Doug wrote:

On Wed, 10 Oct 2007 23:31:20 GMT, "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.

Aye, there's the rub.

Here in Connecticut where the frost line in mid-winter can easily get
down 40 to 48 inches, to get to that 55 degree point means burying
everything down at least 6 to 8 ft. That's pretty costly and sometimes
impossible here in New England with its bedrock and rocky soil.
While digging just 48 inches, the code required footing depth, I've
had to have 6 foot diameter boulders pulled out on a regular basis.
The old joke about farming in New England was that farmers mainly grew
stones...

CT is where I'm originally from and I've done plenty of trenching there
myself. You just have to bring in the correct equipment to do the job.
With the trenched vertical coil installation you don't need a wide
trench so you can bring in one of the Vermeer monsters for a day and
have your deep trench in no time since they have machines that will
trench through granite if needed. Not a cheap machine, but when you only
need it for a day...


A public school near me thought they'd install a ground source heat
pump to replace their oil fired boilers. They eventually gave up on
the idea when they discovered that the installation costs were
something like 5 times the cost of a conventional boiler replacement
and a payback time of 15 to 20 years.

A school i.e. commercial building vs. residence isn't a real good
comparison.


They'd be better off simply putting the money in the bank.

Air to Air heat pumps around here are pretty much useless, at least in
terms of cost savings. As my building inspector said bluntly "they
aren't worth a damn in New England".

Exactly, which is why geothermal heat pumps are necessary there and most
other places for the much greater efficiency due to the much more stable
source/sink temperature.


The two electric utility companies that serve most of CT have raised
their rates 25 to 40% in just the last 12 months. Thus any alternative
is now much better than electric heating or hot water making.

The best alternative is a lot more insulation. Also, I thought electric
generation / delivery had been unbundled in CT like most other areas, so
you have multiple supplier choices.