Designing an energy-saving compressed air system

AS BCAS continues to highlight its 10% Taskforce energy-saving campaign, this latest update will highlight the various options available to calculate the annual running cost of an air compressor, while also advising on how best to design an energy-saving system.

Energy saving is on everyone's mind at the moment. With rising energy costs putting major financial pressures on us all, it's no surprise that the compressed air sector is experiencing similar issues. 

And with compressed air said to account for 10% of a site's electricity bill, it's no wonder that teams are working hard to design compressed air systems that are as efficient as possible. 

Designing an energy-saving system

The air compressor will undoubtedly be one of the largest energy-consuming systems for a manufacturing site - and the usage and design of this system will dictate its overall energy consumption. 

Poor system design, incorrectly dimensioned distribution piping and purification equipment can lead to avoidable pressure loss, so it’s important to consider these points thoroughly when designing asystem. Pressure loss will, of course, increase costs with the need to generate compressed air at a higher pressure.

How to calculate your system’s annual cost

For operators seeking to maximise energy savings, it’s important to calculate the system’s total yearly cost.

• Option 1 - To check on the electrical consumption of a compressor, operators will need to obtain the reading by sub-metering the compressor house. This will be in kilowatt hours (kWh).
• Option 2 - A data logging system will also help to determine the yearly cost of the compressor system. This needs to be installed for a period of at least seven days. With this system in place, the pattern of demand, otherwise known as a demand profile, and the off-load running time when there is no demand for air can be determined. This does not account for the ‘off-load’ power consumption, when the compressor is consuming energy without generating air.
• Option 3 - And finally, option 3 allows the annual cost of the system to be calculated by estimating the energy consumption of each air compressor.

This can be carried out by following this working example: a 75kW compressor operates at 7 bar. It is on load for 80% of the production time, which is 2,000 hours per year. Energy consumption of the compressor = 75 x 0.8 x 2,000 = 120,000 kWh/year. If electricity costs £0.1249/kWh, the annual energy cost is £14,988. Should production time increase to 6,000 hours per year, for example, then the annual energy cost would rise to £44,964.

Using whole life cost as a basis for comparison

With a range of options available to monitor the annual cost of the air compressor system, it’s important to compare alternatives based on whole life cost, not just the initial capital outlay. By opting for equipment that is a higher cost but is more efficient, operators will benefit from lower running costs in the long term.

For more information, please speak to a BCAS member who can assist in this area by emailing [email protected], while a free copy of the system design guide can be found at: tinyurl.com/mrhucbtt

Vanda Jones is executive director of BCAS

For more information:

www.bcas.org.uk

Tel: 0207 935 2464