Making wasted air hiss-tory02 April 2013

Badly-sized compressors, leaky pipes and lackadaisical practice mean profits are vanishing into thin air on many a factory floor. Max Gosney delivers a giant sticking plaster in the form of a 10-step guide to cutting compressed air loss

1 Test for leaks
The Magic Circle could be flooded with applications from manufacturers, judging by compressed air habits. Sites are performing a trick that would make seasoned contortionists squirm as they squeeze thick wads of cash out of tiny holes in pipe work, statistics reveal.

A crack spanning just 3mm can cost £1,000 a year in wasted energy, according to the Carbon Trust. So stop fixating over the kW of your compressor and start prioritising the performance gains from mending leaky pipes, says Andy Jones, general manager at compressor manufacturer Mattei. "You can splash out on the latest, most efficient compressor but it's absolutely pointless if you're pumping 40% of the air it generates into the atmosphere."

Energy waste has a habit of escalating quickly, too. Well-meaning maintenance teams turn up the system pressure to compensate for the escaping air; more air seeps out of the hole; and the increase in pressure causes the compressor to sap more electricity (a 1.5 bar increase in pressure will increase power consumption by 8%).

Protect your system by scheduling quarterly leak checks into your maintenance strategy. Spotting holes can be as simple as listening for the rasp of escaping air, or coating pipes in soapy water and looking out for air bubbles. Alternatively, if you want to go more high-tech in your war on waste, you can bring in ultrasonic leak detectors.

Kits are available from £750 or can be hired from £150 per week. Many compressor equipment suppliers will also offer testing services.

2 Get the correct size compressor
Whether it's ignorance, fear or ego, some very human flaws come to the surface when most sites go compressor shopping. "Historically, people have wanted to buy the biggest compressor," reflects Colin Mander, regional sales director at Gardner Denver. "It's a bit like how we used to buy our cars, when everyone would want a big engine without really ever needing it."

Stories of wanton super-sizing are folklore among compressed air suppliers. Mattei's Jones recounts a typical fable. "One company was running a 75kW compressor when 45kW was good enough. The excess capacity was wasting £12,000 in energy costs. If that firm had switched, they'd have delivered payback within a year – try finding that return from any other financial product."

It's worth remembering that sudden efficiency gains in one area of the factory can also impact on overall use, adds Jones: "Continuous improvement programmes may have boosted a line's efficiency so much that the demand for compressed air has dropped off." Keep tabs by regularly measuring air use against production levels. Contact the British Compressed Air Society for help or your chosen air supplier.

3 Build in flexibility
A graph of a typical site's air demand is going to have more peaks and troughs than a ramble through the Lake District. So it's important to have a compressed air system kitted out to deliver flexibility.
Think about installing air receivers with reserve capacity so you can meet spikes in demand.

Design your compressed air distribution system into zones that can be shut down during quieter periods. These could be synchronised with shopfloor shifts via time-operated valves. Fitting your air rings with interlocks will allow you to close down local supply until an air-using machine starts running.

Versatility should also be on your wish list when choosing a compressor. Don't get bamboozled by the variable-speed drives (VSD) vs fixed-speed drive (FSD) debate – it's rumbled on for almost as long as the chicken or egg conundrum.

A VSD is great if you experience a wide range of air demands and rarely need over 75% of your compressor's full load capacity. VSDs are more energy efficient at lower demands but have a higher price tag – £7,000 to retrofit a 55kW compressor.

FSDs will be better for sites with steady, predictable air demands. However, two fixed-speed drives might be better than one VSD where air demands veer from high to low in a predictable pattern. Jones of Mattei explains: "If demand is high during the day and quieter during a night shift, then you might be better off with two fixed-speed compressors rather than one variable-speed drive."
The final decision will be highly personal to your site and should be made after extensive measurement. Contact any of the associations and companies listed in the box opposite for more help.

4 Filter your air
Failing to filter creates the compressor equivalent of a 60-a-day chain smoker. Pipes become dirty, clogged and the circulatory system has to go nineteen to the dozen just to meet ordinary daily demands. Check and change intake, primary, pre- and post-filters periodically. Regular filtering should be part of your factory's DNA, regardless of the type of compressor being used, says Steve Riley, general manager of compressed air equipment manufacturer Beko.

"You talk to some manufacturers who think oil-free compressors offer eternal savings, because you never have to buy filters," he says. "But there are still hydrocarbons in air and all sorts of other nasties, like viruses. Those companies are then shocked to find out their air is below grade two quality."

5 Waste not, want not
To the ordinary eye, it's an air compressor. But real energy aficionados also see a heater-come-kettle. Around 80% of the energy supplied to a compressor can be recovered and used to heat factory buildings and hot water. The trend is increasingly in vogue, reports Gardner Denver's Mander. "More and more customers are looking at heat recovery. You're talking payback within six months in some cases."

One word of warning: plan a heat recovery system thoroughly. Seek expert advice before rigging up a ducting system from compressor to factory outhouse. It may end up causing your compressor to overheat unless you bring in extra fans.

6 Air is not free
Hairdryer, fan, miniature vacuum cleaner... if only the shopfloor's ingenuity with new uses for compressed air was matched by inspiration for saving energy. "The factory worker doesn't realise that when he switches on the airline it costs money," says Beko's Riley. "Workers will blow themselves down at the end of the day to get rid of debris. Not only is that a waste of air, but there's also a danger of contamination."

Attitudes can change with a concerted effort by management. Think hard about engaging the shopfloor with best practice and reducing bills. Set out good practice guidelines and entwine air use reduction targets with department objectives. Appoint a team leader to deliver the changes and empower workers to refine your suggestions. You may also need extra training to make employees wake up to the cost of a spray down after each shift.

7 Plan ahead with maintenance
A proactive maintenance plan is fundamental to getting the best performance out of your system. The blueprint can start with simple monthly leak checks and go right up to thermographic surveys to identify overheating issues. The key thing is to be on the front foot and seek improvements, rather than simply sitting back and waiting for things to go wrong.

Find out more on help with energy surveys at www.carbontrust.com/media/7393/ctg055_energy_surveys.pdf.

8 Adopt a youth policy
There's something very British about getting one more year out of a piece of kit most people considered obsolete in the late 1960s. However, when it comes to compressors, the urge to make do and mend will cost you dear. Energy accounts for 73% of a compressor's costs over a 10-year period – four times more than the initial cost of the machine. Make sure you do some ROI sums on the calculator before deferring on new plant for yet another year.

9 Take the pressure
Fluctuations in system pressure can cause costly inefficiencies. Minimum operating pressure is usually around 6 bar, with a 1.5 bar rise causing a 20% energy drain. Keeping things constant means installing the correct size piping to encourage smooth airflow. Avoid piping that looks like a switchback rollercoaster as long runs will cause pressure to drop. A maximum velocity of 6 m/s in main pipework and 15 m/s in short drops is advised by the British Compressed Air Society.

10 Use your nozzle
Fitting nozzles to your air delivery equipment can save up to 70% of air demand, according to Iain Cameron, international product manager at Meech Air Technology. Nozzles can amplify ambient air by 25:1 and lack the ear-splitting hiss of an uncovered pipe, he explains. "In a food manufacturing plant, you will see cans or bottles being moved around and a quarter-inch open pipe is often used to help this. At 80psi, 5.4 bar, this would consume in excess of 80cfm. Simply by fitting an energy-saving nozzle, you could reduce consumption to 15cfm.

Based on 7p per kW/hr for energy, an open pipe will cost around £1.05 per hour to run; with the nozzle, it will cost 20p per hour to run." A bag of five nozzles (£85) has a potential ROI of just a few days and shows compressor savings don't cost the earth.

Check out the Carbon Trust's 'Compressed air: opportunities for business' report, which was the foundation of our top 10 guide. Download the report at http://www.carbontrust.com/media/20267/ctv050_compressed_air.pdf

Max Gosney

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