SPECIAL REPORT: Rack & Roll

C’mon, admit it. When it comes to designing a new unit or even remodeling, the dishroom seldom gets top priority. Dishmachines, warewashers—whatever you want to call them—don’t often get the limelight they should. 

We place them in whatever space is left after the rest of the floor plan is laid out. We pay the people who operate them less than any other employees. And we expect them to run forever. (I ought to know—I started out in a dishroom in college and worked my way up after graduation.)

But clean dishes are a must. No dishes, no service. And warewashers are among the more expensive pieces of equipment to operate because they use both energy and water. On top of that, they’re typically among the first pieces of equipment that employees turn on every day, and usually the last turned off at night. (Yes, a few of you have cook-and-hold ovens that you use overnight, but you get the point.)

The good news is that the EPA’s Energy Star added commercial dishwashers to its roster of equipment back in 2007, making it easier for you to compare energy and water use of all the models out there. At the time, Energy Star set specs for undercounter, door-type and rack conveyor dishwashers.

Even better news is that the Energy Star folks are working on version 2.0. The third draft is under review now, and a final draft is expected by the end of the year. If it comes out when expected, the specs will likely take effect within a year, meaning even more efficient machines will be coming your way. (The new specs also are expected to include flight-type machines.)

Sizing Up Rack Conveyors

Figuring out what size washer you need takes a little guesswork because most likely your operation is unique. But there are some general rules of thumb. Figure the number of pieces of tableware you use per patron. Multiply that by the number of customers you serve per hour at peak periods. Then divide that number by 20 (the number of dishes that typically fit in a rack). The result is the number of racks per hour your machine needs to wash.

Now you have to decide on the type of machine that’s best. There’s a big lease market for low-temp, chemical sanitizing machines. For our purposes, we’ll stick to hot water, or high-temp machines. Space, speed and dirt load are key factors that will influence your decision from here on out.

Basic rack conveyor washers are single-tank machines and usually start at about 44″ in length. Water is heated in the tank, detergent is added, and the water’s pumped through spray nozzles as the conveyor carries the rack of dishes through the machine.

At the end of the machine, the rack is rinsed with fresh water heated to between 180ºF and 195ºF. This last step is important because it sanitizes. To be NSF certified, a machine has to raise the temperature of the dishware to 165ºF for 15 secs. That’s the purpose of the higher temp range at the rinse manifold: Any lower and the dishware wouldn’t get hot enough to be sanitized properly; any higher and the water would turn to steam and do an inadequate job of rinsing soap off the ware.

You’ll need a booster heater to get your water hot enough. If your water heater is putting out 140ºF water, you might go for a booster that provides a 40ºF rise in temp. More likely you’ll choose one that gives you a 70ºF rise, or if your incoming water is at ambient temps, you most likely will go for a 100ºF rise. More machines today have booster heaters built in. More on that later.

If you add length to the machine, you can add a little distance between the wash tank and the final rinse. That allows some time for the soapy, dirty wash water to drip off the ware before the final rinse. It also prevents food and soapy water from splashing onto the racks in front. (Most washers have strip curtains inside the machine to separate wash and rinse areas, but with all that water flying around, curtains can’t always block everything.)

You can also add a prewash tank, which typically extends the length of the machine another 22″, to 66″. The prewash tank scraps your tableware before it goes into the wash tank. The cleaner your wash water, the less detergent you’ll use, and the less water you’ll have to use (and heat) overall. Dishes also will rinse more easily. And again, you can add length to the machine to further separate the prewash area from the wash tank.

Many models heat the water in the prewash tank to the same 140ºF as the water in the wash tank. At least one manufacturer, however, doesn’t bother with a heater in the prewash tank, on the premise that using hot water can “bake” food soil onto your dishware. If your application makes forgoing a prewash heater feasible, using ambient temp water also saves energy

Finally, some manufacturers offer models with a small rinse tank built into the main tank. A small pump provides a power rinse after the wash and before the fresh water final rinse. The small tank recovers water from the fresh water final rinse for this power rinse. Typically, machines like this are designed so that rinse water cascades into the wash tank as it fills with final rinse water. The wash tank in turn cascades into the prewash tank if there is one.

Most manufacturers also give you the option of a model with a taller opening. Most standard models have an opening about 19″ high. Models with taller openings can accommodate sheet pans more easily (instead of running one through at a time). One maker even has developed a special rack that locks up to six sheet pans into place in an upright position.

Where’s The Water?

When Energy Star set its specs for dishmachines several years ago, water usage was a concern that manufacturers already were beginning to address. When Energy Star set its standard, about 25% of models on the market could achieve the ‘Star rating. Since then, more models have met the Energy Star requirements, and market penetration is higher—hence time to upgrade the standard.

Presently, single-tank machines must use <0.7 gal./rack to qualify, and multiple-tank warewashers must use <0.54 gal./rack. The new standard will be tougher, but not to worry. Several new models on the market now should meet the new specs easily.

Water use has improved dramatically in the past few years. Manufacturers boast usage figures from around 0.62 gal./rack down to an astounding 0.15 gal./rack. How is this possible? The secret for many is in the final rinse. But manufacturers have other tricks up their sleeves as well.

Again, the purpose of the fresh water final rinse is to remove any remaining detergent from your dishes and to raise their surface temp to more than 165ºF. The less water it takes to accomplish these two tasks, the less water the machine will use overall. Plate coverage is key.

One manufacturer uses a nozzle design that produces larger drops of water. The larger drops, the engineers say, cover more surface area, heating and rinsing dishes faster. Another manufacturer has arranged its spray nozzles on an arched manifold; the spray pattern from each nozzle overlaps spray from its neighbor, providing better coverage. Several models have spray arms both above and below the racks to get the most coverage with the least amount of water possible.

Logic might suggest otherwise, but the power rinse on many models, with its attendant small tank inside the bigger wash tank, also helps save water. Since the power rinse uses water collected from the final rinse, it’s usually several degrees warmer than the wash water. It brings the surface temp of dishware closer to the desired 165ºF before the rack reaches the final rinse. Cleaner, warmer dishes need less final rinse water to finish the job.

Another manufacturer has incorporated filters into the bottom of each tank in its multi-tank units that are automatically flushed with a small amount of water periodically. This keeps the water cleaner, which reduces detergent use and ultimately water use as well. The units also have an automatic water level control that diverts water to whichever tank needs it.

Need A Boost?

Energy savings is a primary benefit of using less water—use less, heat less. Many rack conveyors now incorporate a booster heater in the machine itself to get the heat you need. That typically puts the booster closer to the final rinse manifold, giving water less distance in which to cool. The booster doesn’t have to be set quite as high, and it works less to produce hot water.

Because these machines use less water, they don’t require boosters nearly as large as older models. Their smaller size is one reason more manufacturers are building them into their machines. For a 40ºF rise in temp, many machines now use only about a 10kW or 12kW heater. Having the booster on board also can provide some residual heat to the wash water tank depending on where the booster is situated.

And Waste Heat Recovery

The bigger change since we last wrote about the category is the number of manufacturers who have added heat recovery to their rack conveyors. These systems provide a number of benefits, not least of which is dramatic energy savings.

Waste heat recovery systems use heat exchangers to pull heat from the hot moist exhaust air generated inside the machines as well as some of the heat radiating from the sanitized dishware. Inlet water runs in a coil through the heat exchanger before it goes to the booster heater. Because the heat exchanger raises the temp of incoming water 10ºF or more, manufacturers say you can use cold instead of hot incoming water.

Some models place the heat exchanger on the receiving end of the machine where most of the heat and steam is generated. It adds a few inches of length to the overall unit. At least one maker positions the heat exchanger at the loading end of the machine, however. Pulling hot, moist air back through the machine and across the heat exchanger, the maker says, provides better heat recovery and also transfers some heat to dishware as it enters the machine.

Wherever the exchanger is located, it has the added benefit of condensing a lot of the steam in the machine. Taking both the heat and steam out of the air before it’s vented means a cooler, more comfortable dishroom. It also means your HVAC system has to move a lower volume of air to exhaust the machine, saving more money. One manufacturer says its heat exchanger can reduce the amount of air that you have to vent by as much as 90%.

Save Your Energy

Manufacturers are achieving energy savings from a number of other improvements, too. Many new models have an energy-saving or idle mode. Switches inside the warewasher sense when racks pass through and turn appropriate pumps on and off.

When a rack enters the machine, for example, it trips a switch that turns on the wash pump. The rack trips another switch that turns on the power rinse or final rinse pump, and when the rack has cleared the receiving end, all the pumps will shut off if there’s no rack in the machine.

While many models have a vent fan switch, so you can turn off the fan when the machine’s not in use, some models tie the fan directly to the machine’s operation. When racks are running through the machine, the vent fan’s on. When the machine’s not running, the fan automatically shuts off.

Since most of the energy required to run the machine is used to heat the wash and rinse water, insulation also helps save money. More and more units have insulation built into the doors, sides, top and bottom as standard equipment. Insulation also keeps the dishroom more comfortable and saves HVAC costs.

Even accessories are far more energy efficient than a few years ago. One equipment maker introduced a new blower dryer two years ago, trimming its length to 33″ from 6′ and reducing its power to 10kW from 42kW. The new unit also has a list price of $8,000, which is $14,000 less than the model it replaced.

Save On Labor

Newer rack conveyor models help save your employees’ energy, too. Manufacturers are building labor savings into warewashers with more sophisticated digital controls and simpler operation.

One manufacturer has gone so far as to simplify its latest model to a single button that automatically fills the machine, heats the water, injects detergent and readies the machine for the first rack.

Most machines feature auto-fill as well as door-activated drains and self-draining pumps. Many now also feature self-cleaning cycles that flush wash chambers and water tanks, and even rinse off the heat exchanger if the unit has one.

To make cleaning the rest of the machine simple, some manufacturers have color-coded parts that need to be removed for cleaning such as spray arms. In some cases, makers have even color-coded the parts in each section so employees are sure to put spray arms back in the right position, for example. In one case, a manufacturer purposely designed its self-cleaning spray arms so they can’t be removed, leaving employees one less task to worry about.

Other labor- and/or time-saving features include audible signals that notify employees when it’s time to delime a machine (some units also feature an automatic deliming cycle); a dirty-water alarm, indicating it may be time to clean out the filters; a low-water alarm in case the auto-fill feature isn’t working properly; and a low-temperature alarm.

Digital controls have become common and just as reliable as electromechanical controls, even in the often wet dishroom. One maker offers a glass touchscreen control panel that displays all the workings of the machine. Employees can even pull up the instruction manual. Another model has a control panel that lights up in amber when the unit is heating and turns green when ready.

Digital controls also usually feature self-diagnostics that let employees know when the machine needs more detergent, service, or other cleaning or maintenance tasks. And many models also allow communication between the machine and a computer, providing service alerts or HACCP data.

Safety features are pretty standard from one maker to another. Look for features such as a door interlock that prevents the machine from operating when the door’s open, a table limit switch (sometimes offered as an option) that shuts off the conveyor when too many racks accumulate on the receiving table, and a conveyor jam limit switch that turns off the conveyor belt if it gets stuck.

If you stick to major manufacturers, you can be assured of solid construction. If you choose a regional manufacturer, be sure to look for sturdy all-300 Series stainless welded construction using heavy-gauge, self-draining, all-stainless pump motors and impellers and one-piece cast stainless spray-arm assemblies. Parts made of plastic, or metal that isn’t stainless, suggest the machine is likely an inferior model. Even pump seals on most machines are made of durable material like ceramic.

Also look for intangibles such as easy access for serviceability, easily accessible scrap baskets and filters (some models allow you to remove and clean baskets while the machine is running), length of manufacturer’s warranty and the maker’s service network.

Clean dishes are a big deal to patrons, even if dishmachines are the last item on your punch list. Fortunately, the latest rack conveyor warewashers are energy- and water-efficient workhorses.