Ducting - if have multiple ducts, what will be the cfm in each duct
Ducting - if have multiple ducts, what will be the cfm in each duct
(OP)
Problem Statement:
I have an whole-house dehumidifier (Aprilaire 1770A) that can be used to duct (8" diameter inlet/outlet) to specific locations in a dedicated area. In other words, i am using this dehumidifier for my crawlspace (1,850 sqft) and i need to duct (both for the supply and return) so that i can efficiently dehumidify the entire crawlspace.
Knowns:
- Dehumidifier has 500 cfm at a static pressure of 0.9" w.c. per 100 ft. (total for supply and return). Unit has a maximum static pressure of 1.5" w.c.
- 8" duct inlet and 8" duct outlet built into the unit
Questions:
Assuming that no plenum is used.
Say i come out of the dehumidifier (supply) with an 8" duct and then branch off with (6) individual 8" ducts (with the total of all of them being 50 ft. or less), will each of the (6) ducts have, theoretically, the same cfm as the outlet (main trunk) duct of 500 cfm or will i need to have a plenum coming directly out of the dehumidifier that feeds the (6) individual ducts?
Thanks in advance for your inputs,
Andy
I have an whole-house dehumidifier (Aprilaire 1770A) that can be used to duct (8" diameter inlet/outlet) to specific locations in a dedicated area. In other words, i am using this dehumidifier for my crawlspace (1,850 sqft) and i need to duct (both for the supply and return) so that i can efficiently dehumidify the entire crawlspace.
Knowns:
- Dehumidifier has 500 cfm at a static pressure of 0.9" w.c. per 100 ft. (total for supply and return). Unit has a maximum static pressure of 1.5" w.c.
- 8" duct inlet and 8" duct outlet built into the unit
Questions:
Assuming that no plenum is used.
Say i come out of the dehumidifier (supply) with an 8" duct and then branch off with (6) individual 8" ducts (with the total of all of them being 50 ft. or less), will each of the (6) ducts have, theoretically, the same cfm as the outlet (main trunk) duct of 500 cfm or will i need to have a plenum coming directly out of the dehumidifier that feeds the (6) individual ducts?
Thanks in advance for your inputs,
Andy





RE: Ducting - if have multiple ducts, what will be the cfm in each duct
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
Waramanga...
The Aprilaire 1770A comes with an 8" inlet and 8" outlet for 8" ducts. The issue i am having is one area of my crawlspace is not dehumidifying b/c there are obstructions in the way (pillars, tight opening, etc) so i was thinking about ducting it to specific areas.
If i use a plenum for the supply/return, would it not equalize the cfm in each of the ducts (meaning each duct assuming they are all the same diameter will have the same cfm as the supply cfm?
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
This is becouse head loss (pressure drop) is a function of Velosity Squared/Diameter. For the 8 inch pipe it is:
11.4 x 10**-9 * V**2/D per foot of pipe
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
THANK you so very much! This is what this site is all about - to help other search for solutions so i thank you for giving me a direction on how to balance the system.
Thanks again
Andy
RE: Ducting - if have multiple ducts, what will be the cfm in each duct
WOuld i need a plenum prior to branching off 6 lines? Also, would i need a plenum with returning the 6 lines back to the unit?