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Posted by Curbie on September 12, 2009, 8:03 pm


I finished translating this paper to spread-sheet two nights ago:

To me it's interesting but lacks a few critical components, it sort of
ignores thermal mass for one, the depletion of heating and the
saturation of cooling, and although useful as a informational aid, in
my view has very little value as a DIY tool.

I'm now translating a more complex and I believe more accurate paper,
which I started last night:


Thanks for the link, but most of those sites sell other people's
papers, and with a little searching I can usually find them, because
they where originally posted for free.

I'd like to raise a yellow flag on that site's implementation of that
idea, hopefully warning people about spending money on this plan, the
math is real twitchy leading to at least one inconsistent (but
important) notion (so far); the idea that a Ditch-Witch can dig the

I can't fit the pieces of this site's earth-tube cooling claims
together mathematically with a depth that is within the Ditch-Witch's
capabilities. I'll put some simplified math at the end of this post
for those that are interested in my claim.

I also looked at their wind-turbine plan and found equally twitchy
math there leading me to some real questions about the thoughtfulness
of that sites plans.

The DIY nature and cost of their earth-tube cooling plan is appealing
and some of the math is sound, but thermal math is complex and slow
going for me so I'm not ready to raise a red flag on them yet, but I'm
certainly having a hard time understanding how they claim thermal
engineering expertise and can't seem to handle simple slope and depth

I'm not saying that something like this idea won't work, but this site
seems to have enough twitchy math and ideas to really concern me about
using any of their plans directly.

For what it's worth.


My claim:
The site says that a "somewhat greater slope" than the 1 to 2" for
every 10' is required to keep condensation from pooling in the cooling
tubes and preventing harmful bacteria growth.

So, if for the sake of verification we use only a slightly "somewhat
greater slope" of 2.5-3" along with the longest tube run of 150' in
their parallel tube layout, the simplified math look like this:

150' / 10' * {2.5 or 3"} = ~{3 or 4'} of additional depth

Now this is the depth of the return of the longest pipe, it is in
addition to the 4' depth for the start of the run, and the starting 4'
depth plus an additional ~3 or 4' = ~7 or 8' and is well outside
Ditch-Witch's capabilities.

The Ditch-Witch's trench bottom will also follow surface contours
which seems a strange way for someone claiming engineering expertise
to advise digging a sloped trench.

Posted by harry on September 14, 2009, 5:25 pm



I never heard of a "ditch witch"   :-)   If you want a trench with a
constant fall the best thing to use is a laser.  And dig on an
overcast day.!
Start from the lowest end of the trench is best if possible.

Posted by Don T on September 14, 2009, 8:52 pm

 Ditch witches could only have been invented in a crazed and rotten society
that is America. The only way to finish a lengthy trench alive while dodging
all the flying, random, bullets is to mechanize the trenching tool. Get it
done fast. Fool.


Don Thompson

Stolen from Dan:  "Just thinking, besides, I watched 2 dogs mating once,
and that makes me an expert. "

There is nothing more frightening than active ignorance.

It is a worthy thing to fight for one's freedom;
it is another sight finer to fight for another man's.
~Mark Twain

Posted by vaughn on September 14, 2009, 9:42 pm

In another life, a much younger me walked several miles behind one of these
babies: http://www.ditchwitch.com/trenchers-plows/walk-behind/1230-trencher
Note that 36" is the maximum depth that it will trench to .

Also, here in the USA, to trench to the depths previously mentioned (8 feet
or possibly more), would require heavy equipment and steel safety sheeting.
Unless you have free access to such equipment, you are talking big money!


Posted by Curbie on September 15, 2009, 7:53 am


Agreed, a Ditch-Witch wouldn't cut it, the general concept I'm playing
with is a Down-hole Heat Exchanger (DHE) usually thought of in terms
of deep geo-thermal heaters. Off the top of my head, it seems from
cursory math that the horizontal ditching would be the main cost
factor, so a deviation of these ideas might be a grid of vertical
holes drilled down to a depth of 30' feet, which I think 20-30' is the
coolest strata of earth.

The concept I'm thinking about is a PCV pipe within a PCV pipe, the
outer much larger pipe (say 4" dia) would be filled with water and
heat exchange between the water in the pipe and the earth outside the
pipe would cool the water which would then be airlifted back to the
surface in the inner smaller pipe (say 1" dia) to a second air heat

The idea being that holes drilled to 30' is much easier on a DIY scale
than digging 8' trenches, although this concept runs right back into
the thermal mass and thermal lag questions which I haven't been able
to solve yet mathematically yet, so I have no clue how many pipes
would be needed or the spacing within the grid?

Just sort of thinking out loud.


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