GETTING WARMED UP

As a rule of thumb, electrical devices designed to generate heat are power hogs—simply because significant thermal energy tends to cost a lot of Joules. Two exceptions in our house are a heating pad and a heated mattress pad: targeted, small-scale heat.

Heating pad (initial long pulse, becoming choppy thermostatic cycling), followed by a space heater run for a little over three minutes.

The plot above shows a heating pad turned on (at minute 7), staying on for about half-an-hour. In this time, the pad averaged 30 W (48 W when on). A heating pad on your lap, in your chair, or for your feet can eliminate the discomfort of sitting/working in a cold environment. Compare this to a space heater, seen in the latter part of the plot, running for just over three minutes. Despite running for only about one-tenth as long, the space heater accounts for 85% of the above-baseline power expenditure pictured here (84 Wh for the space heater vs. 15 Wh for the heating pad). We also see from this example the stability of the TED data: the baseline is flat, and the top of the space heater pulse is pretty flat also, showing very little fractional wavering (and what wavering there is may just as likely be attributed to actual variation in the heater).

Mattress pad heater (also barely visible around 19:00 in the 24 hour plot above). The heater was turned on one click at minute 16, then advanced another click every five minutes starting around minute 36. The pad automatically comes on full-scale for the first four minutes to pre-charge the thermal mass.

The mattress pad, like the heating pad, is about as modest as it gets when it comes to energy for heating. The pad we have has dual controls for each side of the bed, and this test represents only one side. The maximum scale is 30 W per side, with five equal steps of about 6 W. Now that the vertical scale only extends to about 70 W, we can see the TED measurement dithering at the 1 W level. In this case, I evaluated the baseline to be at 38.5 W, and the test consumed 10.7 Wh above baseline activity.

GARAGE DOOR OPENER

This one will make appearances in some of the forthcoming examples, so let’s get it out of the way.

Opening and closing of the garage door, showing also the light (a compact fluorescent) staying on for about five minutes each time.

Raising the door required 1299 J, or 0.36 Wh, while the light (staying on for 290 seconds) consumed 4263 J (1.18 Wh), so that the light accounts for more than three-quarters of the total expenditure. Imagine what an incandescent would do! On the way down, the closing action required 951 J. All together, the opening and closing cost 2.95 Wh—even when the light was allowed to stay on. It is often easy to turn off the light manually, so why not make it a habit? One lesson from these small numbers: opening and closing the garage door is not a serious energy concern.

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