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Dual duct HVAC systems
Dual duct HVAC systems provide a central source of
conditioned air through a hot supply duct and a cold
supply duct serving multiple zones. Each zone has
mixing boxes to control room temperatures.
Configuring for smoke control of dual duct HVAC
systems utilizes mixing box air flows for pressurization.
Cold air ducts are often relied upon for air supply due to
their larger size.
See Table 6 below for control settings.
Multi-zone HVAC systems
Multi-zone HVAC systems provide separate air mixes for
each HVAC zone with multi-zone units.
Most systems are limited to about 12 zones due to
energy efficiency considerations.
Table 6: Dual duct smoke control settings
Smoke zone
Exhaust air damper OPEN
Hot duct damper CLOSED
Cold duct damper CLOSED
Table 7: Multi-zone smoke control settings
Smoke zone
Exhaust air damper OPEN
Supply air damper CLOSED
VM-1 Smoke Management Application Guide
Adjacent zones
Exhaust air damper CLOSED
Exhaust air damper CLOSED
Hot duct damper CLOSED
Cold duct damper CLOSED
Adjacent zones
Exhaust air damper CLOSED Exhaust air damper OPEN
Supply air damper OPEN
For smoke control, multi-zone systems maximize air to
zones designated for pressurization around the fire.
Cold air ducts are often relied upon for air supply due to
their larger size.
See Table 7 below for control settings.
Variable air volume systems (VAV)
VAV systems serve multiple building zones with
conditioned air at required volumes.
Terminal units in each building zone contain dampers to
control air volume and may contain fans and heating
coils.
Damper positioning and controlling of supply and return
fans to provide maximum air volume are needed for
smoke control applications using VAV systems.
Static pressure controls must be reset to permit
maximum air flow without duct collapse or rupture.
See Table 8 on page 36 for control settings.
Dual duct central system
Supply fan ON
Return fan ON
Exhaust air damper OPEN
Outside air damper OPEN
Return air damper CLOSED
Reset static pressure control to
maximize air flow and prevent duct
failure
Multi-zone central system
Supply fan ON
Return fan ON
Outside air damper OPEN
Return air damper CLOSED
Reset static pressure control to
maximize air flow and prevent duct
failure
Chapter 2: Smoke control system hardware
Remote zones on same dual duct system
Exhaust air damper CLOSED
Hot duct damper CLOSED
Cold duct damper CLOSED
Remote zones on same multi-zone system
Exhaust air damper CLOSED
Supply air damper CLOSED
35
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