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tips for integrating fire protection, HVAC systems
These nine guidelines will help fire protection
engineers integrate fire and life safety systems with HVAC systems.
There are many active and passive systems that provide life safety to occupants in high-rise buildings. Often they are integrated or work in unison to provide the safety intended. It is important to understand how they relate to each other in order to provide a proper approach to the design and installation of these systems.
Below are some important items to be considered
when integrating fire and life safety systems with HVAC systems for both active
smoke control and the recently introduced post-fire salvage, or smoke removal.
1. Prioritize control of any HVAC equipment used
for smoke control so that the fire alarm control is the highest level of
priority. This will override any other control signals to allow for the
required airflow quantity for exhaust/makeup air, life safety damper closure
and opening, and required unit shutdown. This may require bypassing hands-off
automatic (HOA) or variable frequency drive (VFD) controls when life safety
functions occur.
2. Each HVAC item that is required for smoke
control or life safety systems (air handling unit smoke detectors, fire/smoke
or smoke dampers, stair pressurization fans, smoke exhaust fans) may require a
dedicated wiring connection to the fire alarm system. This is a parallel path
from the HVAC control system if the fire alarm system is used for life safety
control of the building management system (BMS). The BMS can monitor these
connections, but no control can be given through the BMS unless the BMS is
listed for smoke control. If the BMS is used for smoke control, and is listed,
then the manner in which the fire alarm and BMS share signals needs to be
incorporated into the design.
3. Carefully review which type of activation is
required for smoke control systems. Is it activated by the fire sprinkler
system or the smoke detection system? For areas such as high-rise hotel tower
corridors, a common method of activation is by smoke detection in the corridor.
For low-rise podium smoke control zoning, a common method of activation is
through fire sprinkler waterflow.
- If it is activated by fire sprinkler, then the
sprinkler system zoning must match the smoke control zoning. Modifications
to zone boundaries during construction will require modifications to
sprinkler systems in the field.
- If it is activated by smoke detector, then the
detectors must be zoned to identify which units will activate the smoke
control system and which will not.
- Some properties use both fire sprinkler and smoke
detection to activate the same smoke control system. In these cases, both
systems need to be coordinated with zone boundaries.
4. Coordinate zoning of HVAC equipment with
the smoke control zoning. This will reduce the number of life safety dampers
(smoke and combination fire/smoke) required in the system and allow proper unit
shutdown and activation for a specific area without affecting other zones. Only
a single zone in alarm will be affected for the active smoke control systems,
but the fire alarm zone typically notifies both the area under emergency and
adjacent spaces for evacuation and instruction. This is also important with
fire/smoke dampers. Rather than splitting the branch ductwork within the
adjacent zone, split the ductwork inside the zone to reduce the amount of
fire/smoke dampers needed.
5. HVAC fans can be used for post-fire
salvage duty (smoke removal) provided they are equipped with the proper
accessories for a given jurisdiction. The 2012 IBC lists the base requirements
for post-fire salvage systems in Section 403.4.7. For Southern Nevada, for
example, amendments have been added to the code to further define the equipment
requirements. These include an approved secondary source of power in addition
to normal power, additional fan belts, and service factor similar to active
smoke control fans (IBC Section 909 compliant). Elevated operational
temperature requirements are not typically necessary for post-fire salvage
systems because the fans are operated after the emergency event where they
exhaust cold smoke. The designer should verify that any local amendments to the
smoke removal systems have not added any requirements for equipment.
6. For smoke removal systems, dedicated fire alarm
connections to the associated purge fans are not required. This control can be
completed by a signal from the post-fire salvage panel (either integral to the
main active smoke graphics panel or separate) to the BMS to implement the type
of control that is required to achieve the 15-minute air change for both
exhaust and makeup air.
7. The design should consider the benefits of
using either dedicated equipment or nondedicated equipment (HVAC fans).
Dedicated fans are those used only for smoke control purposes and do not operate
under normal HVAC conditions. They are typically used for stairwell
pressurization and smoke exhaust systems. Because they are not used frequently
they do not require as much maintenance, but they do require more frequent
testing. Nondedicated fans (HVAC dual-purpose fans) are allowed by code and can
provide benefit to smoke control systems to reduce costs. They are used for
normal HVAC and smoke control and can be beneficial because they are maintained
more frequently. However, maintenance needs to be performed such that it does
not impact the smoke control operation. This includes any changes to VFD
controls. The expected temperature of smoke must also be taken into account
when selecting the temperature rating for active smoke control equipment (through
either UL 705 Power Ventilator listed smoke exhaust fans or by providing
calculations to clarify a reduced temperature rating, which may be 200 to 250 F
for air handling unit fans).
8. The International Building Code requires
ductwork that penetrates fire-resistance rated walls to be protected with fire
dampers, smoke dampers, or combination fire/smoke dampers. Fire dampers are
less expensive to install and maintain because they do not require power and
smoke detection for control. Often fire/smoke dampers are the default because
it is sometimes difficult to determine what type of wall is being penetrated.
The design of the system needs to take into account the type of wall and the
required damper to minimize costs, both upfront and ongoing, as well as reduce
the complexity of the system. The layout of the ductwork also needs to be
considered to minimize the amount of dampers. It is better to make one
penetration into a corridor and feed the corridor with one duct than to
penetrate with several lateral branch ducts, which require more dampers.
9. VFDs are a great way to control the amount of air required under
both HVAC and smoke control functions. Most VFDs are programmable to allow
setpoints to be used for smoke control functions. The VFDs need to be designed
and installed such that the setpoints established during smoke control testing
are not changed in the field due to HVAC controls or other functions. It is
important to recognize the relationship that the VFD plays in both smoke
control and normal HVAC use. In addition, VFDs should be located in areas that
provide a level of protection to the panel so that during a fire condition,
they are not impacted by the fire.