Gongol.com Archives: September 2021

Brian Gongol

September 22, 2021

Science and Technology Save the world: Run your dishwasher overnight

The BBC (specifically, its smart speech-based network, Radio 4, where even the fidelity of the Big Ben chimes is a matter of robust debate) airs a program called "More or Less", on which the main topic of discussion is statistics. It seems an unlikely concept to attract much interest, but it is the kind of novel program that gains 23,000 followers on Twitter in addition to a robust listening audience. ■ Among the questions they've sought to answer with numbers is this: Is an automatic dishwasher more efficient than a person washing dishes by hand? ■ For starters, the question is basically settled: Dishwashers that earn an Energy Star rating from the EPA are both extremely efficient, typically using an almost trivial amount of electricity and less water for a total cycle than would flow from a normal kitchen sink in just two or three minutes. As long as a relatively modern dishwasher is being run with more than just a single place setting, it's likely to be the most efficient route by quite some margin. ■ But one aspect of the question in particular deserves a second look. The knock against automatic dishwashers is that they use electricity instead of elbow grease. That much seems indisputable. But in addition to using far less electricity than in the past, state-of-the-art dishwashers (and clothes washers, for that matter) offer timer delays. This permits a household to time-shift its cleaning to an off-peak hour, like the middle of the night. ■ Domestic water use tends to be diurnal, with two peaks: In the morning and again in the evening. That's when most of the bathing, cooking, drinking, washing, brushing, and flushing happens. Any time a household can shift some of its water consumption to off-peak hours, that helps the local water and wastewater utilities to smooth out their own energy and water use. ■ If every household could shave 5% or 10% off their peak water use and move it to a low-demand time like the middle of the night, the net effect could be very helpful to utilities. And the consequences for overall environmental efficiency would add up even more in places like Iowa, where a majority of the electricity now comes from wind turbines. Time-shifting consumption helps not only the water supply but also the electrical grid (and the two are closely related, since water utilities are major consumers of electricity). ■ Peak demand can be problematic for both electrical utilities and water utilities. Reducing consumption through higher efficiency is obviously helpful, but consumption-smoothing is helpful, too. Taking the pressure off peak electrical demand translates into less reliance on carbon-generating power plants, and easing peak demand on water supplies allows pumps and tanks to balance supplies more efficiently. Rivers flow and winds blow at all hours, so running the dishwasher in the middle of the night makes one a good steward of renewable resources.

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