Make Smart Choices to Reduce Dishwasher Operating Costs
By Kristin Kamm, E Source Sr. Research Associate, www.esource.com -- Foodservice Equipment & Supplies, 4/2/2007
Prodigious hot water consumption makes the dishwasher one of the biggest energy-users in a commercial kitchen. Each dishwasher consumes an average of about 225 million Btu (MBtu) of energy per year. By taking a look at their machine, and checking the set-point temperature of their water heater, operators may find easy ways to save energy in the kitchen.Commercial kitchens tend to use two main types of dishwashers: those that consume high- or low-temperature water for washing and sterilizing dishes. Both take in water from the kitchen's water heater. High-temperature units use a booster heater to produce very hot water (180°F. or 83°C.) to sterilize dishes during the rinse cycle. Some dishwashers also feature built-in burners or heating elements to keep the wash water up to temperature. Low-temperature units use less energy, when running at optimal settings, because they use water straight from the hot water heater at 140°F. (60°C.) without requiring any booster heating. These dishwashers use a chemical sanitizing agent in the final rinse cycle.
Although low-temperature dishwashers use less energy than high-temperature units, operating costs tend to be about the same because of the cost of the sanitization chemicals required. Also, operators should consider some of the environmental drawbacks to flushing the chemicals down the drain. Some users complain that the dishes smell like chemicals and that the chemicals bleach out the porcelain dishes sometimes used in fine-dining restaurants. Users may turn the temperature of the water heater tank above the recommended set point of 140°F. to improve the effectiveness of the cleaning. Doing so detracts from energy savings.
High-temperature dishwashers are making a comeback in commercial kitchens after having lost market share to low-temperature dishwashers due to the energy crisis in the 1970s. Many commercial kitchen operators like high-temperature units because they feel that they clean dishes more effectively than low-temperature units. Also, since they blast the dishes with high-temperature water, the dishes dry faster.
Operators that choose high-temperature dishwashers should consider installing a gas booster heater instead of electric - depending on local energy prices, energy cost savings often more than make up for increased capital and installation cost. Installation costs tend to be higher because gas units require ventilation whereas electric units do not.
Here are some more tips for cutting the costs of dishwasher operation:
Purchase or rent a water-efficient dishwasher. Their low water consumption per rack for conveyer or door-type units distinguishes high-efficiency dishwashers - both low- and high-temperature models. (This may not apply to undercounter units.) Purchasing or renting a dishwasher with a rating from NSF International, of less than one gallon per rack, reduces the amount of water heating necessary. This rating is available on the NSF web site
Use proper water heater settings and ensure that the distribution system is leak-free. Set the water heater temperature to 140°F. (60°C.), insulate hot water lines, regularly ensure that the water heater temperature/pressure-relief valve is operational, and fix any leaks.
Use proper dishwasher set points and operation mode. Set rinse pressure to 15 to 25 pounds per square inch (100 to 172 kilopascals) to avoid excess water use, set the wash-tank temperature to 160°F. (71°C.), and set the booster heater set point to 180°F. (83°C.), which is in accordance with NSF guidelines. Check that wash curtains for conveyor washers are not missing or too short to prevent heat from escaping. Also, run the dishwasher only when full, because it uses the same amount of hot water regardless of load size. And avoid putting pots in the racks because dishwashers can't really clean a pot - they can only sanitize it. Most kitchens have sanitizing sinks, so it is unnecessary to sanitize pots in the dishwasher. Don't run the dishwasher in manual mode, or the machine will likely run too long without automatic shutoffs.
Turn off equipment when not in use. Turn off high-temperature dishwashers at night so that built-in burners or heating elements will not consume energy and save about $500 per year (at an electricity rate of $0.13/kWh). Turning off the dishmachine exhaust hood can save another $250 per year. Make sure that the booster heater is shut off at night for a savings of $60 per year; even if you turn off the dishwasher itself, the booster heater might have a separate manual switch.
