Warewasher Energy Management

Warewashers — they’re the workhorses of the back of the house. They clean. They sanitize. And now they can even help lower energy consumption. Sure, you can specify a qualified energy-efficient model and call it a day, but more often than not, user error and maintenance neglects will cut into your energy- and water-saving potential over the long haul. So we asked Amin Delagah, project engineer and resident water guru for the Food Service Technology Center in San Ramon, Calif., to review some of the best practices for optimal performance and maintenance to maximize both energy and water for four main dishwasher types.

Type: Undercounter and Door-Type

Description: Undercounter units, which wash one rack of dishes in about two minutes, fall into two main groups: low-temp models that use chemicals for the final sanitizing rinse and high-temp models that use hot water for this stage. And these units now have their own Energy Star ratings. Foodservice operators that typically use undercounter and door-type units include cafés, small restaurants, bars and some quick-serve operations, where staff use them to wash glassware and other smaller wares. Door-type units are easy to load and unload because of their countertop position. These units can handle a variety of wares, from regular dish and silverware to pots and pans, using a single rack measuring about 20 inches by 20 inches.

Optimal Operation

  • Make sure to use the correct type of rack for the unit, otherwise wares or the rack itself could get stuck and cause the machine to work harder.
  • Fully load the dishwasher before running it to save energy and water.
  • For low-temp models that don’t have their own hot water boosters, make sure the main hot water system/source is not located too far away from the unit, otherwise by the time the water reaches the washer it might not be hot enough to wash the rack properly, leading to poor performance and extra energy usage.
  • For both low-temp and high-temp models, if space is available, collect wares and wash them in batches — one rack after another in a fixed period of time — to maximize the hot water available at that time, rather than forcing the unit to have to rev back up after every 20 minutes (or however long the delay between washes might be).
  • Monitor and regularly calibrate the pressure gauge — most dishwashers operate at 20 PSI for optimal pressure (plus or minus 5 PSI). Pressure at 15 PSI could lead to poor performance and cause the machine to work harder. Pressure at 25 or more PSI could use extra energy and water combined.

Maintenance Monitoring

  • Regularly descale the machine to prevent it from breaking down. Depending on use and the hardness of the water, some undercounter washers might need more regular maintenance than others. While a technician must perform some descaling, chemicals are available for periodic manual maintenance by the operator.
  • For hard water regions, consider a water softener or other form of filtration to lengthen the time between descaling and keep the unit operating at maximum efficiency.
  • Monitor the rinse and wash arms for plugged-up food or debris.
  • Monitor the pressure gauge and routinely inspect for potential breakage.

Type: Conveyor

Description: These machines pull multiple racks through the wash and rinse cycles. Staff can load the racks from left to right or right to left. Highly customizable, foodservice operators can opt to include a prewash section, which might feature a scrapper and/or spray valve, and they can have an additional power rinse prior to the final sanitizing stage. High-volume, high-throughput operations rely on these workhorses.

Optimal Operation

  • Similar to undercounter and door-type washers, fully load these units to maximize energy and water use per wash.
  • Monitor both the pressure and the temperature gauges to maximize performance. NSF requires a minimum temperature of 180 degrees F for the final rinse, 160 degrees F for the power rinse and 150 degrees F for the power wash. Temperatures that are too high can actually cause the air temperature of the dishroom to rise, thus causing the warewasher to use more energy and stress the HVAC system.
  • Similar to using undercounter and door-type machines, batch washing helps maximize the hot water currently available. Depending on the size of the countertop space, it’s possible to line up 5 to 10 racks and run them through sequentially to help the machine run more efficiently.
  • Use custom racks for specialty wares. For example, cutting boards and sheet trays need their own racks; laying them flat in a traditional rack could cause water overflow and the unit to malfunction. Improper rack use could also cause excess water to fill up and dilute the sanitizing chemical dose. Operators should use the special racks for steam table and refrigerated prep table parts.
  • Ensure proper prerinsing; make sure scrappers are not running constantly, which can lead to extra water and energy use. Another common mistake operators make is using an industrial hose instead of the proper prerinse sprayer specified for the unit.
  • Make sure the loading and unloading tables that connect to the dishwasher slope toward the unit, with the loading table sloping downward and the unloading sloping upward. That way, water from occasional overspray will run back into the dishwasher, not off the table into a drain.
  • Many operators dump their washer tanks at the end of a meal period to clean the machine and refill the tank. Make sure to close the drain before refilling, otherwise, like an unplugged, running bathtub, the unit could continuously work to fill the accidentally unplugged tank. Consider units with automatic valve closing to prevent manual errors like this.

Maintenance Monitoring

  • Replace any worn racks, or they can get stuck in the machine and cause it to continually operate, thereby using more water and energy.
  • Routinely inspect the splash curtains — make sure they are not worn out and that they are cleaned regularly and put back correctly. This minimizes overspray, which, in addition to wasted water, could cause the machine to use more energy and chemicals.
  • Monitor the electrical components, particularly the autoflow function. If the flow is off, operators might seek to manually fill the tanks, but if done improperly, this can lead to an overflow of water and an overuse of energy needed to heat that water.

Type: Flight-Type

Description: These larger, high-volume models run constantly and take multiple staffers to operate and have distinct prewash, wash and rinse cycles. Wares are placed on a moving conveyor with fixed dividers.

Optimal Operation

  • Ensure the unit is properly staffed and staff members are properly trained. Too few staffers could slow down the loading and unloading process, causing the unit to run racks that are not fully loaded. Many of these units take at least two or more staff members to operate efficiently, and they should be sure to load these units from both ends at once.
  • Determine a baseline energy and water usage upon installation of the unit. If possible, install submeters to monitor usage. Overuse could signal operational or maintenance issues before they’re more clearly known.
  • Turn off the unit after a peak meal period to save water and energy; many of these units have adequate recovery times.
  • Consider models that reuse rinse water for the prerinse cycle. This can reduce water and energy consumption by at least 30 percent.

Maintenance Monitoring

  • Monitor the sanitizing rinse sensors for wear and tear. Also, make sure the rubber or plastic pipes are installed properly, otherwise they could continually trip the conveyor to engage, thus using more energy and water.
  • Clean out the machine after every meal period or tank-dumping cycle to remove food and debris and prevent malfunctions.
  • Fix any leaks — a puddle of water below the machine is a good visual indicator that a repair is necessary.
  • While heat exchangers are available for all warewasher types, they are most commonly used with flight-type machines to conserve energy and bring down the air temperature of the dishroom. Check with the manufacturer to determine proper operation and maintenance needs.

The Importance of the Spray Valve

“We use a pressure sprayer that sprays about 60 PSI of water and helps to reduce the amount of food residue off of the dishes prior to washing, and this has saved us about a third of the water and energy needed to heat the water,” says Joey Terrell, a Denny’s franchisee in Joliet, Ill. “The cost of this spray valve is about $60 to $90, so the savings are substantial.”

How To Measure Hot Water Use Versus Specs

  • l Measure hot water use at an open drain from the dishwasher
  • l Weigh the amount of wastewater on a scale in pounds
  • l Divide the specific weight by 8.33 pounds/gallon
  • l On a door-type unit, measure water use of one rack (gal/rack)
  • l On a conveyor unit, measure water use in one minute of continuous operation (gal/min)
  • l Compare numbers to original specs