Posted by Curbie on September 9, 2009, 7:59 am
I was digging around on the net to find any information earth
temperature at depth for my root cellar when I backed into this site.
I almost skipped it because of its title "Free Home Air Conditioning"
but scanned the page (long and rambling) for any useful information
and scam tags ("give me your money"), and found some interesting
information and no scam tags (I think).
The general idea is to lay out and bury a parallel set of 4" PVC-DWV
thin-wall drain/sewer pipe (ASTM D-3034) at a depth of ~6' with an
equal spacing of 6'. This is a closed loop system where the tubes
slope away from the house for heat exchange on the out-bound half of
the loop, and sloped towards the on the in-bound half of the loop. The
idea here being the between the slope and the air flow the condensate
will be pushed along the pipe back to a common sump at the house where
the condensate can be pumped out of the loop to prevent bacteria
Each tube is said to have about 75 CFM of air flow capacity with their
basic 9 tube system design delivers a claimed 36,000 Btu/hr
performance at 700 CFM of air flow, if I read this properly, the claim
is for 3 tons summer cooling and 36,000 Btu/hr for winter heat
supplement from the same system.
I googled "mb-soft.com/solar/saving" scam and that turned up nothing.
Has anyone had experience with this system or has any of the math
I'm trying to piece together a spread-sheet from the information out
Posted by Ken Maltby on September 9, 2009, 8:39 am
The 55F figure has been around a long time. Here is
a Google result that seems to match a lot that I have
read in years past.:
Not sure that they don't have an agenda or commercial
interest, but the basic idea matches what I've heard.
Posted by harry on September 10, 2009, 5:59 pm
Yes, I have one in my house that I installed myself. Because it
doesn't turn out masses of ice cold air it's hard to say what
difference it makes in Summer but it's certainly a few degrees colder
than the air going in.. Mine has forced air circulation and is
primarily for heating in Winter. The problem is with installing one
is that there is no data for pipe sizes & spacing as you have found
One problem not mentioned in your description is rain and water
draining througn the ground. You really need a sheet plastic barrier
"umbrella" to stop rainwater from leeching away your stored heat. ie
buried above the pipe matrix.
It would take a lot of instrumentation I don't have to quantify how
well it works.
I don't believe my system is optimal, I think I got the airways too
My system is an insulated concrete block with copper pipes embedded. I
have two fans, one on suck and the other on blow. There is a
differential thermostat switches them on/off.
I did consider the 4" pipes buried in the ground but it seemed to me
that heat stored would leak away if there was no insulation.
The concrete block is part of the retaining wall in my earth shielded
There's lots of stuff here. More than when I installed mine.
Posted by Curbie on September 11, 2009, 4:03 am
It seems there is a bunch of different design parameters for this
concept and its design is highly math dependant. Designs can be open
or closed loop and optimized for summer cooling, winter heating, or
best case for both.
I chased down the math last night, two versions one 1990 and a 200?
version, read through the versions which seem to have both fluid and
thermal dynamic components, the older one looks less squirrelly, so
I'll start there.
In fishing around for people with experience with this concept I got
feedback ranging from "it works, OK" to "it works great" with the
difference seeming to be how much engineering went into the design.
On Thu, 10 Sep 2009 10:59:48 -0700 (PDT), harry
Posted by harry on September 12, 2009, 5:50 pm
I only had it running for one Winter so far . I consider it to be for
heating, there being little use for A/C here in the UK. Unless global
warming picks up in a big way that is.
I think my pipes are too small for the mass of concrete. I probably
wouldn't do it the same way if I was starting again. It really needs
some permanent instrumentation. I can only guess what's happening in
there at the moment.
I can monitor air temp going in and coming out but I have no means of
measuring the air speed to workout how much energy is being stored/