HVAC Internal Duct Airflow Speed 2

[bsberg]

Does anyone out there know the mean and distribution of airflow velocities internally in an airconditioning and heating duct. I've been told it varies from 0 - 25 m/s, but would like to find out more for some design calculations.

 

[quark]

Check this link.

http://www.roofunitsltd.co.uk/sharing/system.pdf

 

[VEEKRISH]

Quark mate, thanks. I wonder if the link will provide the answer to bsberg, but, the link you have provided is a good one and worth reading.

 

[quark]

Veekrish!

My main wish is not to trivialize the things by just saying 'x' fpm in main duct, 'y'fpm in branch and 'z'fpm at girlls.

Generally main duct velocity is from 1500 - 2500fpm and in branches it is 800 - 1500 fpm and at supply grills it is 400 - 600 fpm.From these ranges how will you come to a single value? (that is by knowing the design philosophy).

That link I have provided gives comprehensive (and free) data.

25m/s is quite high velocity. Even in high fume generation applications (welding shops and foundaries etc.)it is maintained at 15m/s.

Regards,

 

[VEEKRISH]

Quark, as I understand the question, what BSBERG wants to know is how to evaluate the velocity of the air over a Duct Cross-section. assuming the velocity at the duct surface will be zero and increase towards the core. I feel this is what BSBERG is trying to evaluate. I'm not sure why one would like to do this. Maybe BSBERG can correct me if my presumption is wrong. Regards.

 

[FCIBSE]

It can not be 0 m/s, and 25 m/s is way too high for normal commerical/institutional HVAC system. For normal AC ductwork, the velocity of air flow should be kept around 4 to 7 m/s according to my personal opinion. One nice thing about HVAC engineering is that It's not an exact science.

 

[paulkeating]

Dear FCIBSE,
That then begs the question - is HVAC a science or is it merely the application of a science??!!
Answers on a postcard ......

 

[DouginMB]

HVAC design is definitely not a science. There are too many subjective parameters involved with the design.

 

[FCIBSE]

I consider HVAC engineering is not an exact science, but an application of a combination of science, trade practices and arts; a little more scientific than drainage design within the plumbing discipline. HVAC engineering is considered an art, because we can't build any model for the system performance before the building is done and all buildings are different from each other.