Industrial Ventilation
Design Procedure
Industrial Ventilation Design
Procedure
1.
2.
3.
4.
5.
6.
7.
8.
Find Q
Determine d
Calculate actual V
Calculate VP
Find VP loss coefficients
Calculate Fan SP
Calculate Fan TP
Choose Fan rpm from Fan Table
Design Procedure
2
Losses
 Inches of water
 Percent of velocity pressure
 Friction losses
 Elbow losses
 Other losses
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Hood entry losses
Orifice losses
Expansion and Contraction losses
Air cleaner losses
Stack losses
Design Procedure
3
Review Of Design Tables
 Refer to FIGURE 5-15 to find hood entry loss
coefficients.
 Refer to FIGURE 5-16 to find elbow losses.
 Refer to TABLE 5-5 and TABLE 5-6 to find friction loss
for the given diameter and velocity.
 Refer to TABLE 5-7A and TABLE 5-7B to find velocity
for a given VP.
 Refer to TABLE 5-8 to find area for a given diameter.
 Refer to TABLE 5-10 to find Air Density Correction
Factor for a given temperature and barometric
pressure.
 Review rest of the tables given in chapter 5.
Design Procedure
4
Review Of Design Tables
 For solving various problems given in chapter # 5 the
corresponding figures are given in chapter # 10.
 For solving design problem 4, tables 10.70.1 to
10.70.4 will be useful.
 Before solving the design problems go through the
figure and data given in chapter 10.
Design Procedure
5
Review Of Design Tables
 Refer to TABLE 3-1 to find the various ranges of capture
velocities.
 Refer to TABLE 3-2 to find the range of minimum duct
velocities for various contaminants.
 Go through all the figures in chapter # 3 representing
various hoods.
Design Procedure
6
Design Procedure
 GIVEN DATA:
 Ventilation system:
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Laboratory Hood
Volumetric Flow Rate, Q = 1500 CFM
Minimum Transport Velocity, V = 4000 FPM
Stamped elbow with R / D = 2
Design Procedure
7
Design Procedure
 Download DESIGN PROBLEM-1
 Line 1: Inlet Section
 Line 2: Target Volume Flow Rate, Q = 1500 CFM (Given).
 Line 3: Minimum Transport Velocity, V = 4000 FPM (Given).
 Line 4: Maximum Duct Diameter, D = 8.29”
We know Q = V * A
Hence Duct Area = Q / A
= 1500 / 4000 = 0.375 Sq. Ft.
We know A
= (Pi * D2) / 4
Hence, D
= 8.29”
Design Procedure
8
Design Procedure
 Line 5: Selected duct diameter = 8”
We got Maximum Duct Diameter D = 8.29”
We have to choose a diameter that is less than maximum
selected diameter so that minimum transport velocity is
not maintained in the duct.
So, let’s choose 8” diameter.
Note: Your choice is limited by the sizes given in the
table.
 Line 6: Duct Area = 0.349 Sq. ft.
Duct Area (from TABLE 5-8 at D = 8”) = 0.349 Sq. ft.
 Line 7: Actual Duct Velocity = 4298 FPM
Velocity = Q / Area = 1500 / 0.349 = 4928 fpm
Design Procedure
9
Design Procedure
 Line 8: Duct Velocity Pressure = 1.15” WG
Duct VP (from TABLE 5-7A at V = 4298 FPM) = 1.15”
WG
 Line 9-16 = N/A
(since there are no slots)
 Line 17: Duct Entry Loss Coefficient = 0.49
Given, hood has a flanged duct end
From TABLE 5-15 for a hood that has a flanged duct
end, entry loss coefficient is 0.49
Design Procedure
10
Design Procedure
 Line 18: Acceleration Factor ( 1 or 0) = 1
Since acceleration factor is 1 for hoods.
 Line 19: Duct Entry Loss per VP (17 + 18) = 1.49” WG
 Line 20: Duct Entry Loss (8 * 19) = 1.714
 Line 21: Other Losses = 0
 Line 22: Hood Static Pressure, SPh (16+20+21) = 1.714” WG
 Line 23: Straight Duct Length = 35 ft (Given)
 Line 24: Friction Factor (Hf) = 0.0304
From TABLE 5-5 at D = 8” and V = 4000 FPM Hf = 0.0304
 Line 25: Friction Loss per VP (23 * 24) = 1.064
 Line 26: No. of 900 degree Elbows = 1
Design Procedure
11
Design Procedure
 Line 27: Elbow Loss Coefficient = 0.13
From TABLE 5-16 for a stamped elbow and R/D = 2
 Line 28: Elbow Loss Factor (26 * Loss Factor(27)) = 0.13
 Line 28-32 = N/A
Since there are no branch entries
 Line 33: Duct Loss per VP (25 + 28 + 31+ 32) = 1.1940
 Line 34: Duct Loss (8 * 33) = 1.3731
 Line 35: Duct Segment SP Loss (22 + 34) = 3.087” WG
 Line 36: Other Losses = N / A
 Line 37: Cumulative Static Pressure = 3.087” WG
 Line 38: Governing Static Pressure = -3.087” WG
Design Procedure
12
Design Procedure
 Line 39-42 = N / A
 Line 1: Outlet Section
 Line 2-8 same as for inlet section
 Line 9-22 = N / A as outlet is exhaust that is it will not have
suction part
 Line 23: Straight Duct Length = 10 ft (Given)
 Line 24: Friction Factor (Hf) = 0.0304
From TABLE 5-5 at D = 8” and V = 4000 FPM Hf = 0.0304
 Line 25: Friction Loss per VP (23 * 24) = 0.3019
 Line 26: No. of 900 degree Elbows = 1
Design Procedure
13
Design Procedure
 Line 27: Elbow Loss Coefficient = 0.13
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From TABLE 5-16 for a stamped elbow and R/D = 2
Line 28: Elbow Loss Factor (26 * Loss Factor(27)) = 0.13
Line 28-32 = N/A
Since there are no branch entries
Line 33: Duct Loss per VP (25 + 28 + 31+ 32) = 0.4319
Line 34: Duct Loss (8 * 33) = 0.4990
Line 35: Duct Segment SP Loss (22 + 34) = 0.499” WG
Line 36: Other Losses = N / A
Line 37: Cumulative Static Pressure = 0.499” WG
Line 38: Governing Static Pressure = -0.499” WG
Design Procedure
14
Design Procedure
Final Calculations:
 The Fan SP = Spo – SPin - VPin
= 0.499 – (-3.087) – 1.15
= 2.436 FPM
 The Fan TP = VPo + SPo – SPin - VPin
= 1.15 + 0.499 – (-3.087) – 1.15
= 3.586 FPM
 BHP
= (Fan TP * Q) / 6362 * η
= (3.586 * 1500) / (6362 * 0.9)
= 0.94 hp
Where:
η = Mechanical Efficiency (here taken as 0.9)
You have completed the design of laboratory hood.
Design Procedure
15
Design Problems
 Download DESIGN PROBLEM –2, 3, 4 and start doing
the problems
 All are of the same procedure with minor changes.
 For fan pressure calculations refer 5.8 in the text
book.
 Refer 5.9 to know the corrections for velocity
changes.
 Refer 5.13 in the text book to get an idea of
corrections for non-standard density.
 Go through various problems given in the text book.
Design Procedure
16
CALCULATION OF Vpr
 For design problems 3 and 4 you need to calculate
corrected volumetric flow rate and VPr.
 For calculating corrected volumetric flow rate and VPr
formulae are given in the design spread sheets.
 Refer to the spread sheet solution and word solution
given carefully.
Design Procedure
17