In April of this year, the Queensland division of the Australia Institute of Refrigeration, Air-conditioning and Heating (AIRAH) held an education session on the design and compliance of car park ventilation using jet fans.
Now even though this seems to be a very specific example of a performance solution, this case highlights an aspect of achieving compliance with performance-based solutions that needs further discussion and direction from the Australian Building Codes Board (ABCB) to ensure a harmonised approach Australia-wide.
The car park ventilation system using jet fans may impact on the life safety systems for fire suppression and smoke control. These critical fire safety systems may be adversely affected by the ventilation system, and hence a detailed assessment of the ventilation system design is required to meet the performance requirements of the NCC. The NCC performance requirements are EP1.4 and EP2.2.
While there are professional designers with the capabilities to develop these performance solutions, it is difficult for inexperienced individuals without a specialty in this area to assess that a design complies with the requirements. The guidelines provided by Fire & Rescue New South Wales (FRNSW) are a step in the right direction.
The guidance within the NCC is insufficient and therefore the FRNSW government department has provided a Fire Safety Guideline – Guidance for impulse fans in car parks V1 – Oct 2014 to assist with providing a more consistent approach to the design and compliance in accordance with the performance provisions. The concern with the use of jet fans is the impact on the deactivation of the jet fan, and the impact of the jet fan airstream on fire system sprinkler heads.
While the FRNSW guidelines are a good document, they are not part of the NCC, or referenced within the NCC. To date, only FRNSW have developed a set of guidelines, and whilst other states such as Queensland are looking at adopting the FRNSW guidelines, they are going through their own process of assessing the requirements and understanding the impacts of this performance solution. This results in a significant delay, increased costs and uncertainty for building developers and designers.
This is important because, in some instances, the jet fans can provide an acceptable solution at a much reduced cost and reduced impact on structural and architectural car park design when compared to a traditional design. The assessment of the jet fan solution is currently an industry-driven process which is typically accepted by the building certifier/surveyor once sufficient evidence has been provided by the designer. This highlights other concerns with the CFD method used for verification of the performance of the physics of these complex engineering designs.
Looking in more detail at CFD analysis, we find it can be a highly inaccurate method of assessment. Computational fluid dynamics (CFD) is the use of applied mathematics, physics and computational software to visualize how a gas or liquid flows, as well as how the gas or liquid affects objects as it flows past. Computational fluid dynamics is based on the Navier-Stokes equations.
When using CFD, make sure that an appropriate method is used for the particular configuration you are investigating. Used properly, modern CFD solvers (using a wide variety of methods) can yield remarkably accurate predictions. The more you know about the strengths and limitations about the computational fluid dynamics modelling methods at your disposal, the better your ability to get good results. The use of CFD should be restricted to highly skilled individuals with in-depth knowledge of not only the mathematics, but also the real world verification of the CFD analysis.
This raises two questions:
- How does anyone outside the specialised engineering field of CFD analysis assess whether the CFD analysis has been applied appropriately to the situation?
- How do you ensure the person doing the CFD analysis has the required level of understanding of the software, the mathematics and practical applications of CFD to the solution represented?
After all, fire safety systems are lifesaving systems, and while cheaper alternative solutions for carpark ventilation are available and may be implemented, the verification of their performance impacts on fire safety systems is still, I think, unclear.