Nov 2, 2009 #1 skuntz Chemical Mar 16, 2008 69 I am measuring airflow in a circular duct with a hot wire anemometer. Is there a rule of thumb for how long the upstream and downstream sections need to be?
I am measuring airflow in a circular duct with a hot wire anemometer. Is there a rule of thumb for how long the upstream and downstream sections need to be?
Nov 2, 2009 #2 M MintJulep Mechanical Jun 12, 2003 9,991 At least 6 and preferably 10 diamaters upstream to any "things". It's good to have the same downstream too. This is generally impossible in most real systems. Upvote 0 Downvote
At least 6 and preferably 10 diamaters upstream to any "things". It's good to have the same downstream too. This is generally impossible in most real systems.
Nov 2, 2009 #3 rmw Mechanical Feb 6, 2002 5,724 Is that going to be a stationary anemometer or are you going to traverse the duct with it? rmw Upvote 0 Downvote
Nov 3, 2009 Thread starter #4 skuntz Chemical Mar 16, 2008 69 It will be stationary. Upvote 0 Downvote
Nov 3, 2009 #5 AbbyNormal Mechanical Nov 17, 2003 780 if you have a questionable straight section, use the 80/20 rule. Put the probe 80% down the length. Example there is an 8 foot run between two elbows, install it 8x0.8 = 6.4 feet down stream of first elbow. Try traversing it there first, see what you get. Use that to scale up/down what the stationary reading gives you. The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install Upvote 0 Downvote
if you have a questionable straight section, use the 80/20 rule. Put the probe 80% down the length. Example there is an 8 foot run between two elbows, install it 8x0.8 = 6.4 feet down stream of first elbow. Try traversing it there first, see what you get. Use that to scale up/down what the stationary reading gives you. The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install
