The volumetric flow rate of smoke generated from the fire in large space often reaches to hundreds of thousands CMH because of extended floor height and as it’s more difficult to isolate the smoke to the limited area, comparing to normal-scale building, design and operation of effective smoke control system for large space is more than important. In this study, with the analysis model for such a large space as exhibition hall or conference room in conventional center, design of mechanical smoke exhaust system was conducted based on currently-available design standard which was then followed by numerical analysis of the design using 3D numerical analysis method. For conference room at 2.0 MW heat release rate, 99,173 CMH flow rate is required, if smoke layer is maintained at 60% of the floor height and for exhibition hall at 8.8 MW with 80% of floor height, flow rate required is 219,802 CMH, which are incorporated into the design. In view of 3D numerical analysis, accuracy of the design according to algebraic expression is sufficient.
Construction of the structure with large space began in earnest in 1980s in line with the construction of indoor stadium for the booming international indoor sports events in Korea, which has maintained a growing tendency along with increasing number of large and complex buildings. The volumetric flow rate of smoke generated from the fire in large space often reaches to hundreds of thousands CMH because of extended floor height and as it’s more difficult to isolate the smoke to the limited area, comparing to normal-scale building, design and operation of effective smoke control system for large space is more than important.
Recognizing the hazards caused by fire smoke in large space in many countries, smoke control design guideline for large space has been developed and proposed worldwide since 1980s [
In this study, design of smoke safety system by mechanical smoke exhaust in conventional center was presented with the application of currently-available design standard then followed by 3D numerical analysis method.
In this study, design which was intended to apply mechanical smoke exhaust system in large space to a full-scale space analysis model for large space was conducted based on design guideline [
Major design factors for mechanical smoke exhaust system in large space include the followings. Heat Release Rate (Q) refers to initial fire development character which was assumed as Equation (1) that t-squared fire is selected and then hear release rate in steady-state character is occurred.
Q = α t 2 (1)
where, α is the fire growth coefficient and t is the time elapsed since the fire occurred. Convective Portion of Heat Release Rate, (Qc) is considered 70% of total Heat Release Rate.
Conditions of axisymmetric plumes were applied and mass flow rate of plume, (mp) representing smoke generation is determined according to following Equation (2)
m p = ( 0.071 Q c 1 / 3 H s 5 / 3 ) + 0.0018 Q c (2)
where, Hs is the smoke layer height.
Mechanical air is supplied at the bottom of smoke layer and to ensure the plume is generated and rises stably, air flow velocity is limited to 1 m/s.
To maintain the smoke exhaust efficiency on ceiling, flow rate per exhaust outlet and the spacing between exhaust outlets need to be designed to avoid plugholing. Maximum flow rate of exhaust outlet (Vmax) per outlet is determined according to Equation (3) below:
V max = 4.16 γ d 5 / 2 ( T s − T o T o ) 1 / 2 (3)
where, γ is location factor, d is depth of smoke layer below the outlet, Ts is temperature of smoke layer and To is ambient temperature.
And the minimum distance between exhaust outlets (Smin) is determined according to following Equation (4)
S min = 0.065 V e 1 / 2 (4)
where, Ve is exhaust flow rate per outlet.
The building subject to mechanical smoke exhaust system for large space is, as seen in
Floor height of conference room in S convention center (
Plume flow rate or smoke generation on assumption that smoke layer is maintained at 8.4 m height or 60% of floor height was estimated at 99,173 CMH
and smoke exhaust system was designed to accommodate 100% of such smoke generation and on the other hand, when smoke layer is maintained at 7.0 m or 50% of floor height, smoke exhaust requirement will be reduced to 77,590 CMH.
But smoke exhaust system was not considered in existing conference room and thus, air duct needs to be provided to apply the smoke exhaust system. Ceiling duct for HVAC was installed in conference room and as exhaust capacity for HVAC was designed with 33,000 CMH per compartment, exhaust fan with additional capacity, as seen in
Floor height of exhibition hall in S Convention center was designed with 11.1 m and heat release rate was estimated at 8.8 MW referring to heat release rate per unit area of shops when the fire occurred at exhibition hall [
Given the relatively lower floor height of exhibition hall comparing to conference room, it’s designed to maintain the smoke layer at 8.9 m or 80% of floor
height and in such a case, smoke exhaust requirement of 219,802 CMH was estimated as a result of calculating the plume flow rate or smoke generation. Like conference room, smoke exhaust system was not considered for exhibition hall too, and thus air supply and exhaust design was implemented to apply smoke exhaust system. When it comes to exhibition hall, whole space is open as a single space and ceiling duct was provided for HVAC and maximum 282,800 CMH smoke exhaust capacity could be secured, making use of air flow for HVAC. Air supply for smoke exhaust system is designed to perform at the bottom of wall in exhibition hall and the air supply capacity up to 282,800 CMH could be secured when using the air flow for HVAC.
For basic design of large capacity smoke exhaust system for S convention center which was conducted previously, design feasibility was reviewed using numerical analysis method. In numerical analysis, 3D program, FDS 6.3.2 which is commonly used for the fire was used [
Before implementing numerical analysis of conference room, numerical analysis model as seen in
(a) (b)
one of three compartments. Exhaust outlet was provided on top of the ceiling and air supply inlet was provided at the bottom of the wall. Heat release rate and flow rate at 60% of floor height was 2.0 MW and 99,173 CMH, respectively and at 50% of floor height, it is 2.0 MW and 77,590 CMH, respectively. As grid system of conference room for numerical analysis, the grid space is 0.5 m and total number of cells is about 340,000.
Figures 5-7 show the numerical analysis results at 60% of floor height in conference room.
Figures 8-10 show the numerical analysis results in conference room at 50% of floor height.
A numerical analysis model was developed as seen in
219,802 CMH, respectively, at 80% of floor height. As grid system of exhibition hall for numerical analysis, the grid space is 0.5 m and total number of cells is
about 700,000.
Figures 12-14 show the numerical analysis results of exhibition hall.
In this study, with the analysis model for such a large space as exhibition hall or conference room at conventional center, design of mechanical smoke exhaust system was conducted based on currently-available design standard which was then followed by numerical analysis of the design using 3D numerical analysis method. Consequently, following conclusion was made:
1) For conference room at 2.0 MW heat release rate, plume of smoke generation was estimated at 99,173 CMH, if smoke layer is maintained at 8.4 m or 60% of floor height. As a result of 3D numerical analysis, smoke layer height was maintained at 8.3 m.
2) Smoke exhaust requirements could be reduced to 77,590 CMH, if the smoke layer is maintained at 7.0 m height or 50% of floor height of conference room. As a result of 3D numerical analysis after setting the heat release rate and airflow at 2.0 MW and 77,590 CMH, respectively, in conference room, smoke layer height was maintained at 6.7 m.
3) For exhibition hall at 8.8 MW heat release rate, plume of smoke generation was estimated at 219,802 CMH, if smoke layer is maintained at 8.9 m or 80% of floor height. As a result of 3D numerical analysis, smoke layer height was maintained at 8.2 m.
This study was conducted by the support of the project, “Development of performance-based fire safety design of the building and improvement of fire safety” (16AUDP-B100356-02) which is under the management of Korea Agency for Infrastructure Technology Advancement as part of the urban architecture research project for the Ministry of Land, Infrastructure and Transport, for which we extend our deep thanks.
Kim, J.-Y. and Ahn, C.-S. (2017) Design of Mechanical Smoke Exhaust System in Large Space of Convention Center. Open Journal of Fluid Dynamics, 7, 386-396. https://doi.org/10.4236/ojfd.2017.73026