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air flow metering

air flow metering

air flow metering

(OP)
what is the more practical ways of measuring air flow in ducts and at diffuser outlets
please let us have your oppinion?

RE: air flow metering

1.    Hire a certified test and balance contractor.

2.    Standard flows in duct is best with a pitot traverse. How to measure flow http://www.dwyer-inst.com/Products/AirMeas.cfm

3.    Grilles are measured with a flow hood. Such as http://buy.tsi.com/cgi-bin/ecom/prodline.pl?1284891242000&;web=TSI&grp=AL&line=AB&lv=1

4.    Smacna has an excellent testing and balance publication. http://www.smacna.org/bookstore/index.cfm?fuseaction=search_results&cfid=10274787&cftoken=22426741


 

RE: air flow metering

Balometer for measuring airflow in diffusers, pitot tube for measuring airflow in ducts.

See Alnor for balometers

RE: air flow metering

(OP)
how practical is it use a pitot tube to determine duct velocity? my concern is if the pitot tube is not held 100% perpendicular with the air stream, how accurate is the velocity reading?

RE: air flow metering

It that concerns you, use a pot head pitot which is less sensitive to yaw angles.
B.E.

RE: air flow metering

An annubar is less sensitive to variations in the flow profile, in that it averages. Similar fundamentals to a pitot traverse, but can be used for permanent installation.  Oft-used in VAV measuring stations.

Flow hood is the only good way for diffusers.
 

RE: air flow metering

(OP)
what is your experience of using a hot wire anemometer for measuring inline duct velocity (instead of pitot tubes)?

RE: air flow metering

For permanent installs for continuous monitoring I like to use Greenhecks's temperature compensating air flow measuring stations.

www.ellisconsultingengineers.com

RE: air flow metering

I have used hot wire anemometers in general site testing including duct traverses, but not against a standard.

They usually list in around 5% accuracy and are not as directional as a pitot.  Gut feeling is that the hot RTD resistance measurement would be more robust than a low static dp, and thus more likely to be accurate between trips to the lab.

Quality means a lot with instruments though.  You gets what you pays for.
 

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