Compressed air accounts for an average 12% of industrial electricity usage across Europe, and up to 40% on some plants, according to research conducted by compressor manufacturer Atlas Copco. Yet, says the firm, this utility is often overlooked as a target for efficiency improvement , despite the potential for significant savings.
And, given that up to 94% of the electrical energy used by air compressors is converted into heat – and that's without considering other problem areas, such as sizing, operations and distribution, including leaks – 'significant' appears a conservative description.
Regrettably, so much has been the case for years. However, several recent developments, both technical and regulatory, look set to enable and/or force at least some change. Primary among electromechanical developments are the emergence of accessible heat recovery systems, more efficient primary compressor designs and higher-efficiency versions of the electric motors and variable speed drives (VSDs) providing motive power (see panel, p40). As for the legislative side, the top three are: the ISO 11011 standard; EC 640/2009 Eco-design directive for electric motors and VSDs; and the upcoming 2009/125/EC Eco-design regulation concerning industrial compressors.
Looking at standards and regulations, first up is the global compressed air energy standard ISO 11011, which was ratified in August 2013. This sets regularised benchmarks for auditors assessing compressed air estates as whole systems, all the way from the compressor room supply, through how air is distributed via the pipework infrastructure, out to the demand side. BCAS (British Compressed Air Society) technical officer Greg Bordiak makes the point that this now encourages auditors to examine plants' air applications too, and, where appropriate, help users to consider alternative approaches. "For example, if they're using air jets, instead of air knifes, to cool products on a production line, they may as well be blowing money away – and auditors should now tell them that," he asserts.
Atlas Copco's Keith Findlay, who looks after the firm's AIRScan air audit team, agrees, and adds that ESOS (Energy Saving Opportunities Scheme, which applies to all firms with more than £40 million turnover and demands action by 5 December 2015) is likely to increase uptake of ISO 11011. Why? Because using the energy standard ISO 50001 (for which ISO 11011 is compressed air-specific) is one pragmatic way to comply with the regulations while also reaping the benefits of its mandatory energy audit.
Eliminating wasteful practices
"Under ISO 11011, data must be analysed, reported and documented, along with an estimate of potential energy savings," explains Findlay. And he asks, why would anyone not want to take advantage of that information and "eliminate wasteful practices, leaks, artificial demand and inappropriate use"?
It's a different story with EC 640/2009, which applies directly to the electric motors and drives, and mandates increasingly energy-efficient machines. Whereas the requirement was for nearly all new motors with a rated output from 0.75 to 375kW to meet the high-efficiency IE2 specification, since 1 January premium-efficiency IE3 motors have been compulsory for all new machines from 7.5 to 375kW. IE2 motors are no longer permitted for sale within the EU unless used with a VSD. This ruling will then be extended to include motors down to 0.75kW, from
1 January 2017 – again with the proviso that IE2 be permitted for VSD-based applications.
Clearly, there are capital cost implications but, as Andy Jones, managing director of compressors manufacturer Mattei, says, IE3 motors (or IE2 with drives) yield rapid paybacks. "As an example, the Carbon Trust suggests that an 11kW IE3 motor in continuous use consumes almost £250 less energy per year than an IE1 model." However, he adds that there's more to improving energy efficiency than upgrading the motor. "Replacing an ageing compressor with a modern-day equivalent will almost certainly deliver energy and carbon savings – but the system also needs to be appropriately designed and leak-free for them to be fully realised."
Just so, and that leads us neatly to the big news for compressors themselves – the EC's decision to adopt 2009/125/EC, which mandates ecodesign requirements for all new 'standard' rotary (vane and screw) and piston air compressors, delivering 5—1,280 l/sec and 2—64 l/sec respectively and driven by three-phase electric motors. 'Standard' essentially means fixed-speed basic packages, with the definition specifying outlet pressures of 7—14 bar(g) – meaning a wide range of power ratings, dependent on the mix between pressure and volume flow.
With the regulation due to be published by the end of this year, and then phased in – much the same as for electric motors – effective dates will be 2017 and 2019. Note that turbo-compressors, low-pressure machines and VSD-based units are currently excluded. Note also that the regulation won't apply to compressors designed for: gases other than filtered ambient air; operation in potentially explosive atmospheres as defined in Directive 94/9/EC; ambient temperatures above 40°C and/or inlet air temperatures below -15°C or above 100°C.
According to BCAS's Bordiak, however, just four years from now this means that some 40% of in-scope compressors currently on the market will no longer be available, because they won't meet the efficiency levels. He makes no bones about BCAS's disappointment with the European outcome, insisting that a 'business as usual' approach could have saved far more energy.
"Compressor manufacturers would have come up with higher-efficiency designs anyway, due to the nature of competition, and electric motor improvements could also be passed on," says Bordiak. "But now the industry will have to accept a much narrower range of products, as manufacturers put all their effort into designing in relatively small energy improvements to ensure compliance."
That being the case, best advice is to re-engage with good practice now, reconsidering your compressed air estate from a total system perspective. Atlas Copco's Findlay suggests starting by reviewing your piping infrastructure, checking first for leaks – accepted industry wide as the greatest source of energy waste, and responsible for up to 40% of losses at an unforgivable number of sites.
"A leak as small as 5mm costs an estimated £3,800 in wasted energy over the course of a year," he asserts. Indeed, Findlay says one recent leak detection programme at an unnamed UK vehicle manufacturer identified leaks costing £102,000 a year, while another at a confectionery manufacturer pinpointed £31,000 worth of leaks.
"Process leaks are another reason for overspending on energy and these can be corrected by replacing production line equipment," he continues. We might add that improving local pressure controls also helps – as does shutting down compressors when not in use, using simple automatic timers, if appropriate.
And while on the subject of air distribution, Carl Sharpe, energy efficiency and air specialist at Boge, also advises users to turn output pressure down where possible. "Every bar of unnecessary pressure costs 7% in kW. So, tightening up your pipework and turning the pressure down leads to very quick wins that don't cost a lot of money to implement."
Meanwhile, Bordiak reminds us that it's also all about getting compressed air from generation to the point of use losing minimum energy. "So, good practice involves using smooth-bore piping [non-ferrous or plastic, except in environments such as steel foundries] with professional fittings, and minimising restrictions due to bends and valves." For the latter, he recommends using designs that present minimum flow resistance: for example, ball types rather than diaphragm valves, which change the air flow direction internally. "The additional expense of the installation is massively outweighed by the savings in running costs."
Unrealistic user demands
He also comments on some users' unrealistic air purity demands. "If they specify Class 1 under ISO 8573 Part 1 [compressed air contaminants and purity classes for solids, humidity and oil], not only will the system be incredibly expensive to purchase and maintain, but the scale of filters, desiccant driers, etc, will also cost them dear in energy. So, think about what you actually need and where. Plenty of plants site high-purity equipment at the compressor end when only a couple of production units need that purity. Sometimes, it's important to focus air treatment on the point of use."
And remember health and safety and your legal obligations. Most important here is PSSR (Pressure Systems Safety Regulations 2000), with Regulation 12 alluding to unintended releases of energy. As Bordiak says, a high-pressure leak from a small orifice is inaudible, at around 40kHz, so these are the most dangerous. That's why regular inspection by a competent person – who draws up the written scheme and determines the frequency of examination – is essential.
Compressed air accounts for an average 12% of industrial electricity usage across Europe, and up to 40% on some plants, according to research conducted by compressor manufacturer Atlas Copco. Yet, says the firm, this utility is often overlooked as a target for efficiency improvement , despite the potential for significant savings.
And, given that up to 94% of the electrical energy used by air compressors is converted into heat – and that's without considering other problem areas, such as sizing, operations and distribution, including leaks – 'significant' appears a conservative description.
Regrettably, so much has been the case for years. However, several recent developments, both technical and regulatory, look set to enable and/or force at least some change. Primary among electromechanical developments are the emergence of accessible heat recovery systems, more efficient primary compressor designs and higher-efficiency versions of the electric motors and variable speed drives (VSDs) providing motive power. As for the legislative side, the top three are: the ISO 11011 standard; EC 640/2009 Eco-design directive for electric motors and VSDs; and the upcoming 2009/125/EC Eco-design regulation concerning industrial compressors.
Looking at standards and regulations, first up is the global compressed air energy standard ISO 11011, which was ratified in August 2013. This sets regularised benchmarks for auditors assessing compressed air estates as whole systems, all the way from the compressor room supply, through how air is distributed via the pipework infrastructure, out to the demand side. BCAS (British Compressed Air Society) technical officer Greg Bordiak makes the point that this now encourages auditors to examine plants' air applications too, and, where appropriate, help users to consider alternative approaches. "For example, if they're using air jets, instead of air knifes, to cool products on a production line, they may as well be blowing money away – and auditors should now tell them that," he asserts.
Atlas Copco's Keith Findlay, who looks after the firm's AIRScan air audit team, agrees, and adds that ESOS (Energy Saving Opportunities Scheme, which applies to all firms with more than £40 million turnover and demands action by 5 December 2015) is likely to increase uptake of ISO 11011. Why? Because using the energy standard ISO 50001 (for which ISO 11011 is compressed air-specific) is one pragmatic way to comply with the regulations while also reaping the benefits of its mandatory energy audit.
Eliminating wasteful practices
"Under ISO 11011, data must be analysed, reported and documented, along with an estimate of potential energy savings," explains Findlay. And he asks, why would anyone not want to take advantage of that information and "eliminate wasteful practices, leaks, artificial demand and inappropriate use"?
It's a different story with EC 640/2009, which applies directly to the electric motors and drives, and mandates increasingly energy-efficient machines. Whereas the requirement was for nearly all new motors with a rated output from 0.75 to 375kW to meet the high-efficiency IE2 specification, since 1 January premium-efficiency IE3 motors have been compulsory for all new machines from 7.5 to 375kW. IE2 motors are no longer permitted for sale within the EU unless used with a VSD. This ruling will then be extended to include motors down to 0.75kW, from
1 January 2017 – again with the proviso that IE2 be permitted for VSD-based applications.
Clearly, there are capital cost implications but, as Andy Jones, managing director of compressors manufacturer Mattei, says, IE3 motors (or IE2 with drives) yield rapid paybacks. "As an example, the Carbon Trust suggests that an 11kW IE3 motor in continuous use consumes almost £250 less energy per year than an IE1 model." However, he adds that there's more to improving energy efficiency than upgrading the motor. "Replacing an ageing compressor with a modern-day equivalent will almost certainly deliver energy and carbon savings – but the system also needs to be appropriately designed and leak-free for them to be fully realised."
Just so, and that leads us neatly to the big news for compressors themselves – the EC's decision to adopt 2009/125/EC, which mandates ecodesign requirements for all new 'standard' rotary (vane and screw) and piston air compressors, delivering 5—1,280 l/sec and 2—64 l/sec respectively and driven by three-phase electric motors. 'Standard' essentially means fixed-speed basic packages, with the definition specifying outlet pressures of 7—14 bar(g) – meaning a wide range of power ratings, dependent on the mix between pressure and volume flow.
With the regulation due to be published by the end of this year, and then phased in – much the same as for electric motors – effective dates will be 2017 and 2019. Note that turbo-compressors, low-pressure machines and VSD-based units are currently excluded. Note also that the regulation won't apply to compressors designed for: gases other than filtered ambient air; operation in potentially explosive atmospheres as defined in Directive 94/9/EC; ambient temperatures above 40°C and/or inlet air temperatures below -15°C or above 100°C.
According to BCAS's Bordiak, however, just four years from now this means that some 40% of in-scope compressors currently on the market will no longer be available, because they won't meet the efficiency levels. He makes no bones about BCAS's disappointment with the European outcome, insisting that a 'business as usual' approach could have saved far more energy.
"Compressor manufacturers would have come up with higher-efficiency designs anyway, due to the nature of competition, and electric motor improvements could also be passed on," says Bordiak. "But now the industry will have to accept a much narrower range of products, as manufacturers put all their effort into designing in relatively small energy improvements to ensure compliance."
That being the case, best advice is to re-engage with good practice now, reconsidering your compressed air estate from a total system perspective. Atlas Copco's Findlay suggests starting by reviewing your piping infrastructure, checking first for leaks – accepted industry wide as the greatest source of energy waste, and responsible for up to 40% of losses at an unforgivable number of sites.
"A leak as small as 5mm costs an estimated £3,800 in wasted energy over the course of a year," he asserts. Indeed, Findlay says one recent leak detection programme at an unnamed UK vehicle manufacturer identified leaks costing £102,000 a year, while another at a confectionery manufacturer pinpointed £31,000 worth of leaks.
"Process leaks are another reason for overspending on energy and these can be corrected by replacing production line equipment," he continues. We might add that improving local pressure controls also helps – as does shutting down compressors when not in use, using simple automatic timers, if appropriate.
And while on the subject of air distribution, Carl Sharpe, energy efficiency and air specialist at Boge, also advises users to turn output pressure down where possible. "Every bar of unnecessary pressure costs 7% in kW. So, tightening up your pipework and turning the pressure down leads to very quick wins that don't cost a lot of money to implement."
Meanwhile, Bordiak reminds us that it's also all about getting compressed air from generation to the point of use losing minimum energy. "So, good practice involves using smooth-bore piping [non-ferrous or plastic, except in environments such as steel foundries] with professional fittings, and minimising restrictions due to bends and valves." For the latter, he recommends using designs that present minimum flow resistance: for example, ball types rather than diaphragm valves, which change the air flow direction internally. "The additional expense of the installation is massively outweighed by the savings in running costs."
Unrealistic user demands
He also comments on some users' unrealistic air purity demands. "If they specify Class 1 under ISO 8573 Part 1 [compressed air contaminants and purity classes for solids, humidity and oil], not only will the system be incredibly expensive to purchase and maintain, but the scale of filters, desiccant driers, etc, will also cost them dear in energy. So, think about what you actually need and where. Plenty of plants site high-purity equipment at the compressor end when only a couple of production units need that purity. Sometimes, it's important to focus air treatment on the point of use."
And remember health and safety and your legal obligations. Most important here is PSSR (Pressure Systems Safety Regulations 2000), with Regulation 12 alluding to unintended releases of energy. As Bordiak says, a high-pressure leak from a small orifice is inaudible, at around 40kHz, so these are the most dangerous. That's why regular inspection by a competent person – who draws up the written scheme and determines the frequency of examination – is essential.
Electromechanical moves
Beyond swapping out motors on continuously running compressors for higher-efficiency machines and/or variable speed drives (and remember, some are eligible for Enhanced Capital Allowance), two increasingly accessible approaches to technology-led energy savings are heat recovery and better primary compressor designs.
Looking at the former, Atlas Copco's latest retrofit energy recovery units for its GA series compressors are claimed to convert up to 94% of usually wasted thermal energy into hot water at up to 90°C, for process and facility applications. Given that, coincidentally, as much as 94% of the electrical energy consumed by compressors is converted into heat, that's an 88% return.
Even allowing some contingency, Boge's energy efficiency and air specialist Carl Sharpe reckons that 78% of input electrical energy is ripe for reclaiming. "All these systems are based on heat exchangers on the cooling oil circuit and are designed to heat water, for example, for radiators or process steam. ROI is very quick: our calculations show just a matter of months because 78% of, say, 30kW is equivalent to quite a big gas boiler saved."
That was certainly the case at textiles manufacturer Autofil Worldwide, which last year reported average savings of £37,000 a year since commissioning Atlas Copco's air compressor energy recovery technology. The firm, which produces polyester yarns at its Sherwood Park, Nottingham, plant for the automotive sector, is using the recovered heat to raise the temperature of its process water.
Autofil engineering manager Steve Charlton explains that the system is controlled by Atlas Copco's ES 360 optimiser, and comprises 12 compressors, including three GA 160+ units and a GA 250 machine connected to a standalone ER-S5 energy recovery unit. The latter ensures that hot oil from the air end is diverted to a stainless steel plate heat exchanger, where it is transferred to water on the other side.
Based on the compressor running for 8,424 hours per year, the system is recovering more than 1.4 million KWh of energy.
As for higher-efficiency primary compressor designs, there are claims and counter claims, but one worth looking at is sliding vane rotary compressors (SVRCs). Andy Jones, managing director of Mattei, hints that it can "significantly improve the efficiency of the compression process". He says that Mattei's R&D department in Italy is already on the case.
"We have some exciting patents in place, which will allow us to improve the energy efficiency of a compressed air system to previously unheard of levels in the very near future," he insists. Referring to the IMechE international compressors conference in 2013, he singles out a paper by professor Roberto Cipollone on SVRCs, which, he says, could become the most energy-efficient 7bar compressors on the market.
And note: prof Cipollone stated that further savings might be achieved by reducing machine speeds and improving lubrication.