Making smart choices with compressed air

There are several well-known - but probably misunderstood - facts about compressed air usage and systems throughout Australian industry. A consequence of this is that your compressed air system is an ideal place to start when looking into energy-efficiency opportunities.

Facts about compressed air

Firstly, compressed air is used extensively by industry. In fact, around 15% of all electricity used by industry is used to compress air.

Secondly, compressed air is a highly inefficient form of energy. It takes roughly ten times more energy to perform a task with compressed air compared to using electricity directly. This is because 90% of the electrical energy consumed by a compressor is discharged as waste heat.

Thirdly, compressed air is wasted profusely. It is not uncommon to discover that 50% of the air being generated by a compressor is not being used for productive activities. Air leaks are the most widely known compressed air waste, but other wastes include system losses, artificial demands and inappropriate use.

Fact number four is that the cost of electricity to run a compressor is the largest financial component of compressed air systems. Over ten years, the cost of energy consumption for a compressed air system will be 10 to 30 times the initial capital investment cost. In inefficient systems, this proportion can be even higher.

Opportunities to save energy

With the preceding four facts in mind, it is easy to see why the opportunities to save energy with compressed air are so significant. Having a strong understanding of your productive demands and eliminating non-productive demands is a good first step. It’s very important to also understand the efficiency profile of the system to determine if a reduction in demand will result in a decrease in energy consumption.

Heat recovery is also an area that is normally overlooked. With so much heat energy available, why not find opportunities to use it? Preheat water to a boiler, or even use the heat to provide warmth to a factory or office space.

Energy-efficiency technologies

There are many technologies on the market today that can be employed to reduce energy consumption. Variable frequency drives are the ‘buzz’ at the moment, but other technologies are superior for air compressors, such as permanent magnet motor technology with variable speed control, which does not suffer from reduced efficiency at part load and benefits from unlimited starts. Two-stage compressors are around 15% more efficient than traditional single-stage compressors, and in conjunction with variable speed control offer the ultimate in efficiency.

For oil-free systems, three-stage centrifugal compressors are highly efficient and should be considered alongside variable speed controlled oil-free screw compressors in systems with high demand variability. Take care however, because the technology that you choose may not be the best for your needs due to any number of secondary issues relating to environmental conditions, maintenance or power quality.

Air-energy auditing

Using the services of a professional air-energy auditing team to help you determine the savings available is critically important. The wrong advice or applying the wrong technologies can result in excessive ongoing costs for the life of your system. You should consider using companies with independent consulting services and sophisticated auditing tools and procedures to properly analyse your system.

It’s important to make smart choices with your compressed air system - you can significantly reduce your energy use and potentially save thousands of dollars each year! Quentin St Baker is a mechanical engineer and national manager for the Energy Efficiency Services division at CAPS Australia, and represents CAPS on the Energy Efficiency Council. He has extensive experience in the compressed air industry and has provided assistance to many well-known organisations to identify and implement energy-efficiency solutions.