Compressor selection: The pressure's on

Compressed air is the UK’s fourth utility and an essential part of manufacturing and processing.  As it accounts for about 10% of the total electricity consumed in the industrial sector, it is imperative that compressed air equipment is as efficient as it can be. To maximise efficiencies, compressors must be fit for purpose and specified to closely match the end user’s needs. Regrettably there are many incidents where this is not the case.

It is not uncommon, for example, to see standard industrial compressors used for applications where a lower pressure compressor or blower would adequately meet the end user’s needs. We recently saw an example of an 8 bar compressed system being used for agitating effluent tanks which in reality required just 500mBar pressure. Not only is this a waste of energy to initially compress the air to levels higher than required, but there are likely to be greater maintenance costs for the customer. 

In other applications it could simply be a case of moving something from A to B, and this is where a blower may provide an efficient solution.  Blowers are designed to deliver high volumes of air at low pressure in an oil-free design. There are positive displacement rotary lobe machines, low pressure single stage screw compressors and new ‘hybrid screw-blowers’ (designed to discharge at pressures around 1.5 barG or lower in an energy efficient way) available on the market. Suitable applications for blowers include transport of bulk materials in the food, construction and synthetic industry.

Equally, we often find compressors rated at 10 bar and above working in a system that only requires 6 or 7 bar pressure; again this is a very inefficient way to operate a compressed air system as every 1 bar increase in pressure increases energy consumption by approximately 7%.

Low pressure products, i.e. those below 4 barG, have an important role to play in delivering energy efficient air. However, while low pressure systems and blowers make up a significant percentage of total compressor sales each year, detailed knowledge of them and their applications within the wider market is low. 

Recently, a blowers and low pressure compressors working group was set up by BCAS (British Compressed Air Society) as a forum to boost awareness and understanding of low pressure products.  It aims to encourage more people within the industry to specify blowers and low pressure compressors in applications where they would be more suitable than high pressure compressors – even if this means referring the customer to another company. 

We need to encourage correct specification in the compressed air market – and we hope that the newly introduced ISO 11011 standard will help. ISO 11011 was introduced in August 2013, and contains a framework for the assessment and auditing of compressed air systems. 

Prior to ISO 11011 there was a lack of industry standards and guidelines, so energy audits would vary. Individual manufacturers and suppliers had to decide for themselves how to measure compressor energy consumption, and what recommendations to make to their customers. Now that we can all adopt the principles set out in ISO 11011, energy audits should be regularised and we should all be offering similar advice.

By increasing end user knowledge the compressed air industry can help ensure that customers are using the right products, in turn maximising energy and cost savings.