When I check for proper airflow, I have several
ways I check it. I measure the air speed with
a velometer and convert to CFM, measure with a
flow hood, and even checked using temp rise method
on electric heaters (gas too on rare occations, gets
pretty close. I use this as a last resort).
The only time I pull out my magnahilic (spelling?)
is if I measure low air flow and need to determine where
my resistance is.
hmmmm back up.... I have used it on rare occation to traverse the duct with a pitot tube and calculate air flow
on a very unusual duct job.
I've asked a duct balancing man (all he does is balance BIG jobs..... Schools, hospitals, etc).
Everytime I'm around him I try to absorb as much info as I can in a short amount of time.
errrr back to what I was trying to say....
I talked to the balancing man about measuring static pressures and if I could use it along with the fan curve
in the manufacturers data to determine CFM.
He told me the fan curve is used by engineers to design the duct system. You can't use it to determine CFM.
He says he checks with a flow hood or traverses the duct
with one of his high tech gadgets (he showed me some of them..... those meters made me want to drool.... too bad they cost a small fortune. He was talking to me one time about a hospital he balanced where they wanted so many pascals of possitive pressure in the operating rooms. It couldnt' be any more, or any less... he had to get some highly sensitive meters to measure it... he didnt' have it with him at that time... arghhhh there I go getting side tracked again.....
he said you can't determine CFM using fan curves or available static on nameplate.
He said you have to measure it.
He gets the static pressures to put in his report so the engineer will be happy.
He said once the proper airflow has been determined and you have the static pressures wrote down on the unit.... then if you have a prob later you will know what the original setup was quickly. As in if some liner come loose, then that ducts static would be higher than what was originally recorded.
All this to ask...
is there something I'm missing?
I see lots of posts on here about checking the static
but I'm not seeing what it will tell you.
I know how to measure it... just not sure how you guys are applying it.
One of the biggest reasons I'm asking this is on account of
the ECM motors out there....
If I measure the air flow with the velometer or flow hood,
its bound to come out what the blower is set up for...
but what if there is a prob with the duct that could
have the motor operating out of its normal operating range.
[Edited by wormy on 05-04-2005 at 07:53 PM]