Dishwashers: minimising water consumption

28 April 2005
Dishwashers: minimising water consumption

Without individual meters on each machine, it can be difficult to isolate the exact amounts of water used for warewashing and, with supply charges averaging £1.20-£1.30 per 1,000 litres, water might not seem a major cost. But a standard conveyor dishwasher is generally thought to account for about 80% of a kitchen's total water consumption. Relative levels of water economy are also recognised as the key to a host of other costs.

"If you consider the energy needed to raise the water to the requisite temperature and look at the amounts of detergent and rinse aid diluted by it, the amount of water used becomes highly critical," observes Tim Bender, product development manager at Hobart UK. "Basically, the more water a machine uses, the more chemicals it will use." That pushes up costs significantly, while increased chemical outflow is more damaging to the environment.

Such ancillary costs can be massive on larger machines of the conveyorised rack and flight types. Warewashing system specialist Metos estimates that a standard conveyor machine can account for 30-45% of a kitchen's total electricity consumption and 80% of its chemical consumption.

On the smaller front-loading machines widely used in pubs and restaurants, wash tank capacity is worth investigation. Different makes of machine offering the same throughput can range from 12-15 litres on some of the latest machines with low-profile tanks and beefed-up water handling system to 40 litres on some older designs.

Tank capacities are not always quoted in supplier literature, but should be available on request. However, they tell only part of the story. Most commercial washers employ water-conserving continuous recycling systems where 10% of the hot-wash water is flushed away on each cycle and automatically topped up with the hotter (85¡C) water used in the rinse cycle.

There is the alternative of a "wash-and-dump", or fresh-water machine, but these have the downside of a wash cycle time two to three times longer and greater water consumption, typically from eight litres per cycle with a similar amount for the rinse. "On a spreadsheet comparison, a fresh-water machine isn't going to come out well against a recycling machine," says Malcolm Martin, marketing manager at Miele Professional, which finds fresh-water machines its most popular customer choice on front-loading models.

"But while water consumption is higher, detergent usage doesn't increase, and users often favour this kind of machine for operational benefits, particularly hygiene and the ability to thermally disinfect ware," he comments. Key applications are hospital wards and nursing homes, where the number of cycles per hour may not be critical.

For mainstream applications like pubs, however, the standard type of washer with a two- to three-minute, constantly topped-up cycle, scores on speed and water usage. "For many independent caterers, water consumption still tends to come a long way down the list of purchasing concerns," says Simon Aspin, marketing manager at Winterhalter UK. "But for some of the big national accounts, we now have to submit documentation on water usage per wash, plus information on tank capacity and how regularly the water will need to be changed."

That last question can be the most critical. The more "soupy" the water in the tank becomes, the sooner it becomes necessary to flush out the whole lot and start again. Dishwasher users can deal with this problem partly through training, notably by insisting that staff pre-rinse dirty ware before they place it in the machine. But in many applications, the number of washes achieved by a machine depends on the effectiveness of its filter system.

An increasingly popular answer is a continuous centrifugal system which in some ways corresponds to the cyclone systems seen on Dyson vacuum cleaners. Suspended debris in the wash water passes through a small unit which causes a vortex effect, separating out suspended matter in the water. Examples on cabinet and pass-through washers include Winterhalter's Cyclo Mediamat, Hobart's Genius-X and Meiko's Eco systems. Meiko also fits a vortex-action Aktiv Plus four-stage filtering system on larger machines and this sucks off the excess foam, including debris.

"The more you can take out of the water, the slower the breakdown of the detergent, so the less you use," says Bill Downie, managing director of Meiko UK. "By the same token, the more water you use the greater the power needed to heat the tank. But you do need a certain amount of water to wash and rinse effectively. If a supplier is claiming to clean 150 racks an hour using 180 litres an hour, you need to question the results."

lson Dish and Glass Washing Machines, believes the extra costs of specialist filtration is justified on large warewashing systems, but questions whether the difference is that great compared with standard mechanical filters.

Nelson sees water as just one component within the total life-cost of machines. "Users also need to consider eco-friendliness, such as double-skinned insulation to keep heating costs down," he says. Ease of cleaning is also very significant. This has been improved with features such as rounded corners and one-piece moulded interiors. n


Aberna 01252 532222

Angelo-Po UK 01332 638030

Classic Glass and Dishwashing Systems 01889 272300

Dawson Foodservice Equipment 01226 350450

Hobart UK 0700 210101

Meiko UK 01753 215120

Metos 01707 393399

Miele Professional 08453 303618

Nelson Dish and Glass Washing Machines 0800 592833

Valera 01708 869593

Winterhalter UK 01908 359000

Caveat emptor

There's some talk in the industry that the next generation of machines will attempt to operate on cold water and even eliminate dependency on chemicals. Such dramatic breakthroughs are probably a few years away yet, but John Nelson, managing director of Nelson Dish and Glass Washing Machines, believes manufacturers of quality machines may be reaching the point where they cannot refine their current models much further.

"However, at the lower end of the market, there's a whole mountain to climb," he says. "On many machines, manufacturers haven't changed product design much since the 1970s." This keeps prices down but also affects performance, says Nelson, who's scathing about older models "dumped" in the UK from Turkey and other Mediterranean countries. He claims these are often sold to UK caterers via mail-order companies accessible mainly through 0800 numbers or the internet, and often with no address or manufacturing base clearly stated. Such "hidden" suppliers may be around for only a short time and then disappear to be resurrected under a different name.

Caterers should therefore adopt a "buyer beware" policy and, since they cannot afford to be without their machines for long, always insist on a full after-sales service package.

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