Regardless of ESOS Compressed Air Systems are expensive

Michael Douglas, managing Director of Glaston Compressor Services explains why, when considering compressed air systems, only a comprehensive and inclusive approach will result in cost-effective air production.

Compressed air has long been essential for a wide range of manufacturing, process and automation technologies and in some situations its importance is underlined by the fact that users regard it as the ‘fifth utility’. Over time the complexity and efficiency of compressed air systems has dramatically increased and today this is even more important as a result of the Energy Savings Opportunities Scheme (ESOS). ESOS is the UK governments’ response to the EU’s efficiency directive and is essentially a mandatory energy assessment audit applicable to all UK companies with a minimum of 250 employees, or an annual turnover in excess of £42m. It is estimated that generating compressed air accounts for 12% of all industrial energy usage across Europe and whilst the ESOS initiative is a positive step towards a better understanding of energy usage, it does not oblige companies to carry out improvements. However, the commercial reality is that the focus on energy efficiency will only intensify. Therefore, why would any forward-thinking company not wish to implement changes that could result in significant cost-savings, especially over the longer term, giving them a competitive edge, regardless of whether ESOS is applicable to them or not?

Looking at the bigger picture

As the range of compressed air applications grows, so does the demand for increased air quality along with the requirement for optimum reliability and efficiency. However, many ‘systems’ still operate as they did 20 or 30 years ago where, due to a lack of user awareness, they are often referred to as just ‘the compressor’. Therefore, the bigger picture of the system as a whole is ignored. To gain the most from optimising compressed air system efficiency though requires an integrated, system approach. The role of the air treatment equipment, system controller, air distribution network and even the user, should not be under-estimated – they all have a significant effect on system reliability, efficiency and performance.

Greater cost-awareness needed

When talking about energy costs, users are usually able to quote the price per Kilowatt Hour but hesitate when asked how much their plant’s cooling water costs per cubic metre. Ask them how much a cubic metre of compressed air costs and many will be at a complete loss. This is due in part to most purchasing decisions being more concerned with the initial investment cost of the system, instead of accurately considering the long-term operating costs. Even with a perfectly optimised system, energy costs for compressed air production can amount to approximately 71% of total operating costs, whereas the initial purchase investment (excluding installation) accounts for approximately just 15% and for servicing an additional 14%. The larger the compressor the larger the operating cost element becomes.

The once common excuse that it’s not possible to ascertain accurate data cost-effectively regarding actual compressed air costs to assess potential energy-savings is no longer valid. System providers like Glaston have long since offered convenient analysis procedures and equipment. At moderate cost, key data such as pressure, pressure losses, air consumption values and air leakages can be gathered, analysed and documented within a couple of days. Furthermore, with constantly rising energy costs and the potential for increased legislation in the future, Glaston remain committed to producing quality compressed air with minimum energy consumption.

Glaston welcomed the results both from an EU study on energy savings in compressed air systems as part of the EU ‘Save II’ project and the ‘Efficient Compressed Air’ campaign (2002 to 2004). These studies, along with the more recent demands of ESOS are making users more aware of the need to comply and to optimise the efficiency of their compressed air systems.

Another fundamental finding of the EU study was that such potential savings could not be realised simply by improving individual components within a system, they could only be achieved through an integrated system optimisation approach, as most non-optimised systems show weaknesses in all areas.

Deceptive contentions

When the EU study was published, some manufacturers promoted individual products such as workshop compressors, variable speed compressors, or solitary air treatment components that would supposedly provide energy savings of up to 40%. However, significant reductions in energy consumption cannot be achieved simply by adding single components to an existing compressed air system. This would simply be repeating the errors of the past.

The seminars and compressed air audits of the ‘Efficient Compressed Air’ project also confirmed that system optimisation is only possible through an integrated approach.
The Golden Rules – Check everything first!

A detailed overall picture of the existing system is essential when considering new investment in compressed air equipment. The following steps are recommended:

  • Check air consumption, air quality and time dependent operation for all air consuming equipment.
  •  Note location, material type and sizing of the main air supply lines.
  • Produce a schematic diagram of the air production and treatment systems.
  • Use data-loggers, perform a detailed compressed air analysis over a period of at least ten days to include the following data; total air consumption, compressor partial load volumes, pressure measurement upstream and downstream of air treatment equipment and in areas with supply bottlenecks.
  • Assess all leakage losses of compressed air.

Evaluation of this data provides the key information required to calculate actual compressed air costs.

Aim for centralised systems

To achieve maximum energy efficiency, as many items of compressed air equipment as possible should operate at the same pressure. De-centralised compressor systems, network areas operating at a different pressure, or air quality and the use of small oil-free compressors for the purposes of particular processes, should only be considered in exceptional circumstances. In the long-term, such solutions invariably drive up energy costs and unnecessarily restrict flexibility with regards to possible future plans for expanding production or system modernisation.

Problems with compressed air quality usually occur due to moisture and insufficient compressed air drying. These can be identified via pressure dew point measurement and attention should only be turned to the compressor and associated equipment after this measurement has been taken.

Anyone trying to solve these problems simply by installing a master control system will usually find out quite quickly that no ‘off-the-shelf’ solution will work effectively. Compressed air dryers must be precisely tailored to match compressor outputs and the individual compressors should be correctly sized for compatibility with one another. Only then will a master control system be able to select the correct compressor combination at the appropriate moment.

Design strategy

A really efficient compressed air supply can only be achieved through a comprehensive design strategy that meets all specific compressed air requirements and which involves every system element. As a long established compressed air provider with an experienced team of sales/service engineers Glaston is well placed to provide key requirements such as:

  • The monitoring and analysis of existing compressed air installations.
  • Guidance and formulation of energy saving proposals to satisfy ESOS requirements.
  • The specifying and supply of new equipment or services to achieve energy savings.
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