Measuring Heat Exchanger Flow Rates?

[Looby]

So, I bought myself a handy-dandy digital pressure gauge (plus snubber &
P/T port adapter) to check the flow rate on my new WF Envision ND038.
Works great, readable to 0.1 ft of head ...man I got this sucker NAILED!

Pulled up the WF pressure drop tables with delta-P versus GPM at various
temperatures and... OOPS! noticed that WF doesn't mention antifreeze
corrections in conjunction with flow rate measurements. No mention in
the ClimateMaster manuals -- and nothing obvious on TheGoogle, either.

My first thought was to guesstimate an antifreeze correction from the loop
piping pressure drop tables, but then noticed that the 1.25" PE pipe tables
show a 20%-ish penalty for methanol versus water (no antifreeze) -- but
another table for p-drop per 100' of 1" rubber hose (from ClimateMaster)
shows virtually no difference at all between methanol and water PD's.

Anyone have experience with this? Why the big difference in antifreeze
effects for different kinds of pipe? Should HeatEx p-drop measurements
be corrected for antifreeze? How much correction for 20% v/v methanol?

BTW, my system is working very well -- except that I'd really like to
see 2-3°F higher temps at the registers. I'm trying to get a good GPM
measurement to see if it would be worthwhile to add a second/larger
circ pump. A 20% difference between uncorrected and 'corrected' PDs
is the difference between the near-optimum and bare-minimum flows
recommended by WF.

FWIW, I'm seeing delta-P = 6.1 ft head (2.6+ PSI) at 42°F EWT.

...TIA,

Looby

[waterpirate]

I do not know why the penalty for methanol? Methanol is usually the fluid of choice where it is legal because it does not add viscosity which adds friction loss. Also in the world of "c" factors for pipe rubber hose is the worse. Maybe WF thought the c factor was so low allready they did not add for antifreeze.

[hardchines]

Excuse my obvious question but why not just install a flow gauge?

[waterpirate]

Flow meters are a "potential" source of a problem on a closed loop system. The Pete's ports are accepted as a better way.

[Looby]

Excuse my obvious question but why not just install a flow gauge?

I didn't want to open the system, install a flow meter,
and re-purge -- just to find out whether I should open
the system, install a second circ pump, and re-purge.

Also, unlike a dedicated flow meter, a digital pressure
gauge is a handy-dandy tool with many uses (such as
checking loop pressure) -- and it was under $100.

As waterpirate points out, inline flow meters are a
potential source of problems, and I have no need to
monitor GPM continuously. Just want one 'baseline'
initial measurement and very occasional re-checks.

The pressure gauge gives me precise (+/- 0.1 ftwc)
p-drop measurements -- the only problem is that I'm
not sure how to accurately convert delta-P to GPM.

...the answer is out there, somewhere,

Looby

[hardchines]

I did not know that it was involved to install a flow meter so I understand your point. I run open loop so I have more variables to deal with, and I am a like to see what is going on kinda guy! I have visual flow gauges (sorta fail safe) on both units and EWT, LWT's, and HWG in and out Omaga digital
temperature gauges so at a glance I can see what is going on. I do not push this set up as most would think it is over kill, but I like it.

[Mark Custis]

So I can "see the flow".

Lobby: Look in the manual for converstion tables.

[waterpirate]

I live and die by the bucket and stop watch for well work, but I am not sure how to apply that concept to a closed loop system that does not employ a tank?

The rubber hose gets a bad rap on the friction loss chart when compared to other pipes c factor, that plus the viscosity reduction is a killer. I was misinformed as to the impact that methanol had in a loop system. So it is the lesser evil, but still evil?

[hardchines]

OK Loopy return your new toy and pick up a flow meter! Or a bucket!

[Looby]

I have yet to see a table from a manufacturer with these effects listed
in enough detail to expect good accuracy.

There's plenty of info for p-drop versus GPM versus temperature, with
ethanol, methanol, glycol, and jus' plain water -- but only for the loop
piping. I plotted WF's heat exchanger p-drop data for the Envision 038
(apparently, without antifreeze) -- and also a set of curves with a 20%
'correction' for methanol. Only problem is, I don't know whether the
'corrected' data is better/worse than WF's uncorrected values straight
from the tables:

The other issue is that it assumes that the heat exchanger is perfectly clear.
If the heat exchanger is restricted for any reason it will cause the flow to
drop and the pressure drop to increase. So if you're checking flow by
pressure drop, flow will appear to INCREASE as the heat exchanger becomes
more and more restricted.

Heat exchanger fouling shouldn't be a problem in a closed-loop system.
Also, any significant heat exchanger blockage/restriction should show up
as a LARGE increase in exchanger p-drop. Reduced flow will increase the
circ pump's output pressure a bit, and reduce the loop piping's p-drop --
so, the exchanger p-drop should rise dramatically.

a bucket and stopwatch is a surprisingly accurate way to measure flow

True 'nuff. Now, all I need is a 0.125" bucket that'll fit through a P/T port.

Looby