A lot of hot air

28 September 2000



Time taken to evaluate which dryers are best for an OPL is well spent. Nicholas Marshall reports on some of the issues facing the purchaser.


Dryers used in on-premises laundries are often not given the attention they deserve, they are not fit-and-forget machines.

When dryers are wrongly selected, installed or maintained and when they are operated incorrectly, energy can be squandered and poor drying performance will result. Even more crucial, dangerous situations may arise.

Large capacities

Dryers must have the capacity to tackle workload peaks adequately. If they cannot, a production bottleneck is inevitable. It is usually wise to specify a dryer with a slightly larger capacity than that which might theoretically appear appropriate.

The type of dryer chosen will depend on the particular needs of the OPL. When ultimate efficiency is required, machine suppliers tend to suggest axial air-flow machines. In these, the air flows from the back of the drum to the front, passing through the load. Seals prevent leakage of air around the drum so energy is used to maximum effect.

Machines with vertical, downward air-flow do remain popular and they include the slender type designed to be used where floor space is severely limited. In machines with vertical air flow, particularly fast drying can be achieved due to the vigorous nature of the air movement and the concentration of heat. There is a disadvantage from an energy use point of view, drying air is able to bypass the drum, leaking round its curved surface.

Gas is much favoured as the heating medium as it is economical and allows the dryer to reach working temperature quickly. Stringency applies to the installation of gas-heated dryers, all the necessary regulations have to be satisfied.

The gas burner is located at the rear of axial air-flow machines and at the top of vertical air-flow models. Air is drawn over the burner and, provided the dryer is properly maintained, products of combustion are harmlessly diluted in the air flow and expelled to atmosphere.

Electrically-heated machines tend to take some time to reach working temperature and their potential optimum economic performance can be significantly reduced if they are not used continuously during the working day.

A steam-heated machine can be ideal in a laundry where steam is already available, if this is the case, a dryer can be particularly economical to run.

Steam on

However, most OPLs, unlike large commercial and healthcare laundries, do not have a steam generating system.

Glen Harvey, technical manager, Electrolux Laundry Systems, points out that steam entering a heating battery in bursts can shorten the life of the battery. Electrolux employ a system that avoids on/off burst action. Steam supply is constant but air is allowed to flow through louvres and bypass the heating battery when it is not required.

The system has a good effect in the cool-down stage because cool air can flow through the drum immediately. Without a bypass arrangement, heat in the battery tubes has to be dissipated before the correct coolness is achieved in the air-flow.

A number of equipment suppliers highlight how OPL dryer performance is eroded through operator error. Inadequate attention to machine operation tends to happen most frequently in the type of establishment where non-laundry department staff are using OPL equipment. Busy nurses, for example, may only visit the OPL fleetingly and not have the time or inclination to evaluate exactly what sort of drying a certain load needs.

Automation is really the answer and microprocessor controls can be a real boon. Microprocessor controls allow fine tuning of dryer operation to suit the needs of the individual OPL.

Mike Bassett, technical director of Armstrong Commercial Laundry Systems, which supplies Huebsch and Speed Queen equipment, says that a belief that microprocessor controls equate to complexity often needs to be overcome. Microprocessor controls allow push-button automation, but some buyers specify manual controls as familiarity makes them feel comfortable.

Specialist

Malcolm Martin, product manager at Miele, underlines how the control precision with microprocessor technology allows exceptional drying performance to be achieved in specialist laundry applications in addition to the general OPL.

The Warner Howard company, which supplies various dryer brands including Cissell, draws attention to how, if required, programme customisation can be easily achieved.

Tony Thomas, head of the technical division of JLA, supplier of tumblers from American Dryer, Maytag , says “The biggest advance in tumble dryers is the introduction of the microprocessor. Programs have built-in cool down and different levels of dryness can be achieved through the auto-dry cycles. This eliminates operator error and the risk of potential hazards by not activating the cool down process.

“Special dryness levels can be achieved through the auto-dry cycles allowing a degree of moisture retention for finishing/ironing purposes.” Anglowest, which offers the Viking range of tumble dryers, points to how a large-diameter door eases loading and unloading. Anglowest has announced a new 100lb dryer, fitting in between 170lb and 75lb models.

Mike Bassett draws attention to the fire hazard that dryer operation can pose if the cool-down cycle is not used. A hot and wet load left in a dryer drum, or in a trolley, can spontaneously combust, perhaps in as short a time as an hour or two.

The risk of spontaneous combustion is increased if the hot, wet items contain inflammable substances such as oils. The risk, he says, highlights the need for proper training of all staff who operate OPL equipment.

Dryers must be installed correctly for safety and operational efficiency. They must have sufficient air to work correctly, and the ducting provided to take air out to atmosphere must be fully adequate.

Glen Harvey says that smooth galvanised piping running at high level and terminating in a elbow with a short downward-facing section is ideal. No mesh should be at the end of the ducting, if there is, it will collect lint.

Exhaust ducting should end at least two metres away from where the make-up air enters the building and from any doors or opening windows.

If the distance is less, there is a likelihood that damp air, lint, and combustion products from exhaust ducting will be sucked back into the OPL.



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