Hand dryers don’t have to be louder to be quicker at drying your hands, as a well-designed hand dryer can be both efficient and quiet in operation.
The impact of a noisy environment
Noisy environments pose a variety of issues; while to most people they are unpleasant, they can be upsetting for more sensitive people such as small children and the elderly.
Noise generated by hand dryers in public washrooms although not dangerous can be extraordinarily undesirable and contribute to general noise pollution. Some hand dryers can reach noise levels up to 84 dB, equivalent to the sound emitted by diesel trucks. Humans perceive such volumes twice as loud as the 70 dB sound of a vacuum cleaner.
The effects of noisy hand dryers in washrooms
The noise is often amplified in a confined space with hard surfaces. In many buildings, hand dryer noise is not always confined to the bathroom, as it may be heard in nearby rooms as well. Because noise can break people’s concentration, this is of particular concern in schools, hospitals, theatres, libraries and any other area where a quiet atmosphere is desired.
As hand drying is a fundamental step in hand hygiene, and hand dryers offer an attractive combination of low-cost operation and drying efficiency, they are the most popular drying method and a mainstay in public washrooms. Therefore, it is desirable to make them as quiet as possible.
What makes an automatic hand dryer noisy?
The primary sources of noise in a hand dryer are the air outlet nozzles and the fan/motor, or ‘blower’ unit. This means that the optimum design of these two parts can reduce their noise levels while maintaining high drying efficiency.
Generally, warm air hand dryers work by maintaining a relatively large, turbulent, three-dimensional stream of hot air and thereby generate different air flows that intersect and collide. This interaction between air flows produces noise. In contrast, high-speed air-curtain hand dryers create a thin, laminar, two-dimensional blade of air with minimal air collision and reduced noise.
Noise reduction benefits of high-speed air-curtain hand dryers
High-speed air curtain hand dryers are considerably quieter than traditional warm air hand dryers.
- High-speed hand dryers generate noise for a shorter period, as they dry hands in a third of the time required by traditional hand dryers. While most warm air hand dryers need 30-40 seconds to dry a pair of hands thoroughly, high-speed air-curtain had dryers like the Jet Towel perform the same task in approximately 10 seconds, reducing the amount of noise by two thirds.
- The air inlets and outlets in high-speed air-curtain hand dryers are also smaller and therefore provide less opportunity for noise to escape from the body of the dryer.
- Finally, as a lower air volume is generated, the motor needs to displace less air. This means that the whole motor can be smaller which consequently produces less noise.
Effective design for noise abatement
Fine-tuning the high-speed air curtain dryers can further reduce noise. Mitsubishi Electric launched the first high-speed air-curtain hand dryer, known as Jet Towel, in 1993. Since then, it has mastered the art of noise reduction and continuously developed its hand dryers to include every practical method available to reduce noise.
- Using highly efficient motors, installing soundwave-absorbing mountings, or inserting dust filters that can deaden vibrations.
- Removing the sound frequencies that are particularly annoying, I.E. the higher and lower pitched ones, contributes to creating a less irritating, less ‘noisy’ sound. This can be done by identifying the frequencies within an annoying sound signature and generating reciprocal wave patterns so that peaks cancel out troughs and vice versa.
- Reducing the noise escaping from the motor. Mitsubishi Electric engineers designed a long air duct that was deliberately shaped to create a twisting air passage that reduces the amount of noise emitted from the fan/motor unit.
- For the ‘hands-in’ model, the Jet Towel Smart, the drying cavity and the opposing air-flows can be sources of further noise, but two additional noise abatement features combat this: a silencer in the drying chamber and; wave-shaped air nozzles which help avoid turbulence created by the two opposing air sheets.
The adjustments cut the noise level by 1 dB, which may not sound like much but are equivalent to shifting from the sound of a passenger car (77 dB) to living room music (76 dB).
All these acoustic improvements make Jet Towel models the quietest high-speed air-curtain hand dryers on the market. By emitting only 56-62 dB when in operation, Mitsubishi Electric Jet Towels are pleasantly quiet to use.
The Mitsubishi Electric study explains how the design of hand dryers can significantly reduce noise levels and bring some peace and quiet to busy washroom areas.