Ground Source Heat Pumps
From: Sherri Zann Rosenthal (
Date: Tue, 8 Apr 1997 01:16:05 -0500
Eno Commons is also planning to use the ground source (geothermal) heat
pump, for many of the reasons Merlin cited in his post. For us, doing away
with the noise of outdoor air conditioning units was probably the biggest
factor in favor of geothermal heat pumps. 

However, though I think they're neat, I do not think these are the greenest
things to ever hit the HVAC scene since sealed ducts. For one thing, they
use electricity. Line losses from electrical transmission result in some
loss of efficiency, when net inputs are considered. Total pollution created
depends in part on the mix of stuff used to create electricity in your

The best source I've seen to compare heating and cooling technologies is
the 1993 EPA report "Space Conditioning: the next frontier," EPA
#430-R-93-004. I called the EPA's 800 number and got one for free. It is
quite a tome, filled with charts showing regional results for best HVAC
systems in all sorts of scenarios, and exactly what pollution is produced
by each system. Although the summary sections really tout geothermal, my
conclusion from studying the charts is that an efficient gas furnace and AC
combination is less expensive than geothermal to install, not much more
costly to run, and is quite good on net pollution--except for carbon
dioxide, of which it produces quite a bit more. Interestingly, a member of
Eno Commons who does atmospheric modeling for the EPA says that the jury is
still out on how harmful carbon dioxide emissions are, or whether they
actually help crop and plant life. 

If so many folks didn't think they need air conditioning here in the south,
I'd have felt more strongly that efficient gas furnaces were a good option.
As it is, I'm happy and excited about our choice of geothermal. Final
thoughts: The electrical coops are not now members of the geothermal
consortium, so aren't offering the same incentives. If there's an electric
coop in your area, encourage them to join the consortium--and also the
photovoltaic working group formed by utilities, which the coops also have
not joined.

Sherri Zann Rosenthal
Eno Commons, Durham, NC  
Where most of the clearing and grading are done, and a third of the water
system is in. Tomorrow the sewer line construction starts. Only eight more
lots available, each one with its own charm.

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