Sunday, December 18, 2016

heat 2

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Last August, I was thinking about how my winter heating needs related to my electrical energy use. Whatever the source, requiring less heating requires less electricity in most cases (unless your primary heat comes from a wood stove perhaps?).

To require less heat, I blocked off the sun porch with a heavy curtain and closed the heating vents to isolate the that room from the rest of the house. Why heat a leaky room? The house has started forming icicles. I have some of the finest icicles in Lion's Head. But the icicles are not forming on the sun porch eaves! As you can see in this pic from a couple years ago, they hadn't formed by mid Jan 2015 either so we will have to see if I have reduced my heating requirement.

My faithful old (made in 1994) Brock furnace has been checked out thoroughly by two service techs, last year and this year. Oil furnaces must have a cleaning each season. Each tech showed me interesting things about the old monster and we've got it tuned up quite nicely and running well. I get about 85% efficiency out the flue but I remind myself that the chimney stack runs through wonderful heat storage (the old chimney masonry) so the flue gas warms up the house a bit more as it exits. I should measure the temperature of the flue gas at the chimney cap about 20 feet up from the furnace. I'll bet that most of the heat stays in the house. I'll call that the "free" exhaust heat ex-changer.

As I will show below, the oil furnace burns heating oil but it uses a fair bit of electricity, about 620 watts while it is running. About half of that electricity is doing useful work contributing to combustion, about 1/2 of the electricity is turned into heat through inefficiency and is "wasted". I remind myself that this waste heat helps to heat the house, so about 310 watts of the electricity is heat input which I need, the rest runs the two motors and the spark coil in the furnace which is also good.

Neither of the techs found my intermittent fault: the furnace tripping reset in the middle of the night for no apparent reason. I replaced the controller and photocell with new Honeywell parts from Amazon for $100 then followed the tests as described by Honeywell and shown to me by experienced furnace techs twice now. Good training on the web too like Steve Lavimoniere, one of my favorite burner techs on Youtube.

I am not recommending you work on your own furnace, not at all! But the more you know about your machines, the better decisions you'll make.

In my experience, both gentlemen seemed more interested in selling and installing a new high efficiency propane furnace than in solving my problem. I had to do that myself. I also fixed some rather sloppy wiring under the twist connectors at the controller. This is how one tech left the orange wire, the output of the controller to the compressor/fan/spark. The start up surge on this line is probably 8-10 Amps. He worked on the connector for several minutes. How long do you suppose this connection, with only a few strands of the wire, would last? Was he making a "time bomb"? I wonder.

I first looked at my furnace on the smart meter back in November. Now it is coming on regularly, about every 1/2 hour for about 20 minutes when the outside temperature is about -10C. It runs 24/7 at this temperature although the spacing between cycles and the run time will vary with the outside and what I tell it I want for the inside temperature (the setpoint).

This is clean recording of a single furnace cycle without anything else going on in the house.

During this test, the house base load is steady at about 80 watts. The furnace starts at 8:50 which both the burner compressor/fan and ignitor coming on. The house usage jumps to about 375 watts. Subttracting the base load gives a furnace draw of (375-80=) 305 watts. The furnace runs for about two minutes until the main furnace air mover fan comes on and the total load becomes about 700 watts. Again, subtracting the base load gives a peak draw for the furnace of (700-80=) 620 watts. Combustion stops when the thermostat reachs set point and the compressor and the spark stop operating. The total usage falls at about 8:58 to 500 watts or (500-80=) 420 watts. The furnace stops at 9:03.

Fairly clear by itself but when the furnace is seen on the smart meter with all the other things going on in the house, the picture is a little more confusing. This is the last few hours early morning at -9C outside. With the additions I have made to the chart, I can pick out consistent markers on the waveform to assign some measurements for the furnace.

When I view the furnace during one of the peak periods, when the other appliances are inhibited (off with timers), its signature becomes a lot clearer. The timers kick in on this pic at 7:00. I got up this morning at about 6:00. From 6:00 to 7:00, I am doing a load of laundry and doing things around the house and shop. Before 6 is the furnace with the refrigerator and freezer mixed in and a lower overnight set point, so it wasn't working as often. The outside and inside set point temperatures will have to be a part of the furnace data.

I would like to be able to build a chart of furnace cycle time versus temperature as I have done for the other major appliances (fridge, freezer and water heater).

I haven't shown you those yet - coming up.

I also talked about adding internal insulation in the form of a Mooney Wall. The idea is to reduce the thermal bridges in the wood by crossing the strapping at right angles to the rafters and studs. This pic shows my progress.

I was a bit concerned about double vapour barrier effects but I found some interesting reading about that here. I believe that since I am going to cover the wall with air and water vapor permeable tongue and groove wood strips there will be lots of gaps in the covering. If there is any condensation on the inside of the poly, it should be able to escape back into the room? I am doing the smaller of the two rooms upstairs as an experiment.

Thank you for your interest,

George Plhak
Lion's Head, Ontario, Canada

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Unknown said...

Great write up and interesting data you gathered. I also like your view of the latent chimney exhaust as a heat exchanger. Changed my view on my own similar configuration. I'm mainly writing to ask if you could share that hardware setup you've got with what appears to be EPS foam on your Mooney wall. Again, looking to do similar and have been looking for hardware solutions for attaching the EPS properly. Thank you!

George Plhak said...

Thank you for your comment. I am using deck screws and large washers to attach the foam to the rafters. Any sort of washer would probably work but the ones I found in the local home building store seem to be made for this purpose. They are stamped from sheet metal, about 1-1/4 inches in diameter, and have a dimple at the center hole so that the screw head does not protrude above the washer. They were available in bulk and were reasonable in cost. Search "insulation attachment washers" to see pics of all sorts available but I was lucky to find the one type I used locally.