Can you plant trees in geothermal well fields?

[Tanya Olson]

Does anyone have experience with planting in and around geothermal well fields (for heating and cooling)? Apparently multiple wells are drilled @ 400′ deep and stay 6′ below the surface. They are filled with water and have some lateral piping (4″ I think) to the building. Can I plant trees as long as they are not cottonwoods or willows? Do I look for trees with shallow root systems? Do I avoid planting anywhere near the wells?

I can’t find anything about it online.

Thanks in advance!

[Steve Mercer]

Most of those wells are lined with steel well casings I wouldn’t think it would be a problem if that were the case. You would have to check to make sure they were lined. Usually the wells are drilled and lined with steel well casings and then the water pipes are placed inside the well casings they have to run loops of pipe down into the well. They pump the water down in the well and either cool or heat the water depending on the time of the year and the water loops back up from the bottom of the well and is pumped back into the building in insulated lined pipes where the energy is transfered to the buildings HVAC system. The trees generally will not damage the pipes unless there is a water leak in the pipe. If the client has a water leak in this type of installation they have bigger issues than worrying about the damage from the trees.

s.

[Thomas J. Johnson]

I would give the wells plenty of room… tree roots will work their way into sewer lines and wreak havoc, I don’t know why geothermal wells would be any different. Do they require maintenance? Are there access issues? I’d ask the Geothermal contractor / consultant on the project.

[Lawrence Greene]

Before your plant selection, I would ask which type of Geothermal well is being installed. Is it a closed system or is it an open system.
Some of the open systems discharge water to the surface.

[Steve Mercer]

The reason tree roots work their way into sewer lines is because the sewer lines are leaking water. Especially the old style clay tiles. I would be intrested to know if anyone has had any of the same problems with the new style plastic sewer lines.

[Tanya Olson]

No – in fact our local well driller says that since he’s been using plastic pipe he has found no roots in and around any of his wells.

[Tanya Olson]

Closed system. The geothermal well consultant thinks maybe small trees planted between lateral lines would probably be ok. The laterals are 5′ deep and 15′ apart. I was hoping for large shade trees, but I would imagine their roots could easily be 5′ deep at 7′ from the trunk.
As far as maintenance, I don’t think they have to access any of the individual wells…thanks for your advice. I’m going to present all of the information to the client and see what they want to do. My feeling is that a flowering crabapple would work fine, but I sure would hate to be wrong!

[Thomas J. Johnson]

Here’s another idea Tanya… I don’t know if your project is commercial or residential. If it’s commercial, instead of pushing the limits of how close / deep you can get a tree to the lateral lines, why not emphasis their existence? You could plant small trees / large shrubs in the setback area and then plant a line of low shrubs/ground cover (something showy and distinctive) over the lateral geothermal lines. Maybe you could have a simple stepper path that runs parallel to the lines and design a small placard that says something to the effect of “This building is heated and cooled with geothermal wells that reduce energy consumption by 40%. You are standing over them right now.”

Then again, flowering crabapples would be lovely… One thought though: Do geothermal wells significantly effect the ground temperature enough to alter the cycles of flowering trees? Would a flowering crab think it’s June in February because it’s roots are warm? Would it attempt to flower but die because the weather isn’t what it thinks it is? I don’t know the answer myself but you see plants effected by micro-climates all the time. For example, this fall, I noticed the Euonymous in my Moms exposed front yard hard already dropped it’s leafs while the one closest to her house (warmer, protected) was just beginning to reach peak color. I wonder how warm soils would effect things…

[Tanya Olson]

Great point Thomas. We have a terrible problem with winter kill already because of the warm winter days followed by bitter cold. I don’t know how conductive the pipe is to the surrounding ground – I wouldn’t imagine it would be very conductive or the heat would all be lost before it gets to the building. It must some amount of heat loss because the drawings specify R2 insulation for any for any loopfield piping that passes within 5′ of any wall, structure or water pipe.
Thanks everyone for helping me think through this and with all of your suggestions. It has really helped. It makes my sole proprietorship seem a lot less ‘sole’. Thanks!

[Steve Mercer]

Well just remember especially with a Shade Tree it probably will only be a potential problem 40 or 50 years from now. If your client is in their mid-20’s they aren’t likely to be in the same house in 40 years, If your clients are in their late 40’s or early 50’s the root incursion won’t be a problem that they will be dealing with either.

s.

[Tanya Olson]

Ha! If only I didn’t live in such a small town….of course I’ll be in my 80’s by then too and they wouldn’t hunt down a little old lady would they???

[Steve Mercer]

Absolutely NOT! Unless you are taping in to geology where the earth’s crust is thin and hot water is close to the surface like in Yosemite. Most Geothermal wells are pumping water down into the well and the tapping into the constant ground temperature which is usually 50 degrees. That means in the summer you are pumping water that is hotter than 50 into the well and when it comes back up out of the well the water is 50 degrees. That water has to be in a thoroughly insulated pipe free of ground water or else you will lose to many BTUs and the system will be of no benefit to the HVAC system. If it is heating the ground around the pipe you are losing BTU’s that the HVac system could be using. I don’t know what part of the country you are installing this in but I would recommend installing the pipe from the building to the wells in Insuseal (http://www.insulseal.com/photos.html) or Flexsul-seal (http://www.flexsulseal.com/index.php) pipe.

s.

[Rob Halpern]

Tanya,

So if you could have any effect on root zone temperature, you’d want to keep it chilled in winter (ah mulch) rather than risk any warming

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