Greetings, I had a new system installed in late fall and was wondering if it is possible to run out of heat from the ground loop. I am located in Manitoba Canada and it can get very cold here. Currently -30c. System is a 4 ton waterfurance versatech 1800' of 3/4 pipe. 3- 300' trenches at 8' deep 100' of 1.25" from heat to loop header (50' out and 50' return. currently the entering water temp is 2c and leaving water temp is -2c. Should I be concerned the ground temp is already so low? I am having no problems keeping the house at my desired temps just a fear that I will be making permafrost out in my loop. I am freeze protected to -20c with my loop fluid. (methanol water mix). Any thoughts?

Yes, it's not unheard of to be "under looped". On the other hand, you may find that it stabilizes just below 0C entering (due to the latent heat of freezing).

It does seem to be holding at about 0c entering and -5c leaving currently. There is a terrible cold snap here currently with daytime highs of -27c and lows of -33c at night and it is having no problems at all keeping the house warm. I understand I am maybe a little small on my loop at 1800' for the 4 ton but I also don't feel I am running anywhere near the full capacity of the 4 ton as my run times are 30-40 mins out of 1 hour. Would it have made a difference if the system had been installed in the spring so I would have had all summer to put heat into the ground before I started removing it for winter or would the amount of heat absorbed into the ground not really play a roll in the winter heat cycle?

Both settling of dirt around a new loop and heating of the ground with summer AC have some effect. I wouldn't want to guess how much.

Looks like that unit has a lower limit of -1.1C EWT. I expect that you are going to have a problem staying above that.

I was pretty sure the freeze alarm was set at 15f but you're saying it will have trouble operating below the -1.1c?

As long as you have good flow, the EWT should not be the problem.

You delta T of 5 degree C indicates that the flow is a bit on the low side, you are pushing all the flow for a 4 ton unit through 3 parallel loops, 4 or 5 parallel loops would be better. Also your heat pump is a commercial unit, any reason for that? Not the most efficient one out there either. The lower limit is not -1.1F, but low temp, low flow, and not the best quality unit might getting the limit closer to you.

But usually -3 to -4C EWT don't bother me too much, you seem to be well above it.

Well it’s almost 2 months later and still holding at 0 ewt. The reason for the commercial unit was cost, I got a price I couldn’t refuse. This winter compared to last has proven so far to be using about half the kw as last year on electric furnace. I should save about 1000 dollars this winter in heating costs so as long as I have no component failures I will be payed for in 10 years (fingers crossed)

If your loop is still at 0 degree celsius, it means it is adequately sized and performing well. Enjoy your geo system. Your geo unit should run with a 300-350 % efficiency over an electric furnace, this winter seems to be colder than last year....

Only when the ground loop is less than 0C does the capacity start to fade. It's a "magic number"/

Ground water above 0C has a specific heat of ~4.2 joules per gram per degree-C of temperature drop, but at 0C liquid water has a nice 334 joules per gram heat of fusion to overcome to turn it into 0C ice.

But once frozen the ice has a specific heat of only 2 joules/gram per degree-C, so it gets colder faster, with only about half the thermal mass to draw from than when it is in a liquid state

The specific heat other components of the soil don't change very much with temperature- they aren't undergoing the phase change that gives the ground moisture the very high apparent-mass at 0C.

Great explanation about latent heat, I knew about it in btu of 144 btu from water to ice but never really thought about it in this application. Thanks