My plastic tank have 1000L, was tested in the first start to 85C.
All 4 beer keg with 9 bar.
All works good, from 2013.
Pictures here
http://ecorenovator.org/forum/geothe...mp-backup.html
Now I work with 55C on tanktop and 50C on tankbottom, the Arduino controller start the heat pump just onece a day at 3PM when the outside temperature is maximal.
I instaled an external 24k AC unit with a 10mm copper coil 40m (I'm sure 30 is enough)
You can see some data here
https://personal.xively.com/feeds/899471984