How do modern dishwashers take way longer to run and clean better yet use less energy and water?
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As others said: they trade time for water. I would not say that modern dishwashers get dishes “cleaner” than old ones: they expect you to put them in fairly clean to start with.
My parent’s KitchenAid was made by Hobart, who makes commercial dishwashers too. Other than one burned out (and replaced) motor, it lasted for more than 30 years. It had a beast of a motor, lots of spray jets, a huge and largely self-cleaning filter, filled up its tub before starting, had a Sani Cycle, two soap dispensers (both automatically opening) and a food disposer.
But the big expense was hot water. The cycle plan was like:
Drain (get rid of spilled liquids in the tub)
Pre-rinse 1
Pre-rinse 2
Pre-wash (5 min) -first soap compartment
Main wash (15 min) – main soap compartment
Rinse 1 (5 min)
Rinse 2 (5min)
(Heat water for Sani if selected)
Final Rinse (rinse aid dispense) (8 min)
Hot Air Dry
The whole thing took about an hour. Each wash and rinse cycle put several inches of water in the bottom of the tub.
Today a dishwasher fills with just barely enough water to be able to pump. The “pipes” have a narrower diameter (saves water) and they use a much smaller pump (saves power). As a result there are only a relatively few spray jets, and no water pressure available to spray-clean the filter do you have to remove it and clean it yourself. And the cycle plan is like this:
Prewash (cold water) – 8 min
Main wash (warmer water) – 60 min
Rinse 1 – 20 min
Rinse 2 (hot water, Sani, rinse aid) – 20 min
Dry (passive by default) – 0-30 minutes. (Some machines use condensation drying after the cycle is over).
The efficiency is gained by heating the water less, using much less water, and using smaller pump motors.
A completely different way to look at it: for maximum efficiency, we want the water going down the drain to be as dirty and as cold as we can possibly make it- except for that final rinse, which for safety’s sake should be hot and crystal-clean. So we do as much of the wash with dirty water as we can, and run the wash for a very long time to dissolve as much dirt (grease) as we can-fully saturating the wash water with “dirt” before dumping that water and replacing it.
If you’ve seen a commercial kitchen, they do this. They recycle dirty wash water with a pump and use that to flush big food particles. A spray rinse (a small bit of warm clean water) rinses that dirty water off (which then gets recycled). Only then do dishes go into a commercial dishwasher- which, mostly, makes sure the dishes have been duly cleaned and sanitized at the cost of only about 1 gallon per load.
Hobart now only makes commercial gear. The KitchenAid brand is owned by Whirlpool.
There is some subterfuge in the Energy Star ratings, by the way. If you have to pre-rinse dishes in the sink, it doesn’t count against the dishwasher’s EmergyGuide. Worse yet: if the machine itself last s 8 years instead of 30- there’s a huge hidden cost and environmental impact.
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