This is a very interesting paper to read for those of you interested in how the construction of a borehole field affects GSHP performance.

Key introductory points:

Bore hole fields are planned for decades.
 
Energy extraction or injection, even only for seasonal use, may introduce a growing thermal anomaly in the ground.
 
The thermal reach of individual boreholes may interfere with each other.
 
In practical applications, 5 m separation distance is recommended for avoiding substantial interference between boreholes.
 
While thermal interaction amongst two nearby boreholes may be acceptable, interference will be more significant in arrays of multiple boreholes. To the point that some don't perform hardly at all and thus don't need to be drilled (and improve the project's economics).

See:

http://www.linkedin.com/red...cking_anet

Hope you find this interesting / fascinating!

Best regards,

Bill

Reading this article prompted me to go look at how my borehole field is performing, 7 years after installation.

Here's a chart that shows Entering Water Temp clearly a function of near term heat removal from the structure or heat injection into the structure. The chart covers the time period between when I installed my Web Energy Logger (WEL) (2008) and now. The chart shows no long term borehole heating / cooling.

http://www.welserver.com/cgi-bin/pl...vgHEHR.png   

And here's one more chart that shows that heat removal/injection from/to the structure is mostly dependent on weather conditions (as you would expect for a residential structure - no plant lighting going on inside). This one stops at the end of 2014 because it shows averages for full years.

http://www.welserver.com/cgi-bin/pl...Yearly.png  

It was interesting to read the concepts expressed in the paper, and look at actual data to help understand the concepts.

Best regards,

Bill

Your measurement is the difference between theory and practice. Add ground water flow and other factors and everything goes out of the window. Also the memory effect is larger in larger commercial loop fields, especially in the south with cooling dominant loads.

"Also the memory effect is larger in larger commercial loop fields, especially in the south with cooling dominant loads. "

Also the North with large cooling dominated loads.
Unfortunately like anything else GIGO abounds in large loop field design where some are tanked by not having enough space or loops to reject all the btus collected in a building and some are tanked with the stupid first notion of staying within a degree or two of deep ground temperature (thus tanking first cost and any hope for a reasonable ROI).

Most residential boreholes can be spaced further apart (like 20+ feet) to reduce possible problems with interference or non-straight holes.

Most residential boreholes can be spaced further apart (like 20+ feet) to reduce possible problems with interference or non-straight holes.

that really applies to all boreholes (resi or commercial).