GeoMax 2 by Heatcontroller.  Apparently rebranded CM, I think.  4 tons, vertical config. 

Those numbers correspond to extracting 52kBtuh - a bit high for a 4 ton unit.

Posted By engineer on 12 Dec 2010 01:17 PM
Those numbers correspond to extracting 52kBtuh - a bit high for a 4 ton unit.

I got slightly less than 50KBTU/h, still way too high. That is what my 6 Ton unit is extracting right now. If real, that would be really good! Stuart, how did you do the measurements? What thermometers? At least it appears that your unit is performing fine.

Ok.  For the pressure measurements, I used a digital dwyer gauge.  For any duct temperatures, I used the DATs, and for the ground loop, I used 2 digital meat probe thermometers strapped to the main pipes going from the manifold to the geo unit.  Both probe sensors are tightly clamped and insulated.  In order to minimize differences, I also swapped the 2 thermometers and took readings, the results were similar.
I am also working on a better way to clamp some sort of thermometer to the piping.  Will report any further results as they become available.

Sorry to resurrect a threat, but this leads me into Reynolds numbers. I understand that fluid has to move at a certain speed through the pipe in order to swirl around and extract heat, and that if it is gently moving through the loop, it won't pick up as much. I know that Reynolds numbers are a way to try to quantify this.

I found the following formula:
R=(3160 x GPM x SpecificGravity)/( Diameter x Viscosity)
Where GPM is gallons per minute, Diameter is in inches, and Viscosity is "cp?"
I *think* I have my numbers right:
R=(3160 x 4 x 1.02) / (1 x 9) for a 25% solution of propylene glycol at about 30F. And 4 gpm per loop, since I have about 16 gpm total, split into 4 parallel loops.

My R ends up being only 1400 ???? Don't I need to try to get 2500 or more? Or is my formula off?

Posted By decafdrinker on 21 Feb 2011 08:01 AM

My R ends up being only 1400 ???? .... Or is my formula off?

That Re looks about right, according to the tables in WF's p-drop
calculation manual -- but I can't vouch for the formula you posted
without some reverse-engineering of the units.

http://waterfurnace.ca/Engineer/Misc%20References/Pressure%20Drop%20Calculation%20Instructions.pdf

Anyhoo, a major source of headaches with p-glycol is that its viscosity
increases very rapidly with falling temperatures, so you get a Reynolds#
"double whammy" at low brine temps. Calculations for p-glycol at 30F
are of little use at 25F.

As far as "needing" a higher Re, I can agree with the turbulence-deniers at
least to the extent that if your measured coax and air handler delta-Ts are
reasonably close to manufacturers' specs, it's unlikely that loop mods or
antifreeze tweaking will improve system efficiency by very much.