Compressed air is produced by forcing air into a container and keeping it at a pressure greater than atmospheric pressure. The energy released by a compressed air unit can then be used as a power source for:
- pneumatic handtools
- glass manufacturing
- automotive manufacturing
- soda and beer production
- spray painting
- vehicle braking systems
- scuba-diving airtanks and bouyancy devices
- air guns
- heating, ventilation and air conditioning (HVAC) control systems
- mineral sorting
An advantage of pneumatic tools is that several can be run in a system without each needing its own internal motor. This means the tools can be more compact, lighter and easier to use in confined spaces.
The cost of running compressed air systems is often many times that of other energy transfer methods. Although air itself is a clean resource in endless supply, it requires substantial electrical energy to compress it for industrial use.
As much as 30% of a site’s electricity use can be consumed by this process. Also, up to 90% of the energy used to compress air can be wasted in the process. On top of this, up to 50% of compressed air is lost in leakages, even in new equipment.
Recent innovations have led to methods of capturing the heat energy previously wasted in air compression. Additionally, compressing air can be an almost entirely clean process when the initial energy is obtained from the wind or sun. Where compressed air equipment is required, optimisation of its efficiency is essential.
Compressed air energy storage (CAES) is a grid-scale method of storing energy that’s generated at one time then contained for later use. ‘Excess’ energy generated at off-peak can be stored as compressed air and then converted back into electricity for supply during peak demand. An entire CAES system can consist of little more than steel, water and air—powered by wind or sun. A CAES station is therefore a renewable energy plant.
A good air compressor energy-efficiency strategy relies on an integrated approach that includes the following elements:
Reduce demand for compressed air services
Compressed air is often used as an energy source because it is clean, readily available and simple to use. But compressed air is also the most expensive energy source in most industrial plants. So, as a first step, it is important to review and reduce demand for compressed air services.
Optimise the use of existing air compressor systems
The energy efficiency of existing compressed air systems can be improved through using the minimum pressure for the required task, eliminating leaks, improving air compressor controls, fixing pressure drops, and utilising air receivers and heat recovery units. An idling compressor on average uses 40% of its full load so should be switched off when not in use.
Upgrade air compressor system
Upgrades to system components can be implemented to help save energy as well as deliver other benefits, such as reduced maintenance. Firstly, air demand (quantity and quality) should be established by ensuring that steps to reduce demand for compressed air services have been undertaken. Potential upgrades include switching to modern compressors that are the best type and size for the job, and redesign of system layout to reduce friction and pressure drop in pipes.
Variable speed drives
Modern variable speed drives adjust compressor output to meet changes demand, unlike older constant-speed models. One variable-speed 100hp compressor is much more efficient than 4 fixed-speed 25hp units. It also enables easier control. Variable speed drives, however, can be more sensitive and require more maintenance. They may be best used as part of a broader system as a complement to smaller, constant-speed units.
Use more energy-efficient technologies than compressed air, such as electric motors rather than air-powered motors. Electrical power-tools, in many cases, are more cost-effective alternatives.
Portable electric tools
As the power-to-weight ratio of small electric motors, lightweight gearboxes, more powerful and lighter batteries and smart controls is improving, portable electric tools (both mains-powered and battery) are beginning to compete with compressed air equipment, even in vehicle assembly.
Smaller decentralised air compressors
Many firms historically have left their large centralised compressed air systems on to service small parts of the facility during after hour periods. Many businesses are finding that it pays to invest in a smaller compressed air system to use for those specific areas of the factory or laboratory rather than running the large centralised compressed air system constantly.
Modern control systems can assist in efficient coordination of of multiple compressor units, improve the effectiveness of variable speed drives, and provide data to imform tuning and maintenance.
Some companies leave their air compressors on for convenience assuming that, because they have a variable speed drive, the compressors do not use much energy. However, even when on standby mode with a variable speed drive, air compressors are typically using around half of their full-capacity power. Modern components and controls can reduce standby energy use by 50% or more.
Compressed air Sustainability Victoria
I am your compressed air guide (PDF 2MB) NSW Government
Compressed air tools, tip sheets and case studies US Department of Energy
Compressed Air Technology Overview UK Carbon Trust