Pumping Heat -- Back and Forth

In January, I wrote about pumping heat from well-water to house which was finally in place, after I'd been talking about it for about twenty years. I did note one problem: the pumps for the compressors were less than 70 feet down in a 208-foot well, which meant that the water level dropped below the upper one when both pumps were running. After the weather moderated, Bagnall Electric came back and reinstalled their pumps on longer hoses, supposedly 10% up from the bottom. After that there was no problem running both compressors at once, and I test-run the oil burner one night per month through heating season, with PRI-D Complete Diesel Treatment supposedly increasing the life of the fuel oil in the tank because a tank will last several years that way. Maybe it will be okay; the idea is that if there's a long power outage in winter, then the (propane) backup generator can make enough electricity to run the oil burner and keep us from freezing for a few weeks.

It so happens that for more than twenty years I've been cooling this house, for part of each summer, by running whole-house fans in the night and closing up during the day, amusing my wife by opening and shutting doors and windows to make air-paths so that everything gets cooled off. Last year that didn't work quite as well because one of the fans went away and the attic into which they had vented was sealed with foam insulation, but it still sort of worked: even last night with a series of thunderstorms, I could open some windows so that air flowed, well, mainly into the east porch, through the sitting room and living room to the kitchen and then dining room and up the back stairs and into the remaining fan and up into the attic and down the new pull-down ladder and out through the window of an unused bedroom. And that worked, except when the bedroom was not unused, or when the night wasn't cool enough, or simply because my thirteen-year-old insists on her right to take a shower in the afternoon and often a bath as well, which heated things up.

Now it doesn't matter. One compressor gets heat from the well-water and does almost all of the work of providing her hot water. Part of the heat naturally goes into the air. The other compressor receives the heat from the air and puts it back into the well-water. It's not free, but it is less electricity (water-heating plus that part of the air-cooling) than the water-heating alone would have been in previous years. Recycling!

Or maybe not.

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.