exhaust and replacement air systems. Determine the number and location of
velocity pressure readings required for round and rectangular ducts
according to ACGIH-2092S. Drill traverse access holes. [Round ducts
require two traverse access holes positioned 90 degrees apart.]
[Rectangular ducts may require several traverse access holes.]
Take pitot traverses away from air disturbing devices (i.e. elbows, branch
entries, duct expansions, and hood transitions). Minimum distances are:
a.
Five (5) duct diameter of straight duct after the fan outlet; and
b.
Seven and one-half (7.5) duct diameters of straight duct after an
air disturbing device.
When these distances of straight duct are not available, use a schematic
drawing to note the disturbance producing device, and distance between the
pitot traverse and the device.
Confirm one velocity pressure reading for each access hole after completing
a traverse. Accept traverse data when the difference between the original
and confirmation measurement is plus or minus 10 percent; otherwise repeat
the traverse. Plug holes with cap plugs immediately after each traverse.
Convert velocity pressure readings to velocity before averaging the duct
velocity. Calculate average velocity from velocity pressure readings and
volume flow rates for the following locations:
a.
Replacement air fan outlet;
b.
Replacement air duct branch;
c.
Exhaust air duct branch, including hoods [and submains];
d.
Exhaust fan inlet or outlet;
[e.
Air pollution control device inlet; and]
[f.
Outside and return air ducts in recirculating replacement air
system.]
3.2.2.3
Air Velocity Meter Readings
A flow hood may be used for measuring office and restroom replacement air
quantities. Do not substitute air velocity meter readings for manometer
and pitot tube readings. Use air velocity meters to estimate the following:
a.
Velocity exiting from replacement air systems without ductwork;
b.
Crossdrafts in a room;
c.
Hood capture velocity;
d.
Duct velocities less than 3 m/s 600 fpm; and
[e.
Slot velocities.]
3.2.2.4
Static Pressure Readings
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SECTION 15951N
Page 30
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