How many people have data on closed loop incoming temps (either bore or horizontal) for a ten year period. Is anyone seeing degradation of EWT over this time?

Probably not many on this forum.

There is a classic 74 page doc out there by McQuay that claims multiyear degradation on the order of 1 degree per year in the case of gigantic (100s of bores) commercial borefields when seasonal heating and cooling loads are out of balance. That seems plausible to me, depending on aquifer effects.

I very much doubt there would be measurable year-on-year degradations in the case of isolated single family residential systems.

This is my opinion, not supported by data or experience.

For residential systems, we are in the 3rd year of monitoring. Our climate is heat dominated (90%, Buffalo, NY). We are 0.2 degrees warmer in the EWT then last year at the end of August, so we cannot measure any degradation.

Probably not many on this forum.

There is a classic 74 page doc out there by McQuay that claims multiyear degradation on the order of 1 degree per year in the case of gigantic (100s of bores) commercial borefields when seasonal heating and cooling loads are out of balance. That seems plausible to me, depending on aquifer effects.

Thanks. It is particularly the unbalanced loads that interest me. We are in south central Alberta and due to down slope off the hills to the west we have very little need for air conditioning. I know of several installs (large) were they are adding another boiler every couple of years. As the units seemed to work the first year or two, I am assuming degradation is the cause. I don't have access to the actual data at this time as one of the Engineers that was involved has withdrawn due to conflict with the supplier. Also have seen some spec's that call for enough power to run the compressors that the home could be heated electrically and be cheaper!

For residential systems, we are in the 3rd year of monitoring. Our climate is heat dominated (90%, Buffalo, NY). We are 0.2 degrees warmer in the EWT then last year at the end of August, so we cannot measure any degradation.

It will be interesting to see if this is just start up and it stabilizes or if it climbs exponentially (each year would it need to take a little bit more cold out of the bore?). If over the next ten years it climbed 2 or 3 or 5 degrees, would it defeat your original calculations? See previous. My concerns are for the opposite of yours as we are cold dominate.

The graphs I have seen showed a pretty linear change over 10+ years. Note that this is for deep boreholes not influenced by ground water. Anything else should not be effected much.

In properly designed systems, one with a horizontal closed loop and one with a vertical closed loop, would it be correct to say that EWT degradation (if any) of the horizontal loop may be less than the EWT degradation (if any) of the vertical loop since surface temperatures over time may help mitigate the effect on the horizontal loop since it is closer to the surface (with everything else being equal)? I'm trying to be politically correct with the "if any" notes since this topic is debated. :-)

I would agree with you geome

Posted By FBBP on 31 Aug 2010 12:40 AM

For residential systems, we are in the 3rd year of monitoring. Our climate is heat dominated (90%, Buffalo, NY). We are 0.2 degrees warmer in the EWT then last year at the end of August, so we cannot measure any degradation.

It will be interesting to see if this is just start up and it stabilizes or if it climbs exponentially (each year would it need to take a little bit more cold out of the bore?). If over the next ten years it climbed 2 or 3 or 5 degrees, would it defeat your original calculations? See previous. My concerns are for the opposite of yours as we are cold dominate.

Bore hole spacing and ground conductivity would play a huge role  in this.   Some commercial loop design programs will model the loop for 10, 15 and 20 years.  This would allow enough loop to be installed up front to insure long term use.

I hope any long term change in loop performance will not be a big issue since I want to get the 200 year estimated life out of our HDPE loop, and just replace geothermal units when necessary. I better start exercising. Bloody Mary's count as a vegetable, right?

After a while every ground loop should reach its equilibrium. If you just extract heat, like most do in Europe, without A/C mode, you can compensate for it with more loop. If I remember correctly, borehole depth is almost twice as much for that reason reason is rock with the same conductivity. I remember that issue came up at an IGSHPA training course, and Dr. Bose and I ran the numbers. It was a german or a swiss guy who developed the algorithm. The result was that you compensate with loop length, we ran it out for 99 years. Yes, horizontal fields recharge better, within one months of shutting off the system in the spring the ground loop is back to 50 degrees, which is the average ground temperature. Next year we have 2 years of data logged, I will post it here.

Guys I greatly enjoyed this thread. I've been very interested in energy storage, especially when it concerns geothermal or borefield energy storage. There doesn't seem to be much data out there on this topic. This is a little off topic, but one very interesting site I found was on Drake's Landing. It is a "mostly" solar heated community in a heating dominated, climate (Alberta, CA).

http://www.dlsc.ca/

The central aspect of the community heating system is the borefield, basically just a much larger version of what some closed loop people have for their individual homes (less the solar chargers, tanks, etc.)

I wonder if its possible to show that for every case as a source loop or borefiled temperature drops due to the connected heat load, the rate at which heat from the surrounding ground moves into the source loop will go up. So assuming the load stays the same as the loop temperature drops at some point it will stabailize depending on connecated load, ground conductivity/composition, and flowrate.

Another question I had is how do you know when "charging a loop" with solar collectors or other waste heat source makes sense? As the loop/borefield temperature increases in the summer the heat lose to soil/rock surrounding the loop and borefield will go up. At some point the heat lose will be equal to the heat input from the source (solar cells or other). At that point the net effect is an energy loss due to pumping power (assuming it is not a passive system).

Just a thought.

-Joel









Geothermal energy storage... is a very interesting topic to me and I have spent lots of time reading anything I could fine