Using CFD to Assess the Smoke Control System in Corridor - Case Study Example

Using СFD to assess the smoke control system in corridor STUDENT NAME: STUDENT NO: COURSE: FACULTY: UNIVERSITY: SUPERVISOR: DATE OF SUBMISSION: Table of Contents Table of Contents ii Table of figures iii PART 1: NATURAL AND MECHANICAL SMOKE VENTILATION SYSTEMS 4 SUMMARY 4 INTRODUCTION 4 MECHANICAL VENTILATION 5 Recommendations for Mechanical Smoke Ventilation Systems 6 Impacts of using mechanical ventilation 6 NATURAL SMOKE VENTILATION 7 SIZING AND DESIGN 7 Natural and mechanical firefighting shafts 8 CONCLUSION 9 PART 2: CFD MODELING IN PERFORMANCE OF THE SMOKE CONTROL SYSTEM AND CORRIDOR ARRANGEMENT 10 SUMMARY 10 INTRODUCTION 10 Aims of using CFD modeling 11 Assumptions 11 Conditions for the system model 12 Design scenarios 12 SIMULATIONS IN CFD 15 How CFD makes predictions 15 Position and design of the fire flat 16 Design of the Staircase 16 Distances within the lobby 16 CONCLUSION 17 RECOMMENDATIONS 17 References 18 Table of figures Figure 1: Mechanical ventilation 5 Figure 2: Smokes vents for natural ventilation systems 6 Figure 3: operation of the natural ventilation system 7 Figure 4: Fire & smoke ventilation systems 8 Figure 5: alignment of the occupant’s direction to the exit. 8 Figure 6: Atrium fire control analysis and fire locations 13 Figure 7: balcony spill plume 14 Figure 8: smoke layer depth 15 PART 1: NATURAL AND MECHANICAL SMOKE VENTILATION SYSTEMS SUMMARY Occupants need to have proper safety in the buildings. Therefore, inclusion of smoke ventilation systems in corridors of the residential apartment blocks is necessary to improve on safety. Smoke control systems have different categories under which they belong, can be natural venting, pressurization or mechanical ventilation. Majorly these three aim at keeping away smoke from the escape routes, to conserve smoke or keep it off the fire area so that it does not circulate to other areas, to ease firefighting operations and to protect life and cut down the loss of property. INTRODUCTION Smoke detection and safety control is essential in high-rise buildings. Therefore, regulations are required to govern the safety issues in occupational buildings. Recommendations by ADB on safety precautions in high-rise buildings provide a regulation on how safety issues should be handled. Building safety management has smoke control and management system that has varying safety management systems including natural ventilation and mechanical ventilation system. Natural ventilation uses the smoke’s buoyancy to eliminate smoke from the building while mechanical ventilation system uses pressurization of smoke to the exit vents from the building. However, all the smoke management systems must comply with ADB regulations as well as BS 7974 and BS9999. Fire management regulations set by ADB, BS9999 or BS 7974 give clear defines, and requirements that are fit in designing such provisions like door widths, fire exits, and building tunnels. Based on the design theory fire management system will have to follow the regulations set by these provision to ensure adequate fire management system. This report discusses mechanical and natural smoke system ventilation Systems, considering smoke management system in terms fire control, design of the building and size of the fire. However, each fire management system design will always adhere to the set regulations. MECHANICAL VENTILATION Smoke movement is the most critical issue that needs understanding in terms of its spread and effect to the occupants. This behavior is requires careful undertaking to lower the effects that can be caused in case of fire incident. Mechanical ventilation, utilizes the principle of depressurization to lower and control smoke effect in a building. However, mechanical smoke venting works creation of tenable conditions in case of fire in the compartment or in corridors (Randall, 2013, 76). Further, when the targeted area with smoke of fire has a mechanical smoke ventilation system, it creates a depressurizing effect in that area developing a differential scheme between the smoke and the corridor space (figure 1). As far as the mechanical system is concerned, potency and performance increase raises the efficiency in containing of the occurrences and the system must work to depressurize the surrounding area. Generally, in mechanical ventilation system heat and smoke is depressurized and smoke is eliminated from the area. Higher pressure is developed in the surrounding area; this prevents flow of smoke to other areas, which is achieved through installation of external air inlet vents in the building. All the same, it is essential to conserve the in air flow to prevent over depressurization in the area. This can damage the smoke extraction vents. Recommendations for Mechanical Smoke Ventilation Systems All residential and commercial buildings that are above 11m and or are above 3-storey, ADB recommends for disjoining between the corridors and the common staircase. This is to ensure that ensure that the occupant can safely escape without adverse effects of the temperature (figure 2). Additionally, this ADB advocates for common corridors to have ventilation with air open ventilation that is approximately 1.5m2 and directly accessible to the outside or, 1.5m2 natural smoke shafts. Impacts of using mechanical ventilation Every, system has its ups and downs, thus for the mechanical ventilation system, considers space optimization in the buildings, making mechanical system more efficient, the design system is simple, and follow the set smoke management regulations. The only drawback in mechanical ventilation system is that it requires the use of CFD for computational purposes. NATURAL SMOKE VENTILATION In natural smoke ventilation, heat and smoke is extracted from the corridors and solely through smoke’s natural buoyancy (figure 3). Hence, such factors like the corridor size, rate of extraction, air-vent shaft size and fire loading are a key determinant in designing the natural ventilation system. Hence, a computational fluid dynamics helps in designing a fire safety management system that utilizes smoke’s natural buoyancy. SIZING AND DESIGN When planning on the design to use in smoke-management ventilation shafts, there is a need consult fire engineers. More importantly, occupants should be well informed about the safety regulations to ensure they are ready for any incident. Space and proper planning is essential in natural and mechanical ventilation management systems. This is to ensure that there is proper and enough floor space for escape and easy clearance from the building. It should be notable that most natural and mechanical ventilation systems shafts range between 0.25m2 to 0.6m2, which is the standard regulations set by the BS 9999 regulations. This is to ensure that the design meets the system requirements for design parameters for all residential buildings. It is necessary that the building design to have easily accessible staircase that is disconnected from the entire building to ease the occupant’s evacuation. Natural and mechanical firefighting shafts Assembly shops, offices, recreation and industrial buildings must follow the provisions given in BS 9999:2008 and ADB concerning fire fighting and design parameters. Moreover, residential buildings follow the same design regulations as the industrial buildings to construct exit shafts and firefighting shafts. Additionally, it is a regulation by ADB that there should be a firefighting shaft. The regulation dictates that shafts to have uniform size, which allow free, flow of smoke from the building, which must be facing to the outside (fig 4). BS 9999 requires that design of smoke shafts to e in conformity with British design regulations provided BRE guide. According to this guide, smoke shaft design should have a lobby ventilator cross sectional area to be not less than 1.5 m2. From the BRE report, it is required to allow for more shaft space area, which should be large to accommodate occupants in case of exit. Nevertheless, smoke ventilation system is able of draw out more smoke and heat out of any area. Depending on the design parameters, mechanical ventilation will be efficient depending on the system design parameters, which range from the size to the direction of the airflow. Therefore, major factors that promote fire propagation can be minimized through adjustment of the fire exit points to control fire propagation in the corridors and ease the occupants exit (figure 5) CONCLUSION When planning on the design to use it is essential to focus on alternative design features that would ensure the fire safety in all residential buildings in accounted for. Mechanical ventilation is very apprehensive to use in the design system to build a safe smoke-management system design. Since these designs can deliver a safe system that require less financing when employed and used in some buildings that would have incurred higher costs in installing smoke management systems. It is very necessary to use approaches that are used in assessing design performance it ought to be cost saving and can provide the required firefighting requirements in any given residential building. It notable that all buildings have different geometrics and floor designs that must be followed when planning on the best smoke management plan. Hence, the only sure way to design an effective and efficient fire-fighting system is through consulting a fire engineer who always will serve as the best approach to have a fortunate plan that would give an encouraging design. Therefore, through consulting and it is a sure way to ensure that there is proper planning and safety measures that can be followed and made a precedence when designing the corridors as well as access points to the residential buildings. Lastly, proper firefighting design is paramount to have effective operations and ease of access to the ventilation areas and always adhere to the fire management guidelines. PART 2: CFD MODELING IN PERFORMANCE OF THE SMOKE CONTROL SYSTEM AND CORRIDOR ARRANGEMENT SUMMARY Smoke movement mechanisms have been discussed in the earlier section of this report, which included the causes and effects of wind to fire in a building. Smoke and air move in almost the same pattern and it is therefore possible to make calculations for smoke spread similar to calculation of general airflow and ventilation in areas. However, areas that are nearer to the fire, where the smoke is hotter, there happen to have extra smoke movement because of temperature variance causing buoyancy a factor in the system. CFD is the computer program used here which to show the different constituents of the building such as rooms and corridors. The sections of the building are linked via leakage paths including windows, doors or ventilation ducts for example. INTRODUCTION To cover the general study, in this section Computational Fluid Dynamics (CFD) models are used to study the effectiveness of smoke system in a building, which gives a complete picture on the system design. Fire Dynamics Simulator (FDS) in CFD is used in this study for the purpose of system analysis (Awbi, 2013, 352). The expected fire load building is determined using the CFD simulator for a selection that is fit for the lobby area of the given 15-storey building. Further, using this simulation of the lobby area, to exhaust the system design, smoke movement was studied. Movement of the smoke is studied in the simulator and an analysis of the interconnected corridors used to represent the expected fires that may arise and spread in the lobby area. The CFD study is set for a 15-storey building, which must be analyzed to give the real picture of how the design can be handled to manage fire. For a 15-storey building that has uniform floors, it is likely that occupants might get confused during escape. Therefore, there is a need to have a model that is set to help in controlling the movement from the building. Smoke concentration in the building can cause higher chances to increase in the amounts of smoke in the building corridors. Consequently, this lowers occupant’s visibility when evacuating from the building thus blocking the occupant’s possibility to escape. Aims of using CFD modeling In a 15-storey building, CFD models help in providing relevant information that is usable in performance or development of the subject being modeled. In addition, the modeling is also applied to provide justification of a solution in fire engineering. Assumptions It is assumed that, CFD model works on basis of the availability of full details about layout of the building, spaces and connections between areas, as well as the fire’s temperature, location and smoke density within the fire compartment. Information regarding cracks around windows and doors, closed and open doors and windows, and general environmental conditions are also necessary. Conditions for the system model The system model should be located at the corridors of the building in the third floor to take a clear observation; When placing the model, the system should be placed at least at a height of 2.5m in the lobby area; All the doors must be of the standard size of 2m by 0.8 m throughout the building; and Fire must be maintained at a manageable level in case it increases. Design scenarios The design scenario for the CFD model provides detailed information that is critical in determining the alternate system model. Additionally, it provides detailed information that is required in the event of firefighting and control measures. In the simulation, the fire specified is a ‘burner’ with a specified area in the building. Across all the models, fire is centrally located within the fire flat and different scenario is used for each case. Many conditions may be included in the design scenario including the weather, materials burned, HAVC system status and doors that are open or closed. It is ideal to provide a design analysis, which should include the design scenarios that provide the system with a certain level of assurance to control smoke in the system. There is a need to have realistic fire designs and include the fires at the communication spaces as well as the atrium. Figure 6: Atrium fire control analysis and fire locations Figure 6 A is an illustration of the open pathway given by the communication space. Further, it has an illustration of a separated space that is isolated by smoke barriers from the atrium. In conjunction with the smoke control system, smoke movement is restricted controlled via vertical or horizontal barriers by pressurization. In figure 6 B, has smoke in the atrium rise to the ceiling. In such cases smokes control is through smoke exhaust, though it does not restrict other approaches. Regardless of this, the occupants cannot get because the intensity of fire is very high to a distance (Xie, 2013). Thus, a person should maintain a certain distance of about 7.5 m for a given period without encountering high effects. For such scenario in the atrium with fire, the benefit of the sprinklers is not taken into account for such a case. In other cases where the ceilings are so high, activation can be delayed and the spray evaporate before the smoke triggers the system. Figure 6C illustrates smoke flow from the balcony spill plume into the atrium (figure 7). Thus in such a scenario smoke blocks the parts balconies and lobby above the fire. Such fires are beyond control and capability of the smoke control technology. Thus, all occupants must comply with the smoke distance regulations set in the ADB provisions. Fully developed fire with plume formed by smoke in the lobby area is shown in figure 6 D. If the sprinkler was working properly, such case would not happen if the buildings had been properly designed. It should be noted that, it is not recommendable to have smoke exhaust that pass through the plenum that has a suspended ceiling. Figure 7: balcony spill plume In most cases, the smoke layer is indicated as a fraction of the floor height to the ceiling. Thus as the smoke rises it forms a layer near the ceiling as illustrated in figure 8. At the ceiling height, the smoke forms a ceiling jet, which is approximately 10 % of the floor-to-ceiling height. Figure 8: smoke layer depth SIMULATIONS IN CFD When using CFD in firefighting management, it gives an insight of flow patterns that appear to be difficult, or impossible. Thus, it depends on; Data structures and numerical algorithms How CFD makes predictions Using the given design components, CFD solve mathematical equations using the problem at hand, which follows: Analysts to get the problem; Methods and models; Software; and The computer hardware. Position and design of the fire flat In the lobby area, the building has a standard window that is located straight to the corridors. The fire flat front door is not more than 23.25 m from the stairway and the corridors are 1.7 m wide. Design of the Staircase In a 15-storey model, it should have at least a single staircase for all floors and a fire exit at the end of all corridors of the building. CFD model provides a design with enough space that would allow free escape from the building by the occupants. Distances within the lobby BS9999 and ADB regulations require that all buildings to have reasonable distance to the fire exits of the building. Additionally, the CFD model provided actual specifications that are ideal in designing a fire model. Using the atrium model, as based upon a fire compartment, which leads firstly to a corridor before reaching the staircase; common corridors were taken as straight, with a width of 1.7m and a length of 23.25m. Typically, this width is ideally fair. However, regardless of the ventilation system in the building, residential buildings in recent years have restrictions on the length of single-direction corridors, with a maximum of 7.5m as specified by Approved Document B. Further, CFD assessment shows that: There are appropriate conditions must be observed in the building while ensuring clear and safer evacuation. Offer safety levels, which are equal to or higher than required for compliance with the relevant standards. CFD is used in demonstrating the suitability of the equipment. Additionally, results of the simulations allow assessment of the most suitable smoke control system for the building in question. CONCLUSION Smoke control systems have to use two major ventilation systems, mechanical and natural smoke ventilation systems. These work by eliminating the exit of smoke and heat as it allows the entry of fresh air. In natural systems, air flows in naturally, as smoke and heat move out due to their lightweight and are diluted by the incoming air. In the mechanical ventilation systems, the heat and smoke are forced to exit the room through a process of pressurization in the affected room. RECOMMENDATIONS It is substantial to design any smoke ventilation system that has stairs free from the smoke accumulation; in case of fire outbreak occupants can safely exit. When designing any system it is necessary to consider tenable conditions that will allow space for travelling via corridors/lobbies when escaping. References Awbi, H.B., 2013, Ventilation of Buildings, Routledge, NY, New York. Antony, W. & Ruba, S., 2012, Natural Ventilation High Rise Buildings SALIB & WOOD, Routledge, NY, New York. Chadderton, D. V., 2013, Building Services Engineering, Routledge, NY, New York Randall, T., 2013, Environmental Design: An Introduction for Architects and Engineers, Taylor & Francis, NY, New York. Xie, L, 2013, Modeling and Computation in Engineering II, CRC Press, New York. Read More