Andy Jones, general manager of rotary vane compressor manufacturer Mattei, is advising compressed air users to consider ten important factors, which can help them use the utility efficiently, cost effectively and safely:
1. Understand electrical consumption
Some businesses might have a misconception that compressed air is ‘free’ once they have invested in the equipment. In reality, the initial purchase actually makes up a very small part of the total lifetime costs of a compressor – the main cost will always be the energy required to produce the compressed air.
The electricity consumed during operation over a five year period accounts for around 75% of the total cost of ownership, including the initial capital outlay for the compressor.
2. Regularly assess the system
It’s essential for businesses to understand how much compressed air they use, how much it costs them and if the compressors are appropriate for their production processes – but it’s likely the vast majority don’t.
The best way to assess a compressed air system is through data logging, or a more detailed energy audit. The forthcoming ISO 110011 standard, Compressed Air – Energy Efficiency Assessment (due to be implemented in 2013), will hopefully encourage end users to assess their compressed air systems and subsequently take actions to reduce their energy use. It should also standardise the energy audits offered by compressed air companies.
3. Check whether air demands are fixed or variable
Some companies are using variable speed compressors when fixed speed machines would be more appropriate, and vice versa. Variable speed compressors will only save energy if there are true peaks and troughs in the demand for air, and if these variations fall within the efficient working band of the compressor. Again, data logging can reveal which type of compressor is most appropriate.
4. Decide what air quality is needed or appropriate
In recent years we have seen an increase in demand for ‘oil-free’ compressors to produce ‘oil-free’ compressed air. Although there is often a legitimate reason for this request, before investing in costly equipment we would urge purchasers to thoroughly assess the actual purity of air required and specify it using ISO 8573-1:2010 to see if ‘oil-free’ air is needed and, if it is, if class one rather than class zero would be sufficient.
It must be remembered that, despite its name, class zero doesn’t mean zero contamination. In reality, class zero simply has to have less contamination in a cubic metre of air than class one does, with the levels actually being agreed by the end user and compressor manufacturer. It’s also important to note that oil-free air can still be delivered through an oil lubricated compressor, providing there is an adequate level of filtration.
The more stringent the purity, the higher the cost is to achieve it – so it’s also important to consider whether or not the entire system requires the highest purity or just a particular area, which could then be served by point of use air treatment or a dedicated smaller compressor.
5. Ensure the compressor is installed and sited correctly
The efficiency of any compressor is largely dependent on the way it’s installed, and where it’s sited.
One of the main considerations should be air flow into the compressor – it needs to be unrestricted, cool, reasonably clean and free from solid and gaseous impurities. The distance between the compressor and where the compressed air is actually used can have important implications too. Meanwhile, pipes should be suitably sized for the air delivery capacity of the compressor/s, with bends kept to an absolute minimum.
6. Check noise levels
Noise levels should be considered to ensure employees aren’t adversely affected. All compressor manufacturers have to state the noise levels in accordance to international standards, with the current one being EN ISO 2151:2008. This means it is relatively straightforward to check the suitability of a compressor for a particular environment.
7. Regularly check for leaks
In many companies in excess of 30% of air generated is wasted through leaks. Mattei often see compressed air systems with around 150 to 300 leaks and, for a company that uses 50m3 of compressed air per minute, if they were repaired this could lead to potential savings of around £63,000.
Leaks are simple to identify and rectify, and it’s cost effective – the average cost of a Mattei leak detection survey is less than ten percent of the overall leakage costs. Leak detection surveys should ideally be done on an annual basis, and always before a new compressor is installed.
8. Undertake regular services and maintenance
If a compressed air system isn’t properly maintained on a regular basis it will not run as efficiently as it should. This will increase its running costs and it could end up posing a danger – in very extreme cases a poorly maintained compressor might even catch fire or explode.
It is for this reason that written schemes of examinations are a legal requirement under the Pressure Systems Safety Regulations 2000. The document contains a wide range of information, including the parts of the system that need to be examined, the nature of the examination required, the preparatory work needed and the maximum interval between examinations. There is a potential fine of up to £20,000 for not having this document.
9. Always use compressed air safely
We still hear of dangerous practices going on, such as people using compressed air to dust off machinery, work benches and even their clothes. If compressed air penetrates the skin and gets into the bloodstream an air bubble could reach the heart or lungs, which could prove fatal. And, as it travels at a phenomenal speed, if it hits an eye or an ear it may lead to blindness or loss of hearing respectively.
10. Recover heat where possible and appropriate
Compressors generate a lot of heat, and in some installations this can be recovered and put to good use in the production process, for water heating, for example, or – although not as efficient – local space heating.