How important is it to run both heating and cooling over the year for system efficiency?

So I have heard anecdotally it's good to run the system in the summer to put heat back underground for the winter heating. I'm wondering how true this is? Are there any studies of GSHP efficiencies without running cooling in the summer? (I did a quick estimate and we only put about half as much heat into the ground in the summer as we pull out in the winter...)

I'm sort of wondering if you only use heating will the ground temperature around the well gradually drop more than the ambient ground can warm it back up...

 

short answer is "yes". reality is much more complex. It depends on lots of things such as what is your ground (dry soil, wet soil, dry rock, wet rock, or some combo), what is your natural ground temp vs the temp variation of the fluid in your loop, how long is your winter vs how long does the ground have to recover, are these vertical wells or horizontal wells, etc.

I can confirm that my vertical well design was affected by this situation and ended up larger because of the unbalanced loads - I'm in a heating climate and pull much more heat from the ground then I replace in the summer with cooling. Looplink RLC includes the unbalanced heat pull/push in their calcs (which is based on design equations promulgated by IGSHPA)

 

I find little carryover of heat from my systems (Verticle Bore) from summer cooling to winter heating. In my case the average ground temperature 20'-200' deep is 54F. My loop tempertures drop below that when heating season starts as soon as 2 weeks after cooling all summer. I am getting very little heat loading in the ground. I assume any heat loading dissipates quickly in my area during the shoulder season when time passes with very little run time.

Heat loading the ground depends on the geology of the ground, loopfield design and how much heat you are rejecting over time. It is usually not considered viable in residential applications.