more on time of use electricity

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My whole home energy monitor and software allows me to see what is essentially a strip chart recording of my home's electrical energy use. I can go back in time and zoom in for a couple of months, back to when it was installed. It is summer here so I don't need heat and I don't have air conditioning so my data is relatively simple. I am still learning the software by trying to isolate my appliances, essentially taking pictures of their usage on the chart while I run them.

McMaster tells me that the software is learning about me! It is supposed to provide individualized recommendations as shown in the demo at plotwatt. But I am told that it will take a month or two for it to learn about my usage. I am learning about my usage primarily using the BlueLine software from the maker of the hardware. More about the hardware later.

This is my electricity usage over the last 24 hours. I am showing you a screen capture from the BlueLine software. I have added the black info.

The W peaks are my water heater. How do I know this? I have learned to recognize the water heater from its peak and its timing. The water heater uses 3kW. The vertical axis of the chart at the left is labeled in kW. The water heater senses that its internal temperature has fallen to the set point (which I can vary on the heater) and switches on its heating coils about every six hours for about 10 minutes. If I use hot water, it may come on sooner. If I use a lot of hot water, it may run for longer. It is almost like a clock and it uses a lot of power so it stands out on the chart. Before I installed the inhibit timer, the water heater could end up starting during my peak period. The peak is the rectangle I have drawn on the chart. You can see that the water heater starts when it is allowed to, just after 6pm.

The D on the chart is my dishwasher. Unlike yesterday, I went to the breaker panel and turned off the water heater so that it could not start. Yesterday the water heater came on at the same time, I wanted to run another load of dishes to see the electrical use of the dishwasher alone. More about that test in a moment.

I have also labeled two mystery spikes as ? on the chart. One is during my peak time at about 4:30 and the other is earlier, about 10:30 in the morning. Both are big users but only for a very short time. The first spike is greater than 3kW and the second reaches 4.5kW. I don't think I was even at home when the first one occurred and possibly not when the second happened. I was in and out a fair bit yesterday.

The BlueLine software allows me to click and drag to zoom. When I zoom the second spike, the one during my peak period, I see a single data point that lasts only a minute. This is possibly because the sensor and the BlueLine system takes samples probably about every minute and only that one sample showed this 4.5kW. I have no idea what these are caused by but will continue to watch for them.

This is the dishwasher this morning after turning off the hot water heater breaker. It is a fairly complex looking signature to say the least. I will try to compute the kWh used for one wash cycle and add it below later. So perhaps the no heat dry function works sometimes, sometimes not (intermittent) or I was fooled in my guess about the no heat by the operation of the water heater or another appliance? The BlueLine measures everything connected to my meter. To be sure, I would repeat the exact test again. A good experiment needs careful design and measurement, sometimes repeated measurement..

It occurs to me that having this record of the actual energy use of the appliance will help to evaluate the performance of any replacement appliances. It is the actual energy rather than some computed or implied kwhr per year like on the sticker in the showroom or on the web ratings. The yearly total will depend on how often I use the machine but I cannot change the energy per cycle, per use. For example, if I get a new dishwasher with a more efficient motor or something else that saves energy, I should see the result in the chart.

Speaking of being fooled

The BlueLine sensor which is attached to my electric meter on the outside of the house includes a thermometer to read outside temperature. This is presumably so that the software can know how much heating or cooling might be required. The green line on this chart shows the temperature reaching 40C at about 4-5pm. It was hot that day but no way was it 40C (104F) outside! What is going on?

My electric meter is on the north side of my house, the side that almost never gets direct sunlight, or so I thought. At the red arrow you can see the sliver of sunlight that hits the meter from about 4 to 5pm in the afternoon at this time of year! Just at the time of year that cooling might be important, the sensor gets fooled by some stray sunlight. If it mattered to me, I would add a small screen or panel to block the light from that angle. It would only happen for a short part of the year.

It also occurs to me that today, Canada Day is a holiday so my electrical rates are non-peak all day. The water meter inhibit controller that I added earlier in the week knows about weekends, but it does not know about holidays. So today, being a Friday, my water heater is currently inhibited the same as the other week days, from 12 to 6pm. It doesn't concern me though. I know that the stored water in the tank stays very hot even for six hours after it has last been on.

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

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