Subject: Re: Active Thermal Mass

From: [email-masked] (Nick Pine)
Date: 24 Mar 1995 05:52:37 -0500

Tim Sheridan <[email-masked]> wrote:

>Hey there sun worshipers..

Hi Tim :-)

>I was wondering if anyone knows how effective it would be to run a 
>network of tubes under a home to use the top 10 or twenty feet of soil as 
>an active thermal mass..

It might work, but the heat would go downwards too, and perhaps sideways,
being washed away with underground water.
 
>Would this method allow a continous heat sink in the summer

Yes, and you can calculate how much heat you can sink, roughly.
Possible problems are that the ground heats up quickly (no enough
thermal mass and ground conductivity) and that the air-ground surface
area is not large enough for significant cooling (you can transfer
about 1 Btu/hour with a 1 degree temperature difference and 1 square
foot, at the air-soil interface.) Aa more cost effective way to cool a
house might be to use a window-sized fan and an airshaft to bring up cool
air from near a basement or crawl space floor to the top of the house
in the summer time...

>and a heat scorce in the winter without a lot of above ground mass?

I guess around here it would be about a 55 degree heat source. Same
heat transfer rate problems, base on contact area. Also one has to
beware of molds, mice, etc. Another way to make a heat source in the
winter is to put some water in the attic, somehow, which gets heated
by south-facing glazing below, and reverse the fan in the aforementioned
airshaft, to bring heat down from the top of the house in the winter.
Norman Saunders talks about this...
 
>Has anyone tried just sinking pipes 10 or 20 feet (down and back) say 
>every few feet..  Or would this provide enough surface area?

How many pipes? What diameter?

>Any good references on the conductance of such materials as top soil, PVC 
>and copper pipe?

You can try the ASHRAE Handbook of Fundamentals, available in large or
technical libraries. You will probably want to look into the heat
capacity of topsoil, too.

Nick