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Conveyor Dishwasher Report Highlights Machine & Operational Flaws, Opportunities for Significant Energy, Water Savings
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Courtesy: Glenn Hasek | News Source:

NATIONAL REPORT—A field study of rack and flight conveyor dishwashers conducted by Pacific Gas and Electric Company Food Service Technology Center (FSTC) documents the energy and water savings and economic benefits of replacing an old inefficient dishwasher with a new efficient or best-in-class dishwasher.

The study, entitled “Conveyor Dishwasher Performance Field Evaluation Report,” highlights how dishwashers become less efficient over time and how many dishwashers fail to operate to their design specifications. Summary data from the nine dishwashers monitored during the study were added to nine other dishwashers previously monitored by FSTC in the last five years. One of the testing sites was the Claremont Hotel, Club and Spa in Berkeley, Calif.

A goal of the project was to develop a more accurate commercial dishwasher water and energy use estimate that could provide the foundation on which to base utility incentives, third-party dishwasher retro-commissioning and replacement programs, market transformation initiatives and water heater sizing guidelines.

The goal in each test site was to measure the total water and energy use of the conveyor dishwasher and to estimate the operating cost—including water/sewer, gas, and electricity.

“If you are using a lot of water, you are using a lot of energy to heat that water,” says Amin Delagah, Research Engineer IV, Fisher-Nickel, Inc. (operator of FSTC).

Energy & Water Eaters in the Kitchen

For the sites in which a dishwasher replacement occurred, the FSTC research team provided analysis to support the development of a calculated incentive based on the estimated energy and water savings associated with the new machine. Identifying savings opportunities is important because conveyor dishwashers are the single most water and energy intensive appliance operating in commercial kitchens.

The FSTC team installed instrumentation and data logging equipment in the test sites to measure and record the energy and water use of each dishwasher. For each test site, the facility was characterized by the type of foodservice facility, operating days and hours, type of dishwasher and booster heater, dishwasher make and model, and dishwasher specifications. The monitoring period and total monitoring days for each dishwasher was logged along with measurement points for the dishwasher monitored.

Testing took place from May 2014 to June 2015. Data, including rinse and fill water use, rinse flow rate, dishwasher and booster heater energy use, and rinse time, was collected at five second intervals and stored with a time stamp in the memory of the data acquisition system. Overall, over 70 measured or calculated parameters were analyzed to identify the most important parameters to use to normalize the results for each dishwasher for a fair comparison of other dishwashers in its classification.

For each dishwasher, the data was quantified for water and energy use per hour of rinse operation. The conveyor dishwashers were classified into four groups including conventional rack, high efficiency rack, conventional flight and high-efficiency flight machines to derive savings estimates from replacing older machines with high-efficiency replacements.

New Models Much More Efficient

The normalized results from 18 sites showed roughly a 70 percent reduction in water and 55 percent reduction in energy use by replacing old conveyor dishwashers with new high-efficiency models. Specifically, the water use of the average conventional rack conveyor, at 691 gallons per hour of rinse operation, was reduced by 65 percent when replaced by an average high-efficiency unit, using 261 gallons per hour. Similarly, the energy use was reduced by roughly 55 percent. The water savings from flight conveyor dishwashers was even greater—representing a reduction of 75 percent. Water use of the average conventional rack conveyor, at 1,115 gallons per hour of rinse operation, was reduced to 267 gallons for the average high-efficiency unit. Similarly, the energy consumption was reduced by 55 percent.

Old inefficient conveyor dishwashers were replaced with Energy Star qualified high-efficiency models at four sites. The average cost savings per site based on average California utility rates was approximately $22,000 per year. In each case, the cost savings were driven by the substantial reduction in water use.

“Older machines do not have good diagnostics,” Delagah says. “A lot of these machines can become really inefficient. Malfunctions don’t get caught.”

Claremont Hotel, Club and Spa Example

At the Claremont Hotel, Club and Spa, there are three restaurants—the Bayview Café, The Paragon Restaurant and Bar, and Meritage at the Claremont. The nameplate was missing on the dishwasher, but it is estimated that the unit was 20 years old during the study and is one of the older Stero STPCW series machines that is rated at 336 gallons of rinse water use per hour. The unit uses steam heat for all its water heating functions. Monitoring started on September 16, 2014 and continued until February 11, 2015. Data was collected for a total of 133 days with gaps between several dates in October where data was lost due to disruptions in supply power to the instrumentation box. There were numerous monitoring challenges with this site due to the age of the machine and its steam based heating system. Many components on the dishwasher were not working properly including the automatic tank fill operation, steam leakage into one or two wash tanks (which elevated the tank temperatures) and the heat exchanger to maintain fill and rinse temperatures was not keeping up. Also, the blower dryer was no longer operational.

On an average day, the flight conveyor used 6,018 gallons of water. Tanks fills, for the most part, were not close to the manufacturer’s specifications. Daily water waste over the period ranged from zero to 4,916 gallons per day. The dishwasher averaged 4.9 tank fill and dump operations per day with an average fill of 477 gallons which is 3.5 times more than equipment specifications. Rinse water use was 8.6 gpm which is 50 percent over the manufacturer’s specifications at 5.6 gpm. There were other problems with the machine as well.

Studies of the dish washing machines at the Claremont Hotel, Club and Spa and the other sites demonstrated that model specifications, according to FSTC, “were a crude way to estimate real world water use.”

The testing at the Claremont Hotel, Club and Spa and other sites highlighted the many inefficiencies inherent in dishwashing operations. Ultimately, it was determined that the specified rinse flow rate is not a good proxy of real water use when it only accounts for approximately a quarter to one-half of the total real world use. The research showed that old conveyor dishwashers consume two to three times more water than was predicted based on the rated rinse flow and tank volume specifications. High-efficiency conveyor dishwashers used 70 percent to 85 percent more than the rated specifications. The new machines operated more closely in line with the specifications than older machines as they benefited from advanced features that mitigated water waste.

Machine Wrong-Sizing Quite Common

In its research, FSTC found that facility operators oftentimes will perceive that the operating time of their machine is higher than it actually is, leading to the oversizing of new machines—again, more waste.

“A lot of these facilities don’t need the machines they are using,” Delagah says.

Inefficiencies found during FSTC research also emphasize the need for proper machine maintenance in order to eliminate water and energy waste.

A significant finding was that the majority of conveyor dishwashers installed in facilities are not set up to wash and rinse medium to large back of the house wares without incurring substantially higher water use during operation. Most conveyor dishwashers are designed to wash front of the house cups, glasses and dishes, with the larger back of house wares providing a challenge for the machine. Some of the overspray issues caused by washing large wares could be mitigated with the specification of taller cavity machines and incorporating specialized racks for washing sheet pans and other flat wares at an angle that allows water to drain back into the correct tank instead of horizontally spraying through the machine.

Importance of Submetering

To better document actual water and energy consumption, FSTC recommends submetering conveyor dishwashers for water use.

“You should really be submetering your dish machines,” Delagah says. “Technically, it is not very difficult to submeter. It allows the facility to keep up to speed on the operation of the machine by identifying maintenance issues and when staff training is appropriate to get back to the benchmark operating parameters documented when the machine was commissioned.”

Alternatively, FSTC encourages the purchase of smart dishwashers that minimize water and energy use while having integrated water and energy meters and logging and communications hardware.

At the end of the study, FSTC recommends, “There is also a need to fund additional field monitoring projects on high-efficiency dishwashers just entering the market that utilize second-generation heat recovery systems. Quantifying the water and energy use of these emerging technologies can support future incentive programs and provide a solid foundation to enhance the Energy Star specifications for commercial dishwashers. As more and more dishwasher manufacturers continue to add models with integrated heat recovery systems, third-party research is needed to validate real world savings potential of the designs. This research would be a compliment to the proposed design guide for commercial dishwashers, serving as the basis for a phase two design guide on the application of heat recovery in commercial dish rooms.”

Delagah says reports like the Conveyor Dishwasher Performance Field Evaluation Report will help build momentum toward better testing. Another goal is to highlight what machines are doing right and to emphasize there is an opportunity to adopt ‘best in class’ technology.”

Watch for an article soon on the smartest, most efficient dish machines available.

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