In a compressed air system, the most important item is the air compressor itself. In choosing an air compressor you must evaluate its reliability and efficiency. The majority of the lifetime cost of the compressor system is made up of energy consumption costs, maintenance and repairs. The actual initial cost of machinery is only a small percentage of the overall cost; it is therefore wise to choose an air compressor that will be the most cost effective, which almost certainly won’t be the lowest priced unit.
The components to evaluate in a compressor include:
Consider the package efficiency. The manufacturer will rate the performance and efficiency and in the UK this is disappointingly held as manufactures confidential information. However, in America they use the Compressed Air and Gas Institue’s (CAGI) Data Sheet; this is a reporting standard that aids end-users when comparing similar units with an open book policy on the compressors efficiency. Allways ask yourself: if a compressor supplier won’t give you the detailed package efficiency what are they hiding? Here at Glaston we always supply this data as we are confident we supply the most efficient compressors.
Discharge temperatures must be reduced in high ambient temperatures; this is done by fans and coolers. In air cooled units, low-noise radial fans use less electricity and provide better cooling compared with axial fans. The ability to easily duct air in and out of the compressor unit must also be considered. Topside exhaust often simplifies ducting for heat recovery and reduces footprint.
Efficiency and simplicity are significant to consider. Direct- coupled, 1 to 1 drives offer the efficiency with no loss in transmission efficiency and require no maintenance. Belt drives require only simple maintenance and offer benefits such as flexibility in pressure selection. Automatic belt-tensioning devices are necessary to ensure transmission efficiency and protect bearings from excess stress.
For the interconnecting piping it is important to have rigid piping with flexible connections to eliminate leaks. It is also worth considering modern aluminium pipework as the internals are smoother so it is more efficient and it is quicker to install and modify at a later date.
The control panel must be user friendly but most importantly must be reliable and run the compressor efficiently. Not only should it indicate operational status, but it should provide maintenance interval reminders, diagnostic information and external communications, as well as the capability for remote monitoring and control.
Vibrations can loosen fluid and air fittings as well as electrical connections. Some compressors mount the motor and air end on vibration isolators to eliminate this source of stress. Adding additional isolators under the compressor package provides an additional layer of vibration protection, and for most rotary screw compressors these isolators eliminate the needs for special foundations.
As motor efficiency affects electrical consumption it is vital to ensure the compressor motor meets IE2 (high efficiency motors) or better. In addition the higher the IP rating the better. The higher the IP rating the better the motor and the more resilient it is to airborne dust and moisture.
A noise-insulated enclosure can reduce the compressor noise emissions well below required safety limits which can eliminate the need for a compressor room. This can save thousands of pounds in site preparation costs.