Wednesday, June 29, 2016

exposing my dishwasher energy hog

INDEX to the series

This is part two about seeing my home energy use with a whole house energy monitor and some electrical detective work. If possible, I want to sensibly shift my time of use (TOU) to non-peak. To do this, I need to look carefully at my electrical energy in total and as the separate appliances, understanding the amount of energy use and when it occurs.

I have been given a special incentive and tools as a participant in the McMaster University FlexPlan Study. This is turning out to be an individual quest. Everyone's energy use is different. My electric utility bill currently gives me lots of info, but only in total monthly buckets. I need to understand how my use is made up if I am going to make sensible energy saving decisions.

As part of this study I temporarily have a different cost structure than the rest of Ontario residential electricity users. My peak time is now from 12noon to 6pm. I only have peak and non-peak. During my peak, my cost of electricity is almost FIVE TIMES the non peak rate (54 cents/kilowatt-hour versus 11c/kWh). That's a pretty powerful incentive to not use peak power! There may be other participants with different rate structures to test different behavior. I am not sure. I do not pay delivery or other charges while in the study. The study goes for a year and started for me at the beginning of June. Starting during the summer is simpler for me since the furnace is not operating and I am not using as many lights so the data is a bit simpler.

This morning I decided to run a full load of dishes, about two or three days worth for me. I've rinsed them as I loaded so there is no need to run a rinse cycle. Straight wash, no heat. I learn about each major appliance by watching it's power "signature", essentially a recording of the power it draws minute by minute, illustrated as a graph by the software. I can watch energy use in real time and I can zoom out to see the history. I try to catch each appliance running by itself with nothing else major running at the same time to confuse the signature. There is a certain "background" that does not go away (the fridge, the freezer, the network and computers) that varies a bit about 350 watts, but the major appliances stand out against the background easily. They use a lot more power.

The is what I see realtime in the software. I started the dishwasher at 5:30am. There was a false start so I reset the machine and started it again. It ran a full cycle over almost and HOUR AND A HALF, using up to 4.5kW! That is the most energy use I have recorded so far!

For the first few minutes the machine fills hot water and then to make sure, heats the water loaded by itself with a built in heater. I must check the temperature of the water heater. Most dishwashers recommend a higher than normal hot water inlet temperature. The same heater can be used at the end to dry the dishes. I have the button pushed for "NO HEAT DRY" so I am expecting the heater to come on at the beginning and then to see the motor activity.

The reality is different. The heat dry is coming on at the end and it tells me that on the front panel of the machine (first picture). So that isn't working right. If I am around when it reaches this point, I can pop open the door to stop the machine but I seldom am around at the right moment.

This is the same data over a 12 hour period. Last night and this morning together if you like. Here the dishwasher really stands out against the background and the previous hog champion, the water heater. I can see in the data that things have been quiet electrically overnight. The water heater came on about 2am and did its usual run of 3kW for about 10 minutes. No hot water has been used in about 12 hours.

The water heater came on shortly after the dishwasher. That's the two of them combined sucking electrity. And the most draw I have witnessed so far. The water heater was the biggest yet. It will be interesting to record the dishwasher with the water heater off but it seems inevitable for the two of them to come on as a pair?

Is it time to research a new dishwasher? This old KitchenAid has a mechanical timer which I have already fixed twice. It was complicated and obviously not fixed correctly as far as the non heat dry. I don't want to go into it again if I can avoid. My exact model is a KitchenAid KDSM-21AC. I can't find that model at Energy Star. A US govt site and I am in Canada. The listed KitchenAid models (not sure of age, probably recent) all seem to be annual energy use 260 kWh (I wonder how they figure that out but I suppose it is standard methodology they use so that results are comparable?) and water use about 3-3.5 gallons per cycle except for one model which uses only 2. On the Canadian site (link below) all 557 dishwasher have a range of energy use from 136 to 325kWh so the KitchenAid are currently running in the middle of the pack.

I am guessing that my dishwasher is from the 90's. One of the pages of the product manual gives a date code of 1/87 (Jan 1987?). The label inside the dishwasher door gives the rating as 115 volts 13 amps or about 1500 watts (1.5kW).

Understanding my dishwasher energy signature
1) During the hour and a half at the beginning of the recording, not much is going on.
2) I start the dishwasher but cancel the cycle after a few minutes to make some changes, open and close the door and restart.
3) The dishwasher starts up again and almost imediately, the water heater kicks in. The combined load of the two applicances is 4.5kW.
4) The dishwasher is going through its cycles, the motor pumps and various things happen but the heater is not on. The water heater has shut off.
5) The final "spin" and the dishwasher heater/dryer comes on, in spite of my having it OFF! It uses 3kW.

(click on any picture to enlarge it) For the purposes of calculated the energy use of the dishwasher and water heater together, I drew three rectangles A, B and C.
A) is about 20 minutes of 4.2kW or (4.2 times .3 hour) or 1.4kWh
B) is about 30 minutes of 1.1kW or (1.1 times .5 hour) or 0.55kWh
C) is about 25 minutes of 3.2kW or (3.2 times .4 hour) or 1.28kWh

So the total used by the dishwasher and water heater during this cycle is 1.4+0.55+1.28 or 3.23 kWh. Off peak, the cost is 3.23x0.11 or 36 cents. ON PEAK, the cost would have been 3.23x0.54 or $1.74!

I am reading the data off the screen capture. I am surprised that the software does not do more of this calculation for me? I have asked McMaster.

Natural Resources Canada ratings for dishwashers

US Energy Star ratings for dishwashers

Thanks for your interest
George Plhak
Lion's Head, Ontario, Canada

INDEX to the series


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