Fires are scary, a chemical reaction that can strangely assume lifelike qualities and can easily get out of control. Wouldn’t it be nice if there was some way to predict or calculate potential high-risk areas in building spaces where fires may start and how they would spread? Computational fluid dynamics (CFD) is an analytical tool to calculate fluid flows, with or without solid interaction. It is vital that fire design service providers use CFD and CAD modelling services to help design an effective fire protection system.
Understanding how CFD analysis works may seem a little bit like a physics lesson, but it’s actually worth considering.
Fluids flow according to their physical properties, such as pressure, velocity, temperature, density and viscosity. This is what happens in a CFD analysis in simple terms:
- To analyse fluid flow, a model of the physical case and a numerical method is created digitally.
- The model can vary according to changes in the values of heat transfer, mass transfer, phase change, chemical reaction, etc.
- Depending on the software (typically Autodesk CFD, AnsysCFD, OpenFOAM, etc.), the amount of physical prototypes can be reduced and a product development process can be generated for fire protection design.
What does fire protection design for a building entail?
Buildings may have different fire protection needs, eg, the fire protection needs for warehouses or storage facilities differ from those of office buildings. The design for any building involves an integrated approach, such as follows:
- System designers analyse building components.
- Building function, occupancy, installed systems and footprint are considered.
- Building owners, management, architects, engineers, consultants and contractors and their input are inherent in the design process and design data.
- Fire protection design must adhere to the fire codes of the concerned region.
The main goals of fire protection systems are:
- To save lives
- To save property
- To preserve business continuity
How does it fulfil those goals? The basic strategy for fire protection systems involve:
- Detection
- Alarms and notification
- Suppression
Fire protection engineers can design systems to detect, contain, control or extinguish a fire, in its early stages, as follows:
Detection Systems
- Smoke detectors sense smoke and trigger alarms.
- Smart detectors can sense different alarm thresholds.
- Heat detectors can trigger alarms before smoke detectors.
Alarms and Notification Systems
- Two types of alarms – 1. To alert building occupants, 2. To alert emergency responders
- Fire alarms can direct fire responders to where the alarm is. Through AutoCAD floor plan integration, an AutoCAD screen with building management or building security can show which floor the alarm was activated on and can print a floor plan of that spot, which is then handed to emergency responders.
- Speakers provide alerts in addition to bell alarms, instructing occupants where to go or whether to stay in their space.
- Alert systems may be designed to close designated doors, turn off elevators and interface with suppression systems, such as sprinklers.
- Alert systems may connect to ventilation components, smoke-management systems or stairwell pressure systems.
Suppression Systems
- Sprinklers, which can reduce the chances of death and property loss due to fire by 50-65 percent compared to occupied spaces without sprinklers
- Sprinkler heads activated individually by fire, each one with a heat-sensitive element within which activates the sprinkler head during high temperatures
- Gaseous or chemical suppression used where water may damage equipment
With all these systems in place, how does CFD help?
The CFD software works by creating a separate model, although a replica, of the original project, created from building plans, that can graphically and numerically represent and follow the spread of fire, including its heat and smoke. Then, this data is used to create a fire strategy that is efficient, integrates the fire detection, alarms and suppression systems and follows the fire safety regulations of the region.
As CFD calculates fluid flows, using mathematical formulae and analysis, it can be successfully applied in HVAC, hydraulic systems and water systems. A 3D model is created, from CFD data and the data from building plans, with an imaginary fire inside. The building and the fire inside it are separated, or broken down, into extremely small blocks (running into millions) or simple shapes where the mathematical formulae used in CFD can be applied on individual blocks and combinations of blocks.
One of the several results of the calculations that are part of CFD is that it can help create a fire suppression model, which works something like this:
- The ratio between fluid mixing time scale and the flame chemical time scale is used to create a suppression model.
- When the fluid mixing time scale is short compared to the chemical time scale for combustion, the fire can be extinguished.
- Suppressants are introduced to increase the chemical time required for combustion.
- The effectiveness of suppression models in stressed and obstructed flows are analysed by using validation data.
- CFD analyses how changes in geometry can change the distribution of suppression.
- Design can determine the most ideal fire protection with minimal suppressant system mass and cost.
Other benefits of using CFD include the following:
- Cloud-based CFD simulation can help optimise HVAC systems for fire safety and smoke management.
- CFD simulations can monitor CO levels under normal conditions.
- CFD simulation results can help plot the magnitude, velocity and direction of air flows, helping to predict how fires can spread from any given space.
- CFD simulations can help decide how to lower CO concentration levels in enclosed spaces, such as underground parking lots. This can help plan where to place jet fans to generate air flow. The CFD simulation can be run again with the fans to plot the new air flow velocity and check the effect on CO concentration levels.
- CFD simulations can calculate the quantities of required supply and exhaust air to provide a smoke control system that is code compliant.
- CFD modelling helps design public spaces with easy and safe egress, in case of fire or other emergencies.
- CFD simulations can show the effects of sprinklers on fires.
Computational fluid dynamics makes predictive models of fire protection applications more accurate, making it a key factor in fire protection design. The capacity and means of egress have requirements imposed by building codes, which can be accurately calculated using CFD. The CFD simulations can also help fire design service providers view the performance of smoke management and general visibility in case of fire. These providers depend on the high quality and accuracy of their CAD modelling services and 2D CAD services, which is increasingly being sourced from offshore firms with CFD project experience.
XS CAD has valuable experience providing CFD modelling and CFD simulations, 2D CAD drawings, BIM modelling services, MEP engineering design and drafting services for global building engineering firms. Our range of services for fire protection design engineers across the world include fire protection design, HVAC design services, MEP drafting, public health system drafting and building services coordination using various tools such as Revit, Navisworks, AutoCAD, BIM 360 Design, etc.
No comments:
Post a Comment