CONTAM simulation results of ‘Neutral zone position control type pressure differential system’
I conducted a simulation of applying 'Neutral zone position control type pressure differential system' to a tall building in South Korea.
1. Building overview
It is a tall building consisting of parking lots (B7F~B1F), commercial facilities(1F~2F), and apartment complexes (3F~43F, 6 households/floor), and has a structure in which one corridor in the center is connected to the 9 vertical shafts. The parking lots on each floor are connected to each other through vehicle ramps.
 |
| Figure 1 - Basement floor |
 |
| Figure 2 - 3rd floor |
2. Overview of 'Neutral zone position control type pressure differential system'
- Installation of 9 dampers connecting each of the 9 vertical shafts and the parking lot on the first basement floor (See Figure 1).
- Installation of 9 dampers connecting each of the 9 vertical shafts and outdoor air on the rooftop.
3. Scenario conditions
- Scenario common conditions (cold weather, dawn): outside temperature -10.4℃, atmospheric pressure 100,499 Pa, wind speed 9.7m/s, wind direction 0˚ (northern wind), parking lot temperature on the first basement floor -10.4℃
- Scenario 1 (right before a fire occurs, all dampers are closed): All doors are closed, all vertical shafts have a temperature of 20℃
- Scenario 2 (immediately after the fire occurs, only all dampers on the first basement floor are opened): All doors are closed, all vertical shafts have a temperature of 20℃, and the damper opening area is 1m^2.
- Scenario 3 (immediately after the fire occurs, only all dampers on the first basement floor are opened): All doors are closed, all vertical shafts have a temperature of 20℃, and the damper opening area is 6m^2.
4. Simulation results
A. Neutral zone locations in the vertical shafts
- Locations of neutral zone in Scenario 1: 19th or 20th floor (there is no neutral zone in vertical shaft 4 in Figure 1)
- Locations of neutral zone in Scenario 2: 1st floor
- Locations of neutral zone in scenario 3: 1st floor
B. Pressure differential at the door of ‘Household 1’ on the 3rd floor (=corridor pressure compared to household)
- Scenario 1 : -27.6Pa (If a fire breaks out in this household, smoke immediately spreads through the corridor to the vertical shaft)
- Scenario 2 : +9.7Pa (When a fire breaks out in this household, the pressure on the corridor is higher, so smoke cannot spread into the corridor side. However, because the differential pressure value is not high enough, if the fire fully grows, smoke can spread into the corridor side)
- Scenario 3: +10.7Pa (When a fire breaks out in this household, the pressure on the corridor side is higher, so smoke cannot spread into the corridor side. However, because the differential pressure value is not high enough, if the fire fully grows, smoke can spread into the corridor side)
5. Review
- In Scenarios 2 and 3, when the fire fully develops, the problem of smoke spreading from the fire place to the corridor seems to be solved by pressurization of the corridor or vestibules only for the lower floors of about the 10th floor or lower.
- Even if a fire fully develops on a floor with a floor height of approximately 3 m, the minimum differential pressure at the entrance door that can prevent the spread of smoke is approximately 25 Pa (the minimum differential pressure required in a building with partially installed sprinkler equipment). In case of scenario 2, the pressure differential at the door of the unit is more than 25Pa from the 10th floor to the upper, and in case of scenario 3, from the 9th floor to the upper.
- Opening the first floor door during evacuation is not a problem as it contributes to lowering the neutral zone position. However, to prepare for fires in the summer, it is necessary to apply the air lock door concept to the first floor doors to keep the opening area of the lower floor small.
- In Scenario 2 and 3, the neutral zone has come down to the first floor, so the airflow due to the stack effect at all floors can be considered to be formed from the inside of the building toward the outside air(ambient). This is expected to help prevent flames from spreading to upper floors through the fire room windows.
- The differential pressure of the door that can be opened varies depending on the width of the door and the door closer setting force, but generally should not exceed about 60Pa. In scenario 2, a pressure of more than 60Pa applies from the 27th floor to the upper, and in scenario 3, from the 26th floor to the upper. This means that in the case of the elderly or the weak on the 26th or 27th floor or higher, a situation may arise where evacuation itself is impossible because the door cannot be opened. This seems to be the biggest weakness of the 'Neutral zone position control type pressure differential system' in the event of a fire on the lower floor of a tall building.
However, as fires occur in higher floors, if the location of the neutral zone is controlled by adjusting the damper opening area, the number of floors where this problem occurs will gradually decrease. On the other hand, in the event of a low-rise fire, immediately starting an evacuation from a high-rise to a low-rise may not be a good decision.
- As the temperature of the ambient air becomes similar to the temperature inside the building, the maximum differential pressure between the vertical shaft and the ambient air at the same height caused by the stack effect gradually decreases. This means that the pressure of the vertical shaft compared to ambient air, which can be adjusted through 'neutral zone position control', decreases as the temperature difference decreases. Therefore, smoke control through differential pressure control may become difficult. This could be another major weakness of this system.
Meanwhile, according to NFPA's U.S. residential fire statistics (2011-2015), there was a statistical survey that found that fires occur twice as often in winter compared to summer, and the number of fire deaths is three times higher. Additionally, the investment cost per unit area is known to be approximately 2 to 7 $/m^2 for sprinkler systems, approximately 1 to 3 $/m^2 for fire alarm systems, and approximately 10 to 30 $/m^2 for smoke control systems. Because the investment cost of the smoke control system is relatively large, it is not easy to apply this system widely. The existing smoke control system is positioned as a limited system that is only applied to high-rise or underground buildings where escape takes a long time, or large-scale buildings where sprinkler operation is limited due to high ceilings.
Considering these points comprehensively, the 'neutral position control type smoke control system that includes installing a smoke window in the room where the occupants are' has the potential to be repositioned as a smoke control system that all buildings must basically have. There is a need for further research and analysis.
- Additionally, an additional simulation was conducted to determine the impact of opening the fire floor door under the condition of applying the air lock door concept to the first floor doors. As a result, it appears that smoke within the household does not spread to the vertical shaft unless the household door, annex door, and staircase door are opened at the same time for a considerable period of time.
6. Conclusion
- The above simulation results appear to be a basis for proving the following.
a. There is a significant possibility that the 'Neutral zone position control type pressure differential system' can prevent smoke from a fire within a household in a tall building from spreading toward the corridor, and thus is an effective system in preventing mass casualties.
댓글
댓글 쓰기