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BIM-Compatible CFD and Its Automation for Natural Ventilation Simulation



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eptember 24, 2014 By Antoine Poussier

Building information modeling (BIM) is an approach whereby all physical and functional attributes of a facility are captured in digital form. This provides a diversity of users with the information required to make decisions across the entire lifecycle of the building, from concept to maintenance and potentially, demolition. BIM goes beyond spatial dimensions to consider time and cost as well as relationships between building components, similar to a bill of material and/or assembly structure in the manufacturing context. The digital model is meant to contain all geometry, site characteristics, operational parameters, and more – what were historically disparate sets of discipline-specific information – in one complete, accessible package. “BIM compatibility” would refer to a computer-aided engineering (CAE) analyst’s ability to interact with this virtual model using simulation software. BIM-compatible computational fluid dynamics (CFD) would make airflow simulation “smarter” by taking advantage of the information already contained within the digital model of the building.

Natural ventilation may sound less techy than mechanical ventilation. It is a ventilation strategy that makes the most of ambient wind flow with a fundamental physical understanding of buoyancy and cross-ventilation. However, when it comes to conducting a CFD analysis that simulates the detailed behavior of natural flow, one faces a much more technical challenge. Simulating natural ventilation is as complicated as nature with all of its uncertainties.

The Building and Construction Authority of Singapore helps to create a set of complex conditions adjusted to the country’s specific circumstances. The organization provides a guideline within Green Mark Certification, the green building rating system of Singapore. scSTREAM, the BIM-compatible CFD software, is especially suitable for this purpose. It makes many processes much simpler, and streamlines geometry preparation by importing a simplified model directly from BIM. Automation of the CFD analysis lessens the burden even more. Once a user embeds the criteria into the code, the automated system will help define computational boundary settings, computational domain, geometry attributes and more.

Image-2 is an example: the building has four units and only three of them will be simulated. (The process of selecting units can be found in the Green Mark Certification Appendix C.) If the user moves those selected units into a separate folder, the automation system will take the 1.2m planes for the post-processor to show velocity on them.

After the velocity contour is obtained, the automation takes each plane out, shows velocity contour on only one of those planes, and finally calculates the area of each plane yielding the area-weighted average velocity. The area-weighted average velocity is the final value to be reported for the purpose of Green Mark Certification.

The ability to automate certain procedures is very powerful. As BIM-based automation saves lots of time and prevents human-related errors, the scheme can be applied for other applications, too. Does your firm have lots of laboratory projects where you have to create the same settings time and time again? Have you ever considered automating this process?