Why isn't an expansion tank required

imatellerslie

on a geothermal ground loop? Is the tubing just allowed to expand and contract as the system fluid temperature changes?

David_5

Never gave it a thought but,

my guess is that the water temperature doesn't change very much so there is little expansion.

David

ed wallace

geothermal loop

because its an open system water comes in then goes right out again??

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imatellerslie

In this case I'm talking about a closed

ground loop. It circulates a water/antifreeze mix in a closed system.

GMcD

Closed geothermal loops and expansion tanks

Essentially, yes. The high density polyethylene pipe has some minor amount of stretch, and there is usually less than a 10F delta T in these loops, so there is minimal expansion. It's still good practice to use a small expansion tank anyway to maintain a steady state pressure.

imatellerslie

Thanks Geoff...

that makes sense to me, and I'll probably put it in the spec. The literature for the system I'm considering (Econar) says to expect a 10-15 F degree delta t on the ground loop, but I'm more concerned about the change in temperature of the loop between seasons. At the end of winter, the loop avg temp could be quite low when compared to the avg temp at the end of summer.

Brandon

Non-Pressurized

There are products on the market today for ground loops that are designed as open systems. Very much like a purge cart on a small scale. They work very well, and if you manifold the loops inside you can actually purge with the system. If you want some info, we handle the line. There are some other distributors also. Manufacturer is B&D out of Scranton, IA.

Good Luck!

imatellerslie

I'm interested...

Where is this open system vented to atmosphere, and why? Is that to allow air to continuously purge from the system? Where is the circ placed in relation to the vent? Seems like the vent would have to be on the suction side of the circ or you'd have a water spout, so how do you give the pump enough suction head?

Brandon

It works just like a purge cart. The "pump kit" is a resevoir. The pumps pull from the bottom of the resevoir, so there is a standing water column on them. Once air enters the resevoir it rises to the top and can't enter the system again. Along with the continous purge, you can check water level, add anti-freeze or inhibitors, change a pump and not have to re-pressurize. With a special tool you can even direct read gpm with out doing pressure drop calcs. Few people that buy it once ever go back to the pressurized system.

imatellerslie

Thanks for the info

It sounds like a very good system, and one that I'll want.

Jeff Krawic_3

expansion

(Dusting off the old cranium...) Now if my memory is right, and thats NO guarantee, I believe water will expand approximately 4% when raised 100 degrees fahrenheit. So a 10 degree delta has .4% expansion. Anyone else remember if this is right??????? I used to remember this stuff pretty well................