Brochure
D
0.968 D
0.865 D
0.679 D
0.321 D
0.032 D
0.135 D
0.939 D
0.765 D
0.563 D
0.437 D
0.235 D
0.061 D
0.074 D
0.288 D
0.500 D
0.712 D
0.926 D
Performing duct traversals
For maximum airflow accuracy, several readings
must be taken across a traverse plane, converted to
velocity, then averaged. The illustration in Figure
1 shows the points along the traverse plane where
measurements should be taken, either in rectangular
or circular ducts.
•
A minimum of 25 points must be measured in a
rectangular duct traverse.
•
When traversing a duct side less than 18 in. (450
mm), take readings from the center of equal areas
that are no more than 6 in. (150 mm) apart, with a
minimum of two points per side of the duct.
•
The preferred location of the traverse in a supply
duct should be in a straight section of duct with 10
straight duct diameters upstream, and 3 straight
duct diameters downstream of the traverse plane,
although a minimum of 5 duct diameters upstream
and 1 duct diameter downstream may give
adequate results.
•
When the traverse is located close to the fan, flow
conditions are usually more favorable upstream on the
return side. The traverse on the upstream side should
be 0.5 duct diameters upstream of the fan inlet.
Equivalent diameter =
√ (4HV/π)
H = horizontal duct dimension
V = vertical duct dimension
π = 3.14
Recommended maximum duct velocities
Application
Main Ducts* Branch Ducts
Supply
(fpm)
Return
(fpm)
Supply
(fpm)
Return
(fpm)
Apartments 1000 800 600 600
Auditoriums 1300 1100 1000 800
Banks 2000 1500 1600 1200
Hospital Rooms 1500 1300 1200 1000
Hotel Rooms 1500 1300 1200 1000
Industrial 3000 1800 2200 1500
Libraries 2000 1500 1600 1200
Meeting Rooms 2000 1500 1600 1200
Offices 2000 1500 1600 1200
Residences 1000 800 600 600
Restaurants 2000 1500 1600 1200
Retail Stores 2000 1500 1600 1200
Theaters 1300 1100 1000 800
*Use branch duct values when sound control is critical
Courtesy of TABB (Testing, Adjusting and Balancing Bureau)
Typical design air velocities
Air path element Face velocities (fpm)
Outdoor Air Intake* 400 (7000 cfm and greater)
Exhaust* 500 (5000 cfm and greater)
Throw-Away Filter 200-800**
Heating Coil (Steam / Hot Water) 400-500 (200 min., 1500 max.)
Cooling Coil 500-600
Face 30/30 400-600
Return Through Undercutting of Door 200-300
* Velocities for louver net free area; remaining velocities for total face area
** 300 fpm typical upper limit for most inexpensive throw-away filters
Courtesy of TABB (Testing, Adjusting and Balancing Bureau)
Residential ventilation air requirements (cfm)
ASHRAE 62.2-2004 recommends a mechanical exhaust, supply, or
combination thereof be installed for each residence to provide outdoor
air ventilation at rates no less than the following:
Floor Area (ft2) Bedrooms
0-1 2-3 4-5 6-7 >7
<1500 30 45 60 75 90
1501-3000 45 60 75 90 105
3001-4500 60 75 90 105 120
4501-6000 75 90 105 120 135
6001-7500 90 105 120 135 150
>7500 105 120 135 150 165
Adapted from ASHRAE Standard 62.2-2004
•
Assumes two persons in a one-bedroom dwelling unit, and an addi-
tional person for each additional bedroom.
•
Increase ventilation rate by 7.5 cfm per additional person if higher
occupant densities are known.
©2006 Fluke Corporation. All rights reserved. Specifications subject to change without notice.
Printed in the U.S.A. 12/2006 2806211 F-EN-N Rev A
Figure 1. Measuring points and traverse lines for rectangular and circular ducts.
Helpful tips
1. When performing a duct traverse, always ensure the nose of the
Pitot tube is parallel to the duct wall and facing the airflow.
2. Take readings in long, straight runs of duct, where possible.
Avoid taking readings immediately downstream of elbows or
other obstructions in the airway.
Log-Tchebycheff Rule for
Rectangular Ducts
Number of Points
or Traverse Lines
Position Relative to
Inner Wall
5
0.074, 0.288, 0.500,
0.712, 0.926
6
0.061, 0.235, 0.437,
0.563, 0.765, 0.939
7
0.053, 0.203, 0.366,
0.500, 0.634, 0.797,
0.947
Number of
Points per
Diameter
Position Relative to Inner
Wall
6 0.032, 0.135, 0.321, 0.679,
0.865, 0.968
8 0.021, 0.117, 0.184, 0.345,
0.655, 0.816, 0.883, 0.981
10 0.019, 0.153, 0.217, 0.361,
0.639, 0.783, 0.847, 0.923,
0.981