I had an open loop geothermal system installed last spring at my home in South Jersey.  I'm not getting the efficiency out of the system that I had hoped.   There was no change in the electric bill during the summer cooling season as compared to the previous two summers.  Now we're well into the winter heating season and once again, no change in energy costs as compared to the previous two years.

I was told at the start of the project the distance between the source and return wells should be a minimum of 50 feet.  The well installer assured me he was specially trained in geothermal systems and that he had put in the wells for a good number of systems in our area.  After the electric bills came in showing there were no savings for both heating and cooling the house I went outside and measured the distance between the source and return wells.  The wells are just 37 feet apart.

Can anyone tell me what the minimum distance between the wells should be?  And if the distance between the wells is the problem, any suggestions on how to approach the well guy to rectify his error?

Thanks.

50 ft is thrown around a lot but you really need to take a look at the subsurface geology as some areas are going to require more and others less.  In South Jersey you may be O.K. if installed in an unconsolidated high-yield aquifer in the coastal plain physiographic province. 

To start, you first need to measure your Entering Water Temperature (EWT) and Leaving Water Temperature (LWT) with the unit running to see if the distance could be the problem.

-Adam
Hydrogeologist

Adam is right, water temperatures will tell if wells are too close.

How close do the temps need to be to determine the well distance as the problem?

In heating mode, your unit operates with the highest efficiency when it sees the highest entering water temperatures.  If the unit is operating properly with about 1.5 gpm/ton, then it may extract anywhere from 4 to 10 degrees F. 

Unaffected groundwater at depths of 30' or so in Southern New Jersey should be about 54 to 55 deg F. 

-Adam

Entering water temps will drop if well is too close.

The 50 foot number is a generalist number (as others have said). Without more information all anyone can do is make wild guesses. Groundwater flow is complex (I know, I deal with it routinely doing cleanups of contaminated groundwater). If you have a 1 ton system with a 1.5 gpm flow rate and a sandy aquifer 37 feet is more than enough. If you have a tight aquifer and a 10 ton unit or if the aquifer has short circuited then you may not have enough space.

What is the aquifer type (sand? clayeysand? silty sand? etc)
What is the hydraulic conductivity?
Is the return well the same depth as the withdrawal well?
How deep are the wells?
How thick is the aquifer?
Was a pump test done on either well? If yes, what is the radius of influence of the pump test?
What direction is the normal groundwater flow (i.e. did you put the withdrawal well downgradient of the return well?)
What is the annual groundwater flow rate (feet / day or feet / year)?

If you can provide some/all of the above information I can probably answer your question.


The real question is, what is the flow pattern and what is the radius of influence? What is the soil type and hydraulic conductivity? If you start pumping without returning water, how fast does the water level in the well drop? How large is your system and what is the flow rate?

If you think there is interference or short circuiting you could always just divert some of the return water to you lawn for irrigation purposes.