Measure of success

Nothing can be managed until it has first been measured. This fundamental rule of good management practice applies as much to compressed air systems as any other facet of a business.

Businesses are crying out for tighter control of their compressed air because it’s an enormous drain on energy. A fifth of a typical factory’s electricity bill is to pay for the production of compressed air, but it can be as much as 30% of total site electricity usage. With energy accounting for up to 86% of operating costs there is clearly enormous pressure to boost efficiency.

Thankfully, there is a way. The ISO 11011:2013 standard takes a huge step towards standardising energy audits by setting requirements for conducting and reporting the results of a compressed air system assessment. Even more crucially, it considers the entire system, from energy inputs to the work performed as the result of these inputs.

The standard places compressed air systems into three sub-systems:

• Supply – the conversion of primary energy resource to compressed air energy
• Transmission – the movement of compressed air energy from where it is generated to where it is used
• Demand – the total of all compressed air consumers, including productive end-use applications and compressed air waste.

ISO 11011:2013 contains guidelines 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.

An audit in line with this standard is a good first step to saving energy in compressed air systems, but it’s not enough on its own. Here are four further practical steps you can take to reduce the energy demand from your system:

Install heat recovery

Even in modern compressors, energy is inevitably lost through frictional forces which manifest themselves as heat. This is wasted energy unless it is recovered. In an oil lubricated screw compressor, up to 94% of the heat generated in a compressor can be reclaimed by recovering the heat generated. However, there are ways to turn excess heat into something that can be used for heating the building or process duties. 

Minimise leakage

Even new compressed air systems can lose up to 10% of their air; the leak rate of an unmanaged compressed air system can be as high as 50%. Indeed, a 3mm hole in a pipe could cost over £1000 a year in wasted energy. The best ways to minimise air leakage are through detection, monitoring and repair. The latest compressor controls allow you to detect leaks and amounts automatically. It’s also possible to retrofit existing controls with this function. It will pay you to ask your service provider to include leak detection and/or an annual energy audit into its service offering.

Reduce operating pressure

For every 1 bar reduction in pressure you can save 6 to 10% on running costs so it makes good business sense to ensure that your compressor system is running at its optimum with the lowest possible pressure drops. Regular effective maintenance will help.

Match output to demand

Intelligent electronic sequential controllers regulate multiple compressors around a single set pressure and make compressors available to match demand as closely as possible. For example, instead of using a 100kW compressor at 60% utilisation, the system might select two 30kW compressors at 100% utilisation, improving efficiency.

Some systems need variable compressed air, perhaps due to changing production patterns, for example. Fixed speed compressors generally consume between 20 and 70% of their full load power when idling or in off-loaded running.  However, a variable speed compressor uses a special drive to control the speed. As well as reducing the power cost, this diminishes power surges from starting motors, reducing wear and tear, and delivering a more constant pressure.

 

Money-back opportunities

• The mandatory CRC (Carbon Reduction Commitment) Energy Efficiency Scheme is an initiative aimed at improving energy efficiency and cutting emissions in large organisations. It offers tax benefits and financial rebates to those showing a commitment to carbon reduction. 
• The ECA (Enhanced Capital Allowance) Scheme also provides businesses with enhanced tax relief for investments in equipment that meets published energy-saving criteria.