What are the maximum air speed at the supply diffuser?

700 fpm for residintial

1000 fpm for the public

1400 fpm for industrial

Above velocities are I think at the main duct. At the supply diffuser, the velocity should be400 -500 FPM for low velocity Air Conditioning Applications.

I agreed mr.riaz with 400-500 fpm (2.0-2.5)m/s , It was called terminal velocity. In selection of diffusers plz check the NC level , the lower NC more better (30NC)  .

neck size:

1. 150mm X 150mm - 50lps (105cfm) --- 6"X 6"

2. 225mm X 225mm- 100 lps( 211 cfm)--9" X 9"

3. 300 mm X 300mm -381 lps(381 cfm)--12"X12" ----maintain up to this diffusers , 300 cfm above can create noise above 30NC.

Thanks

It depends on noise and throw but normally it is 2.5 - 3.5 m/s

the speed is to FPM to insure a quiet sound level

the maximum flow rate and velocity depends in the type of usage generally it ranges from 2.4 mtr/sec to 3.4 mtr /sec in ideal condition in case of special industrial application refer to ashrae standard and DW 144/143 and SMACNA standards