Integration: HVAC fans and smoke control
Fire, life safety, and HVAC systems must be integrated by the engineer to achieve reliability in smoke control systems. This includes mechanical equipment, physical barriers, or a combination of both.
- Explain the basics of a smoke control system.
- Assess the codes and standards that must be applied when designing a smoke control system.
- Identify the ways to test and document the successful design of the system.
The 2015 edition of NFPA 92: Standard for Smoke Control Systems, defines dedicated smoke control systems and nondedicated smoke control systems as:
- Dedicated smoke control system: Smoke control systems and components that are installed for the sole purpose of providing smoke control and that upon activation of the systems operate specifically to perform the smoke-control function.
- Nondedicated smoke control system: A smoke control system that shares components with some other system(s), such as the building HVAC system, which changes its modes of operation to achieve the smoke control objective.
The most recent edition of the International Building Code (IBC) requires the implementation of smoke control systems in a limited number of building scenarios. Atriums connecting more than two stories, underground buildings with occupied levels more than 30 ft below the finished floor of the lowest level of exit discharge, windowless detention or correctional facilities, stage ventilation, and/or assembly spaces using smoke-protected seating are required to be provided with a smoke control system. Although high-rise structures only require smoke-removal systems for post-salvage operations, implementation of smoke control systems in high-rise towers is a common occurrence. Additional requirements based on local jurisdictions, corporate-brand requirements, or as a result of possible alternate means and methods may also require the smoke control system.
The most common building component in which truly dedicated smoke control systems are used is a pressurized exit or smoke-proof enclosure, such as a high-rise pressurized stairway. This is due to strict requirements imposed by codes and standards, which regulate how these building components are to be serviced and subsequently allowed openings within dedicated exit enclosures. Other building components where dedicated smoke control systems will predominantly be used are pressurized elevator hoistway systems or atriums.
Outside of these buildings components, smoke control systems most likely to be encountered are typically nondedicated smoke control systems, or hybrid systems, which combine the use of dedicated and nondedicated equipment. For example, multi-use buildings (i.e., hotel resorts and casinos) with podium-level smoke control systems where high ceilings are furnished will typically be designed to the air-change or exhaust method. With activation of the associated smoke zone, it is common for mechanical makeup air to be provided by building normal-use air-handling fans. Smoke exhaust will be provided by either dedicated smoke-exhaust fans for hybrid systems, or at times by the return side of air-handling units or general-exhaust fans that double as smoke-exhaust fans, for true nondedicated systems.
Typical smoke control systems provided in high-rise towers will be classified as hybrid systems and will customarily be designed to use either the pressurization method or air-change method of smoke control. Within these vertical structures, common vertical shafts can serve to transfer conditioned air to each level during normal use. During a fire scenario, these same vertical shafts will provide exhaust or supply air, as needed, when the system is configured for smoke control. Supply air for the air-change method of smoke control oftentimes will be furnished by a nondedicated rooftop air conditioning unit and exhaust provided by a dedicated smoke-exhaust fan for both pressurization and air-change methods.
Advantages, disadvantages of systems
The above nondedicated and hybrid system examples integrate equipment used on a day-to-day basis for normal building conditioning and ventilation requirements in addition to serving life safety functions. A considerable benefit of incorporating this methodology of design is that system impairments are more likely to be identified and addressed promptly. Dedicated smoke control system impairments have the potential of not being recognized as readily, which can negatively impact the effectiveness or impair the system during a life safety scenario. Other benefits to employing nondedicated system designs is the consolidation of equipment functionality, which results in less building area being tied to the housing and placement of equipment.
These systems also can reduce control-system components. A reduction in the overall number of fans and air-distribution duct systems can be accomplished when integrated (nondedicated) systems are applied. Furthermore, in most cases there will be a reduction in the costs related to equipment acquisition and maintenance.
Once operational, for many properties, ongoing tenant improvements and renovations are a common occurrence. Caution needs to be taken when this occurs, especially when nondedicated systems are involved. These types of activities have the potential to negatively impact smoke control systems, particularly integrated systems, unless a complete understanding of the intended design and functionality of impacted equipment and systems is recognized at the onset of the project by the responsible design professional. Unintentional impairment to smoke control systems can occur due to smoke-zone boundary reconfigurations, equipment modifications, equipment replacements, equipment additions, or alterations to system programming, among numerous other possible scenarios.
With the implementation, construction, and installation of smoke control systems, certification or commissioning of these systems by a qualified special inspection agency is required by many of the governing codes. Section 1705.18 of the 2015 edition of IBC states, "Smoke control systems shall be tested by a special inspector." Subsequent subsections provide the general scope of testing requirements and required qualifications the inspector shall meet.
Section 11.8.1 of the 2015 edition of NFPA 1: Fire Code requires newly installed smoke control systems be inspected by the authority having jurisdiction (AHJ) in accordance with NFPA 92. Furthermore, section 9.3.1 of the 2015 edition of NFPA 101: Life Safety Code indicates smoke control systems will be inspected and tested in accordance with NFPA 92. Section 9.3.3 of NFPA 101 states, "Acceptance testing shall be performed by a special inspector ... " The 2015 edition of NFPA 4: Standard for Integrated Fire Protection and Life Safety System Testing provides standardized testing protocols for integrated life safety systems, which may be applied to the commissioning of smoke control systems.
Commissioning of smoke control systems will be in accordance with the approved design documentation, applicable building code, and AHJ requirements. System commissioning by a special inspection agency requires confirmation of each smoke control system in its entirety, including installation and the ability to achieve intended design criteria. The commissioning process for smoke control systems by the special inspection agency is ideally executed in a consistent, specific progression of activities as follows; test plan preparation, field/equipment inspections and testing, system sequence testing, performance testing, and secondary power confirmation. With the phasing of construction being common practice, the following progression of commissioning activities will be applied to each individual smoke-control zone to the greatest extent possible.
Qualified contractors will complete equipment installation, programming, sequence pretesting, system air balancing, and confirmation of proper performance of all smoke control systems and associated components. Coordination and oversight of this effort are to be provided by the general contractor for the project. The responsibility or role of the special inspection agency is only to inspect and witness testing of complete and functional systems. Otherwise, there may be conflict-of-interest issues if their level of involvement is beyond the previously stated scope of services.