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.

--