SCS Series Manual — P/N 15712:L 7/18/16 19
General System Components Concepts of Smoke Control
Dual Duct Systems. Dual duct systems have separate
heating and cooling coils, each located in a separate com-
partment. These types of systems also have separate ducts
to supply hot and cold air from each coil compartment to
mixing boxes. The mixing boxes are used to mix the hot
and cold air which will be supplied to the area served.
Multizone Systems. Multizone systems are similar to
dual duct systems because they have heating and cooling
coils located in separate compartments. The difference is
that multizone systems mix the air at the unit and supply
the mixture through low-pressure ducts to each space.
Variable Air Volume Systems. Variable Air Volume
(VAV) systems usually supply central cooling only. The
individual areas served by these types of systems typically
reheat the air near or in the area to be served or have other
sources of heating. Some VAV systems connect a bypass
from the intake side of the supply fan to the outlet side of
the supply fan, as shown in Figure 2.10, to reduce supply air volumes and pressure in the duct work. 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 unit fans serving a fire area must be shut off for smoke con-
trol applications. During a fire condition, terminal unit fans serving other areas may continue to operate normally.
Figure 2.9 Dual Duct System
Figure 2.10 VAV System with Fan Powered Terminals
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