Table of Contents
Advertisement
Figure 11: Supply ductwork with plenum return
Duct
Ductwork, however, can be used for the return air as
well, as shown in Figure 12. In most commercial
buildings today, both the supply and the return ductwork
(where used) is typically located in the area above a
suspended ceiling. Return air ductwork is required from
the smoke zone boundary to exhaust fans when routed
through other zones.
Figure 12: Ducted return
VM-1 Smoke Management Application Guide
Plenum
Chapter 1: Fire geometry and smoke movement in buildings
Multiple-zone systems
Multiple-zone systems are similar to dual duct systems
in that they have separate heating and cooling coils
located in a separate compartment. The difference in
these systems is that multiple-zone systems mix the air
at the unit and supply the mixture through low-pressure
ducts to each space served.
Dual duct systems
Dual duct systems have parallel heating and cooling
coils, each located in a separate compartment. Systems
of this type also have separate ducts to supply hot and
cold air from each coil compartment into mixing boxes.
The mixing boxes are used to mix the hot and cold air to
be supplied to the area served. See Figure 13 on page
14.
Variable air volume systems
Variable air volume (VAV) systems usually supply
central cooling only. The individual areas served by this
type of system will reheat the air near or in the area
being served or have other sources of heating. Some
VAV systems connect a bypass from the intake side of a
supply fan to the outlet side of a supply fan, as shown in
Figure 14 on page 14, to reduce supply air volumes and
pressure in the ductwork. Such bypasses must be
closed for smoke control applications to ensure sufficient
pressurization of protected areas.
Fan-powered terminals
Fan-powered terminals are used in conjunction with VAV
systems to provide the reheat capability of cool air being
supplied to a particular area and to circulate air within
the space. Terminal fans servicing a fire area must be
shut off for smoke control applications. During a fire
condition, terminal fans serving other areas may
continue to operate normally.
13
Advertisement
Table of Contents
