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The essential condtions for duct design
(a) The design meets requirements
(b) Design with high performance with low cost
(c) Design with High reliability
1-good air distribution is the most important cfm/meter square
2-average level noise criteria
3-air velocity in the room from50 to300 fpm
4-good looking design
5-the cost
6-the critical path be short as possible
low cost = aspect ratio near to 1:1
low noise according to usage of space
low friction loses
take the ratio of duct in terms of width and height as one : four ratio,avoid unnecessary turns and curves
Good efficiency.
Less losses.
Proper dimensions ( Maintaining proper cfm) Best material ( Low weight, less corrosive & good life)
Effective duct routing ( Less material to be incorporated i.e. cost effective)
If duct design meant to be the duct sizing, then I would recommend following SMACNA or DW standards, and ASHRAE handbook
If the system manages to give you the amount of air as required by the design of the duct i.e if the flow of air in your grilles/diffusers matches the design requirement you system is okay.
But for effective running of the system, we also need to check the following points.
i) The material quality of the duct.
ii) To check the installation of the duct and its air tightness by performing air leakage tests.
iii) Check how much is the noise criteria by proper installation of sound attenuators.
iv) Check the duct routing and avoid lots of bend, as it results in air/pressure loss.
