Free air calculation.

[coolhandlew]

Hi all, I'm in the process of servicing an AHU system as part of a building refurb that our company is doing. Does anyone know roughly the free air area of a 600x600 4 way supply diffuser? You know the sort, aluminium painted white, that sits in t-bar ceiling grid.
I need this to apply to my anemometer m/s readings to give client the volumes.
I know they will vary by manufacturer but a ball park figure will help a lot.
Thanks

[Brian_UK]

Best/easiest way is to make up a cardboard air collection hood, calibrate it and then take all of your readings with the hood.

edit: Just checked with Lindab catalogue, they don't give free areas (damn). Looks like you'll have to measure the slots yourself. ;)

[solas]

Hello

If the air distribution system incorporates a moderate number of air terminals, I would recommend hiring a propriety 'flow measuring hood' for the job. These instruments employ balometer technology to measure the volume flow rate and normally include digital displays with high resolution. It is important to examine the calibration certificate before you leave the store to verify the instruments accuracy. It can be very difficult to attain accurate and consistant readings without the appropriate equipment.
Depending on the quantity of terminals to be measured, alot of time can be saved if you have an assistant to identify the terminal and record the respective flow rates while comparing against design figures.

Hope this helps.

Solas

[eggs]

46% according to the downloads here (http://www.grille.co.uk/more_info.asp?current_id=92)

ooooooPs, I've always used 60% in my calcs :o, my systems always work though.

Eggs

[drmile]

0.11m2
Milenko

[Magoo]

use an anomometer and a tape measure.
Lineal metres flow x metres squared is total flow.
Lots of lineal flow readings and average. Not rocket science stuff.

magoo

[eggs]

Not rocket science stuff.
magoo

Neither is reading the question. :(


Does anyone know roughly the free air area of a 600x600 4 way supply diffuser?

Eggs

[coolhandlew]

use an anomometer and a tape measure.
Lineal metres flow x metres squared is total flow.
Lots of lineal flow readings and average. Not rocket science stuff.

magoo
I'm well aware of that, but there has to be a correction factor for restrictions ie. louvres etc

[Magoo]

For "eggs "and everyone else there is a standard for a difuser hood testing forget about louvers .., what ever comes out is actual, my initial comment stands.
For commissioning a/c diffusers a square test hood that reduces from square to round with a fixed discharge diameter, add anemometer will give the actual flow rates, the angle from square to round to meet standard is 11 degrees. Then use calcultor and flow rates. Like I said earlier not rocket science. The more cross reference readings the better, increases the accurracy.