# Ventilation ducting static pressure calculation

• 09-13-2011, 09:05 AM
amrs
Ventilation ducting static pressure calculation
Hello,

I was hoping for a formula to help me calculate static pressure in custom-made (smooth metal) ventilation ducting, given the following information:

1. Length of duct in meters
2. Area of cross-section in meters squared
3. Air flow in meters cubed per hour

Any pointers would be greatly appreciated!

amrs
• 09-14-2011, 05:14 AM
lynn comstock
Why? Is this a theoretical question or related to a real world design?
Is the duct perfectly straight without fittings?
Is "smooth" frictionless? There is a tool for real duct calculations. Get a free one at http://www.crownproductsco.com/freeductulator.htm
What kind of velocity is your target?
See if http://www.engineeringtoolbox.com/du...ons-d_883.html helps you.
• 09-14-2011, 09:06 AM
amrs
Hi Lynn,

Many thanks for those pointers.

The reason I need this is that we're installing new ducting in a suspended ceiling (for a new ventilation system), however the architecture of the ceiling is not uniform and there are various obstacles to go around. If we were to use standard round ducting I would be able to use manufacturer supplied data to measure static pressure for the different duct sizes and different volumes to figure out the overall static pressure in the whole system.

However, to get around the problems in our suspended ceiling, we're going for custom-made rectangular ducting. The manufacturer is able to make the size to our specification but isn't able to tell me what the static pressure would be.

I'm only looking for an estimate, just to make sure we're not overleading the machine.
• 09-15-2011, 01:12 AM
lynn comstock
The ductulator are great tools for what you are doing.
Many show the duct fitting pressure drop information on the backside.
Good luck.
• 09-15-2011, 10:54 AM
Freeagent
Quote:

Originally Posted by amrs
Hello,

I was hoping for a formula to help me calculate static pressure in custom-made (smooth metal) ventilation ducting, given the following information:

1. Length of duct in meters
2. Area of cross-section in meters squared
3. Air flow in meters cubed per hour

Any pointers would be greatly appreciated!

amrs

If you do a Google search for static pressure calculator, you should come up with a few spreadsheets. Here are some:
http://www.bry-air.com/tech-center/r...c/default.html

http://www.captiveaire.com/CATALOGCONTENT/DUCTWORK/DOC/STATIC PRESSURE CALCULATOR.XLS

There are methods of calculating equivalent diameter of rectangular ducts. For example:

http://www.hvac-toolbox.com/equivale...ter-d_443.html

I used the captive air one to check our ductwork - easy enough to use.