Measuring Heat Exchanger Flow Rates?
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.
One measurement is worth a thousand expert opinions.