Saturday, May 06, 2017

heat 3

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(click graph to enlarge)

It has been interesting to record how hard my furnace works as the outside temperature changes. The points are observations of the running time of the furnace and how often it comes on taken first thing in the morning from my smart meter compared to the outside temperature. The process takes about the same time as a morning cup of coffee to record one point. The graph fills in as I add more points but I can already clearly see the trend (the line).

I divide the run time by the time between cycles to get a fraction (and then a percentage) which I've called the Duty Cycle. This is how much of the time the furnace runs. The colder it gets outside, the more the furnace runs, using electricity and oil in my case to generate heat for the house.

As an example, here is the smart meter graph from this morning with some measurements I have made from the graph.

Being overnight, the only things going on in the house electrically (other than the base load) are the furnace (the peaks that I have put dimensions on), the refrigerator and the freezer. The fridge and freezer are the "choppiness" in the graph. They use much less electricity than the furnace.

I can pick them out with difficulty but I don't need to since I am only interested in when the furnace is running. The water heater is also "running" but it does not appear in this section of chart because it cycles over a much longer time (six to twelve hours) so it does not show up in this time period from about 1:30am to 6am. So the furnace is relatively easy to measure.

The dimension lines I add to a screen capture with a drafting tool (CorelDraw). The dimensions are cm which I convert to time by noting the length of an hour on the graph bottom scale. The top set of numbers is the furnace run time, the middle set is the time between runs (the cycle time) and the bottom number I use to convert centimeters to time.

Here is the calculation for this morning's data point at 4 degrees C. The spreadsheet is here.

Since I don't have smart meter data from last year I can't compare historically like I could with degree days. Next year I should be able to see the effect of improvements to insulation for example. When I get a new, more efficient furnace I should be able to see a difference in this chart.

"You can't manage what you don't measure" - Peter Drucker

Thanks for your interest.

George Plhak
Lion's Head, Ontario, Canada

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