Towards a new age of efficiency

With the global financial crisis and environmental pressures intensifying, the drive to reduce energy consumption is on. Katherine Crichton writes.

WITH the imminent arrival of the Government’s Carbon Pollution Reduction Scheme and with electricity prices set to double in the next few years, the race is now on to improve the design and use of one of the biggest energy users on the factory floor – the compressor.

Arguably, one of the most significant technological advancements in compressor design was the introduction of the variable speed (or frequency controlled) compressed air system.

While it’s not a new technology, VSDs are increasing in popularity as the market aims to find ways of reducing energy consumption and costs.

According to Dino Alessio, marketing manager, Champion Compressors, the current trend of returning to ‘older’ technologies such as VSDs, heat recovery, regenerative systems etc, has been driven by rising electricity costs, increased concern about the environment and the advent of the global financial crisis.

“Previously there wasn’t a market for these kinds of technologies as electricity prices were relatively low and the payback just wasn’t there, but this has now changed,” Alessio explained.

Alessio told Manufacturers’ Monthly there is a growing market for what he refers to as ‘power save’ options, where manufacturers/customers can literally pick and choose energy efficiency options that best suit their application.

“We are trying to encourage compressor users to choose the power save option that is best for their application. For example there is no point getting a heat recovery system built into your compressor if you don’t need any hot water on your site.

“This is how we view VSD compressors; as another power save option, but only if the technology is suited to the application,” he said.

And fitting the energy reduction solution to the application is where VSD compressors can simultaneously be the hero and villain for users.

VSD vs fixed speed

Often touted as the panacea to energy efficiency, in certain applications VSD compressors can be the most efficient option, but as Alessio warns, often the technology is sold into applications where they are massively oversized.

“Often the way sellers justify selling VSD systems is by saying the compressor can work to a reduced load, where often the user would have actually been better off implementing two smaller on/off (fixed speed) compressors.

“Also we see VSD systems installed in applications where they are working at 100% load, which offsets the any benefits the compressors could offer,” he said.

This is because VSD compressors are designed to operate at an optimum of 70% load. When compressor loads reach above or below 85%, the VSD compressor’s efficiency drops away.

According to Alessio, the ‘sweet spot’ or optimum load range for VSDs is about 30-70%, but he stresses this applies to a widely fluctuating load.

“If you are running multiple shifts which use varying amounts of compressed air generally between this range, then you would get the most out of your VSD motor. On the other hand, if air usage tends to ‘step-up’ from say 30% to 70%, then two fixed machines still might offer better value.”

With standard compressor systems now designed to turn off when idle, Alessio says often a standard machine with modifications such as a larger air receiver can eliminate or reduce any efficiencies generally experienced by on/off load machines in some applications.

“For most applications, conventional on/off load compressors are still the more cost-effective compressor solution,” Alessio said.

Multi stage compression

Whether using VSD or fixed speed compressors, another consideration to increase the overall efficiency of the compressor system is to install multi stage compressors, typically two stage as opposed to single stage machines.

In some cases, this is required as a pre requisite to meet the higher pressure demands in a particular compressed air application, which cannot be achieved over a single stage.

According to David Green, GM, Sales and Marketing at CAPS, two-stage compressors, which have a low-pressure stage and a high-pressure stage, are inherently more efficient than single stage systems because they include an intercooler which removes heat during compression, making the total compression process approach more closely the ideal ‘Isothermal Compression’ system.

“Efficiency gains are realised from reduced slippage past the rotors and heat removal during the compression process equating to reductions in power consumption of up to 15% in some cases,” Green said.

For most medium to large capacity industrial applications single and two stage compressor options are available as a choice for customers, whereas for much larger process air applications, typically three, four or even 5 stage compressors are the norm.

“A typical two stage compressor will have a price premium over a single stage compressor, as they have an additional compressor stage and intercooler, but the viability of this premium is based upon the payback realised from increased savings over the single stage option, this is determined by the specific operational air capacity demand requirements over time.

“Multi-stage systems are suited those applications which require a compressor of 90kW or over and need to be run for extended periods of time. In these situations ROI can be less than 12 months in some cases over the equivalent single stage alternative,” he told Manufacturers’ Monthly.

Similarly to VSD compressors, multi-stage systems are not a new concept, but with the drive for reduced energy costs, they are now being promoted as a way of maximising the efficiency of compressed air systems.

“Multi-stage compression is not viable for every installation, but in many cases, particularly medium to large industrial applications, two-stage variable or fixed speed compressors can provide really effective energy savings.

“In saying this, there will always be a place for single stage compressors, as some applications won’t warrant the extra investment in two-stage compression if the payback isn’t there,” Green said.

Efficiency control

Another aspect of compressed air systems which has developed over the years to provide increased energy efficiency is air compressed system control technology.

According to Simon Wood, National Sales Manager BOGE Compressors, using management and monitoring systems enables air compressor users to justify any changes in technology necessary to further improve energy and system efficiency.

“We have developed a complete energy management suite which can provide control of up to 16 compressors along with a comprehensive visualisation and reporting package which can be accessed by up to 50 users via a web server.

“Frequency control adapts the compressor output to the actual demand whilst constantly maintaining the desired pressure. As a result, expensive idling times and motor switches are avoided and tighter pressure bands can be set to assure energy saving efficiency,” Wood explained.

The system has been designed to forecast additional or reduced demand and automatically switches the compressor choice to ensure system optimisation virtually eliminating load/no-load run cycles.

Wood says this optimises the energy used, creating immediate savings in compressed air related energy costs. “Crucially, pressure can be controlled to within 0.1 bar – every 1 bar reduction in pressure nominally saves 10% in generation costs,” he said.

“By working strictly in accordance with the compressed air demand by producing the exact volume of compressed air at the pressure required frequency control minimises idling time and evens out air demand fluctuations. As a result – and when correctly specified – the manufacturer can optimise energy usage and make significant compressed air related energy savings.”

Even though it is possible to estimate energy savings and payback times, Wood says in some cases, manufacturers are still hesitant to making a financial commitment into new energy efficiency equipment.

“This is where it is important that the end user takes a look at the wider implications and considers energy optimisation as a long term, company wide strategy.

“An optimised compressed air system will create energy savings that will impact on electricity bills and inevitably the bottom line. Actively implementing methods and low carbon technologies to reduce the organisations all up carbon impact will only add to enhance the corporate image,” Wood explained.

BOGE Australasia 08 9528 2157.

Champion Compressors 1300 242 674.