Geo Thermal Well Tempature

[mtlogcabin]

QA multiple geo thermal well system is being proposed for the hospital expansion. The wells will be locatednear the existing potable city well site. The public works people are concerned with the water temps of the discharge wells and if it may raise the aquifer temps in a small area (500 ft radius) thus affecting the current treatment of the city water supply. Any links or info I could pass on to them would be greatly appreciated

 

[steveray]

I know we had some concerns that were addressed by our department of public health as far as contamination and clearances to storm and potable and sewer piping, but I have never heard of the temperature concern...only have a bit of planning/ design input experience in my former town, they were looking to convert town hall to a geo system...

Seems like a valid ? there must be an answer somewhere...

 

[Dr. J]

This is a somewhat legit request. However, if properly designed (if) the impact is minimal. A proper design needs to limit the seasonal thermal field temperature change for HVAC purposes, regardless of groundwater impacts.

I don't think a generic link would help you much. This is highly dependant on local conditions - total BTU's rejected to the field, thermal capacity of the specific soil condition, depth of the field, water permeability of the formation the field is in, flowrate through the aquifer, etc.

Now, you did say "discharge well". Is this really a "once though" system - sucking water out of the aquifer, then injecting that water (either colder or hotter) back into the aquifer? This is totally different than a typical closed loop ground coupled system. That opens a whole 'nother can of worms, not the least of which is polluting the groundwater with whatever may be coming out of the building.

You are an AHJ, right - make the designer come up with this.

 

[Alias]

There are two geothermal wells here - one on the middle school and the other on the high school grounds. What I can tell you is that the one at the middle school cannot be used without a reinjection well being drilled due to the arsenic/etc. levels in the well. The high school well does not have this problem and is piped into the city stormwater system where it then discharges into the river.

That's all I know about the subject. I do know that the high school has been heated with geothermal long before it turned into a 'green thing'.

I do agree with Dr. J that the designer should be responsible for the details. If there are questions, invite him/her to do a presentation at a public meeting.

Sue, where the west still lives....................

 

[Min&Max]

I have a much smaller system than what you are identifying but---I have a closed loop system, four wells, comes in at 47 degrees and leaves at 49 degrees. Regardless of the type of system I doudt the tempatures vary much. It has been a while since it was installed but I think the installer indicated the variation of entering and exiting the HVAC unit should not vary much more than 3 degrees.