Re: Geothermal
From: Dahako (
Date: Mon, 9 Mar 1998 12:23:43 -0600
Hi - 

Eno Commons Cohousing in Durham, NC, is going with ground source heat pumps -
commonly called geothermal heating and cooling.  A heat pump extracts energy
from one location and moves it to another using the same technology as your
refrigerator (which is, after all, a heat pump itself).  The regular heat
pumps used for homes exchange energy between air outside the home and air
inside the home.  So, on a cold day, your pump may be trying to get heat from
the 15 degree (F) air outside.  On a hot day, it may be trying to cool your
house when the temperature outside is over 90 degrees.  The greater the
differential, the less efficient and effective the system will be.

A ground source heat pump takes advantage of the relatively stable ground
temperatures - here in NC, the ground four to six feet down is just under 60
degrees all the time.   So, the heat pump (which is inside, up in the attic)
is working with a temperature differential that is rarely more than fifteen
degrees.  The resulting decrease in power usage is pretty neat.  The EPA Green
Star program site has a study done of this kind of system - they recommend
them for almost everywhere in the US.

Our systems at Eno Commons are "Cadillacs".  They include a scrolling
compressor for slowly ramping on and off - with the result that they are very
quiet and can maintain house temperature within one degree either way of the
setting.  They also include a "desuperheater" that routes all excess heat into
the water heater.  For a household of four, I gather we will get about 50
percent of our water heated off the heat pump's excess.  Also, this type of
heat pump, in the winter,  kicks out air closer to human body temperature than
standard pumps, so you can stand over the ducts to shake off a chill, just as
you can with a forced air gas furnace system.

I think I remember that the upfront cost of the system added just under $2000
per home.  With the extremely low energy bills projected by our power company
(about $27 average monthly for the smaller design and about $37 for the larger
design), in our very energy efficient homes, the initial investment will pay
back in around 8 years.  Way before the mortgage.  

Other trade offs we considered:  *we couldn't afford to bring a natural gas
line in for our stoves if we chose not to use gas for everything (furnace,
dryers, stoves); *the nice quiet indoor geothermal unit means no noisy air
conditioners sitting out in the yards. 

Our subcontractor is Waterfurnace.  If you email me directly with your ground
mail address, I think I can dig up a geothermal brochure to give you.

Jessie Handforth Kome
Eno Commons Cohousing
Where the first home is under construction (framing is scheduled this week)
and several more are ready to launch.  We still have six more lots available
and waiting for some good neighbors to join us.  Total prices for cleared lot,
new passive solar home home and share of the commons run from the low $130's
to the mid $170's depending on lot and home size.

Results generated by Tiger Technologies Web hosting using MHonArc.