[bigsmile]

Thanks for the reply, and for the invitation to join. I also believe that when it comes to heating and cooling, GSHP should be the way to go. But the current situation is that the high cost spoiled the whole thing for most people. I really hope that something will be done in the future to bring the price down. But for the moment, I can't resist being drawn to thinking about DIY. What I have in mind is direct exchange setup. It's efficient and also it requires smaller ground loop. The only thing seems to be certain technical difficulties, such as the oil return issue.

If that's the case, I came upon a masters thesis on dx system, in which it is stated that as long as the wells are shallow (20' or so) and the velocity of the refrigerant fast enough, oil return isn't an issue. Does this sounds correct to you?

In your other post, you mentioned the patents on dx system. I guess it may be a good idea for me to read some of the patents. Actually I have came upon a couple of such patents during my random search, but the issue is that the website I read didn't have figures. Just reading the text didn't give me very clear idea. Does the site you mentioned (about patents) have figures?

BTW this is really a great thread. I've spent some effort searching about GSHP, this is the one single most informative result I've found so far.