Hi all!  First-time poster, but I've been lurking a few days, while pondering how to best design a passive solar house in a mixed humid climate.  I found this link, and it kinda turns around everything I've read about radiant and/or geothermal heat, and especially AC:  LINK

So what are the downfalls of this system?  Aside from being very simplistic, what am I not seeing?  Why is it not being used today?  Radon is a concern in my area, so how would that affect this system? 

I appreciate your input.

Actually it's a very old idea. If it was large enough and deep enough it would work. But it would need to be extremely large. Radon could certainly be an issue if it was not prevented from entering the heat exchange media. Water would exchange heat more efficiently than air and you wouldn't need to come up with a way of removing all that condensation from the underground pipes.

But the reason geothermal heat pumps are popular and this system is not is because of the huge size and expense needed to design a system without a heat pump. Now if you happen to have a large cave on your property.......

This guy seems to think it can be done cheaply ($1000 +/-), and relatively small. I did a little more digging around on his website, and he also suggests using an insulated and refilled sub-basement (as in basement under the basement), in new construction, as a source of free heat. He's actually got quite a few off-the-wall ideas, and sounds like somewhat of an eccentric genious. He's a nuclear physicist, so I'm not one to dismiss his ideas lightly. However it is curious that he has offered this information for 7 years, and only 9000 people have tried it.

Here are some interesting studies that provide installations and temperature monitoring, and also both seem to indicate some practical application. The also indicate about 1 ton of cooling for every 200' of pipe, which doesn't seem to be too far off of the recommendation for 450' of underground pipe application being sufficient for most residential applciations (perhaps a bit low, but houses are bigger now than they used to be). Please note that the studies are open-loop systems that have only been monitored for temperature changes and have not been monitored for humidity removal (as opposed to closed-loop with application for humidity removal, humidity removal may actually increase the BTU ratings a bit).

LINK

LINK

gregj,

The pipes are glued so I don't see radon as an issue. As far as the condensation, the concept of the sloping pipe forces the water to run down the pipe to a colection point. By using water in the pipes the water removal must be done inside the building and in a small space like a air handler. With the temp diff from ground to inside being so close, I'm not sure the water extraction would take place. The proposed system has it's draw backs though. It assumes the water is completely drained off. PVC pipe has good Hydrophrobrisik(sp) traits when new, the ability of a surface to shed water by water beads "rolling". But with a bit dust being pulled in from the home, the inside pipe surface would colect dirt. I'll bet mold and other stuff would grow quickly. In the first link, there a was testimonial from a guy in Austraila. He used some sort of clorine tablet to kill the fugus. That doesn't sound so good. In dry climates I could see this system working.

Patrick T.