Energy saving advice
July 26th 2006

Most companies are now facing increased energy bills,however you may be surprised by how much energy costs are actually increasing, some companies will soon see increases of 70% or more.This is additional to the extra that companies are already paying via the Climate Change Levy, which aims to encourage industry to improve energy efficiency.Compressed air is widely used throughout industry, generally viewed as a safe and reliable power source despite it being relatively costly to produce in terms of energy consumption, the good news is that because it is generated on site there are plenty of opportunities to make savings so long as it is correctly managed

Any review of a compressed air system should begin with setting a standard for compressed air quality. Obviously this should take the type of application into account, for example a food manufacturing site will usually require air that has been treated to a much higher standard than a metal fabrication works.

The ISO 8573.1 standard for air quality is a good framework to use when it comes to establishing a standard. Within the ISO standard there are six classes that denote solid particulate, water and oil content. Whatever level of compressed air quality is selected, a careful approach to system design and commissioning will be necessary.

It is highly recommended that compressed air is treated in the compressor room prior to entry into the distribution system (ring main) as well as at each usage point or application. Treating each application point on a case by case basis provides the most cost effective solution because it would not normally be necessary to treat the entire system.

Product Selection

All compressed air systems require some air treatment equipment to remove bulk water and dirt. Equipment available includes filters, dryers, oil vapour removal (OVR) filters, water separators, breathing air purifiers and condensate drains. It is important to use the correct level of filtration so that systems don't become blocked, which could cause compressors to be run at an unnecessarily high level. Filters are available in various grades to give different levels of performance. An OIL-X EVOLUTION grade AO filter, for example, will remove particulate to 1 micron, whilst grade AA will remove particulate down to 0.1 micron in size.

For most non-critical applications a refrigeration dryer that will give a dewpoint temperature of 3C will suffice. Critical applications, such as those found in the food and pharmaceutical sectors or even car spray painting, tend to require an adsorption (desiccant) dryer that will produce a dewpoint of -40C.

The message is, compressed air treatment equipment is necessary, but there is no need to over clean compressed air systems. domnick hunter can offer comprehensive technical support when it comes to system design and product selection.

Usage and energy saving tips

With careful management it is possible to make substantial savings. Some tips on how to make savings are described here.

(1) Air leaks are the most common source of wasted energy in a compressed air system and therefore provide the greatest opportunity to make savings. The Carbon Trust estimates that the leak rate on unmanaged compressed air systems can be as much as 40% of total output and that one of the most common sources of air leakage comes from manual condensate drain valves being left even partially open.

Condensate occurs in all compressed air systems, consisting of water, dirt, oil and wear particles. Removing condensate from filtration and drying systems is simply a case of using a drain valve. However, traditional drains tend to have hidden costs because too often costly compressed air is wasted when valves are opened for too long or become stuck in the open position. Zero air oss drains also known as electronic level sensing drains, detect and discharge only when condensate is present and therefore ensure no loss of valuable compressed air, which means downstream pressure is not affected and ultimately less electrical energy is consumed.

Conducting regular air leak detection tests is a relatively easy way to identify opportunities for savings. When compressed air escapes from piping it generates a frequency of 38Khz, although the sound level varies according to pressure, temperature and humidity, the frequency remains consistent, which allows leaks to be detected ultrasonically without background noises distorting the measurement.

(2) System pressure losses can have a serious impact on compressed air networks because it lowers downstream pressure and reduces the efficiency of pneumatic equipment. Invariably, to compensate for pressure drop, businesses operate compressors at an increased level, which of course equates in higher operating costs.

The OIL-X EVOLUTION filter range from domnick hunter uses design features to smooth and direct air flow, while a coated filter media actively repels oil and water, for reduced pressure drop, which takes some of the strain off compressors and helps to reduce energy bills.

(3) Generally speaking, for water vapour removal in a compressed air system, it is only necessary to dry general purpose air with a refrigeration dryer and use a desiccant dryer for critical applications and external piping. Where necessary the installation of PNEUDRI midi desiccant dryers at strategic points of use is recommended. This is a far more energy efficient solution and midi dryers still reach dewpoints of -40C.

(4) Finally introducing controllers on all desiccant dryers can reduce purge air requirements. Desiccant dryers produce high quality compressed air, however they have high energy consumption due to purge air requirements. Independent studies show that up to 200 per 100 scfm per year can be saved by controlling the purge rates of dryers.

Desiccant dryers have twin chambers of desiccant material. While one chamber is drying the other is regenerating, after a pre-set time they changeover. A Dewpoint Dependent Switching system (DDS) detects any remaining drying capacity and lengthens the cycle time to delay changeover so that the desiccant capacity is fully utilised, the extended cycle period lasts up to a maximum of 60 minutes rather than the usual 5 minute cycle and no purge air is consumed for regeneration during that time.

The DDS system constantly monitors dewpoint reacting to changes in air usage or shift pattern to provide air of the right quality at the lowest possible operating cost.

The Multitronic controller from domnick hunter gives the same results as DDS, designed to replace controllers on most types of desiccant dryer, it gives companies with older installations that are still in good working the opportunity to make good energy savings.

Servicing

Regular checks should be carried out to ensure systems are still performing as intended, new equipment installations and changes to production can all impact on compressed air systems.

All capital equipment is purchased on the basis of its payback period, as energy prices increase, products that can help reduce energy consumption should be specified in any new product selection process. It is also important to think ahead, taking energy costs into consideration, rather than thinking simply in terms of initial purchase costs.

UK companies looking to invest in energy saving equipment may qualify for grant aid or interest free loans from the Carbon Trust. For more information on the Carbon Trust go to www.carbontrust.co.uk To find out more about domnick hunter use the enquiry bar below:

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