Energy Efficient Dishwashers and How They Work
When you think of washing dishes, what comes to mind first? I think first of my brothers having to take their turn - we were six boys and two girls. I think of the appreciation of hostesses at parties where I helped wash up afterwards. Then I think of washing glasses in a sink by a window, making them sparkle in the morning light, and the almost visceral pleasure of that. Do any of these scenes speak to you too?
Instead of washing by hand, nowadays dishes go straight into the dishwasher, where they wait until the dishwasher is full. After washing, the satisfaction of sparkling glasses isn't nearly as strong as it used to be, neither do they seem as clean, but now most of us are adults with a job, so a dishwasher has become a necessity. And the dishes do get clean enough.
Thankfully, washing full loads in the right dishwasher uses less water than washing by hand (see chart below) and the newer dishwashers use much less electricity too, both of which save money on utilities. So there's a benefit in addition to convenience. There aren't many householders left who don't use either large or small dishwashers.
What sizes are there?
Dishwashers come in all sizes, from huge, conveyor belt types for hotels and large restaurants to tiny, counter top types for singles living in apartments. Pictured here is a commercial dishwasher used mostly in restaurants and hotels. It operates via conveyor belt, rather than being hand loaded, which reduces the number of hours needed to hire kitchen assistants (good for the hotel, not so good for the employees).
Once families and then singles started seeing the benefits to using dishwashers, engineers started designing different sizes for different uses. Now you can even buy dishwashers on wheels. Here is a quick history showing how dishwashers evolved.
A little dishwasher history.
Mechanical dishwashers were first designed in the late 1880s and were hand cranked. Models with permanent plumbing were designed in the 1920s. Electrical drying was added in the 1940s. By the 1970s dishwashers had become common in residences. Today 60-65% of homes contain dishwashers.
In 2003 the US Department of Energy established a minimum efficiency standard - 2.3 kWh of energy per load. Today's efficient dishwashers use a quarter of that, averaging only 0.8 kWh per load.
How do dishwashers work?
Most dishwashers have push-button controls located on the outside of the door. This is where you would select the types of cycles you want, whether or not to increase water temperature, and the hours to delay the start time, if you want to have it start later.
Just inside the door are the soap and rinse solution dispensers. Usually there are three dispenser cups - one for pre-rinse soap, one for soap for the regular wash, and the third for a rinse solution that prevents spots on glasses.
Many modern dishwashers have water temperature boosters to take water from the normal 120 degrees up to 150 or even 170 degrees. With the combination of the hot water and intense spray, grime is washed off the dishes easily, negating the need to rinse before washing. This can save a lot of water.
Note that this does not mean sterilizing. For dishes to be sterilized, water would have to be heated to 250 degrees and no dishwasher does that. Some dishwashers "sanitize", but that's a lower temperature.
Inside most home dishwashers there are two trays - the lower one for plates, pans, and silverware, the upper one for glasses, cups, small dishes, and plastics.
In modern dishwashers each tray has its own spray arm that jets water into the dishes while spinning around so all dishes are covered. The pressure of water being forced into the spray arms is what causes them to spin. These spray arms trade off with each other in order to cut down on noise.
The top spray arm is fed through a cap that unlocks and rises to cover the water nozzle on the roof of the interior. When the dishwasher is on, water pours down through that nozzle into the cap and through to the spray arm, which starts spinning and shooting water-jets up and down into the dishes. In the photos to the right, you will see the nozzle, the cap with its lock, and the way the contraption looks when the tray is pushed in.
The last photo shows the bottom spray arm, air heating element, and the water drain in the center of the floor. The bottom spray arm is fed directly from the water pipe underneath. Its spin is also activated by water pressure.
After dishes are washed and rinsed, water drains out the bottom, and the heating element goes on to dry the dishes. In most situations the water heat has already heated the dishes up enough to easily air dry, except for plastics. This cycle can therefore be turned off to save electricity, if you don't mind drying plastics by hand. The entire pre-rinse/wash/rinse/dry process can take anywhere from two to four hours, depending on how much of it you elect to go through.
How can you recognize a really efficient dishwasher?
- In California the new CALGreen Building Code requires that manufacturers post water use information directly on all water-using appliances. This went into effect in Jan 2011, so only the newest dishwashers will have this label.
- Look for the Energy Star label to see if the dishwasher you have is really efficient. Note that some manufacturers claim their dishwasher is "Energy Star qualified." That's not the same as one with the Energy Star label on it.
Don't go by price, but by rating and reviews. There are dishwashers made small for small kitchens that don't cost much, but are still highly efficient.
Stainless steel interiors help contain heat, and the existence of a spot-prevention agent dispenser can indicate a more efficient dishwasher.
Really efficient dishwashers will give you the following choices: Air vs heat dry, increased wash temperature, the ability to skip cycles. It also has an automatic soil detector for rinse water and good insulation so heat doesn't escape.
How do or can they save water?
Skip the pre-rinse cycle, if you rinse dishes by hand before inserting into the dishwasher. Alternatively, don't rinse by hand, but do use the pre-rinse cycle. Either way will save you water.
I usually wash every two or three days when the dishwasher is full. If you wash every day, consider just scraping the dishes, instead of rinsing first, then skip the pre-rinse cycle.
It's also a good idea to heat the water pipes before starting the dishwasher, especially if there is a long distance between your water heater and kitchen sink. Turn on the kitchen tap until hot water comes out, then start the dishwasher. This can save your dishwasher from having to run a longer cycle to make sure the water is hot enough.
Some dishwashers have a soil sensor to monitor the outgoing water. When it reads clear, the dishwasher moves to the next cycle. This can shorten the cycles when dishes clean quickly, thereby saving both water and energy used to heat the water.
How do or can they save energy?
Insulation is key with a good dishwasher, both to reduce heat loss and also to dampen noise. The new dishwasher that was put in my apartment recently fits inside the lower cabinetry and has a two inch thick door, with 3.5 inches around the edge where the seal stops water from leaking. It's very quiet.
As with washing machines, run the dishwasher during off-peak hours to help the city save electricity. That also cuts down your bills in areas where a higher rate is charged for peak hours. Peak hours are those during the day when businesses are open, generally from 9:00 AM to 6:30 PM.
Use "Air Dry" for the drying cycle. Rinse water is hot enough that it should evaporate on its own, except for plastics and the bottoms of down-turned cups. Those can easily be blotted with a dish towel or paper towel.
Additional tips for effective use of the dishwasher:
Face all dishes toward the center. Put plastic items on the top rack. Also make sure dishes are somewhat separated so water can get between them.
To make sure silverware gets clean, insert some with handles up and some with handles down.
Use a liquid dishwasher soap in areas where water is soft, and powdered soap where water is hard.
Run the kitchen tap to get hot water before starting the dishwasher. This will ensure that there is hot water in the pipe that feeds the dishwasher from the start.
If your countertop or portable dishwasher is noisy, throw a blanket over it.
Purchasing a Dishwasher
Prices for the newer, really efficient dishwashers (and other appliances) are coming down, as more and more states pass mandatory building codes that require installation of efficient appliances. This is already happening in California.
Two of the highest rated dishwashers by Consumer Search were Maytags, priced at $500-700 for a medium-sized home dishwasher. Both can be found at your local Home Depot, Sears, and on Amazon.com. The other highly rated dishwasher was a Kenmore Elite, priced at around $1,000 at Sears. If you have a subscription to Consumer Reports, check their ratings on dishwashers as well.
Also, before you purchase check the tub inside a dishwasher to see if it's made of stainless steel or plastic. The plastic breaks down over time in the heat, whereas stainless steel lasts much longer and can be worth the extra cost. This does not apply to other parts of the dishwasher that are not exposed to the hot water and air inside.