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6/26/2014

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High-Speed Hand Dryers Can Be Ultra-Quiet



High-speed, energy-efficient hand dryers are increasingly popular with both facilities managers and end-users, but the noise of some models is causing increasing concern among experts. Fawn Litchfield, Jet Towel Business Development Manager, Mitsubishi Electric explains the issues and suggests a simple solution.

Hand dryers are popular in washroom facilities. For proprietors, they lower costs compared to paper or linen towels, because you do not need to regularly empty bins and refill dispensers. Users perceive them as more hygienic. Many modern high-speed dryers are also energy-efficient, requiring little power per use.

However, with high-speed dryers now reasonably common, more and more people are commenting that they are noisier than older style units. This issue came to the fore earlier this year when research carried out at Goldsmiths, University of London, was picked up by several national newspapers.

Naturally, the research was quite technical in nature and so could have been confusing to the general public, particularly because noise is measured in decibels, which is a logarithmic scale rather than linear. Also, sound decays over distance, so it is often measured at several points that are different distances from the source. Then there is the issue that some frequencies are more annoying than others, and when there are multiple frequencies they can interact to form another level of irritation!

But we can express this in simple terms as follows: high-speed hand dryers can make conversations difficult, can be heard beyond the washroom, frighten young children, and can upset vulnerable groups including the elderly, dementia sufferers, nursing mothers and hearing-aid users, while visually impaired people may have their navigation techniques upset.

Looking at the manufacturers’ performance data we can say that high-speed dryers show an energy saving of between 50 and 90 percent compared to hot air dryers. The data also indicates that they are 25 to 50 percent louder, which seems rather low compared to many people’s subjective assessments and the newspaper comment that, at close quarters, they can sound like a road drill. Clearly, there is a need for further investigation.

The first thing to note is that one or two models of high-speed hand dryers claim very low noise outputs, typically 58dB while competitors exceed 85dB. Qualitative tests seem to confirm these findings.

Clearly, for installations where noise is a consideration, quiet models are preferable. These manufacturers will be keen to promote their product’s quiet operation, and may even have certification from the Noise Abatement Society or similar.

In designing hand dryers for low noise, the first thing to do is to select a low noise motor and mount it with dampers in an enclosure that does not amplify sounds. Equally important is to ensure a low noise air outlet nozzle; this is related to shape, size and materials.

Tests that have compared one make of high-speed hand dryer against another have shown up the interesting phenomenon that the nature of the sound output often varies when in use (i.e. hands in the dryer) compared to when run unused. This implies that the size and shape of the drying chamber can be optimised for noise reduction.

People find some sound frequencies more intrusive than others and acoustics experts understand that sound signatures can be profiled to avoid these, so reducing the annoyance level that hearers experience.

Washrooms necessarily have hard-surfaced walls, ceiling and floors for easy cleaning and best hygiene; unfortunately, these will also echo noise from hand dryers. Theoretically it may be possible to mount dryers at a point where this effect is minimal, but in practice it is nearly always going to be better to use a low noise dryer.

The conclusion is that while some high-speed hand dryers are increasingly attractive to facilities managers, some models main weakness is noise. So quite simply, choose a model with certifiably quiet operation.
About Mitsubishi Jet Towel

Mitsubishi Electric’s first Jet Towel was launched in 1993 and the version now available in Europe is in the eighth generation of its development. It has proved a winner with installers for its high tech elegance, with operators for its low running cost and reliability, and with users for its convenience, speed, hygiene and innovative design. The Jet Towel has high environmental credentials, avoiding the use of paper towels or rolled cloth and lowering power consumption and noise levels to a fraction of alternative hot air dryers.

Further Information

Website: www.jettowel.co.uk, Email: jettowel@meuk.mee.com

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