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June 2007
Rack Up Savings
By: Mike Sherer

If you're in the market for new warewashers, you might be dreading the thought of all the money that goes down the drain in the form of waste water and the energy it takes to heat a machine. If so, consider this: Dish machine makers have made major im-provements in the past few years in water and en-ergy efficiency. And with the EPA's Energy Star program likely to put its imprimatur on dish ma-chines sometime this year, several makers have models that will fit the criteria.

In this story we'll look specifically at the high-temp rack conveyor washer, which, as the name implies, draws racks of dishes through chambers that scrap, wash and rinse them. Pretty straightforward, and since employees can feed racks into these machines on a continuous basis, they're capable of washing a high volume of dishes in a relatively small space. Entry-level machines are 44" wide and wash about 200 racks/hr., while the upper range comes in at 120" wide and features a washing rate of 470 racks/hr.

The size you need, as well as which bells and whis-tles, depends on a number of factors. First, of course, is the size of your operation. How many seats, turnover rate, and type of service (fine dining, casual, etc.) will help you determine how many dishes per hour your machine will need to wash.

Labor plays a big part in the equation. You may buy a machine capable of washing 250-plus racks/hr., but if you staff your dish room with only one em-ployee, that person is unlikely to be able to keep up with loading and unloading the machine. How well your warewasher cleans also depends on how well employees scrap dishes, pots and pans

Space is another limitation. If you're replacing old equipment in existing facilities, you may not have much choice in how you configure your dish room. Even in new construction, the focus tends to be on the cooking lines, prep and storage space, and dish rooms usually get short shrift. Often, you're forced to cram a small machine into whatever space is left. Fortunately, there are ways to get a lot of productiv-ity out of even 44" rack conveyors.

One Tank, Two Tank

Almost all high-temp rack conveyor warewashers are single-tank machines, no matter how large. Simply put, the tank holds, heats and pumps wash water onto the racks of dishes as they pass through the machine. Final rinse water is provided by a booster heater that raises the temperature of the water coming out of the manifold to 180º F, the sanitizing temperature required by most state and local food codes. Rack conveyors can’t get NSF certification unless they accomplish this.

Typically, single-tank machines hold about 20 gals. to 25 gals. of water. While manufacturers offer designs that heat water with gas-fired burners or steam, most warewashers use electric heating elements to bring wash water temperature up to about 160º F.

The difference between a 44” machine and a larger model is in the length of the chambers inside the machine. Wash and rinse chambers are separated by flexible strip curtains. Larger machines may have more wash spray arms or even two pumped wash stations, and more space between wash and rinse sections to allow dirty wash water to drain off the dishes before being rinsed.

A two-tank machine just adds a pre-wash tank and chamber, sometimes called a scrapper unit, to the front of a single-tank rack conveyor. A 66” machine, for example, is a 44” single-tank machine with a 22” pre-wash. The pre-wash tank has its own pump to help effectively remove most soil from dishes before they enter the wash chamber.

In most cases, the pre-wash unit has a separate heating element and thermostat designed to raise incoming water temperature to somewhere between 120ºF and 140º F. Some models offer temperature control on the pre-wash tank. At least one manufacturer uses ambient temp incoming water instead of heated pre-wash water, saying hot water tends to bake food onto dishes before they get to the wash chamber.

Some newer models also have a pumped mini rinse tank to augment the final rinse, but they’re still considered single-tank machines unless they have a pre-wash unit, making them two-tank, or “multiple-tank” machines.

Racked And Ready

Anyone who’s worked in a dish room knows that the longer you soak or spray dishes with hot, soapy water, the easier they are to clean. So, it makes sense that a long, slow ride through a rack conveyor spraying several hundred gallons per minute of hot water will get dishes really clean. But the two problems you have with that are time and the cost of water and energy.

Until recently, the only answer manufacturers had to those two problems were low-temp dish machines. As you probably know, low-temp machines wash dishes at a relatively low temperature of around 120º F, and rinse them with a chemical sanitizer instead of hot water. That saves you the cost of installing a booster heater and the energy used by the heater to raise water temp to 180º F.

Of course, chemical sanitizers are hard on a lot of materials, and hot water still generally does a better, faster job of removing soils. But the productivity of high-temp machines is limited by NSF standards: Dishes have to be exposed to enough hot water in the final rinse to deliver at least 3600 “heat unit equivalents” to the surfaces of the dishes, which means raising their temp to 165º F for 10 secs.

The key to lowering the operating cost of a hot water warewasher lies in two areas: water and energy. Making a machine more energy efficient obviously saves energy costs. Improving water efficiency not only saves on costs of incoming water and sewage, but energy as well. And since the main energy cost of operating a high-temp warewasher is heating the water, that’s where manufacturers have trained their focus.

Approaches vary, with some concentrating on energy savings, others on conserving water, and a few addressing both. Manufacturers taking a holistic approach claim water use as low as 0.4 gal./rack or less. Here are a few of the improvements you’ll see on the latest rack conveyors:

Spray arms and nozzles. Several manufacturers have taken a look at wash arms as a way to deliver more hot water to the surface of your dishes while using less incoming water at the same time. How? Using sophisticated computer design programs, manufacturers have designed the shape of the holes and the spray arms themselves in such a way to do a couple of things.

First, most have designed the spray pattern to create more of a “wall” of water, putting more hot water on the plates. One maker claims supplying water to spray arms through the center of the manifold, rather than the typical E-shaped design of most manifolds, results in more even water distribution. More water cleans dishes faster, and also heats them faster, so the machine uses less rinse water to a) rinse and b) sanitize by bringing dish temp up to 180º F. That saves water and energy.

Second, new nozzle designs help prevent nozzles from clogging with debris or food from dirty dishes. Again, that makes machines more efficient and ensures an even flow of water on all the dishes in a rack.

One manufacturer has even designed its spray nozzles to deliver bigger droplets of water. Bigger drops retain more heat. More heat transfers to the dishes, meaning less rinse water is needed to raise the temp of the dishes in the final sanitizing rinse.

Finally, makers say that both nozzle and spray arm design can deliver water with more velocity, cleaning dishes more effectively with a lower overall flow rate. A couple even use more powerful pump motors to circulate water more quickly.

Auxiliary rinse. You wouldn’t think adding a rinse tank to a rack conveyor would save water let alone energy, but it saves both. A couple of manufacturers have added small (3-gal.) tanks with separate pumps that heat water to 165º F and power-rinse soap off of dishes. Less final rinse water (at 180º F) is needed because dishes are already fairly free of detergent residue and their temp has been raised by the auxiliary rinse. The auxiliary tank is small enough that it doesn’t require a big heating element to keep the water hot (one maker uses a 3kW element, the other a 12kW).

Built-in booster heater. Built-in boosters have a couple of advantages over external heaters. External booster heater manufacturers recommend you locate them 6’ or more from the dish machine. That means they must heat water to as much as 185º to 190º F because it will cool somewhat in the pipes on the way to the final rinse manifold. Water from a built-in booster doesn’t travel as far, so the booster doesn’t have to work as hard.

A few equipment makers also nest built-in boosters in the machine near the wash water tank, conducting some heat to the wash water. That makes your wash water heating element more efficient.

And built-ins are convenient because they’re already plumbed and wired. One switch turns on the entire machine, including the booster heater. Ask yourself how many times dish room employees have gone home at the end of the night after shutting down the dish machines and not remembered to turn off the booster heater. Imagine the energy savings.

Most models that offer a built-in give you a choice of a 40º F rise, 70º F rise, or even 100º F rise in water temp, with heaters ranging from 12kW to 33kW.

Insulation. Some say that because rack conveyors are open-ended, most of the heat loss occurs there, especially in smaller models. But insulation can’t hurt, and though it may add to the price of a machine, it does have advantages.

Insulating the door, top and sides of a rack conveyor will at least prevent heat loss from all but the ends of the machine, which will make it more energy efficient. Maybe not a lot, but every little bit helps.

Insulation definitely makes exterior panels cooler to the touch, helps prevent burns, and helps make the dish room a little more comfortable for employees. It also dampens noise from the machine.

Waste heat recovery. Available on rack conveyors in Europe for some time, waste heat recovery systems are just now finding their way onto models here in the United States . These advanced models have a condenser and a heat exchanger in the vent hood. The condenser converts the steam generated inside the machine back to water that’s recirculated into the wash tank. The heat exchanger transfers heat to incoming water pipes, raising water temperature to about 80º F or more before it goes into the booster heater.

Recirculated rinse and wash water. Many models now let you divert a portion of the final rinse water to the wash tank, saving water needed to replenish the wash tank. It also helps maintain a higher wash water temp without using the heating element. That, of course, saves energy. Some models also let you skim wash water into the pre-wash tank, accomplishing the same thing.

Automated controls. Warewasher makers have made their machines as easy to operate as possible. Most have a simple on-off switch and a temperature gauge. But the number of automated controls inside the machines has grown.

To save energy and water, almost all manufacturers offer variations on a theme, including:

  • Automatic fill: Sensors determine the proper water level and maintain it. (To meet NSF standards, rack conveyors must replenish wash water at a rate of 1.5 gpm. On some models, that comes from recirculated final rinse water; otherwise it’s incoming fresh water.)
  • Auto start: Conveyors and pumps aren’t activated until a rack trips a switch, eliminating the need for a manual start.
  • Auto shut-down: Timers on some models and sensors on others turn off pre-wash, wash and auxiliary rinse pumps and final rinse valve as racks pass by, saving water and energy. Energy’s saved not only by turning off the pump, but because water retains heat better when it’s in the tank and loses heat faster when it’s aerated through the spray arms.

Take a look at our rack conveyor warewasher gallery for a look at the newest models.

Adjusting For A Better Clean

Rack conveyors do a good job of cleaning all sorts of loads, though occasionally dish room employees have to run heavily soiled racks through twice. An option on some models is a conveyor speed switch that lets you choose between about 200 racks/hr. and 130 racks/hr. Other makers offer an optional switch that lets employees stop the conveyor in the wash chamber for a longer wash time.

Other options include table limit switches that shut off the conveyor when the table on the unloading end fills up with racks; side loaders that automatically pull racks into the machine; blower dryers; roller conveyor tables; and motorized rack conveyor tables.

Washing At Red Robin

When the Red Robin Gourmet Burgers store in Commerce, Mich., introduced a new Jackson AJ-44T rack conveyor, a well-trained staff already understood the importance of keeping the machine clean and maintained on a daily basis.

“We have good people who hold themselves up to high standards,” says Red Robin’s Jeff Housel, “and our attention to detail and maintenance of the Jackson machine has paid us back 10-fold with reliability and minimal repairs.”

All rack conveyors should be easy to access and clean, say experts. The biggest enemy of rack conveyors is hard water, which can harm pump seals, heating elements and more. Even if you treat your water, machines should be cleaned and inspected for lime daily, and de-limed weekly or as recommended by the manufacturer.

Features: Upping The Ante

As far as standard features go, you’ll find that most manufacturers have pretty similar offerings. Some are safety features required to meet NSF standards. Here’s what to look for:

  • Anti-jam conveyor: Though systems differ in design, most models will shut down the conveyor motor if the conveyor jams for any reason.
  • Door safety switch: This shuts down all pumps if the door is opened during operation.
  • Door-activated drain: Most models automatically close the drains when the door to the unit is closed. While many models have a manual drain lever to open the drains, some have push-button drains.
  • Low-water heating element protection: Machines are supposed to automatically maintain the water level in the tank. If for any reason the water falls below a certain level, however, the heating element will automatically shut off, so it doesn’t burn out.

Overall, look for sturdy, all-welded construction using 300-series heavy-gauge stainless steel, self-draining all-stainless pump motors and impellers, and one-piece cast stainless spray arm assemblies. You’re not likely to find any parts made of plastic, or metal that isn’t stainless. If you do, the machine is likely an inferior model. Even pump seals on most machines are made of durable material like ceramic.

Conveyor systems are either dual-pawl side-drive or single-pawl center-drive. Makers of both claim that they’re designed to keep the pawls from interfering with spray patterns reaching the dishes. Both designs are reliable, but ask suppliers for warranty or service records to find out how conveyors in particular models perform.

Most models come with two removable scrap screens to keep debris from getting in the pump. Typical designs have a mesh scrap basket that catches most debris and a secondary screen protecting the pump intake.

Openings on most machines are about 20” to accommodate 18 x 26 sheet pans. At least one maker offers machines with 25” clearance standard, and another offers an added 6” height as an option.

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