Testing atrium smoke control systems
Smoke control systems often require unique testing strategies and involve a larger than usual coordination effort between construction disciplines.
By Justin Garner, PE, TBE, Engineered Air Balance Co. Inc.
On a recent hospital project, the test and balance agency was tasked with testing the functionality and performance of two large atrium smoke control systems. Smoke control systems often require unique testing strategies and involve a larger than usual coordination effort between construction disciplines.
These particular systems required coordination with the architect, design mechanical and electrical engineer, life safety consulting engineer, general contractor, mechanical contractor, electrical contractor, controls contractor, and the fire alarm contractor. Further, each piece of the system from each discipline required individual testing prior to the integrated test of the system. This article is a brief description of the total process involved in proving to the Authority Having Jurisdiction (AHJ) that the atrium smoke control systems were operational for the purpose of occupying the building.
Construction and Design Phases
During the design phase of the project, the architect hired a life safety consultant to perform smoke plume analysis and initial airflow calculations utilizing the methodology in NFPA 92B, Standard for Smoke Management Systems in Malls, Atria, and Large Spaces.
The mechanical engineer then used the design airflows from the life safety consultant’s calculations to design the fan systems for each atrium to provide the correct airflow.
The mechanical engineer also provided the required makeup air opening sizes to the architect and scheduled the appropriate DDC control sequences for the systems. The electrical engineer was tasked with including the smoke control fan systems, DDC controls, and fire alarm controls in the emergency power system, and incorporating the correct components into the fire alarm system schematics and specifications.
The architect was tasked to design the smoke barrier enclosure to the required fire and smoke ratings, as well as determining the doors, window panels and hardware required for operation of the system. This design of the smoke control system was included in the construction project documents.
During the construction phase of the project, all components of the system were installed as indicated on the construction drawings.
During the initial TAB inspection of the system, it was noted that a sheetrock furr down (also known as a bulkhead) was installed, obscuring about one-third of the inlet duct for the larger smoke control fan.
Further, no access doors were provided for inspecting the fan equipment or dampers. The general contractor and mechanical contractor were consulted and they agreed to add access doors, but no action was taken on the obstructed ductwork.
The makeup air for the systems was to be provided by sliding electric entry doors and motorized panels at each exterior entrance to the main atrium smoke zone. The smaller atrium had motorized panel windows only.
After inspection, it was noted that the controls contractor did not have any provisions to command the doors and windows. The general contractor was consulted as well as the fire alarm contractor, and both the fire alarm and controls contractors thought the other trade was to control the doors and fans.
Therefore, no controls had been installed by any contractor on the systems.
A meeting was held with the design team, the owner, and the contractors involved to clarify the system operation. The life safety consultant indicated the design intent as listed in the code and the design basis of their model. The architect also commented on their part regarding the windows and doors.
The mechanical engineer clarified that the DDC controls should operate the entire system, with an input from the fire alarm system and a status back to the fire alarm system. This was confirmed through the RFI process and the controls work proceeded.
A pre-TAB review of the systems was performed. During this review, the smoke control zones were identified using the architectural drawings, and the door and window openings for the makeup air paths were measured. The result of these calculations when compared to the design airflows for each fan system indicated that there were not enough makeup air openings for the larger atrium system.
The code specifies that the air velocity at the point of contact with the smoke plume cannot exceed 200 feet per minute.
This issue was discussed with the design team and it was determined that one set of exterior doors was considered in the original calculation, but not scheduled for automatic opening hardware. The design team asked for a system performance test with the doors open and closed to determine if the code criteria could be met.
The initial test of the system was scheduled for late in the evening. Since the controls were not installed, the entire system was manually commanded. The fans were operated at design speed and Pitot tube traverses were used to determine system airflows. All operating data was recorded.
The test of the larger system showed that the fan could not achieve design airflow due to the bulkhead obstruction.
The general contractor promptly removed as much of the obstruction as possible and the system was retested. After the removal, the system could achieve design airflow.
During the second test, velocity profiles of each makeup air entrance were measured using rotating vane anemometers on grids laid out with tape. This testing determined that all exterior doors were required for makeup air to the larger atrium system. The design team and contractor determined and ordered the required hardware and the components for automatic opening.
Unfortunately, the door controls were a long lead-time item and could not be procured within the time required for issuance of a temporary certificate of occupancy. Therefore, additional window panels on the interior vestibule of the large atrium were temporarily removed to create more makeup air openings. The smaller atrium system performed as scheduled with makeup velocities within the code limits.
The DDC and fire alarm system components were installed and tested individually. The DDC controls interface to the motorized doors and windows was problematic and required a great deal of troubleshooting from the general contractor and automatic access contractor. Once these issues were resolved, a final acceptance test was scheduled with the owner and design team to prove functionality a few days before the required temporary occupancy milestone.
A system airflow performance report was submitted to the design engineer for review prior to the acceptance test. It was also agreed that final velocity readings would be taken to prove the temporary makeup solution was acceptable.
To initiate the test with the building operating on normal power, the fire alarm contractor tripped a pull station in each atrium and the smoke control systems were activated.
The automatic doors and window panels opened and the fan systems started and ramped to full airflow. Air velocities were measured at the main entrance doors to the large atrium, but the readings were affected by high winds and did not meet the code criteria. It was agreed to continue testing the functionality of the systems.
Next, normal power was de-energized to the building with the smoke control systems operating, and the emergency power system was activated. The smoke control system shutdown and restart on emergency power was timed and determined to be within acceptable limits.
The smoke systems were then deactivated manually at the fireman’s smoke control override panel and verified for proper operation. After reactivation at the fireman’s panel, the fire alarm system was reset under emergency power.
The design team requested that the smoke control systems be activated by a beam detector in each atrium. Using a rope connected to the atrium ceiling, each beam detector was tripped, initiating the respective smoke control system.
Finally, the building power was returned to normal. The shutdown and restarts of the systems were verified to be within acceptable limits. The only final hurdle for the system was proving the makeup velocities were acceptable.
After studying the weather forecast, the morning of the day for temporary occupancy was determined for a retest of the velocities. The wind was very calm, and the large atrium system was initiated and tested. The door velocities with the temporary panels removed were found to be within the code requirements.
The design engineer was able to write a letter to the AHJ certifying that the systems were operational and the facility was granted a temporary certificate of occupancy on schedule. The final verification of the system came weeks later when the door hardware for the final makeup door was installed and tested satisfactorily.
- The design team members must coordinate and be very careful to include the appropriate components and sequences in the design documents for a functional system.
- The controls and fire alarm contractors must coordinate to provide integration between systems to meet the appropriate control requirements.
- The design team and general contractor must ensure that architectural components do not interfere with proper operation of the system.
- Finally, the TAB firm must be able to suggest and facilitate an appropriate test to verify system performance and sequencing through all operating modes of the system.
This article originally appeared in the TAB Journal, published by the Associated Air Balance Council.