Compressed air

For insight into the operational and energy efficiency of your compressed air system, see the Compressed air energy tool. Based on answers to a series of questions, a report will detail opportunities and key actions you can take to save energy.

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Compressed air is produced by forcing air into a container and keeping it at a pressure greater than the external (atmospheric) pressure. This pneumatic energy is used for many applications, including:

pneumatic handtools
glass manufacturing
fermentation, clarifying and bottling of beverages
spray painting
sandblasting
vehicle braking systems
air guns
heating, ventilation and air conditioning (HVAC) control systems

Pneumatic tools are more compact, lighter and easier to use in confined spaces than motor driven tools.

While air is often a clean resource, it requires substantial electrical energy to compress. As a result, compressed air systems are often more costly to run than other solutions. They can consume up to 30% of a site’s electricity use, 90% of which can be wasted. Half of this energy is lost in leakages, even in new equipment.

Luckily, there are many effective ways to cut down on compressed air energy costs while improving productivity and workplace amenity. A good air compressor energy-efficiency strategy relies on an integrated approach that incorporates several elements, outlined below.

Quick wins

Metering and monitoring

Metering and monitoring is necessary to:

understand energy use and demand patterns
identify inefficiencies and upgrade opportunities
track improvements.

Metering equipment allows measurement of energy baselines and future performance improvements. This can range from simple sub-metering to a comprehensive fit-out with sensors and rapid data logging. While set-up costs can be significant, a high-quality metering and monitoring system can provide a rapid return on investment by identifying areas for quick, cheap action. These include:

adjusting system settings
identifying and rectifying leaks and faulty, inefficient components
rescheduling tasks to reduce peak demand and required equipment capacity
sequencing of compressor unit operation.

A range of data should be collected, including:

compressor energy use
component status
pressure, temperature and air humidity at key locations throughout the system.

Metering data allows development of energy demand profiles of the compressed air system in all operating conditions. The shape of demand profiles can inform strategies for optimising system efficiency. For example, if the profile of energy use rises disproportionately to increases in load, reducing peak loads should provide the most benefit. Spikes or inconsistencies in energy demand profiles can indicate sub-optimal system function and control.

To read more, see the Metering and monitoring guide.

Reduce unnecessary and inappropriate use

The simplest way to reduce energy costs is to stop using compressed air for tasks that can be done in other ways. Identifying unnecessary and inappropriate use can drastically reduce air required on site.

The simplest ways to reduce compressed air use without a complete system redesign include:

using other cleaning techniques such as mechanical or chemical solutions
cooling with fans, natural ventilation, better insulation or a lower pressure air source
drying with waste heat, air from other site sources or electric heat pumps
reducing constant idling and shutting down equipment out of hours.

Compressor controls and settings

Properly tuned controls improve performance of compressors under changing system demand. In many cases, optimal sequencing of compressor units can save up to a third of compressed air system demand.

The following general strategies should be considered:

use the most efficient part load (ideally variable speed) compressor for low demand and trimming
stage operation of fixed-capacity compressors from smallest to largest
switch off idling compressors whenever feasible
choose the most efficient and reliable models available when replacing components such as pressure regulators and actuators (including models with air reuse and economiser features)
reduce lag and resistance by not oversizing pipes and hoses
avoid in-line obstructions and rapid changes in diameter
ensure compressor inlet air is not unnecessarily warm, humid or dirty
use a single small fixed-capacity compressor for small tasks over a large variable capacity unit
adjust load pressures to the minimum setting required while ensuring functionality is not adversely affected.

For a more detailed description of compressor control and sequencing strategies, see the NSW Government’s compressed air guide.

Leak identification and general maintenance

Identifying and fixing leaks is particularly important in compressed air systems, as losses can equate to thousands of dollars in energy costs.

Leak detection can be carried out using a variety of methods. Basic mechanical techniques include listening by ear and applying soapy water to suspect areas. More advanced techniques include the use of ultrasonic detection tools and sensor data logs to identify unusual pressure drops.

Good general maintenance practices can also help prevent excessive energy use, extend equipment life and prevent production downtime. It is a good idea to develop comprehensive and regularly scheduled maintenance practices and assign staff to their oversight.

Other strategies to consider:

keep filters clean and replace them at specified intervals
ensure valves and actuators are operating as expected (not faulty or slow)
ensure motor currents are within expected ranges and motors are not running hot
eliminate slippage and friction in mechanical components such as motor drive belts
keep lubricants clean and topped up
ensure condensate drainage is working to prevent moisture build-up

Optimise and upgrade

Most opportunities for energy savings are found in other equipment than the compressor. It pays to address these energy losses before considering other upgrades. A progressive approach to upgrades can deliver substantial benefits over time.

Storage

Compressed air systems feature a storage tank or ‘receiver’ that is sized to smooth output and meet short-term fluctuations in demand.

Installing a larger receiver may allow for a smaller compressor to be used or dedicated trim compressors to be switched off in some circumstances.

For most compressor systems, ample storage means greater efficiency. This serves to:

allow compressors to be operated close to maximum efficiency without risking system failure
moderate peak demand by drawing down on tank pressure reserves during periods of high demand or high tariffs
reduce the amount of pressure drop in the system when applications are switched on to avoid energy demand spikes.

Vacuum systems

By causing compressed air to expand rapidly, a vacuum can be created for lifting and moving objects. This consumes around 10 times as much energy as an electrically powered mechanical vacuum pump for the same flow rate.

Where a compressed air vacuum is needed for long periods, it may be worth upgrading to more efficient models. Compressed air vacuum systems have been improving through more efficient multi-stage eductors and ejectors and better electronic control systems, but replacement with a standalone electric vacuum pump is usually even more efficient. Unnecessary air volume in vacuum pipes and tubes should also be reduced.

Compressor/motor units

High efficiency compressor units can be up to 25% more efficient than older units. To avoid overpaying for unneeded equipment, a full-system rationalisation should be done before investing in new compressor or motor systems. Avoiding oversizing is a key to getting the most out of high efficiency replacement units.

Instead of replacing with a large ‘like-for-like’ compressor, consider using several smaller air compressors that can support a more decentralised, flexible system. The efficiency of compressors varies depending on how they are operated, so choose one that best meets task requirements.

Alternative approaches

System rationalisation and redesign

Periodically examining the need for compressed air can identify potential energy waste. Software can be used in the design process to help with pipe mapping, pressure drop analysis and layout optimisation.

This process also allows for identification of alternative technologies. Electric equipment uses around one eighth of the energy and is quieter, faster, and more precise. Small electric motors, gearboxes, batteries and smart controls continue to improve.

Where compressed air is still needed for various tasks, assess the quality of air required as there may be opportunities to use a less energy-intensive air source.

Shifting to electric alternatives may require additional electricity supply to parts of the operation, even if total site electricity use is lower. This should be considered when planning and costing major redesign projects. External expert advice should be sought as necessary.

To read more about compressed air alternatives, see the Australian Alliance for Energy Productivity’s review of emerging efficiency improvements and alternative technologies.

Variable speed drives and advanced control

Most compressed air systems have variable loads. Compressors which can operate under part load are required to achieve efficient performance. Using variable speed drives (VSDs) to control compressor output is more efficient than using valves or dampers.

Unlike constant or dual-speed models, modern VSDs adjust compressor output to accurately meet changes in demand. They can maintain pressures between a tight band over a wide capacity range. This improves system functionality as well as reducing energy use.

VSDs can also help maximise the benefits of adopting electric alternatives to compressed air, for example point-of-use electric vacuum pumps.

Modern control systems can assist in efficient coordination of multiple compressor units, improve the effectiveness of VSDs, and provide data for tuning and maintenance.

While many new compressor units are sold as integrated packages that include VSDs and control systems, it is possible to retrofit VSDs onto existing, older compressors.

To read more, see the Motors and variable speed drives guide.

Electric actuators and micro-electric motors

Actuators convert compressed air energy into movement to drive mechanical tasks in the production chain. Converting to electric actuators can reduce compressed air use and improve productivity. Actuators can be gradually converted to electric according to age, efficiency and production priority.

Electric actuators have a number of advantages over traditional air driven devices including:

greater performance
reduced operational and standby energy waste
more speed, precision, and sensitivity
flexible programming and system diagnostics
integration into industry 4.0 ‘smart’ systems

These can remove bottlenecks and reduce downtime, leading to productivity benefits.

Capture wasted energy

Waste heat capture technology is worth considering if there is a need for heat on site. In some circumstances, waste heat can also be converted to electricity. However, it is often more efficient to reduce the heat generated rather than capture unnecessary waste.

Heat demand can be met more efficiently with heat pumps than through heat capture alone. Where compressed air use can’t be avoided, a heat pump using waste heat from a compressor can raise the temperature and improve efficiency of heat recovery.

Valve blow-off air can also be recycled into the system or used for lower pressure applications.

To read more, see the Waste heat recovery guide.

Innovations

Product redesign

While process redesign can greatly reduce compressed air use, product redesign can reduce or remove it entirely. Examples include:

selecting different input materials such as those that don’t require cleaning, coating or painting
adopting different assembly techniques such as gluing instead of screw-fixing
alternative plastic and metal forming processes to reduce production steps
collaborating with suppliers and customers

Compressed air energy storage

Compressed air energy storage (CAES) is a method of compressing air when energy supply is plentiful and cheap (e.g. off-peak or high renewable) and storing it for later use.

The main application for CAES is grid-scale energy storage, although storage at this scale can be less efficient compared to battery storage, due to heat losses. Unlike batteries CAES does not require large amounts of metals and chemicals for energy storage.

Researchers at University of NSW have been examining options for small-scale, onsite CAES applications for buildings and manufacturing plants that can make use of waste heat resulting from compression, thereby improving efficiency. Read more about their research on the UNSW website.

Industry 4.0

Compressed air systems and electric alternatives can be fitted out with ‘smart’ components and sensors making them good candidates for digitalisation. This allows for sophisticated strategies, including:

machine learning trained towards lowest energy use and output
digital ‘twinning’ where computer simulation of the system allows for design optimisation and scenario testing
real-time monitoring of large quantities of data and integration into management reporting and system tuning.

To read more, see the Industry 4.0 guide.