Towards optimum fire protection, HVAC systems
These nine guidelines will help fire protection engineers integrate fire and life safety systems with HVAC systems.
The fire and life safety systems within high-rise buildings, as defined by the 2012 International Building Code (IBC) Section 403, serve to notify occupants of an emergency, suppress or control an active fire, evacuate or manage smoke in a fire area, and pressurize exit stairs for safe exit. The life safety systems often use HVAC fans and dampers to configure the required systems for a specific zone in alarm. Systems and components must be listed and approved for the purpose for which they are installed as indicated in 2012 IBC Section 907.1.3.
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.