Design guideline on air duct from CarrierFull description
As air flows through any conduit there is an associated pressure drop. The Carrier System Design Manual, Air Disribution Part 2 describes an equation for calculating the pressure drop. The…Full description
Full description
Constant Friction Method
Before starting everything up compute the cfm/ room and create simple branching diagram: length
A
B
length
length
AHU cfm
cfm
cfm
Total cfm
1 length
cfm
cfm
2
length
cfm
cfm
3
Fig. 1 length
8
5 length
cfm
7
4
length
cfm
6
length
9
A. Compute for total cfm 1.) Compute for total TR of System 2.) Use Formula: cfm = (total TR) (300cfm/TR) 3.) take the total cfm B. Compute for friction loss (since constant friction method USED ALWAYS AS REFERENCE) 1.) Get length of the farthest terminal from the AHU (approx. using line diagram) 2.) Use formula: (Friction rate) (length of duct system) To get Friction Rate: a.) Plot total cfm and initial velocity on CHART A (AS HRAE FRICTION LOSS CHART) b.) take the value of friction loss on the left side. 3.) take the value of the system friction loss C. Duct Size Computation 1.) take A and B values 2.) plot the values of A and B on CHART A (ASHRAE FRICTION LOSS CHART) 3.) follow :
friction f c
4.) since rectangular/square duct should be used, use C HART B ( round – rect. duct conversion) *As much as possible Limit Aspect ratio to : 3:1 ( the higher the AR thegreater the cost of production)
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D. Create summarization of duct Follow: the table (refer to fig.1) and com plete: Duct Section To A A-B B- 7 7-8
