"Paul M. Eldridge" wrote:
On Sun, 11 May 2008 16:26:42 -0500, "Pete C."
wrote:
Ground source heat pumps take care of that problem for the most part.
Hi Pete,
That may be so, but when you compare the economic performance of a
high-efficiency air source heat pump to that of its geo-based
brethren, the former prevails nine times out of ten and ten times out
of ten if you apply the difference in their respective cost towards
measures that further reduce the home's space conditioning and DHW
requirements.
Admittedly, that's a pretty bold claim but I've run hundreds of
different scenarios using various heat loss factors, weather data,
utility charges, install costs, discount rates, etc. and in my
experience you have to push the assumptions to the far extremes before
you can reverse the results. That said, I'm more than willing to be
proven wrong if someone can provide me with hard data and I certainly
wouldn't object to sharing mine.
Cheers,
Paul
Are you comparing the labor intensive old style deep hole or large
trench array, or the newer much better and much less labor intensive
trenched vertical coil installation?
Hi Pete,
According to the IGSHPA, vertical closed loops are typically more
expensive than their horizontal equivalents, as quoted below.
"Horizontal installations are simpler, requiring lower-cost equipment.
However, they require longer lengths of pipe due to seasonal
variations in soil temperature and moisture content. Since a
horizontal heat exchanger is laid out in trenches, a larger area is
usually required than for a vertical system. Where land is limited,
vertical installations or a compact Slinky horizontal installation can
be ideal. If regional soil conditions include extensive hard rock, a
vertical installation may be the only available choice. Vertical
installations tend to be more expensive due to the increased cost of
drilling versus trenching, but since the heat exchanger is buried
deeper than with a horizontal system, vertical systems are usually
more efficient and can get by with less total pipe."
Source: http://www.igshpa.okstate.edu/geothermal/faq.htm
Are you referring to something other than what is described above and,
if so, can you point me to some online references?
FWIW, I was told by a HVAC contractor based in Moncton, New Brunswick
that a typical 3-ton GSHP installation (new construction) runs in the
range of $25,000.00 for horizontal closed loop and $30,000.00 for
vertical (CDN). Does that more or less jive with your figures?
Cheers,
Paul
Yes, something quite different than the two earlier techniques. I'm not
sure of references, but for the trenched vertical coil method you cut a
fairly narrow (~6" wide) trench something around 8' deep with a big
ditch witch and then take the plastic tubing coil and stretch it out
sideways so the coils of tube overlap at modest intervals and place the
coil in the trench. You then back fill and you're done. Far less labor
intensive then drilling holes or digging a big grid of trenches to put
single tube runs in. What they found was that the soil was such a good
thermal mass that you didn't need to cover nearly as much physical area.
This newer installation method takes perhaps 2 hrs to instal vs. all
day. Otherwise, it's the same tubing and same equipment, just a lot less
installation labor.