permaculture

["Laurence Gaffney" <lgaffney@bigpond.com>]

Having recently installed an "Earth Tube" I have investigated this issue a 
bit.
The Earth Tube I have installed is to provide cooling to only a fresh produce 
storage cupboard so is quite  different to what you want to do. Mine is a 
minimalist (not much to lose) project whereas yours will require  a very 
significant capital outlay if it is to be successful. Design cost may 
outweigh implementation cost.

The following link provides balanced (but very basic) information I think. 

http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12460

The approach has been used successfully & repeatedly in cooling piggeries so 
suggest your research include this angle.

In my view there has not been enough successful projects of this type to date 
to enable development of rules of thumb which one can use with any 
confidence. . 

So its probably back to first principles which will require design, design & 
more design preferably by an engineer experienced/practising in this area of 
thermodynamics.

You will need to know basic stuff like knowing the temperature profile of 
your ground at specific depth over the year.
 
I have seen quite detailed engineering design guides/information for these 
devices so keep googleing.

Laurence Gaffney
Australia