Gas Dishwasher and Booster Heater Savings Evaluation

EXECUTIVE SUMMARY

Dishwashing machines and booster heaters are used in a wide variety of foodservice establishments. These appliances are used to clean and sanitized dishes so that the foodservice facility will be in compliance with the National Sanitation Foundation's Standard 3-82. The introduction of gas fired booster heaters and dishwashing machines has made the economics of retrofitting an existing electric warewashing system feasible under many circumstances. This study monitored the energy consumption and heating load of an existing electric booster heater and conveyor dishwashing machine and a replacement gas booster heater and gas fired conveyor type dishwashing machine. Both systems had a nearly identical dishwashing capacity, but the newer gas fired dishwashing machine had improvements to the wash and rinse cycles that reduce water consumption. The warewashing system was located in a foodservice facility that provided 90% of the meals for residents of a 310 unit apartment style retirement community.

The annual operating costs were computed for the two warewashing systems and simple paybacks were calculated based on the installed cost of the new warewashing system. The operating costs included water and sewer charges and energy use and demand costs. Since it was not possible to simultaneously monitor the warewashing system and building electric demand, it was not possible to directly compute the contribution of the warewashing system to the total building demand. Instead, low, average, and high "contribution factors" were estimated based on a previous study of electric booster heaters (Sachi and Hewett 1990). Applying these factors to the measured peak demand provided a range for the estimated peak demand charge. The actual value is most likely midway between the average and high estimate.

The electric warewashing system had a estimated annual operating cost ranging from $8,316 to $12,927 and the gas warewashing system had an annual operating cost of $3,494. The cost savings are almost evenly split between electric demand and water use cost reductions. The installed cost of the new gas fired booster heater and dishwashing machine was $25,000, which resulted in paybacks for the new system ranging from 2.7 years to 5.2 years. The best estimate of the simple payback is about 3 years. The data also showed that the gas warewashing system used 73% less source energy than did the electric warewashing system.

To account for a very large leakage rate that was present in the pre-retrofit electric system, the pre-period operating costs were normalized to the water consumption measured in the post-period. Normalized water consumption of the pre system was calculated based on manufacturer's information of water consumption at 100% load. The ratio of the pre-period dishwashing machine rated water use to that of the post-period was computed and then multiplied by the measured post-period water consumption to compute an estimated water use for the pre-period. The leakage rate was found to be 0.6 gallons per minute. Visual inspections and discussions with kitchen staff indicated that this leakage rate was reasonable.

Full report (PDF):
Gas Dishwasher and Booster Heater Savings Evaluation