AC duct sizing question

[stephenM]

Hi all,

I'm considering having a ducted AC unit installed for my hall/landing (plus a toilet which is accessed from the hall - supply only!), and would appreciate some advice on duct sizing.

The 2 Fujitsu units I'm considering are either ARYG18LLTB (940 m3/hour on high) or Fujitsu ARYG24LMLA (1100 m3/hour on high).

I'm planning to run 2 supply ducts (one will be direct to a grill - one will split at a T junction to 2 grills) and 2 return ducts on the landing, only 2-3 meters from the unit.

The supply runs are approx:

Duct 1: 8 meters / 3 90 degree bends
Duct 2: 9 meters / 4 90 degree bends

Any help on duct sizing (and suggestions on the best type of duct) would be most appreciated!

Thanks

[nike123]

You need to calculate duct size based on air flow volume and recommended air speed for each part of duct system. You should first calculate each grille air flow and then go upstream. Recommended air speeds are here:
http://www.engineeringtoolbox.com/duct-velocity-d_928.html
Example:
Grille air flow volume 300m3/h
Grille supply branch air speed is 2m/s
300m3/h=0,083m3/s
(0,083m3/s)/(2m/s)=0,0415m2
cca 230mm diameter!
http://www.rkm.com.au/CALCULATORS/CALCULATOR-circle-sphere.html

I recommend these ducts:
http://www.decgroup.biz/english/pdf/%5B1.07%5D%20Acoustical%20and%20Thermical%20insulated%20Sonodec%C2%AE.pdf