Compessed air systems: Efficiency matters

The manufacturing sector should have a real appetite for saving energy. A survey released earlier this year by the manufacturers’ organisation EEF and energy supplier npower demonstrated that since 2002 the industrial price of gas has increased by 122%, and electricity prices have increased by 94%.

It’s not just about the bottom line, however. The EEF/npower survey highlighted that British manufacturers are increasing their investment in strategic energy management and efficiency to not only reduce energy bills, but also their carbon footprint. We all have an obligation to reduce carbon emissions; scientists are now 95% certain that humans have been the dominant cause of global warming since the 1950s, and that climate change poses a threat to global food stocks and to human security – as well as already being responsible for melting sea ice and thawing permafrost in the Arctic, killing off coral reefs in the oceans and leading to heat waves, heavy rains and mega-disasters.

Not all manufacturers realise that compressed air can have a big impact on energy costs and carbon emissions, despite the fact that it’s the industrial sector’s fourth utility, and compressors use a lot of energy. 

Before any improvements can be made, however, it’s essential to carry out an assessment to measure how much compressed air is being used, and to check if the compressors, air treatment and pipework delivery system are appropriate for the production processes. 

In the first instance we would always recommend a data logging exercise to evaluate compressed air needs and the efficiency of the system. Air consumption profiles are recorded and measured over a seven-day period, followed by discussions to identify unusual patterns or planned process changes. Investing in a more detailed energy audit, which should always be carried out in accordance with the international standard ISO 11011:2013, Compressed air – Energy efficiency – Assessment, can paint an even more realistic picture.

These measures will identify whether any improvements can be made to increase efficiency. Sometimes this will involve investment in a new compressor, but in our experience, small, more affordable changes can often have a big impact on energy costs and carbon emissions.

Investing in a new compressor 

Replacing a compressor can have a significant impact on energy costs. One of our aerospace customers uses compressed air to operate machine tools and cleaning equipment. Replacing its existing 90kW compressor with a highly efficient 75kW Mattei Maxima 75 resulted in energy savings approaching £20,000 per annum, and the new installation paid for itself in about 18 months.

If data logging and/or an energy audit reveals a new compressor is required, it’s vital for the manufacturer to seek advice from a compressor specialist, and to avoid the temptation to replace like-for-like. Poor selection is unfortunately all too common in compressed air – Mattei found that one company running a 75kW compressor could actually fulfil its compressed air requirements with a 45kW machine, with estimated savings being in the region of £10,000 a year.  

It is also important to choose the most efficient compressor available (which of course should also match production processes/demand), rather than the cheapest one, because the main cost will always be the energy required to produce the compressed air. The initial purchase price actually makes up a very small part of the total lifetime costs of the equipment, and a slightly higher-priced compressor could pay for itself in just a matter of months by reducing energy consumption. 

Over recent years compressor manufacturers have been investing in making their compressors more efficient, enabling end users to make even greater savings. Some companies are concentrating on the use of more efficient electric motors and drives. I believe that Mattei’s use of vane technology gives us an advantage, as we will be able to improve the efficiency of the compression process too. 

In fact, at the IMECHE International Conference on Compressors and their Systems 2013, a paper given by Professor Roberto Cipollone highlighted the special features of Sliding Vane Rotary Compressors (SVRC) and their potential to be the most energy efficient seven bar compressors available on the market. 

Mattei’s R&D department in Italy carried out successful product trials, and we have some exciting patents in place that will allow us to improve the energy efficiency of a compressor to previously unheard of levels within the very near future.

Environmental factors, for example, can affect air flow, and hence efficiency. Cooler air is denser and makes the compression process more efficient, so if a compressor is sited near to heat-generating plant, or equipment like boilers, furnaces or ovens, the air being drawn into the machine will be warm. The compressor will then have to work harder, reducing efficiency as well as the lifetime of its parts. Simply relocating the compressor could therefore result in savings.

System changes

Making changes to pipework can also improve efficiency. Excessive lengths and bends lower system efficiency, so pipe runs need to be suitably designed and laid out. And although smaller diameter pipe may save on capital cost, greater pressure drops in the system lead to a higher operating cost.

The pipework must also be checked for leaks, and if any are found they need to be repaired. This is a simple and cost-effective exercise (the average cost of a Mattei leak detection survey, for example, is less than 10% of the overall leakage costs). We often see compressed air systems with around 150 to 300 leaks, and a company using 50m3 of compressed air per minute could potentially save around £63,000 by repairing them. 

Of course, sometimes a combination of system improvements and a new compressor are required to deliver optimum savings. For one of our customers in the food manufacturing sector this approach has paid dividends. The company can expect to save in the region of £150,000 over five years as a result of a system upgrade and the installation of Mattei Maxima 75 compressors. 

Heat recovery 

It’s also worth considering the addition of heat recovery. Around 90% of the electrical input used to power a compressor’s motor is turned into heat, but approximately 80% can be recovered through a heat exchanger. Typical uses for the waste heat include water and space heating.  

The energy and carbon savings can be significant, especially if the compressors are operating for long hours. The Carbon Trust suggests that in many cases the cost of recovering warm air can be recouped in less than a year, while hot water systems can pay back in less than two years. 

Improving the efficiency of a compressed air system can have a big impact on manufacturers’ energy costs and carbon emissions, and this doesn’t always need to involve investment in a new compressor. As well as offering a range of energy efficient compressors, Mattei aims to raise awareness about related, cost-effective services that could improve efficiency.