Commercial Dishwashing Introduction

Commercial Dishwashing

Commercial dishwashers, considered to be one of the largest water and energy consumers in the commercial kitchen, often using more than two-thirds of the overall water use.  The equipment 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.

All commercial dishwashers have at least one tank that provides hot water with a temperature ranging from 110°F to 140°F (43.3 C to 60 C).  High-temp machines require an additional booster water heater to provide sanitizing hot water above 82.2°C (180°F) during the rinse cycle.  Lowering the rinse water consumption 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_1 

Water usage across commercial dishwasher classes does not appear to be directly related to the size of the machine and varies from 0.33 Gallons Per Rack (GPR) to 20+ GPR (1.2 L to 75.7 L).  A typical commercial dishwasher consumes approximately 4 GPR (15.1 L).  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 years, high efficiency units offer the potential for substantial energy and water use savings.  The minimal extra cost for efficient dishwashers over standard models suggests a total lifecycle cost for efficient models is always a wise investment when a consumer is already planning to purchase a dishwasher.

The high cost of dishwashers may thwart early replacement (where a pre-existing dishwasher is still operating) efforts based on water and energy savings alone; local utility prices and volume of use for the equipment will dictate the cost-effectiveness for early replacements.  Large restaurants with all day service (often found in large hotels) will have save water at a faster rate than small, single meal service type restaurants.  Utility agencies need to analyze if cost-effective financial incentives are great enough to induce restaurant owners to replace dishwashers still in good operating condition.  Water agencies often accept payback periods as long as 20 years; while restaurant owners seldom invest in any energy and water efficiency with more than a 5 year payback period.

 

Typical Savings for a  

High Efficiency 

Flight-Type 

Dishwasher 

 

 
Medium-Size
 

Food Service 

 

 

 

Large-Size 

Food Service

 

 
 Low Usage 
 

 
 High Usage 
 

 
 Low Usage 
 

 
 High Usage 
 

Annual water
savings (gal/yr)
 

65,000 (246 m3)  

500,000 (1,892 m3)  

120,000 (454 m3)  

1,000,000 (3,784 m3)  

Lifespan water saving 

(AF/20yrs.) 

3.9 

30.5 

7.3 

61.1 

Average annual
water savings (%)
 

25% 

25% 

 

Pre-Rinse Spray Valve

Typically, large restaurants and food service operations utilize commercial dishwashers. Prior to loading the dishwasher, plates and dishes are manually sprayed (pre-rinsed) to remove loose or ‘sticky’ food.  The washing of dishes typically consumes two-thirds of all water use from the restaurant.  The water used in this pre-rinsing operation is often twice the volume of water used by the dishwashing equipment.    The most cost-effective water conservation measure in a commercial food service operation is the improving the efficiency of the pre-rinse spray valve.

pre_rinse_spray_valve_1pre_rinse_spray_valve_2pre_rinse_spray_valve_3 

The time it takes to successfully pre-rinse the dishes is a function of how well the Pre-Rinse Spray Valve PRSV works – better valves clean dishes in less time.  The effectiveness of the PRSV is the amount of force the water exerts on the food residue.  This force is based on two factors; mass and velocity.  The mass is derived from the volume of water; the velocity is derived from the speed the water is ejected from the nozzle onto the food residue.  The same force can be obtained by reducing the volume of water and increasing the velocity

A traditional PRSV uses high volumes of water, usually 2 to 5 gallons per minute (GPM) (7.6 L to 18.9 L).  The US national standard requires PRSV to use no more than 1.6 GPM.  A high- efficiency PRSV uses less than 1.3 GPM and removes food residue faster than the traditional PRSV.   Not only is the water flow rate reduced, the PRSV operator spends less time rinsing the same amount of dishes.

pre_rinse_spray_valve_traditional_1pre_rinse_spray_valve_4 

Water savings will vary by type of food service facility and hours of use.  California Urban Water Conservation Council’s Rinse and Save Program studied the savings from more than 16,000 high-efficiency PRSVs.  The average savings results are as follows:

Per Valve Water Savings

  • 137 gallons per day (518.5 L)
  • 50,000 gallons per year or 0.153 acre-feet per year (189.2 m3)
  • 250,000 gallons over the life of the product of 0.77 acre-feet (946.1 m3)

Per Valve Gas Savings (for 73% of the valves)

  • 0.92 therms per day
  • 336 therms per year
  • 1,679 therms over the life of the product

Per Valve Electric Savings (for 27% of the valves)

  • 20.9 kWh per day
  • 7,629 kWh per year

38,143 kWh over the life of the product


The EPA WaterSense program completed research on pre rinse spray valves in 2011.  The final report from this research is available here. 

In 2014 the Consortium for Energy Efficiency (CEE) adopted a specification for high efficiency PRSVs into its Commercial Kitchens Initiative. The specification offers two levels of efficiency:

  1. Tier 1 qualifying PRSVs save 20% energy and water compared to US federal minimum standards.
  2. Tier 2 qualifying PRSVs save an ADDITIONAL 40% energy and water compared to Tier 1 qualifying units.

A list of qualifying PRSVs can be found on the CEE website

 

 

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