Sunday, July 03, 2016

more TOU and dishwasher continued

INDEX to the series

I am doing another run of the dishwasher this morning. The dishwasher and appliances like it (my clothes washer for example) have complicated cycles with several stages. The appliance will draw different amounts of energy depending on the program it is following. This is my software real time monitor showing me that at the beginning of the normal-no-heat cycle, when the dishwasher is heating the water, the my house is drawing 1.7kW.

The actual electricity the dishwasher is using is about 300 watts less than this since there are other "always on" things that use electricity in my house right now. The fridge and freezer are the biggest parts of the background. There are a few lights on and the computer I am typing on, a few charges, some CO2 and smoke detectors, the garage door openers a few radios that even though they are off still draw some "keep awake" power as well the network and the Blueline Innovations whole hose energy monitor itself. The background varies constantly from about 150watts to 300watts. I almost started the toaster oven but stopped since it is a big energy user. I am running this test of the dishwasher and want it to be uncomplicated by other heavy use appliances. The dishwasher is almost done.

The dial on the right in the screen shot shows my total usage for the month. Since it is the beginning of July, that dial has just reset. Briefly it was near zero but now marches forward through the billing month. It does not show peak/off-peak but I can see that elsewhere in the software.

This is the remote readout from Blueline. The pic is taken just a minute or so after the previous one. That's the dishwasher in the background. I suppose the idea of the remote is that you can carry it with you while you are trying out an appliance in another room? There are apps but I haven't loaded one yet.
The bottom part of the display shows me the outside temperature and the date and time? That part is not correct. I don't know yet what the 333kWh "estimate" is yet. I guess I'll have to read the manual? I don't know what the buttons do. Clearly I haven't explored the functionality of the remote.

Another part of the Blueline energy monitor is this sensor unit strapped to my electrical meter. A technician came and installed the meter and set up the software but I suppose it could be DIY. I see that the Blueline hardware is available on amazon.ca for C$110.

Now as far as Time of Use relates to the dishwasher, it is very clear to me that I should be running the dishwasher during off-peak. I am not sure I am going to change my behavior as a result of having this power monitor?

This is this morning's recording of the dishwasher (D) and water heater (W). I have also shown what I consider the background at the left side of the chart.

In an earlier run, I found that the water heater started shortly after the dishwasher. This time, I had resolved to turn off the water heater so that it would not start after the dishwasher. I turned off the water heater at the bereaker panel shortly before 6am. Then I started the dishwasher at shortly after 6am. When I got back the the software, I saw that the water heater had already started and had been running for about 10 minutes before I turned it off.

As I pointed out before, the water heater starts if its internal temperature sensor detects that the water is below the set point. The dishwasher draws hot water and the water heater replaces that with cold water from the water supply. The new water is much cooler than the tank and causes the internal temperature to fall triggering the sensor to call for heat.

It is just a coincidence that my water heater, without any hot water having been drawn from it, chose to come on at about 5:20. Funny thing about a water heater is that unless you have one of these whole house meters, you cannot tell that it is running!

Note that the peaks from the water heater are simple ON-OFF shapes while the dishwasher has a rather more complicated signature. I don't know what the small addition square on top of the second water heater peak is? That might be the fridge or the freezer, which are normally buried in the background, becoming visible on top of the water heater.

Now I am going to calculate the total electrical energy used by the dishwasher during this run. To do that, I have divided the area under the curve into a number of blocks. Knowing that the height of the blocks represents the power (kW) and the width represents the time (h) I should be able to multiply the height times the width of each to find the kWh of wach block then add them up and have the total kWh.

I am having the read the data off a screen capture. I am amazed that the software does not do this for me. It does not even know that this is the dishwasher. Well perhaps Plotwatt will one day figure it out but not yet, so I am calculating the hard way. I will use the millimeter measure of 21.24mm = 1 hour to find the width of each block by comparison using the CorelDraw dimension feature.

Here is the calculations for the blocks:
A 1.4x0.202=0.283kWh
B 0.8x0.056=0.045kWh
C 1.4x0.135=0.189kWh
D 0.25x0.095=0.024kWh
E 0.8x0.083=0.066kWh
(there is a little space
F 0.8x0.036=0.029kWh
G 1.4x0.115=0.161kWh
H 0.25x0.109=0.027kWh
I 0.8x0.78=0.63kWh
Total = 1.454 kWh

This does not include the energy used to heat the water in the water heater, the water that was used during this run. That energy is included in the water heater draw, at least for this run.

So 1.454kWh would cost me during the peak-period (1.454kWh x C$0.54/kWh) = $0.78. During non-peak, my cost would be (1.454 x C$0.11) = $0.16!

A lot of calculation and thinking to show me that the dishwasher does not cost much if run off peak. I don't use it very often, although I did run it three times in three days to get a relatively clean signature. I hope I will be able to use my figure to compare to new dishwashers? I don't think they give the cost per run but per year.

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











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