Bergy said on July 22nd in another subject:

"21 GPM through a 5 ton is excessive flow. Try to get your flow back down to 15 GPM, in 2nd stage."

I'd appreciate some help to better appreciate how quickly I need to fix this problem.

Background:

I've got a WaterFurnace Envision package unit, 5 ton, 2 stage, variable fan speed.  Installed 2007.  Geographical location is Dallas area.
Operational performance details are here: http://www.welserver.com/WEL0043/ .

It's classically connected to a vertical closed (8 boreholes at 300' using 1" HDPE pipe) loop with no anti-freeze.
For pumping, installer put in 2 Grundfos UP26-116F pumps (1/6th HP each, running at 385 W each) connected in a push-pull configuration.  (Purge cart connections are outside in borehole field.)
An image of the installation is here: http://www.pbase.com/neukranz/image/84286042 .
And an image of the pumps is here: http://www.pbase.com/neukranz/image/84286046 .

Water flow through the coax heat exchanger is 21.2 GPM.  Determined first by measuring pressure drop across the coax heat exchange using a good pressure gage: http://www.pbase.com/neukranz/image/106018293 , and then using WF's PD vs flow graph to establish a formula approximation for the curve, and then extrapolating out to 21.2 GPM.  (Per WF standards, max should be 15 GPM (5 tons * 3.0 GPM/ton)

Last year Docjenser kindly, competently and comprehensively helped me (here on forum) redesign the loop using a variable speed pump, replacing the 2 existing pumps.  I'm waiting for the existing pumps to wear out before making the significant cost investment into a variable speed pump.

This could still be a few years.  I don't know how long Grundfos UP26 series pumps last.

Meanwhile, the key question I have is if 21.2 GPM through a 5 ton WF Envision coax heat exchanger is causing any problems other than possibly a little inefficiency due to excess turbulence.

What are the opinions?  Is it an urgent subject to have less flow going through the heat exchanger, or, can I indeed wait a few more years?

Many thanks!

Best regards,

Bill

Have you tried shutting one of the circulators off? Just take the wires off one of the circulators and check your flow rate.

Bergy

Bite the bullet. The 26-116 are just too inefficient. It is like incandescent light bulbs. The longer they last the lesser you safe. At the very minimum disconnect one.

Posted By Bergy on 28 Jul 2014 05:19 PM
Have you tried shutting one of the circulators off? Just take the wires off one of the circulators and check your flow rate.

No.  Didn't know if the shut down circulator would serve as a blockage, versus simply free rotating.

So, tried it.  I like learning experiments and problem solving.  The experiment is officially started tonight.  After a week I'll evaluation results.  My WEL monitoring system will provide all the results needed.

I unwired the 'push' of the 2 pull/push circulators.

Observation after first cycle with just one circulator running:

1. Unit did not shut down.  Encouraging.  I was nervous that the unpowered pump would be a 'choke point' on the loop.  Not so it turns out.

2. Measured 1.43 Amps.  Will figure Power tomorrow (WEL chart shows drop of about 400 Watts - this makes sense)

3. Measured:
 
EWT=76.9, DeltaT=7.3
EW Pres = 52.5 PSI, LW Pres = 47.5 PSI, DeltaP=5.0 PSI

I'll study this tomorrow to see if it make sense.  Meanwhile, I've changed my loop KBTU/hr and my evap air temps charts from 4 to 2 weeks to see a better before versus after.

Thanks.

Best regards,

Bill

OK, after going through a WEL (monitoring system) repair cycle (electrical surge), WEL0043 is back up and running ( http://www.welserver.com/WEL0043/ ).
 
You may recall that last month I disconnected one of the 2 pumps for my WaterFurnace geo-HVAC 5 ton unit, prompted by many here, as an experiment to learn from.

I continue to run my 5 ton unit with just one loop pump (the 'pulling' portion of the push-pull configuration).  And it continues to work fine.  I marvel at how a non-functioning pump can still be left in the loop circuit without significant performance impact (or that the loop is even runs at all - the non-functioning pumps propeller must be simply doing a 'free-spin,' versus causing a blockage.)

Running a 5.0 psi Pressure Differential (see earlier thread) through the WF Envision chart calculation yields 15.2 GPM at 77 degrees F.  Down considerably from 21.2 gpm.

A key benefit of making this change is I'm running the 5 ton unit with about 385 Watts less of power.

I don't know if this is the 'bottom line,' or, if there are other benefits of running with less gpm through the coax heat exchanger.  I.e., what about long term wear on the coax heat exchanger.

Just by using an 'eyeball' examination, it looks like EER improves a little, from approximately 20 to 21 BTU/W-hr.  This makes sense.

Here's the whole picture for those interested (first number is with both pumps running, second number is with just one pump running):

Outside temp: 95 -> 95 degrees

EWT: 76.6 -> 76.0 degrees
DeltaT: 4.9 -> 7.1 degrees
Flow: 21.1 -> 15.2 GPM

Heat of Exchange: 52 -> 53 kBTU/hr


Compressor Discharge Line 121 -> 123 degrees


EAT: 78.5 -> 77.0 degrees
LAT: 58.0 -> 55.7 degrees
DeltaT: 20.5 -> 21.3 degrees
Air flow: CFM: 1500 -> 1500 CFM

Sub Cooling: 33 ->34 kBTU/hr
EER: 20 - 21 BTU/W-hr


(All of the above from my WEL unit)

This certainly is another lesson that simply cranking down flow with isolation valves does nothing to change performance.

BTW, this is all 1st stage only.  I almost never have to run my unit in 2nd stage.

Hope this is interesting to those here.

I plan to leave the pump turned off.

Best regards,

Bill