Design of Mechanical Smoke Exhaust System in Large Space of Convention Center

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.


Introduction
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 [1] [2] and the study to enhance the reliability of smoke control analysis technologies in large space through a full-scale test is still in process now [3] [4] and recently, the measures to improve the smoke control system focusing on air supply and smoke exhaust efficiency is under review [5] [6] as well.
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.

Design Guideline for Mechanical Smoke Exhaust System in Large Space
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 [1] in which algebraic expression-centered design process was described in detail.
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.
where, α is the fire growth coefficient and t is the time elapsed since the fire oc- where, γ is location factor, d is depth of smoke layer below the outlet, T s is temperature of smoke layer and T o is ambient temperature.
And the minimum distance between exhaust outlets (S min ) is determined according to following Equation (4) where, V e is exhaust flow rate per outlet.

A Full-Scale Large Space Building
The building subject to mechanical smoke exhaust system for large space is, as seen in Table 1, "S Convention Center" which is multi-purpose facilities for cultural & meeting events, sales and business purpose. In the building designed as the strategic hub for the purpose of urban exhibition and conventional industry accommodates large conference rooms and exhibition halls for international events.

Design of Mechanical Smoke Exhaust System in Large Space
Floor height of conference room in S convention center ( Figure 1) was designed with 14 m and the space is divided into 3 compartments. And heat release rate per unit area in case of the fire was estimated at 2.0 MW, referring to the data from the hotel [7].
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  Open Journal of Fluid Dynamics 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 Figure 2(a), is planned with the duct to be connected to each compartment. Air supply for smoke exhaust system is planned at the bottom of the wall in conference room and using existing air supply capacity for HVAC, 33,000 CMH will be secured and smoke exhaust fan to be installed will accommodate additional requirements, as seen in Figure 2(b).
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 [7].
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  Figure 3 shows air supply and exhaust plan for smoke exhaust system of exhibition hall.

Numerical Analysis of Mechanical Smoke Exhaust System in Large Space
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 [8].
Before implementing numerical analysis of conference room, numerical analysis model as seen in Figure 4 was developed. As seen in figure, conference room was divided into 3 compartments and it's assumed that the fire occurred in    Figure 8 shows the temperature distribution in each section 30 minutes after the fire. Figure 9 illustrates the temperature values varying over time by height. It indicates the similar pattern as those at 60%. Figure        about 700,000. Figures 12-14 show the numerical analysis results of exhibition hall. Figure  12 shows temperature distribution in each section in 30 minutes after the fire occurred and Figure 13 illustrates the temperature values varying over time by height which were similar with the pattern of convention hall. Figure 14 shows smoke layer height varying over time at major points. As the exhibition hall has a large area, the time taken for smoke layer to reach the wall and fall was different by location and in 15 minutes, smoke layer was maintained at 8.2 m height.

Conclusions
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: