Recently, there has been an increase in the construction of high-rise buildings designed for office and laboratory use. In new high-rise buildings in Massachusetts, 780 CMR requires all stairwells/elevator hoistways built over 70 feet tall to be equipped with a smoke control system. The laboratory environment in these high-rise buildings typically dictates specific ventilation requirements, which uniquely impact the required smoke control systems.
The required smoke control systems (usually stairwell and elevator pressurization) operate by providing supply air within the stair/elevator shaft to pressurize the shaft and keep smoke out while allowing the doors to open without undue force. These smoke control systems must achieve this performance on both Normal and Emergency (generator) building power.
There are two variables that contribute to the pressure readings in the stair/elevator shafts: 1, the amount of supply air provided inside the shaft, and 2, the airflow conditions in the building. In laboratory environments, the building airflow can vary significantly depending on whether the building is on normal or Emergency power. Typically, both supply and exhaust air run, creating a balanced/neutral environment. Regardless, under emergency building power, it is typical for the building supply air to shut down and only the building exhaust air to continue running, resulting in a negative airflow condition and potentially drastically changing the pressure and door force values.
Both the smoke control and lab air systems must function properly to ensure the safety of building occupants, requiring careful coordination and commissioning to ensure the systems work properly in all scenarios.
Laboratory environments typically need a minimum exhaust flow setpoint to meet the applicable ventilation requirements. To minimize negative impacts on the differential pressure and door opening force readings on Emergency power, the building exhaust air could be programmed through the Building Management System (BMS) to ramp down to this minimum exhaust flow setpoint (as established by the laboratory ventilation system design) on Emergency building power, rather than continuing to run at the Normal building power flow setpoint. This typically results in a building environment compatible with the required smoke control systems, as the building is not too negatively pressurized.
Alternatively, the HVAC systems could be programmed to shut down the supply air any time the smoke control system is active. This makes the normal power airflow condition and the emergency power condition match, allowing the stairs to be balanced, knowing they will meet the specs in both power conditions. Under this approach, care must be exercised to ensure that maximum door-opening forces have not exceeded due to negative pressure conditions.
In summary, stair or elevator pressurization systems within high-rise office/laboratory occupancies can introduce complications when commissioning the smoke control systems. By reviewing the potential issues during design and startup, the system can be adjusted appropriately to avoid problems and delays during final Commissioning and turnover. If you have questions regarding how these requirements apply to your project, please contact us at info@crcfire.com.