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southerntester 11-05-2007 02:14 PM

Geothermal loop pump size?
I am getting ready to start a DIY geothermal project and I want to double check something with you guys here.

My system will be closed loop horizontal with SDR11 3/4" pipe. There will be 6 loops of 500' each for a total of 3000' plus my 40' of 1 1/4" header. I will have a mixture of 25% Dowfrost(glycol) to 75% water. As far as the ft/head, there will be basically no difference in vertical level as my pipes will exit via my basement walls. I want to size my circulation pump correctly. My system has a 2 stage compressor and at full load the capacity is 5.5 tons. Figuring for 3.0gpm per ton I need about 16.5 gpm. What size pump is recommended? I am looking at the Grundfos U26-99f. This might be a little oversized but I want to be certain.

Any thoughts or suggestions would be appreciated. ST.

#CARRIERMAN 11-05-2007 05:54 PM

Hi southerntester

You got kind of a loaded question there. Here is the skinny on the pump systems. You are going with closed loop in your post. However there are true closed loop and there is what some call closed loop that actually uses a pump center with a resivoir. If you are going with a true closed loop the pumps can be sized more for the actual maximum needed gpm. Let me explain. In a true closed loop system you have less resistance because the system is under about 40 psi of pressure and a constant volume control without having to overcome the effects of the atmosphere. This is the method I most prefer because you have less likely hood of outside contamination and very little water loss. If you use a flow center you will want to upsize the flow requirements by about 25% due to atmoshpere changes. The changes that most effect this are thermal. On this type of set up vescosity changes are more prone, this is why I reccomend upsizing the pumps. Not everyone agrees with me on this, but I have never had any call backs in the middle of winter or summer using this method. I promise you that you will thank me if you follow my advice. As far as the rest of it, the heat pump has a flow regulator built into it that runs off of the head pressure of the compressor. Just make sure you do not scrimp on the loops, and do not use the slinky loop design. This is not the best way to do a loop.

Good luck

southerntester 11-05-2007 08:02 PM

Thanks for the reply Carrierman, I really appreciate it.

I am going to use an actual closed loop with an expansion tank but no reservior. My groundloop will actually be oversized a little as I will have 3000ft in the ground and I really don't need that much.

Thanks, ST.

Jasing 05-23-2009 08:52 PM

I used a QT Flow Center
I have a 2.5 ton Mcquay geothermal heat pump with a horizontal closed loop installed, the pump is a nonpressurized QT flow center, it was very simple the unit purges itself, I purchased my complete geothermal heat pump kit from , they were very helpful!

Hop this helps!

dennis.hurst 09-12-2009 09:23 PM


I'm thinking of using the 5 ton version of the Mcquay from Ingramswaterandair, how did your project go? Do you like the system? How is it performing? I'm looking for references before I take such a big jump.

koolkris 10-31-2009 11:13 PM


I was thinking of getting a system from Ingramswaterandair as well, how much cost was your system above the kit from ingrams? also what kind of savings do you gain?

Yoyizit 11-01-2009 11:13 AM

Pump equation
EFF = GPM(HD)/40(HP)
Efficiency is typ. 60% but is sometimes shown on the pump curve
HD is in feet.

Pipe loss example
Cold water in plastic pipe,
ID = 0.5", 4.8 GPM, 5 ft/sec, 8.8 psi drop per 100'

Titans73 12-30-2009 09:43 AM

Geothermal greenhouse
I have built a geothermal greenhouse in an effort to grow a very delicate plant that loves a cool root zone. I have app. 3000 ft of 3/4" HDP pipe underground which runs straight up and back in one continuous 8 finger loop. It starts at and dumps into a 165 gln reservoir tank that sits in a wooden cavern 8' underground. My above ground loop of app. 3000 ft which is 1/2" HDP pipe runs under the plants in 16 individual loops from and to a manifold which also starts and dumps back into the reservoir tank. This is a completely closed loop system using only fresh well water. I do take a stream from the reservoir tank to water the plants which is made up from a simple float system feed from my home well system which is 55 degrees. The reservoir tank is always full. The whole desire of this system is to supply the coolest water possible to the above ground loop. After 2 years in service with decent results I have encountered several issues which I hope maybe someone from this site can help me with. I ran across a string of geothermal posts on this site and one person stated the "slinky" method of running your pipe is not the way to go. I have been told i should have run my piping that way. Can somebody tell me why that way is not the best method and more importantly what is? I have used Grundfos circulation pumps extensively. They don't seem to be able to tolerate the very damp conditions inside the cavern which I keep well insulated and covered for obvious reasons. The pumps are very expensive and not lasting very long. Can someone recommend an alternative pump designed to handle very damp conditions? Lastly I am struggling to size the pumps correctly. I am looking to establish 4gpm of flow from a pump on the discharge of each loop from the reservoir tank that will run 24/7 365 days a year! Thanks

beenthere 12-30-2009 12:17 PM

1/2 has a high head loss if your trying to move 4 GPM through it.

Circulators are not designed for low temp high humidity areas.

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