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Dish-up Some Savings Featured on Sep 29, 2008

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Challenge Details

Have you ever noticed that, if you have X number of people in a house, you probably have exactly X number of ways in which to load the dishwasher? Oh, sure the manufacturers put suggested loading diagrams in their dishwasher owner’s manuals. But, really… who wants instruction on proper bowl versus cup placement? Isn’t loading a dishwasher more of a Zen efficiency thing where you ask the dishes where they want to go? Sometimes it’s hard to listen to the dishes. There’s nothing more plaintive than the cry of a tumbler exiled to the bottom tray with the serving platters. But if you do listen to the dishes, perhaps they’ll also give you a few words of advice. There’s a greener way to wash them.

This Featured Challenge is based on suggestions made by eagleray7_33032 and akhan_27560. To date, their suggestions have received 13 positive votes each in our Challenge Workshop. Eagleray7 is an animal activist from Florida and has taken 55 Challenges to date. Akhan is a member of the Redwoods Group team, currently in second place in the Company League on our 30-Day Leaderboard.

The Carbon Connection
Whether you are washing dishes by hand or using a dishwasher, you know that washing dishes requires hot water. That hot water comes from your hot water heater. Energy is used by the hot water heater to heat cold water in the tank and to keep it hot. As you use hot water, more energy is needed as cold water is piped in to replenish the tank.

Up to 80% of the energy used by a dishwasher is needed to heat the water used in the wash and rinse cycles. Most of that energy is used to heat the water in your home’s hot water heater before it gets to the dishwasher. Modern dishwashers also have electric booster heaters. These booster heaters increase the temperature of the hot water entering the dishwasher so that the water is hot enough to effectively wash dishes. The other 20% of the energy used by a dishwasher includes the electricity used to run the dishwasher’s motor/pump. Dishwashers also have electric heating elements that give users the option of drying dishes more rapidly once the dishes have finished their final rinse cycle.

As you know by now, our use of energy is directly linked to the creation and release of greenhouse gases such as carbon dioxide. Hot water heaters either burn natural gas or use electricity to heat water. And, as you’ve seen, dishwashers use additional electricity to wash and dry loads of dishes. Unless your electricity is coming from a renewable source such as wind or solar, creating that electricity requires the burning of fossil fuels. Burning fossils fuels, such as the natural gas used by a hot water heater, creates greenhouse gases. The less energy you use, the fewer pounds of carbon dioxide get released into Earth’s atmosphere.

Getting It Done
The challenge of this Challenge is to figure out which two buttons to push on your dishwasher, and then remembering to push them each time you start the machine. (Maybe they aren’t literally buttons on your dishwasher. Perhaps they are settings you enter on a touchpad. Same idea.) Instead of selecting the dishwasher’s Normal cycle, you want to select the Energy Saver cycle. This is sometimes called Water Saver or Ecowash; see your dishwasher’s owner’s manual if you can’t figure it out. And then you want to select Air Dry (or sometimes Energy Saver) for the post-wash drying. Again, consult your manual if it isn’t obvious how to turn off the heated drying option. As for remembering to push different buttons than the ones you’re used to, maybe you could write yourself a Post-it note until the new buttons become habit for everyone in the household.

Here are a few suggestions about other things you can do to lower the costs of washing dishes and lower the carbon emissions from dishwasher-related energy use:

• Cut down on the number of times you run the dishwasher. Wait until you have a full load of dishes before you run the dishwasher. Newer dishwashers won’t have a problem with a little dried-on food. Each time you don’t run the dishwasher can save an additional 4.5 lbs of CO2. (Some of the newer models have a cycle that only washes dishes in the top rack and uses about half the amount of water as running a full load; check your owner’s manual to see if your dishwasher has that feature.)
• Stop pre-rinsing your dishes. It should be enough to use a rubber spatula to scrape the excess food off your plates and bowls before loading them into the dishwasher. Rinsing dishes at the sink before putting them into the dishwasher can use an additional 20 gallons of hot water — and that’s more hot water than gets used in 2 complete loads of the dishwasher! Skipping an unnecessary pre-rinse can save another 3.8 lbs of CO2.
• Dishwashers need very hot water — around 140 degrees Fahrenheit. Before around 1994, that meant that a home with a dishwasher needed to have its hot water heater set to 140 degrees. However, dishwashers now have booster heating elements to increase the temperature of water used to wash the dishes. That heating element runs whether you have the water heater set high or not. Don’t heat the water twice and don’t heat all of your water hotter than you need. Lowering your water heater setting from 140 degrees to 120 degrees can save you about 10% of your annual water heating costs.
• You might save extra money by running your dishwasher at off-peak utility hours. Some electric utilities have a lower rate for electricity at night. New dishwashers often have a timer feature that allows you to have the dishwasher run several hours after you load it.

How have you managed to cut down on the number of dishwasher loads you do each week? Which dishwasher setting works best? Share your thoughts, stories, and suggestions with your fellow Rallyers in the Challenge forum section below.

Rules of the Challenge
This Challenge asks that you do two things when using your dishwasher to wash dishes. First, select your dishwasher’s Energy Saver (Water Saver, Ecowash, etc.) cycle instead of the Normal cycle. This will save both hot water and electricity. And second, do not select the Heated Drying option to dry your dishes once they are clean. This will save electricity. By making these two changes in your dishwasher use for the next month, you will save 20.5 lbs of CO2. This Challenge is repeatable.

Learn More
Flex Your Power: Dishwashers and Dishwasher Tips
TreeHugger: How to Green Your Dishwasher
Consumer Energy Center: Dishwashers

See the Math
Let’s see how using the energy-saver features on your dishwasher will affect your energy use and carbon emissions over the next month. Here are the known or estimated numbers being used for this Challenge:

• We do not know how old your dishwasher is. Dishwashers older than 2003 can use twice as much hot water as newer machines. And, even if you have a newer dishwasher, it may or may not be Energy Star rated. This also affects the amount of hot water and electricity it uses per load of dishes cleaned. For the purposes of these calculations, we are going to ignore older dishwashers and use a weighted average of Energy Star versus non-Energy Star dishwashers.
• Button 1 (Energy Saver) First, let’s look at the carbon savings from using your dishwasher’s Energy Saver setting. The Energy Saver setting saves energy (and carbon) in two ways: 1) by using less hot water; and 2) by running less time and using less electricity. We have reviewed a number of dishwasher owner’s manuals and have decided to use 2 gallons of hot water saved per load for non-Energy Star dishwashers and 1 gallon of hot water saved per load for Energy Star dishwashers. On average, heating 1 gallon of water requires an amount of energy (either electricity or natural gas) that contributes about 0.19 pounds of CO2 to the atmosphere. Carbon savings from reduced hot water use are therefore 0.38 pounds of CO2 per load for the non-Energy Star dishwashers and 0.18 pounds of CO2 per load for Energy Star dishwashers.  source
• Energy Saver dishwasher cycles use about 15% less electricity per load than Normal cycles. A typical non-Energy Star dishwasher uses about 2.0 kWh (kilowatt hour) of electricity per Normal cycle load. A typical Energy Star dishwasher uses about 1.5 kWh per Normal cycle load. Applying the 15% electricity savings to each gives us 0.3 kWh saved per load for non-Energy Star dishwashers and 0.23 kWh saved per load for Energy Star dishwashers. On average, creating 1 kWh of electricity by burning fossil fuels releases 1.55 pounds of CO2 into Earth’s atmosphere. Apply this conversion factor to the electricity savings. Carbon savings from reduced use of electricity when using Energy Saver settings are therefore 0.47 pounds of CO2 per load for the non-Energy Star dishwashers and 0.35 pounds of CO2 per load for Energy Star dishwashers.  source
• Find the total carbon emissions savings from using Energy Saver cycles by adding the savings from reduced hot water use to the savings from reduced electricity. This gives us total savings of 0.85 pounds of CO2 per load for non-Energy Star dishwashers and 0.54 pounds of CO2 per load for Energy Star dishwashers.
• Again, since we don’t know the age of your dishwasher and whether or not it is Energy Star rated, we will do a weighted average. We are going to assume two-thirds of your dishwashers are not Energy Star rated. This helps account for dishwashers in service since before 2003. Applying this weighted average to the above numbers gives us 0.75 pounds of CO2 saved per load by using the Energy Saver setting.
• Button 2 (Air dry) Next, let’s calculate the electricity saved per load using the air drying rather than the heated drying option. The heating elements that do the “fast dry” in dishwashers are rated from 900 to 1500 watts and run anywhere from 15 to 30 minutes after the dishwashing cycle has completed. Let’s say the heating element is 1000 watts and that it runs for 15 minutes after each load. 1000 watts is one kilowatt. 15 minutes is one-quarter of an hour. So the heating element is using one-quarter or 0.25 kWh of additional electricity per load.
• Multiply 0.25 kWh per load for heated drying by 1.55 pounds of CO2 generated per 1 kWh electricity. That gives us an additional 0.39 pounds of CO2 generated per load when using the heated drying option. This number applies no matter what the age of the dishwasher or whether or not the dishwasher is Energy Star rated.
• Button 1 + Button 2 Next, we find total carbon savings per load. Add the weighted average saved by choosing the Energy Saver option (0.75 pounds CO2 per load) to the savings from not using heated drying (0.39 pounds CO2 per load) to get a total savings of 1.14 pounds of CO2 per load.
• Loads per month Finally, apply this number to a month of dishwasher use. Energy Star ratings are based on an assumption that the average dishwasher is used for 215 loads of dishes per year. That’s 18 loads per month.
• Total savings Multiply the 1.14 pounds of CO2 saved per load by 18 loads per month to get 20.5 pounds of CO2 saved per month. Based on these energy calculations and reasonable assumptions about current energy prices, completing this Challenge will save you $1.27 in one month. Repeating the Challenge for one full year will save you $15.24.

Remember, your goal is to reduce the amount of hot water and electricity you use. The less hot water you use, the less energy you use to heat the water and the fewer pounds of carbon dioxide you’re responsible for creating. As for heated drying, you didn’t want to melt a spork, did you? Push the right buttons, Rallyers!

Discussion 59 comments so far