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Warewashing Equipment – Commercial Dishwashers

Commercial dishwashers, considered to be one of the largest energy consumers in the commercial kitchen, are a very complex appliance that can vary widely in size and shape.  Classes of commercial dishwashers include under counter, stationary rack door type, rack conveyor machines and very large flight type (continuous conveyor) machines.  Each of these product classes may employ single or multiple wash tanks, and use hot water (high-temp machines) or chemicals (low-temp machines) to achieve final rinse dish sanitization.

While components including pump and conveyor motors consume some energy, the majority of energy used by commercial dishwashers is involved in the heating of water.  All dishwashers have at
least one tank that provides hot water with a temperature ranging from
43.3°C (110°F) to 60°C (140°F).  High-temp machines require an additional booster water heater to provide sanitizing hot water above 82.2°C (180°F) during the rinse cycle.  The amount of water required during a dishwasher's rinse cycle determines the requirements of these water heaters.  Therefore, lowering the rinse water consumption, measured in gallons/rack, not only saves water, but also presents the most significant opportunity for energy savings for this product.  The gallons/rack rating is a function of water use (in gallons per hour) and wash, rinse, dwell, and load time.

commercial dishwasher

* Source: CMA EVA-2000, www.cmadishmachines.com

Water usage across commercial dishwasher classes does not appear to be directly related to the size of the machine and varies from 1.25 litres/rack (0.33 gal/rack) to 87.8 litres/rack (23.2 gal/rack); however, most commercial dishwashers consume approximately 15 litres/rack (4 gal/rack)1.  Proposed  ENERGY STAR specifications provide a maximum rinse water usage based on dishwasher type (i.e., whether the washer is under counter, stationary single tank door, or single tank conveyor) and whether it is high-temp or low-temp.  The proposed specifications range from 2.35 litres/rack (0.62 gal/rack) to 6.4 litres/rack (1.70 gal/rack).

Technologies that can improve the energy and water efficiencies of commercial dishwashers include:

  • Wash tank insulation
  • Wash compartment insulation
  • Sensors to control conveyor movement
  • Multi-staging systems that reuse rinse water to pre-rinse dishes
  • Built-in booster heaters
  • Built-in heat exchangers
  • Advanced rinse nozzles
  • Infrared burners
  • Double wall construction

Since the life expectancy of a commercial dishwasher is 20 to 25 years2, high efficiency units offer the potential for substantial energy and water use savings3.

Savings for a
High Efficiency
Flight-Type
Dishwasher
 
Medium-Volume
Food Service
Establishment
 
High-Volume
Food Service
Establishment
 
 Low Usage 
 
 High Usage 
 
 Low Usage 
 
 High Usage 
Annual water
savings (L/yr)
246,000 1,893,000 454,000 3,785,000
Annual water
savings (gal/yr)
65,000 500,000 120,000 1,000,000
Average annual
water savings (%)
25% 25%
Average annual
energy savings (%)
30% 30%

1 “Commercial Dishwasher Engineering Analysis”, provided by NRCan.
2 “Commercial Kitchen Initiative Description”. Consortium for Energy Efficiency, November 2005.
3 “Good to the Last Drop: Proven Opportunities for Commercial and Institutional Water Conservation”, PNWS/AWAA Water Conservation Committee, February 2006.