Reduce Air Compressor Energy Consumption Whilst Boosting Productivity

There is no doubting the costs involved in running an energy intensive compressed air system. However, it is possible to reduce a compressor’s energy consumption – and therefore its running costs – while at the same time boosting its productivity by applying sensible control measures.

​It is all too easy to be drawn into a belief that compressed air is free. It is a site commodity after all, and thanks to modern compressor technology, air is always available to power tools, actuators or other process equipment. Of course, it is not free, and may indeed be a significant factor in overall site utility costs.

What many plant managers fail to understand is that there is huge potential to improve the efficiency of compressed air production and delivery.

As well as saving energy, reducing compressed air wastage by tightening up on control measures not only cuts costs, but also improves reliability and boosts productivity. Indeed, the efficiency of compressed air systems is largely determined by the effectiveness of their controls.

But what do we mean by ‘effective controls’? Effective compressed air system controls match the compressed air supply with system demand, and compressor manufacturers have developed a number of control measures to achieve this.

At its simplest, the compressor motor is turned on or off in response to the discharge pressure of the machine. Typically, a simple pressure switch provides the necessary motor start/stop signal.

A marginally more sophisticated approach called load/unload (also known as constant speed control) allows the motor to run continuously, but unloads the compressor when the discharge pressure is adequate.

Modulating controls can also be used to throttle the inlet control, varying the compressor output according to demand. Variable speed drives (VSDs), on the other hand, provide closer control of motor speed (and therefore energy consumption) to deliver a more constant supply pressure; they also avoid the large inrush currents experienced when starting up large ac motors.

Control of compressed air systems is not the only issue affecting costs

But the control of compressed air systems is not the only issue affecting costs; downtime can also have a catastrophic impact on production schedules.

The reliability of a compressed air system is largely determined by its age and state of maintenance. Depending on frequency of use and machine type, a typical compressor life cycle is ten to 15 years before it is no longer economically viable to repair and requires replacement.

​Some oil-free models will run for 20 years or more, but the performance of all compressors will eventually degrade over time. A major overhaul involving a motor rewind and refurbished compressor element might keep things running, but the unit’s efficiency will be reduced, leading to higher running costs.

Using VSDs to ensure greater energy efficiency

A new compressor is likely to be more reliable and efficient, and the use of VSDs will ensure greater energy efficiency. A VSD controlled compressor can provide significant energy savings – up to 50 per cent may be possible in some cases.

Modern compressors are more reliable and can run for extended hours between maintenance interventions. Moreover, they deliver cleaner air, thanks to advances in air filtration that will also extend the lifespan of downstream, air-powered equipment. Retaining older plant assets beyond their useful life – that all too frequent ‘make do and mend’ mentality – does not make good economic sense, particularly at a time of soaring energy costs.

Measuring air compressor performance

​There is a well-worn management maxim that states: ‘you cannot manage that which you do not measure’. There are many ways to measure the performance of a compressed air system; for example, a data monitoring device might be deployed to track compressor and pipework performance, including upcoming servicing requirements based on actual usage.

This would provide an early warning of potential compressor or air delivery system problems, as well as a record of the unit’s energy consumption over a period of time, plus an analysis of its energy efficiency performance.

Here at BOGE, for example, we offer an air compressor monitoring system called ‘airstatus’, which includes a fault and maintenance indicator, remote data polling and server-based data retention for up to 24 months.

Offering remote viewing via an internet connection, air status measurements include hours run, indicated faults, and both air and electrical power consumption. And for those maintenance personnel on the move, there’s an app for IOS and Android operating systems that provides system status and alarm indications on a smartphone screen via email and/or SMS.

And for those maintenance personnel on the move, there’s an app for IOS and Android operating systems that provides system status and alarm indications on a smartphone screen via email and/or SMS.

Most compressor manufacturers and consultants offer a one-week audit service involving a site visit and installation of monitoring equipment to measure parameters such as air flow, air pressure and air quality, and provide a report at the end of the period. Some also offer a fixed, remote monitoring system, which will form a permanent part of their compressor installation.

Anyone conducting a compressed air energy assessment should follow the procedures outlined in ISO 11011:2013. This international standard sets requirements for conducting and reporting the results of a compressed air system assessment that considers the entire system, from energy inputs to the work performed as a result of these inputs.

The standard sees compressed air systems as three functional subsystems:

• supply, which includes the conversion of the primary energy resource to compressed air energy;
• transmission, which includes movement of compressed air energy from where it is generated to where it is used;
• demand, which includes the total of all compressed air consumers, including productive end-use applications and various forms of compressed air waste.

The standard also outlines requirements for analysing the data from the assessment, reporting and documentation of assessment findings, and identification of an estimate of energy saving resulting from the assessment process. It also identifies the roles and responsibilities of those involved in the assessment activity.

The importance of compressed air system maintenance

​Unless it is periodically and properly maintained, the performance of a compressed air system will rapidly degrade; it will also become less energy efficient and therefore more expensive to operate. Properly conducted periodic maintenance will ensure that the system continues to cooperate reliably and at peak efficiency.

Poor maintenance, on the other hand, is likely to result in increased energy consumption due to lower compression efficiency, air leakage or pressure variability, and may also lead to higher operating temperatures, contaminated air streams and poor moisture control.

On a typical industrial site, air-powered production systems derive their energy from high pressure air stored in the air delivery and distribution system; air compressors simply replenish this system as air is consumed.

In other words, the energy needed to perform tasks involving compressed air comes from air already stored in the site’s air delivery pipework. The efficiency of a compressed air system is thus affected as much by how air escapes the system as by how it is generated in the compressor itself.

Matching supply with demand requires that both air generation and storage are properly maintained. That means fixing leaks in pipework as well as servicing the compressor itself – a task that can be undertaken either in-house or carried out by experts capable of maintaining and servicing all makes of compressor, as well as their ancillary equipment on a 24/7 basis.

The Chartered Institution of Building Services Engineers sums up the whole maintenance issue rather well: “It is a false economy to ignore maintenance on any type of compressor. It is recommended that manufacturers, or their accredited agents, are used for service work and that genuine spare parts are used.”

We couldn’t agree more!