Compressor efficiency not a load of hot air

With climate change and global warming a concern, manufacturers are finding more efficient ways to operate compressors resulting in financial and environmental benefits.

THEY say the best things in life are free, but with resources such as water and air being used wastefully, everything comes at a price.

Australian manufacturers are counting the cost of inefficient compressed air systems, with air leaks caused by incorrect sizing and pipework, lack of maintenance and a tendency to oversize and over-pressurise machines draining both electricity and profits.

All these factors can result in systems often only working at 40% efficiency, according to Dino Alessio, marketing manager with Champion Compressors.

“The capital cost of a compressor can be as small as 5% of its total lifecycle costs (LCC), yet the cost of energy consumed can be as high as 85%,” Alessio told Manufacturers Monthly.

“If it was a tap and water was leaking, everyone would run to turn it off to save water and money. The same vigilance should be applied to leaking compressed air systems.

“An air leak is 8-9 times more expensive than the same size water leak, but often manufacturers leave it,” he said.

Technology available

The technology exists to allow manufacturers to measure and control how much air they are using.

According to Alessio, one of the best ways to keep compressor systems running efficiently is to conduct air audits.

“A poorly maintained compressed air system will soon become inefficient. Often, users don’t realise when their compressed air system is not performing at its optimum capacity. As far as they are concerned, as long as the machine is still running, it is working fine,” he said.

He also said the audits are a good way for manufacturers to find out the minimum amount of air pressure they need to run an operation.

“A lot of manufacturers employ compressors that produce excessive amounts compressed air and at higher pressures than that required for their applications. Many companies run their compressors at 7 bar (around 100psi) instead of just the 6 they need. Considering 1 bar represents approximately 8% of energy consumption, they are wasting energy and losing money,” Alessio said.

Another cause of inefficient compressor operation is the use of incorrectly sized piping and is a common cause of energy loss.

The right fit

Alessio says many companies have a tendency to undersize their pipe system, failing to upgrade it when they purchase a bigger compressor.

“Inadequately sized pipework restricts air flow. Some manufacturers tend to react by increasing compressor output to overcome the resistance and achieve the same air pressure at the point of use,” he said.

He says manufacturers are also wasting energy by not using the right sized compressor in relation to load requirements.

“There is a tendency for some engineers to oversize air compressors. Not only does this increase capital cost, it also results in increased operational expenses due to excessive electricity consumption,” he said.

“A manufacturer might only need to run a system at 500L/sec but instead decides to use 700L/sec so the system is only operating at 50-70%. They are actually not saving any energy as they are only using a fraction of the compressed air being produced,” he said.

Alessio suggests manufacturers would be better off purchasing the right sized machine for the application and then add a machine or remove the smaller compressor and upgrade as the company expands.

All in the design

As well as more efficient compressor operation, improvements in system design is also helping manufacturers to save money and operate in a way that is more environmentally friendly.

According to Alessio, the use of hybrid machines which allow for multiple stages of compression can make systems more efficient and minimise air loss.

“Inefficiency occurs due to air ‘slippage’ through the gap that exists between the gear and the casting. Under pressure, the air is still going to be forced through this gap.

“In multi-stage or tandem compression, the air is only pressurised up to about 2 or 3 bar in the first stage (30 to 40psi), and from 3 to 7 bar (40 to 100psi) in the second stage. Less is required to achieve these incremental increases in pressure, and as a result, air losses through the gear/casting gap are minimised,” he said.