What is the computation of air flow for an exhaust system?
Equipment with two motors with 8" diameter provision for exhaust system. It is OK if I'm going to use Y connector ( g.i. sheet ) with 10" diameter and 2-8" diameter and split them with flexible duct? Existing supply for exhaust system is 12" diameter.
Asked by Anonymous
Posted Mon, 03/08/2010 - 11:26
Edited Mon, 03/08/2010 - 11:51
Posted Mon, 03/08/2010 - 11:26
Edited Mon, 03/08/2010 - 11:51
Tags: General questions
Yahoo
Technorati
Google
Facebook
Delicious
Digg
StumbleUpon
RedditOther Questions in General questions
In Energy efficiency and durability | Asked by Litawyn Eco-Cottage | Feb 11, 12
In Green building techniques | Asked by Bennett Sandler | Feb 12, 12
In Energy efficiency and durability | Asked by Bruce Miller | Feb 12, 12
In Energy efficiency and durability | Asked by Jayne Masternak | Feb 11, 12
In Mechanicals | Asked by David Meiland | Feb 10, 12
Dear Anonymous,
It would be helpful to know more.
1. What type of equipment?
2. What distance are you running the ducts?
3. How many cfm are you moving?
Duct design is complicated, and is best done by following the Manual D procedure. Some people use rules of thumb, however, although these rules of thumb can get them in trouble.
In case you have forgotten your 7th grade math, the area of a circle (that is, the cross-section of a round duct) is pi r squared. Therefore, the area of a circle is:
8 inch diameter = 50.3 square inches
10 inch diameter = 78.5 square inches
12 inch diameter = 113.1 square inches
If you want some rules of thumb, I've heard this one:
"On a short run a 10" flex duct will carry about 400 cfm. These are guesstimates to close to what they are at short runs:
8" duct, 200 cfm
9" duct, 300 cfm
10" duct, 400 cfm
12" duct, 600 cfm."
That rule of thumb came from here:
http://hvac-talk.com/vbb/showthread.php?t=105192
The use of this rule of thumb is not recommended without verification.
Posted Mon, 03/08/2010 - 12:00