ANN ARBOR, MI — The University of Michigan recently teamed up with Benton Harbor’s Whirlpool Corp. to see if dishwashers really do use less energy and water than traditional hand-washing techniques.
According to the study, dishwashers are more efficient versus hand-washing except for the two-basin method, in which dishes are scrubbed and soaked in hot water and then rinsed in cold water.
“I was surprised to see how well the two-basin method did ,” said Gregory Keoleian, co-author of the study and UM professor of civil and environmental engineering. “It’s slightly better than the dishwashers we evaluated — the two-basin method had an 18% reduction in greenhouse gas emissions.”
The study, published Feb. 12 in “Environmental Research Communications,” also found:
- Avoiding prerinsing and deselecting the “heated dry” setting can significantly reduce the greenhouse gas emissions associated with machine dishwashers.
- The common “running tap” method of manual dishwashing used more energy and more water than any other dishwashing method tested.
- If by-hand dishwashers switched from the running tap to the two-basin method, they could reduce associated greenhouse gas emissions by about two-thirds.
In the observational study, 38 Whirlpool employees were asked to load a dishwasher as they normally would at home, to manually wash dishes like they would at home and to answer survey questions related to their dishwashing behaviors. The study assumed natural gas is used to heat the water, noting that greenhouse gas emissions increase significantly if an electric heater is used.
The study builds on a master’s thesis by lead author Gabriela Porras, according to a UM news release,. Data was collected at Whirlpool’s dishwasher manufacturing plant in Findlay, Ohio, and a small laboratory study was done at the company’s Benton Harbor headquarters.
Dishwashing seems simple, but that’s not the case when developing a model for energy and water use, Keoleian said.
“It’s quite complex because we need to get data on materials that go into the dishwasher,” Keoleian said, which includes the two models tested — one with a plastic tub, the other with stainless steel — and the amount of energy used during manufacturing.
Right now, Keoleian said it’s better to heat water with natural gas in the Midwest. However, as water grids become cleaner, it’s better to use an electric heater when it comes to greenhouse gas emissions.
While previous studies showed consumers can save time, energy and water by using a machine dishwasher, they failed to account for real-world behavior, like prerinsing and varying the cycle selection, the study said, adding that dishwashers are very underutilized by many households.
“Some people don’t have a lot of dishes, so they may not use their dishwasher frequently,” Keoleian said. “Eighty percent of households own one, but 20% use them less than once a week.”
If you’re not in the mood to wash dishes by hand, the study said don’t prerinse before loading dishes into the dishwasher, don’t select the “heat dry” setting and don’t choose the “heavy” cycle over a normal wash, except for tougher loads, to reduce the environmental impact of your appliance., Keoleian said
Also be aware of the kind of detergent used and to follow the manufacturer’s recommendations when it comes to loading the dishwasher, especially for plastics, Keoleian said.
“In terms of loading, plastics should be in the upper rack to minimize its degradation. The lower rack of the machine is hotter and can break down plastics,” Keoleian said.
More information on the study can be viewed here.