On Oct 11, 3:31 pm, "Pete C." wrote:
Cindy Hamilton wrote:

On Oct 11, 6:26 am, "Pete C." wrote:
dpb wrote:

Pete C. wrote:
dpb wrote:
Pete C. wrote:
"Not@home" wrote:
...

My understanding is that heat pumps are more efficient, but need a
supplementary source of heat in areas where the winters are quite cold.
Air source heat pumps need supplemental (usually electric resistive)
heat in cold areas. Geothermal / ground source heat pumps don't since
their coils are below frost lines and soil temps are stable.
I'd revise that slightly as geothermal / ground source heat pumps _may_
not if sufficient heat source/sink capacity is available since
their coils are below frost lines and soil temps are relatively stable.

I'd revise that to "a geothermal heat pump with a correctly sized ground
loop" since in stable 55 or so degree soil a properly sized loop will
always be able to extract sufficient heat.

The point is that the 55F stable point is below the typical loop burial
depth as starters so the ground temperature around the loop will
rise/fall slightly w/ the seasons and it also isn't a perfect conductor.
Particularly when as a heat sink in the summer, temperatures near the
loop in the trench tend to rise.

When we installed the system in TN, it was the first buried ground loop
the installer had done (he had been working exclusively in a new
subdivision on a lake frontage area where loops were submerged in the
lake), so we instrumented the trench in several locations for the
information on how it differed as he was soon going to be in an area
that the distance to lakefront was going to make it impractical.

Even at 6-ft in a place no more extreme than E TN, the soil temperatures
were not constant.

--

As I said, "55 or so". The soil temp is certainly far more stable than
the air temp, and again, a properly sized and installed ground loop will
have no issues. The nice thing about the ground loop is that since it's
just plastic pipe and the trenching is an easy install method, you can
readily calculate the correct loop size and then add 25% as a safety
margin since an oversized loop doesn't cause any issues and only costs a
bit more tubing and trenching. When I do my system I intend to do just
this as well as increase the trench depth some, again with no risk of
causing any problems, only adding safety margin.

55? Good grief! The frost line hereabouts is nearly 4 feet deep. No
wonder
nobody talks about geothermal heat pumps around here. You'd have to
dig
halfway to China to find anything like stable 55.

They also do drilled vertical loop configurations which work just about
everywhere.

And in my 13 feet
of yellow
clay, that's no picnic, even for a trencher.

Trust me, your clay would be a picnic for some of the trenchers that are
available. Vermeer makes one that will cut something like 12" wide x 10'
deep trenches through solid granite. Not something you'll get at your
local rental yard, but they are becoming more common, particularly in
areas of the northeast that have lots of solid shallow rock

Considering that it's a long way down to solid anything around here,
I doubt there's much call for or availability of that kind of
equipment.

Well, I suppose geothermal is fine for those who are interested. I
just was
amazed about the stable 55 degrees recommendation. I'll stick to
forced-air
gas heat, hot water, and clothes drying. My electric bill is the same
year-round,
because what I spend on air-conditioning in the summer is matched
by what I spend heating the hot tub (outdoors, albeit well insulated)
in the
winter.

Cindy Hamilton