It is not too hard to work out how paper towels dry our hands -- it's by the process of absorption. With electric wall mounted hand dryers two quite different mechanisms are responsible. Firstly the airflow generated by an electric fan generates a 'dynamic pressure' which drives off the bulk of the water from wet hands, in much the same way as the drying stage of an automatic car wash. The second mechanism is evaporation, in which the liquid water is changed into a vapour by the action of heated dry air. Evaporation removes any remaining traces of moisture that cannot be driven off by the action of air flow alone, and is much more effective if the hands are rubbed together as this increases the surface area of remaining moisture.
The effectiveness of a hand dryer is ultimately determined by the speed of the fan generating the flow of air (usually measured in rpm) and the power of the heating element (usually measured in kW). These are the key parameters with which to evaluate hand dryers. Generally, the larger the combination of these figures the shorter the drying time.
Paper versus Air
The decision whether to invest in paper towels or an electric hand dryers is generally driven by the following considerations:
Initial outlay -- the cost of an electric hand dryer will almost certainly exceed that of paper towels
Ongoing costs. Here the electric hand dryer generally has the advantage, as costs associated with procuring, storing, checking, refilling and disposing of paper towels are avoided.
Customer experience. This is highly dependent on the installation, with the sleek appearance and performance of high-end electric hand dryers often being preferred in locations such as gyms, theatres, restaurants and nightclubs as they avoid generating large volumes of used paper towels.
The most appropriate casing material is generally determined by the proposed installation environment:
Plastic: cost effective solution suitable for low traffic environments where the risk of vandalism is low, such as small offices.
Enamelled steel: general purpose solution suitable for mainstream applications such as railway stations and shopping centres
Stainless steel: where stylish looks and enduring quality of finish are a requisite
When to Consider Not Installing an Automatic Hand Dryer
Automatic hand dryers use a touchless sensor to activate the device. For most installations this feature is significant benefit, but if installed in a small room this sensor can result in nuisance activation, for example when someone is walking past the unit but not intending to use it. In such situations consideration should be given to the use of a manual hand dryer which is operated by depressing a simple starter button.
Typical Installation Heights
The most appropriate height to install a hand dryer will depend on the specific details of the proposed installation, but the following may be considered as a rule of thumb:
Adult: 1150 mm
Child: 950 mm
Disabled users: 950 mm
(Measurements are from the floor to the bottom of the hand drying unit).
Please note that products must be installed and operated in accordance with the manufacturer's model specific requirements and installation must be carried out by a competent person.