Slashdot Mirror
Tapping the Earth For Home Heating and Cooling
suraj.sun recommends a CNet post giving details of a still little-known energy technology: the ground source heat pump or geo-exchange system. This is distinct from so-called geothermal energy, which taps the heat in the earth to provide energy. Geo-exchange is suitable in scale for small industry — the article describes one commercial re-development of an old mill into apartment and commercial space that put in a geo-exchange at about half the cost of traditional fossil fuel-based alternatives. Even some individual homeowners are opting for this green method of heating and cooling, at a premium in price of about 50 percent (but costs are very much per-project, largely because drilling is involved). "Rather than use underground heat, geothermal heat pumps attached to buildings capitalize on the steady temperature of the ground or deep water wells. In effect, they treat the Earth like a giant energy savings bank, depositing or withdrawing heat depending on the time of year. "
Its been around since at least the 1940s. The building I live in (downtown Austin) uses it and it was built in 1938.
I bought a house in Minnesota (cold winters, hot summers) that was a part of a pilot program in the 80s by Northern States Power (now Xcel Energy), whereby the installation cost was subsidized by NSP for this home and a handful of others.
Upon learning about this from the previous owners, I was naturally concerned about the system's efficacy at heating and moreover cooling the split-level home as compared to traditional gas furnace and air conditioning. It wound up performing identically on both counts, providing as much heated or frosty air as desired seasonally, all for only the price of operating the heat pump; I believe the annual electric cost was roughly $80/year.
To top things off the house was furnished with a traditional gas furnace as a safety backup.
Side note to the OP, the phrase "geothermal" to most homeowners does mean ground-source heat pump technology, not the stuff they use in Greenland.
I have a modest 2000sqft home in northeastern PA (Poconos area, I'm 8 miles south of Camelback ski resort). I had two contractors out to quote ground-source DX (direct exchange) systems, and both quotes were in the mid-$20k range. Too rich for my blood.
I went with a Hallowell cold-weather heat pump for pleasantly less than half that. The Hallowell is mostly sold in Canada and upper New England, but it's been slowly working its way south. When I called them to ask about my application, the guy laughed and said "Man, you're in the tropics!"
It's only been running for a few weeks now, but I've been very impressed so far. It hit -3F two nights ago and the heat pump still ran entirely off the first compressors in stage 1 (stage 2 was still not needed). The air coming out of the vents was warm to the touch. In fact, the system has yet to resort to resistance heat down to -3F exterior temperatures. We keep our house set to 66F. I've been able to kick the heating oil furnace and storage tank to the curb. No more timing oil pre-buys against market prices, no more noisy power venters, no more oil storage tank taking up basement space, no more yearly burner tuneups and vent pipe cleanouts. I even get nice 18 SEER air conditioning to replace my builder-grade central air conditioning unit.
Pictures of the complete home renovation are at:
my house renovation
The entire system is on a dedicated subpanel, and I've put a subpanel meter on it to measure total kWh usage. This will allow me to directly measure operational cost each month.
Another factor that steered me away from ground-source is balancing the break-even time versus the system lifetime. If it takes me 20 years to break even on the ground-source and the system needs replaced not too long after, I haven't really gained anything. If the Hallowell takes me 7 years to break even and the system lasts 2-3 times longer than that, I've saved quite a bit of money. Break-even isn't everything; it has to be balanced against the expected lifetime of the system. Plus, I'd have to factor in the cost of repairing the yard after the loops were dug and installed. They claim that just a 3' circle of ground is disturbed to drill the loops, but one of the guys eventually admitted the machines rip up the yard pretty bad as they drive around the hole to drill the loops at different angles.
I found the guys at Hallowell to be very helpful to talk to. I don't work for them and I have nothing to gain. I simply speak as a satisfied customer. For new construction, rolling a ground-source system into the mortgage would be the way to go. For my existing construction with an established yard, simply setting the Hallowell on an outdoor pad was an excellent path forward for me.
- Chris