VAV Duct Design

[psugreen]

What static and velocity do you use when designing vav ductwork upstream of the vav boxes?

 

[DuctHunter]

0.2" WC with a max velocity of 2000 fpm

 

[CptHk]

psugreen,

What is the program? I'm sure the rule of thumb answers you will get from here would vary depending on how critical sound transmission is in your application.

 

[willard3]

I use the static and velocity required to do the job described to me by the client.

There is no rule of thumb.

 

[psugreen]

Application is a typical office building. There must be a range that is used for static or velocity?

 

[CptHk]

psugreen,

Yes, I believe there is a range that you can start with. If sound is critical, then an acoustical consultant can review the design. Otherwise good design practice should suffice, such as volume dampers at branch take offs, 10' min. duct runs with at least one elbow after the VAV boxes, etc...

We try to stay around 1200 fpm or .1" wc/100', whichever is more stringent, for the duct upstream of the boxes. We tend to not design typical office buildings, but educational and hospital applications where sound transmission is more critical.

We tend to relax the requirement to 1400-1700 fpm for the offices that we have designed, where background white noise is actually desired. Be aware that there are energy and sound penalties as velocities are increased.

Of course there are many other sound considerations regarding the whole duct design, but you were looking for ballpark velocity starting points, no?

 

[DrRTU]

I use an article from Heating/piping/air conditioning December 1984 pages 95 to 100 that lists tables of medium pressure duct sizing. The tables are based upon air volume and acceptable velocity.

 

[mauricestoker]

I would recommend looking at the VAV Advanced Design Guide, available from

energydesignresources.com.

I like the method they recommend, starting at higher feet/100 feet and ending at 0.08ft/100 feet.