Im a hvac tech very into the subject but have a few questions on a direct/refrigerent source with ground temps around 50-60 degrees how do you have enough head pressure for the txv to operate properly . considering you cant charge or run an ac system with a txv when the outdoor ambiant is below 65 and piston 60. and acording to advanced geothermal (my comp of choice) no special indoor equip is needed. second and third is there a valid reason the are not using 410A / inverters/ or 2 stage compressor with these systems I know is overkill and the ac side there are more eff systems that use these above gound . is it just they dont want to price themselves out of the market or are there enginering isues . sorry for the spelling and run on sentices im just a nuckle dragger

Advanced Geothermal, somehow must be connected with Earthlinked DX geothermal. How I don't know. How ever I would go directly to the Earthlinked Site and look at the link I have post. Earthlinked has patented technique, in how it controls refrigerant.. Amazing I would say. and Simple!

http://www.earthlinked.com/residential/how-it-works

* Active Charge Control
* Liquid Flow Control

I don't know Advanced geothermal, but EarthLinked doesn't use a TXV at all.

Jack H is right. The engineering of the EarthLinked system's refrigerant controls makes charging the system and ground loop selection basically FOOL-PROOF. It makes your concern of temps. a non-issue.

As for the 2 stage compressors and R-410a... They don't use 2 stage compressors because of the engineering done in the system that has to maintain refrigerant velocities both for oil return and not pooling the refrigerant in the ground. R-22 is a better, more efficient refrigerant. R-410a runs on higher pressures, and hasn't been perfected yet. For those who don't want to use R-22, you can simply use R-407c.

If they dont use a txv what is there expansion device advanced geothermal say we can use any one on the market and Iknow it works because I have seen it I just want to know the science . do the use automated expansion devices on any known systems which in my mind would resolve the appaiirnt nonissue but i dont like those (one more thing to fail)

Please visit the site JackH referred to. It explains how it works.

The metering device is a sort of a liquid float, but modified. It really is genius. There's absolutely no need for any kind of TXV.