My system was installed in 2010 and works great; I' very happy with it. Lat winter I started to monitor the incoming water temperature and was surprised to see that (at the end of the heating season) the water temp and therefore the ground temp had dropped by 12 degrees. Monitoring summer temperatures showed the temp rose by 8 or 9 degrees. Everything I read about GSHP before install talked about using the "constant" temperature of the ground as a heat exchanger for the system so I assumed that the loops would be designed to return the water at or near the ambient temperature of the underlying rock. It seems that with the water temp dropping 10 degrees the system has to do more work to get heat out of the water and therefore is not as efficient at the end of the season as it is at the beginning. Would it have been more prudent to install additional loop footage? I live in Wake County in North Carolina and am using a Climate Master 27, 3 ton capacity and have two closed loop vertical bores, 270 deep and about a 100' run from the bore holes to the foundation wall. The bore holes were back-filled with bentonite grout. That gives me a total of 1,280' of loop.
Loop temp swing back and forth with the seasons. Remember, you are extracting heat out of the ground all winter long and rejecting heat into the ground all summer. The amount of heat extracted, or rejected, is higher than the surrounding soil can move it so the temps at the loop field increases in the summer and cools in the winter. Bergy
As above, temperature swing is expected. Usually design is based somewhere around a minimum incoming temperature of 30F (in winter) and a maximum incoming temperature of 90F (in summer).
Thank you, I've got that. What I wanted to know is if the amount of loop had been greater would that have significantly reduced the swings in ground temperature; for example if we had bored an additional 270' hole , increasing the amount of loop by 50%. Of course there would have been an additional cost but I'm wondering if in the long run the cost would have been justified.
Unlikely. Ive dealt with conventional guys that spec warmer ewt's and it tripled the borefield on a commercial job. No payback in that.
If your ground loop only dropped by 12 degrees, your loop is oversized already by most standards. One more borehole might have shaved 2-3 degrees off of the swing. The payback would have happened 8 0r 9 generations from now
Higher entering water temp necessarily raises efficiency but often can't win the cost v benefit battle. An installer in NY state boasts using systems with no antifreeze. I shudder to think how much first cost he adds to his systems and how many he has scared away from geo.
Thats crazy. You would have to keep the water temp pretty high so it dosent freeze in the heat pump exchanger. I work with w2w chillers and we have to add 30% glycol to keep the 40deg process water from turning the exchanger into a ice maker.
What fun. Let us all remember that the target moves as the machines work and the ground and conditioned space changes. Any data collected is only a screen shot of what is going on. Hi Joe, Hi Andy. Mark
"Thats crazy. You would have to keep the water temp pretty high so it dosent freeze in the heat pump exchanger." Yes but it is done routinely in cooling dominated states where little heating is required and the loops are sized for serious cooling load. All heat pumps have freeze protection that is field set for open or closed loop systems (15F or ~38F). The individual does this in vertical systems meaning the extra loopage is at a real premium. Pay back non existant.
Back when we did closed loops none had antifreeze. No auxiliary heat strips, either. Then again our "winter" in Jacksonville, Fla runs from around Christmas until the state of the union address sends a blast of warm air down I-95 from DC sometime in early February. Grossly oversizing closed loops, aside from the first cost, eventually additional pumping power will eclipse any compressor efficiency gains.
