Chris Lewis wrote:

According to Duane Bozarth :
If that happened at all frequently, that would indicate the loop is
either too small or not deep enough. In Canada, of course, the ground
cooling is much more significant than it was in TN where I was or in MD
where OP of the thread is.

Ottawa will be slightly worse than MD, but probably not by that much.

Being "that type of guy" , and one of the
first non-lake-loop installations the local fellow did, we put
thermocouples on the loop piping at the intermediate- and
bottom-of-trench levels at the inlet and the outlet ends and monitored
them for a couple of years. IIRC, the bottom of the trench was ~6 ft
and didn't change but about 7F from mean during the year. The mid-level
was more like 12-15F. These are a long time ago, but I think that was
pretty close...

As a FYI: I don't think they do horizontal loops here. For each ton
of heating, they drill a 100' deep 3" diameter vertical hole. IIRC,
they were 10' apart minimum. As it was explained, at peak loading,
you might "lose" a small amount of available operating time due to
freezing the ground.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

I gather that it's not too hard to dig there...in TN that would be
bedrock and pretty expensive drilling...but I'd agree the deeper the
better...as noted, at the time I put in the system in TN, the only local
installer was almsot exclusively working in a development on Tellico
Lake and using the "loop in lake" ploy...