The job of the dryer in the OPL may seem so simple that choosing a new machine can become a too-rapid process in which essential operational criteria are overlooked.

Much-heralded technical advances for dryers have emerged in recent years, and on-premises laundry (OPL) operators are warming to benefits.

Essentially, when selecting one or more new dryers, the OPL operator needs to study energy consumption figures of the models in contention, and the machines’ ability to optimise drying efficiency. Engineering quality and ease of servicing must be thoroughly checked out.

Machine suppliers are united in the view that the best heating efficiency is derived through using mains or tank gas, and that dryer capacity must be on the generous side to ensure that the high performance air flow systems of the latest machines can be used to best advantage.

Bryan Ditcham, area sales manager, Anglowest Distributors, says the dryer capacity should be 15% greater than that of a washer to allow the right level of load movement in the dryer drum for maximum water evaporation. Where floor space is particularly tight, stacking dryers may be considered.

He recommends gas heating for economy – even when steam is available for heating, it will still be more efficient to employ a direct gas-fired system.

A drum-reversing feature can be useful – it is a boon for helping to avoid creasing with polycottons and cottons, especially with larger classifications such as sheets and table linen. However, drum reverse should be avoided for full-dry classifications. When drum rotation is reversed the dwell times can significantly and adversely affect drying performance on items such as towels.

Programmed cool down

As well as assisting in minimising creasing, programmed cool down has a role to play in helping to prevent spontaneous combustion. When using an Anglowest dryer, an operator must set a minimum cool down time of three minutes. If this is not set, the machine will not work.

Additionally, if an operator repeatedly tries to run the machine without a cool-down phase, the dryer will automatically stop functioning and “lock out” further use.

Certain classifications, including some found in catering and hairdressing businesses, can be risky from a spontaneous combustion point of view. Vapour from some hairdressing chemicals can damage the igniters of dryers but, fortunately, such chemicals are being used far less now, for health and safety reasons.

Automatic purge

Mr Ditcham draws attention to the Anglowest automatic purge sequence which means a dryer self-checks for gas safety. Burner ignition is prevented if the self check reveals any problem.

He underlines that arrangements for the supply of make-up air must comply with the latest requirements, and that poor exhaust flow will reduce dryer performance.

The back of the dryer should face an exterior wall, with exhaust air ducted a short distance through rigid metal piping with sealed joints. Outside the building, the ducting should bend down 90° from the horizontal. The end of the ducting should be unobstructed and at least 800mm above any horizontal surface.

Malcolm Martin of Miele emphasises the cost savings achievable with gas heating, and says that drum reverse action alone can contribute to a 15% increase in operational efficiency.

Axial air flow is a major contributor to performance excellence as is in-drum dryness sensing. The sensing capability, achieved through measurement of electrical resistance, means a classification can be dried to the specific, ideal moisture retention level. The quality of the water can affect readings, and the Miele sensing system is adjustable to allow for this.

Miele has developed special attachments which allow face masks – of the type worn by the fire service – to be securely clipped into a dryer drum. Up to 15 masks can be dried in 30 to 40 minutes – drying periods in a cabinet are between three and six hours. The Miele drying process has a high throughput of air, which, together with the optimum drum rotation, prevents moisture from being trapped in the masks which could cause bacterial contamination.

Too small for requirements

Michael Christian, assistant technical manager, Electrolux Laundry Systems, says it is not uncommon for customers to “economise” by buying a dryer that is too small to meet operational requirements. This leads to frustration because it takes too long, and costs too much, to dry loads.

He says the location and size of the laundry room must be considered when choosing a dryer, and important questions posed. Is there room for a free-standing dryer or would it be better to have a machine stacked on top of a washer-extractor? Would a twin stack dryer unit be a better answer? If access is very restricted, dryers that can be serviced from the front as well as the rear provide enhanced convenience with maintenance.

A number of the Electrolux Generation 3000 models can be equipped with Heat Recovery Pipes (HRP). This heat recovery system cuts energy consumption by up to 25% and drying time by up to 10%.

HRP uses an optimised heat exchange principle that transfers heat from the warm exhaust to the cold incoming air. Traditional systems recirculate the actual air, including lint particles. HRP is a closed system so only the actual heat energy in the exhaust air is used – eliminating potential fire hazards caused by the particles.

Compact unit

In contrast to traditional heat exchangers that are bulky and require extensive pipe connections, HRP is a compact add-on unit that mounts directly on the back of the dryer. It is totally self contained and does not require separate utility connections.

Another innovation in the Generation 3000 dryers is Residual Moisture Control (RMC) which measures the actual moisture content in the textiles in the drum 400 times per second using a special lifter and sensor system. With RMC, programs can be set to stop the drying cycle at specific moisture levels – from 0% to 30% moisture.

Electrolux Generation 3000 dryers incorporate advanced microprocessor controls that are simple to program and easy to use. The panels for the new Selecta Control are customised to suit the specific requirements of individual laundry operations.

The OPL user panel allows the creation of programs based on a range of parameters including temperature, drying time, cool down, reversing on/off, Auto Stop and moisture control. The drying cycle is continuously monitored, and automatic temperature regulation ensures that the selected temperature is accurately maintained with very little fluctuation.

This protects sensitive garments from temperature shocks and contributes to a fast, efficient drying cycle.

Standard with Selecta Control, Auto Stop makes it possible to set the drying cycle to stop when the load is fully dry. A buzzer sounds, indicating the end of the cycle, and the dryer continues with an anti-crease action for up to one hour to prevent creasing if the load is not removed.

Selecta Control can be upgraded with the RMC option, allowing programming to stop drying when exact preset moisture levels are reached. In addition, the actual moisture level in the drum can be shown on the display.

Tom Lowes of Armstrong Commercial Laundry Systems says it is vital to ensure that the correct dryer capacity for loads to be processed is chosen – a slightly oversized drum is ideal. Investigation needs to be made to determine which machine on the market will achieve the most energy efficiency. The most economical heat source available must be chosen – it is usually gas or steam.

Axial air flow

He says the three most important recent technical innovations in the dryers offered by Armstrong are axial air flow for maximum energy efficiency; sealed cylinder rims, also for achieving the best energy efficiency; and microprocessor controls allowing precise residual moisture levels to be achieved.

Dick Cardis, marketing manager of JLA, says many OPL operators are still unaware of how much more economical it is to use gas as the heating medium for drying rather than electricity. Electricity prices may be reducing, but gas remains far less costly.

He draws attention to the importance of having a sufficiently large dryer drum to provide efficient drying and to prevent creasing.

Siting of the dryer in the laundry room needs to ensure that the work being dried is not at risk of being contaminated by incoming soiled work. For optimum exhaust air flow efficiency, ducting to the outside should be as short as possible.

While computerisation has brought significant benefits in terms of program precision and energy use reduction, a requirement for operator training remains says Mr Cardis. He also underlines the importance of regular machine maintenance. He contends that hot air recirculation systems need to be looked at carefully, for they may incur build-ups of lint, which are difficult to clear and which impair machine performance, increasing the running cost.