Tips for efficient compressed air management

Top tips: Steps to efficient compressed air management

Compressed air system design

When you design a compressed air system, the key is to get the specification right first time, both to make sure that the compressor is going to fit the processes and to extend its lifespan. To start with, think about the air intake.

For example, don’t site it in a polluted or dusty area, as it will suck the polluted air and dust into the compressor and potentially down the air lines.

Plan from the outset how much filtration you are going to need. Every filter has a cost associated in terms of maintenance and pressure drop. Also consider the size of the air receiver into your compressor room design, and other products such as dryers, drains and oil/water separators.

Compressor life cycle costs

Consider the total life cycle costs of a compressor, not just how much the machine costs to purchase. Typically, a fixed speed compressor costs 7% in purchase price, 11% in maintenance and 82% in energy costs – based on a 75kW compressor running at 8000 hours loaded and subject to regular maintenance. A VSD compressor will on average reduce the portion spent on energy by 35-50%.

Ambient conditions

Did you know that a 5°C increase in air inlet temperature will lead to a 2% reduction in your compressor’s performance? A compressor runs more efficiently if the air coming into it is not too hot, so a simple measure like opening up the vents will eliminate that 2% efficiency loss.

Operational control

Reducing the pressure in your air net by 1 bar (14.5 psi) will save 7% in electrical energy costs. If your processes can run at a lower pressure this is a very simple measure to take.

A central controller can be used to link all compressors and dryers and select the best machine combination to deliver the required air output within a lower pressure band, which will lower the energy bill.

Energy recovery

Heat is an inevitable by-product of air compression. Rather than let this thermal energy vanish into the atmosphere via the cooling system and radiation, it can be reclaimed using an energy recovery system. About 90% of the energy to run a compressor can be recovered and used elsewhere, for example as heat to warm a warehouse, as hot water or steam for industrial processes, or to heat water for hand washing. Re-using this energy helps reduce emissions and lowers your plant’s energy consumption.

Correct maintenance

Correctly maintaining your compressor will have a positive effect on its performance. Incorrect or irregular maintenance will have the opposite effect.

Take oil for example. Oil is a hard-working component and is continually circulating, as it seals, cools and lubricates the working parts of a compressor. Always choose the correct grade of oil that has been designed and tested to ensure operational excellence, and use the correct quantity. Select an oil that removes cleaning additives and anti-foaming agents, rather than a cheaper oil that does not, as it will impact on the compressor’s lifetime.

Filters are another area which can have an impact on the compressor’s performance. Original filters that have been designed and tested for pressure drop and lifetime performance will keep the compressor system running as it did when new.

Air distribution

The air main network should be designed to reduce pressure drop and ensure that the right amount of air reaches the application at the necessary pressure.

Choose pipework of the correct size for the air flow, the pressure and the distance between the compressor and the points of use.

Check for air leaks – a hole of just 6mm in diameter will leak 28 l/s of air and could ultimately cost over £3600/year just to power the air leaks. Also consider the construction of the pipework and the fittings. Steel pipework and joints can be rough, leading to eddy currents and therefore pressure drops.

A smooth-bore aluminum pipe on the other hand will avoid this turbulence and deliver the same pressure at the end of the air net as at the start. A drop in pressure of just 25 millibars will result in a 2% efficiency loss.