Integrating CFD into the design process

[edit] Introduction

With 97 of the top 100 industrial companies on the “FORTUNE Global 500” investing in simulation as a key strategy to solve a range of engineering challenges, it's clear computational fluid dynamics (CFD) has much to offer.

In 2018, sustainable building design has never been more important, with architects seeking ways to integrate technology in the design and build of more energy-efficient structures. Despite the role CFD can play in increasing sustainability, limitations and perceptions currently restrict its wider adoption, particularly among architects and consultants working in SMEs where budgets and resources may not be as expansive.

Modern CFD tools are making strides to address the void and to highlight the huge advantages to integrating high performance software for overcoming challenges - particularly within HVAC designs. In this article, we highlight how CFD can be integrated into the design process, where it can be applied, the common barriers and how these are being addressed, and the opportunities it can bring to those working in the sector.

[edit] Common Applications

CFD has become well known for the integral role it plays in the aerospace and automotive industries, yet it offers huge potential to facilitate improvements to a number of applications in the built environment and HVAC sectors.

Common Problems in the Built Environment:

• Buildings above 10 stories require wind studies. Recent cases have shown the importance of understanding a building's impact on the local micro-climate and environment, as well as highlighting the dangers if due processes are not followed.
• Some government agencies are now mandating BIM studies.
• Hand calculations are often impractical and time-consuming.
• Some physical phenomena cannot be calculated by hand or with calculators - notably passive HVAC and buoyancy driven phenomena.
• Higher end or LEED certification processes don't currently have a streamlined process of achieving their specifications.

[edit] CFD in the Design Process

While every design project is different, there remains a clear goal to create a sustainable design fit for purpose, within a set budget and timeframe.

At present, simulation is often performed at the end of the process and while this still facilitates design improvements, the use of CFD in the early stages could potentially prevent late design changes that prove costly and extend project timeframes.

When integrated into the workflow, CFD can bring huge benefits particularly when working with challenging and complex HVAC environments. The hesitation to use CFD can be attributed to one or more of the common barriers listed below.

Overcoming Common Barriers to Using CFD:

• Time: Time is of the essence in the built environment and there's lots of iterating involved with building designs often changing on a daily or even hourly basis at the request of engineering contractors, clients, HVAC designers or architects. Speedy turn-around times are vital. Modern CFD tools use GPUs to finish simulations in hours instead of days. Faster simulation turnaround times mean you can react to changing requests and iterate faster designs.
• Cost: Every day brings fresh challenges to businesses in the built sector, and as such it's often impractical to commit to software licenses and the large price tags they often bring. Modern tools use a pay-as-you-go approach meaning you can access CFD tools on-demand with no commitment which helps optimise cash flow.
• Ease of Use: Architects and designers want simplicity. They don't have the time to take weeks and months learning to use a complicated system, and want CFD tools to complement their work rather than add barriers.
• Dynamic: Models are in the hands of architects, engineers and HVAC contractors, and are constantly changing. This can make it particularly difficult to simulate the right space - hence the number of iterations are high. A CFD tool that can work quickly and produce these iterations to optimise the final design is essential.
• Resource Limitation: Contractors are often operating under heavy workloads and as such are sometimes too busy to run the simulations themselves. Vendors offer a range of engineering services to support the project team.
• Complexity: Designs have a lot of features and intricacies which aren't necessary in a CFD simulation. Geometry cleanup needs to be fast.
• Simplification: While designers may have the ability to run simulations correctly in the BIM suite, they aren't necessarily trained in running CFD and require the process to be simple.
• Personas: In many cases, BIM users are artists and designers while CFD has been reserved or outsourced to engineers. The perception that CFD can only be performed and understood by engineers has largely contributed to this, and a more integrated relationship between all parties would lead to higher quality conversations and informed decision-making.
• Lack of Integration with BIM Tools: Despite the advantages provided by CFD software applications, they are not always fully integrated within the BIM process. Surprisingly, BIM models of architectural spaces are often not utilised as the object domain in a CFD simulation, despite the advantages and insight that could be provided.
• CFD Technology and Terminology: In many cases, there remains a lack of understanding in the built environment when it comes to CFD. This is mostly due to the fact that its use is occasional. What is a volume mesh? What are boundary conditions? Overall, the learning curve needs to be short and vendors need to facilitate training and education accordingly.
• Value Proposition: There remains a lack of understanding of the value CFD can bring to designs. Higher-quality results and an easier parametric sweep to assess best design parameters would address this issue.

[edit] Opportunities with CFD

Overall, CFD has the potential to provide a number of key opportunities to architects, consultants, designers, manufacturers, and all those working in the built environment.

These include:

• Better thermal comfort for occupants.
• Reduced project times.
• Increased value and marketability for firms.
• Decreased HVAC design changes.
• Reduced risk of lawsuits and easier compliance with health and safety guidelines.
• Improved customer satisfaction.
• Justification for recommendations.
• Reduced capital equipment needed to manage airflow.
• Greater marketability and the potential to win pitches.

[edit] Related articles on Designing Buildings Wiki

• An algorithm in architecture.
• A Practical Guide to Building Thermal Modelling.
• CFD.
• Computational fluid dynamics in building design: An introduction FB 69.
• Convection.
• Conventions for calculating linear thermal transmittance and temperature factors.
• Dynamic thermal modelling of closed loop geothermal heat pump systems.
• Energy targets.
• Heating degree days.
• Heat transfer.
• Indoor air velocity.
• Mass transfer.
• Mechanical ventilation.
• Natural ventilation.
• Passive building design.
• The design of temporary structures and wind adjacent to tall buildings.
• The thermal behaviour of spaces enclosed by fabric membranes (Thesis).
• Thermal behaviour of architectural fabric structures.
• Thermal comfort.
• Thermal dynamic analysis.
• Ventilation.