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Improving whole life costs with energy audits

24 July 2017

Annually, UK industry uses over 20TWh of electricity to compress air, equivalent to the output of four power stations and over 8.1 million tonnes of CO2 emissions. As a result, high-quality energy and performance at a cost-effective price continues to be a key consideration for businesses. Keith Findlay, compressed air audit manager at Gardner Denver, outlines the benefits of energy audits, discussing the improved efficiencies that they can help realise.

Compressed air is often referred to as the fourth utility. It is essential to many sectors as a safe, reliable and versatile source of power. It does however take a considerable amount of energy, generally in the form of electricity, to produce the clean, dry, pressurised air that is needed for so many processes and applications. Naturally, reducing compressed air wastage will save energy and costs, as well as improving reliability and productivity.

Improving total cost of ownership

A key driver for improving innovation and technological advancement is total cost of ownership. Efficient performance at a cost-effective price continues to be a key consideration for customers.

Businesses of all sizes have become increasingly wary of purchasing a compressed air system for a lower upfront cost, only for issues to arise further down the line that mean any savings originally realised have been lost on service and maintenance costs.

Consequently, organisations are moving away from considering the initial purchase price for a piece of equipment alone, and starting to focus on the whole life costs. Servicing and maintenance costs are no longer seen as separate entities, but rather parts of a greater whole.

The British Compressed Air Society recently introduced BS ISO 11011, which has now been adopted as IS ISO 11011, assessing the energy efficiency of a compressed air system. Regardless of the size or scale of operations in questions, businesses could potentially save a significant sum of money on their bottom line.

As such, compressed air systems are now being held to greater account than ever before, which is why undertaking a thorough and detailed energy audit can have a positive impact on reducing total cost of ownership, while delivering those all-important improved efficiencies.

Air demands

Generating compressed air accounts for 10% of total energy costs in industry, so ensuring wastage is kept to an absolute minimum should be a key concern for all operators. And with industry averages suggesting energy costs account for more than 80% of the total cost of ownership of a compressor, data-logging equipment is being used more and more, helping companies identify any inefficiencies and assist with performance optimisation, leak reduction and practical air management processes.

The consequences of not dealing with these issues can be problematic, both with regards to equipment performance and to financial implications.

Leaking profit

Leaks in a compressed air system are often ignored, typically because they are not seen as an immediate health and safety hazard. However, managing air leaks is the single most important energy saving measure that can be taken to help stop compressed air wastage and save money.

A high leak rate causes significant fluctuations in pressure, resulting in hidden costs such as slower running or the stalling of production lines. This can also create a noisy environment for staff.

There are many reasons for leaks in a compressed air system, with regular culprits being manual condensate drain valves being left open, shut-off valves being left open, and leaking hoses, couplings, pipes, flanges and pipe joints.

Issues such as leakages in pipework can account for up to 35 per cent of the total air consumption, and the Carbon Trust reports that a leak as small as 3mm could cost more than £700 a year in wasted energy. Installing permanent flow meters can be an effective means of identifying any changes in compressed air consumption. The latest flow meters available on the market offer a reliable means of evaluating compressed air generation and the associated costs from any downstream inefficiency, and finding and repairing one 3mm leak could potentially save enough money to cover the cost of buying a flow meter.

Minimising a system’s leakages is not a one-off activity, with leaks recurring in different locations. Energy audits can help identify leaks and then ensure these leaks are managed effectively.

Once any leaks have been repaired, check the pressure drop from the compressor to points of use, as it may be possible to reduce the pressure of the compressed air being generated. Otherwise, fixing leaks could increase the pressure of the air in the system, meaning any savings will not be realised. In fact, the increased pressure could actually result in more new leaks.

Energy recovery

Recovering heat generated by a compressor is gaining popularity, and is great example of how an energy audit can illustrate how a business might improve its operational efficiencies.

Evidence has proven that 94% of the heat generated by a compressor can be recovered. This can be achieved through a number of processes, such as warm air recirculation from the compressor to a local area – more commonly known as space heating – or by installing an energy recovery unit fitted to the oil circulation system.

Energy recovery units transfer heat from the compressor oil circulation system to an incoming water supply which can be utilised in different types of processes such as hot water washing, central heating, steam systems and other manufacturing processes where heated water is required.

An energy audit can help determine the possible heat potential from a compressed air system.

Location, location, location

Compressor location is another important area to consider. Units should be positioned in a dry, clean, cool and well-ventilated area. Extra ventilation is always advised to ensure the compressor room remains as near to ambient temperature as possible. It also recommended to site the air inlet to the compressor house on a north-facing wall, if possible, or at least in a shaded area, with a grille to prevent debris from entering.

It also goes without saying that OEM recommended lubricants and genuine spare parts should be used, to ensure the energy efficiency of the compressed air system. A thorough energy audit will also consider these aspects.

Next steps

Before undertaking an energy audit with a business, a reputable supplier should first carry out a pre-assessment survey, looking at a range of variables that will have an affect on compressed air usage. These include: compressor kW sizes; the flow, dew point, pressure and temperature required; the time required to perform a leak survey; shift patterns; cost of electricity on site; and any obvious signs of leaks.

From here, the company will be able to advise if the business will benefit from an energy audit. A typical report from Gardner Denver, for example, will then include the following: an overview of the compressed air system, a power and flow report, temperature data, an air leakage survey, a report on any pipework issues, potential energy saving opportunities and then a proposal of how to implement these suggestions.

Eminent mathematical physicist and engineer Lord Kelvin once famously said: ‘To measure is to know. If you cannot measure it, you cannot improve it.’ This demonstrates exactly why an energy audit can be so valuable, helping to deliver vital cost savings and improved operational efficiencies.