Equal Friction Method
Equal Friction Method
(OP)
To design air duct by Equal Friction Method, the friction factor of 0.1 in wg. Is used as a rule of thumb for all supply duct sizes. And 0.8 is used for sizing the return duct.
When energy cost is high and installed ductwork cost is low, the low friction rate design is more economical.
My question is
Up to which limit can we go lower than this friction factor? Also what are the tips should we follow to avoid any improper flow rate thru duct?
Apreciate your response
When energy cost is high and installed ductwork cost is low, the low friction rate design is more economical.
My question is
Up to which limit can we go lower than this friction factor? Also what are the tips should we follow to avoid any improper flow rate thru duct?
Apreciate your response





RE: Equal Friction Method
RE: Equal Friction Method
FYI Fire/smoke dampers are available up to 3,000 FPM. See Ruskin for example.
ASSADEQ ... Recommend you gain some experience with using the factors you quoted, which are typical for a large percentage of "normal" HVAC applications - i.e. those applications without other special requirements such as grease or particle exhaust. Exceeding these norms on the high side should be done with caution and experience - noise being another factor not yet mentioned. To learn why equal friction is not the best method of sizing primary air ductwork in systems with terminal units of any size, experiment on a "sample" project with a decent static regain duct sizing program. This procedure establishes an initial velocity that provides sufficient energy to account for nearly all static losses in the critical run. Look at the resulting friction factors throughtout the system and the relatively constant inlet static pressure at all boxes (varies by no more than 0.25" to 0.5" WG). Short of becoming a balancing or commissioning agent for a few years, this is the next best way to learn.
RE: Equal Friction Method
RE: Equal Friction Method