Pumping Heat

For about twenty years, I've been talking about someday having geothermal heat instead of the oil I was burning in the basement. A few years ago, we (Peter Darby as contractor, and I as customer) applied for the appropriate permit for an open loop system and the Village of Hamilton declared a moratorium on well-drilling in the village. After they debugged the new permit process on us, we went ahead, and a week ago we started the heat pumps. Day before yesterday the household hot water started coming through a preheater (fed by the heat pump's desuperheater).

Well, the temperature yesterday at 7PM was 9F, and this morning at 7AM it was -15F. (My wire-through-the-wall thermometer didn't believe that, but the three thermometers that are not in contact with the house did. So I guess I do.) In that time range, the old oil furnace was on three times, for a total of 2.1 hours, meaning that the heat pump couldn't cope and the sitting-room temperature was dropping well below its target of 69F. Usually the target is 65, but I don't think it made much difference.

Actually we have two heat pumps, each of which will extract 9 to 10F from 12 gallons per minute from our well (one gallon weighs 8.34 pounds, so one degree-gpm is 60*8.34=500 BTUs/hr, so this is about 54K BTUs/hr for one heat pump, plus the waste heat of compression and circulation, total about 70K BTUs/hr.). Unfortunately we can only run one heat pump at a time for now; the pumps are about 75 feet down in a 208-foot pipe, and more than 14 gpm evidently brings the water level down below them. When the weather moderates, we'll pull the pumps and put them down deeper, so this probably won't happen. In fact the burner started again at 10:30AM, with outside thermometers 7F in bright sun; one of the timers on the system said that the thermostat had been requesting the second heat pump for 84 minutes at that time.

Overnight, the heat pumps more or less alternated. I generated a time-lapse movie of the readouts with an ASUS 901's webcam under Ubuntu running

vlc -I dummy v4l2:// -V image --image-out-width 450 --image-out-height 338 --image-out-ratio 288 --run-time 129600 --image-out-prefix img vlc://quit 2>/dev/null

This collects the images, about one every minute and a half, and then I put them into a movie with

mencoder mf://*.png -mf w=450:h=338:fps=4:type=png -ovc lavc -lavcopts vcodec=mjpeg -oac copy -o output.avi

I got this from How to create a time lapse video with Ubuntu at Code Blip and googled to find hints for a couple of error messages; the main thing was to change the vcodec but I did have to say

ln -sv /usr/share/fonts/truetype/ttf*a/Vera.ttf ~/.mplayer/subfont.ttf

(I don't remember where I got that one.)

It works well enough, and I see that last night the left heat pump turned on at 7:43PM, the right turned on this morning at 7:40AM, and in between we saw

Left+	Left-	Right+	Right-	on	off
7:43P	8:36			53	37
9:13	12:54A			221	16
		1:12	2:21	69	13
		2:35	2:58	23	25
		3:23	4:58	95	17
5:15	7:22			127	18

That's a total of 588 minutes on and 126 off: only 82% on, even while it was asking the burner for two hours of help. When the thermostat calls on the boiler, the heat pump keeps going; in fact the heat pump is just trying to bring a storage tank to temperature, and then it's up to circulators to get that heat through the new highly-insulated carriage house and the old re-insulated house, both of which are pretty large.

It works! Future oil usage will be pretty low.

Or then again, maybe not.