including all supply and return ducts, any ceiling plenums
may have hot water heating coils used for maintaining
used as ducts and all exhaust ducts. Energy consumption,
temperature conditions in the space under partial load
security and sound attenuation shall be major
conditions. Fan-powered terminals located on the
considerations in the routing, sizing and material
perimeter zones and on the top floor of the building
selection for the air distribution ductwork.
shall contain hot water coils for heating.
Ductwork Pressure: Table 5-3 provides pressure
Air Distribution. Ductwork shall be designed in
classification and maximum air velocities for all
accordance with ASHRAE: Handbook of Fundamentals,
ductwork.
Duct Design Chapter, and constructed in accordance with
the ASHRAE: HVAC Systems and Equipment Handbook,
Ductwork construction shall be tested for leakage prior
Duct Construction Chapter, and the SMACNA Design
to installation. Each section tested must have a minimum
of a 6.1 m (20 ft) length straight-run, a minimum of two
designed and constructed to allow no more than 3 percent
elbows and a connection to the terminal. The stated static
leakage of total airflow in systems up to 747 Pa (3.0 in
pressures represent the pressure exerted on the duct
WG). In systems from 747 Pa (3.0 in WG) through 2,488
system and not the total static pressure developed by the
Pa (10.0 in WG) ducts shall be designed and constructed
supply fan. The actual design air velocity shall consider
to limit leakage to 0.5 percent of the total air flow. All
the recommended duct velocities in Table 5-4 when noise
ductwork joints and all connections to air handling and
generation is a controlling factor. Primary air ductwork
air distribution devices shall be sealed with mastic-
(fan connections, risers, main distribution ducts) shall be
Table 5-3
Ductwork Classification
Static Pressure
Air Velocity
Duct Class
250 Pa
(1.0 in W.G.)
< 10 m/s DN
< (2000 FPM DN)
Low Pressure
500 Pa
(2.0 in W.G)
< 10 m/s DN
< (2000 FPM DN)
Low Pressure
750 Pa
(3.0 in W.G.)
< 12.5 m/s DN
< (2500 FPM DN)
Medium Pressure
1000 Pa (+4.0 in W.G.)
< 10 m/s DN
> (2000 FPM UP)
Medium Pressure
1500 Pa (+6.0 in W.G.)
< 10 m/s DN
> (2000 FPM UP)
Medium Pressure
2500 Pa (+10.0 in W.G.)
< 10 m/s DN
> (2000 FPM UP)
High Pressure
136 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
5.8 HVAC Components
Revised March 2005 PBS-P100
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