separator); dirty filters require more energy. Typically in our environment, air compressor inlet pressure is 14.5 psia and the discharge of an air compressor is 100 psig, giving us roughly a 7:1 compression ratio. A compressor with a seriously clogged inlet filter may only be able to draw 10 psia, but still requires 100 psig at the outlet. So the compression ratio increases to 10:1, and the cost of this is increased energy. But the bigger cost is air compressor reliability.
Compressor maintenance should be a factor of hours of operation and the environment that the compressor is operating within. There are 8,760 hours in each year, and many compressor maintenance programs are designed around this. Environmental concerns should also be taken into account, such as cleanliness of cooling air and ambient temperature. Ideally, maintenance programs should be a combination of machine maintenance requirements, hours of operation, and environmental concerns. Where possible, daily inspections and daily log books should be maintained. If this isn’t possible, then equipment condition monitoring should be considered.
Question 3: Describe your process in optimizing the efficiency of a compressed air system?
Not all compressed air systems are the same, but every compressed air systems audit is. We have a standard process for looking at each system, and it starts with our general compressed air system assessment. Any discussion pertaining to improving efficiency must first start with:
What do you have?
What does it cost?
What do you waste?
What do you use/need?
What are your strategies, costs and paybacks for improvement?