HVAC 1. You are needing to size a duct and estimate the pressure drop for a duct
ID: 2086136 • Letter: H
Question
HVAC
1. You are needing to size a duct and estimate the pressure drop for a duct section that provides 2,000 cubic feet per minute (cfim). The duct section has an equivalent length of 300 feet plus the pressure drop of two standard 90° elbows (radius/diameter, R/D -0.75). a. Select a size of round ductwork for this flow rate b. Estimate the pressure drop associated with this duct section in inches of water 2. Given the fan design performance with system curve on the back of this page. What would the resulting new system operation point be (flow rate, pressure) if the fan were slowed down to only 1 /3 of the of the design speed (67% of design speed)? .Explanation / Answer
cfm= 2000
cmm= 609.6
flow rate in m3/s = 10.16
1) friction rate = assume 0.1
by referring friction chart, the diameter of duct is 24mm in diameter.
2) total length of duct= 300 + 2.1 + 2.1= 304.2ft
pressure drop = total length x friction rate
= 304.2 x 0.1
= 30.42 mm of water
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