Healthy soil and sustainable growing

[bennett@frognet.net]

> technique can relate to sustainable growing.  In a nutshell:  it's about
> healthy soil and sustainable growing, and not including commercial self
> promotions in general.
>
  Okay, I'll try this topic out.  If it's "off", then I'm sorry and
moderators can delete.  How's that? :-)
  I'm planning to build a greenhouse; well, actually two of them.  One
will be freestanding 25x48 (have had the hoops for years, so...) the
other will be more of an attached, enclosed 8x16 porch on our house.
  We live in zone 6.  Winter temps sometimes get to 20 deg. below zero
(nighttime) in Jan., but are just as likely to be 50 deg. in the
daytime.  (Like much of the country, we've had some real strange weather
the last few years.)  I don't necessarily want WARM greenhouses, but at
least the one attached to the house, we don't want to freeze.   We'll
use as much solar thermal gain as we can for both greenhouses.  We will
also probably use some composting and livestock sheltering for heat in
the free-standing gh.
  Summertime here for the past 15 - 20 yrs. has meant at least one month
of near drought conditions with temps. in the 90s and above.  It's also
quite humid in the summer.  We're located between hills so don't get as
much breeze as we'd like.
  The challenge:  We need to cool the ghs in the summertime, especially
the one attached to the house.  Traditional electric air-conditioning is
cost prohibitive.  Our weather is too humid for swamp-coolers.   I'm
sort of thinking a geothermal system might be do-able and make sense. 
What do you all think?
  Would just running plastic pipe in a serpintine manner down 3 ft. or so
underground and blowing hot air in and the (hopefully) coold air out
work?  Would the pipe need to be perforated to allow any condensate to
escape?  Would regular squirrel-cage furnace blowers be sufficient to
blow through such piping?
  Comments please.
D.