Wednesday, August 10, 2016

the old water heater

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This is a picture of my utility electric use last night from my smart meter. I was preparing to measure the refrigerator again after superinsulating but the night wasn't cool enough for a comparison to the previous measurement. So I'll tell you about my water heater instead. (click any pic to enlarge)

Last night, everything was OFF but the refrigerator, the water heater and the baseline load. I turned OFF the chest freezer for the night since its signature looks so much like the refrigerator that it makes it difficult to take detailed readings from the graph. I just turned it back ON. It stays frozen solid at least six hours since I don't open the lid. I check the temperature inside periodically to make sure.

On the picture, I can see the clear signature of the water heater, that big square spike at 1am. The water heater uses 3kW which is a lot. It always uses 3kW but the time it stays ON varies. It goes ON for a shorter time if I do not use hot water. About every six hours or so for a few minutes. I hadn't used any hot water since the last time it came on so this energy is not from my use of hot water, but just to keep it hot and ready. Yes there are on-demand water heaters, mine is not.

A water heater has a very distinctive spike energy signature. If I multiply the width of the spike times the height, I can see the energy it is using very, very accurately, every minute. Mathematically, my energy use is the AREA under the curve.

The energy to keep the water hot depends primarily on my temperature set point and my hot water use. Energy also varies with the temperature around the appliance and the amount of insulation it has. I'll zoom in on the water heater graph in a moment.

The marching square wave down at the bottom is the refrigerator. It is like a backwards water heater I suppose, with the same kind of control system. It used to be called bang-bang meaning that it was either ON or OFF, nothing in between. An insulated box that gets cold instead of hot and keeps it that way using a standby amount of electricity by going ON and OFF until you use it by opening a tap or opening a door. Then it uses more energy by staying ON for longer before going OFF. Like the refrigerator and the freezer, the amount of energy can vary with the temperature around it. An air conditioner would also be a bang-bang energy load. I don't have one of those. It is also called "duty cycle" control. The English used to have a cute term "mark-space-ratio". It is also called "hysteresis control". Whatever the name, control is accomplished by ON-OFF-ON-OFF and that is how it looks in the smart meter data, like a square wave that varies in width (time ON). This type of control is very common in appliances and has been around since Edison. It is actually quite efficient.

Because these appliances make nice clean signatures it is possible for me to pick them out by eye on the graph when several of them are added together. This is what my computer should be doing for me. I am having to do it myself but learning in the process and telling you about it.

Some of my other appliances don't look at all like a simple bang-bang. The dishwasher and clothes washer have complicated signatures as the various motors, heaters and relays inside go ON and OFF. Little bang-bangs on their own but they add up to a complicated mess as far as the appliance signature. The messy signature is something I can recognize as the dishwasher but it is not so easy to calculate the area under the curve since it is so irregular.

It should also be possible to add up the amount of energy each appliance uses and keep track of it. With what I have, it would be too tedious for me to do manually on an ongoing basis. For some reason, I am not being provided with the appliance level data by the study. It's a behavioral study. They want to see what I do? Hmmm.

What I am doing is taking advantage of the summer to study my appliance energy characteristics using this new data from my smart meter that I could not see before. I expect that the summer will be easier to understand since I won't have the furnace and other winter loads messing up the measurements. I will put my appliances in a list from highest to lowest use, studying their signatures and taking some detailed measurements while noting the test conditions, like the temperature. That way when I make changes I can have some careful measurements to compare to.

All my appliances will need to be replaced at some point. All are over 20 years old. I would personally like to quantify any improvements I can make before I go blowing large wads of cash on new machines.

Overall, if I can reduce the energy use of the main appliances and keep some of them from coming ON during my peak rate period where I can, I should see a real reduction in the energy portion of my bill.

One of the first things I did was to install a timer on my water heater to cut off power to it during my peak rate period. I have since done the same for my refrigerator and chest freezer. These appliances now do not come on during my peak period. Essentially I am trying to almost leave the grid during my peak.

The Blueline hardware and software which reads my smart meter is a pretty impressive tool and I hear that is about to be improved with a browser and mobile update. What's also becoming apparent is that add-on tools (like Plotwatt) which pick out the appliance level data are value added products that I (we) should expect to pay for as a service. I haven't found one as freeware. No idea of the cost. I can access my raw data but its pretty boring. I will need some tool to disaggregate my data.

Back to that water heater. This is my old water heater. A new one is beside it and ready to be installed.

The outside temperature at the Blueline sensor was 18C at 1am last night. I can read this from another part of the Blueline software. I will take the outside temperature to be the same as the temperature in my basement. This won't work in the winter when the basement temperature will be cooler but not as cold as outside at the meter. I'll have to take a reading of the basement temperature then if I want comparable the standby energy readings. I will have the new water heater in place by then hopefully. I won't get to test this one again so I want a good reading of it's standby energy use for comparison.

I have added two dimensions to the graph. I want to know how long the water heater was ON fairly accurately. I could use a ruler but I am using a graphics program, CorelDraw. The 2.45cm dimension is the length of time that the water heater was ON. The 5.13cm length is the distance from 12.50 (ten minutes to 1am) to 1:15 or 25 minutes. So the water heater was on for 2.45/5.13x25= 11.94 minutes or 0.199 of an hour. Energy is measured in kilowatt-hours so I want hours, not minutes.

I can also see, thanks to the Blueline software, the energy use exactly at any point on the graph by moving my cursor along the graph line. The box that pops up shows me that the energy use at the instant shown by the blue dot is 3.135KW. I am going to subtract a little bit for the baseline and the refrigerator that looks like it has come on within a minute or two of the water heater so I am going to ignore that part. I will take the water heater as 3kW which is it's nameplate rating also.

So the energy used by my water heater during that spike is (3kWx0.199hour=) 0.597kWH or just over half a kilowatt hour. During my off peak, this amount of energy costs me ($0.11x0.597=) $0.065 (six and a half cents) but during my peak rate period, this same energy would cost me ($0.54x0.597=) $0.32 (thirty two cents). This is for one heating cycle, normally the water heater would come on about every six hours. There is a pretty good chance that at least two cycles will occur during my peak, two during my off peak, if I had not added the timer.

By having all the water heater limited to off peak, I figure that I am saving almost $350 per year on my study special billing rates, more than enough justification for a $20 timer. Your payback won't be anywhere near that but I'll bet that you will find savings if you look at your water heater. Some are easier to do than others but the timer should be a no-brainer unless you use a LOT of hot water, and then there may be even better ways to save.

I don't think I posed my rate structure but I talked about it, 11 cents off peak, 54 cents on peak and my peak time is different. I do not pay delivery and other charges for the duration of this study. For me, it is all about timing - stay off the peak!

You will notice of course that my peak/non-peak differential is different from yours but then I am on this study for a year. They gave me a special incentive (a very punishing peak rate) and all this data. They want to see what I will do? I feel like a rat in a maze sometimes. It truly is not easy to SEE where your electricity goes, even when you can see it in a graph.

Do look at the disaggregation article. I think that watching this market develop is going to be interesting.


I mentioned the temperature set point on the water heater. The fridge and the freezer have them as well. For the moment I am leaving the set points as they are. The subject of set points will have to be another discussion. Safety obviously is a key issue.

Thank you for your interest.

George Plhak
Lion's Head, Ontario, Canada

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