Geothermal HVAC Project revisited

GreenPowerManiac · December 2013

Hello everyone,

Have got things nearly wrapped up with the research on laying the closed loop lines and design.

Am buying
400' of slinky loops x 6
B&D 2-230QFC 26-116m flow center
2300' linear feet of straight 3/4" lines. (3/4" throughout) until inside house and manifold.
Total 750' per loop x 6 = 4500' total.
About 21 gallons of PG (Propylene Glycol) safe stuff 25% mix.

Have had several OK's to proceed with this design. The Synergy 3D 6 ton unit is OK. We're going bigger because of a request to eliminate LP gas as heating source.
Was told the extra long loops will increase efficiency enough to keep the electric cooker from coming on until the outside temperature reaches 5-12 degrees.
The unit is variable speed everything integrated at 16-18 gpm or less. The flow center was the slightly bigger model to support any errors in HPL (Head pressure losses).
Has anything been missed?

animatt · December 2013

Re: Geothermal HVAC Project revisited

I did not run your numbers, But the statement of extra long loops would through some flags up to me.

I personally like extra short loops in a design. THis cost minimally more in valving but pays itself back with lower pumping requirements for the life of the system.

a small number of Long loops in parallel can usually satisfy heat transfer before the liquid has actually passed all the way through the tubing. Meaning the extra tubing is just adding resistence to the water flow. THis would be a negative most of the year. During extremes when you need the extra tubing it does help, but only after being a drag most of the time.

A large number of extra short loops should drastically decrease pumping electrical consumption. It would help 24/7/365. You would still need the same sqft of tubing surface area, it is just now fluid flows more efficiently. SO you still get the extreme weather performance you need but also the rest of the year as well.

For something that should have a very long life to me makes sense to design it more efficiently for pumping it especially if costs are marginally different. I have not run numbers on your purposal, just that "extra long loops" caught my attention.

matthew

GreenPowerManiac · December 2013

Re: Geothermal HVAC Project revisited

Hmmm.....

Someone mentioned not to go over 800' per line due to head pressure.

Said the flow center 26-99 was good at about 30 HP. Got the 26-116 instead cause had higher HP ratings.
Trying to make it easier on the system. The synergy 3D is all variable speed everything. My contractor says it's just fine.
Things may be a bit overkill, but that's what he wants. I requested to get off of LP gas. Guess this is a possible answer....

rice81 · May 2014

Re: Geothermal HVAC Project revisited

This is an older thread, but I just came across it. What size pipe are you using? Don't go 1/2". Go at least 3/4". The increased cost is offset by the diminished pump size and reduced energy costs. And as noted above, go with parallel rather than longer loops. Only down side is that in theory you want some turbulent flow to increase the heat transfer along the pipe (Reynolds >2500). Bigger pipe and parallel means slower flow and more laminar flow and reduced heat transfer. Would be interesting to see where the $ tradeoff occurs with all of these factors considered. I would rather pay up front for bigger and more pipe and run a smaller, more efficient pump.

Geothermal HVAC Project revisited

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