Existential Angst wrote:
Awl --

PBS's World Focus had a little ditty on Denmark energy efficiency -- $15
per YEAR heating bills! Holy ****....

ROI on these systems seems to be about 10 years, whose initial cost is about
10% of the house value -- which was either $60,000 or 10% of 60,000 -- heh,
just a zero....

But inyway, one method was a heat pump/AC that uses buried coils (3 feet
underground) as the heat exchanger. I don't know if it's a formal heat pump
as in a minisplit ($15 wouldn't go very far, even with inverter technology),
or if the underground is just a passive equalizing heat resevoir, with water
as the transfer medium.

If I ever get a heat pump I've always thought it would be good to use
the normal air cooled condensor with the last few yards of heat
exchanger/pipe underground to cool it below the air temperature. The
water from the evaporator would flow to the underground heat exchanger
to help keep that effective.


Rainwater is collected in underground tanks, as well, for less critical
water usage.


A hundred or so years ago we had cisterns that stored rain water
underground. It's not anything new. We just got lazy.