Health care facility includes complex smoke-control system
The atrium size and the building code enforced during design required a large amount of outdoor air (OA) to be correctly supplied to the atrium at multiple levels to satisfy the smoke-exhaust requirements and maintain clear egress paths at each level.
This health care project was a 5-level, 400,000-sq-ft cardiovascular center located in a northern climate. The building was designed as a multi-use facility consisting of administration space, education/conference areas, clinic and office space, 48 intensive care unit (ICU)/critical care unit (CCU) patient rooms, interventional cath/electrophysiology labs, operating rooms, and related support functions. Tight site constraints and connections to adjacent buildings led to planning that placed the building air-handling units and fans on level five in a two-level mechanical room, with supply and return ductwork routed vertically in chases to the levels below. A sloping grade from south to north provided for ingress and egress to the building at multiple levels. This condition also created a design opportunity for a multilevel atrium for the building. Figure 6 shows the sloping grade, a west-building entry point, and the glass atrium.
The atrium size and the building code enforced during design required a large amount of outdoor air (OA) to be correctly supplied to the atrium at multiple levels to satisfy the smoke-exhaust requirements and maintain clear egress paths at each level (ground, first, and third). The cold-climate design conditions also required that any make-up air for smoke control be treated prior to entering the building, so as not to impair the effectiveness of any life safety or detection devices.
Building pressurization and ventilation were satisfied through the make-up air requirements with the HVAC design incorporating two OA-pretreat units. Under normal operation, these dedicated OA units provided pretreated OA to each of the building's fifth-floor air-handling units in a measured and fixed air quantity that satisfied the code-required OA-change rates and ventilation-air requirements while meeting the exhaust-air requirements and maintaining adequate building pressurization. Figures 7 and 8 show two of the air units in the level-five mechanical room.
An additional function of these DOAS units was to provide treated make-up air to the atrium in locations and at velocities that met code requirements related to a potential fire origin in the atrium. The smoke-control function was accomplished via the BAS sequencing, which closed supply- and return-air-duct dampers and opened other duct dampers that then diverted air to the atrium supply duct system.
The total air supplied to the atrium during the smoke-mode operation was greater than 90,000 cfm, which was removed through four roof-mounted exhaust fans. Leakage-rated dampers were used in the duct systems that served the atrium and adjacent spaces. Each damper was programmed individually to operate properly depending upon the normal mode or fire mode. Prior to occupancy, the systems were tested with test smoke supplied at various atrium locations and the designated egress paths were kept clear. Fortunately, there has been no actual need for the building to go into a smoke-control mode due to a fire in the atrium.
J. Patrick Banse has more than 35 yr of experience in the consulting engineering field and is part of Smith Seckman Reid's technical guidance team involved with codes and standards updates and QA/QC programs.