D5 Computational Building Simulation

Topic

Computer simulation predicts a building's thermal, energy, and airflow behavior before construction—or diagnoses it afterward—using different tools depending on the specific phenomenon being analyzed. For airflow—whether inside a room or around the entire building—Computational Fluid Dynamics (CFD) programs solve the fundamental equations governing fluid motion; they do this by dividing the space into a fine mesh of cells and calculating air behavior within each one. Near surfaces, this mesh must be particularly fine to capture how the air slows down as it approaches a wall.

In contrast, analyzing thermal and energy behavior over the course of a full year requires a different type of model: a simplified one that divides the building into zones and calculates—hour by hour—heat exchange between those zones, the outdoors, and the HVAC systems. By integrating this balance over thousands of hours, the model determines total annual energy consumption—a calculation that would be unfeasible if performed cell-by-cell, as in fluid dynamics, over such a long timeframe.

These tools are increasingly integrated with the digital building models used in design and construction—specifically, the BIM methodology. This allows geometric and material data to be transferred directly to thermal or structural simulations, eliminating the need to rebuild the model from scratch each time.

Thus, this module—which begins by distinguishing between two different time scales (seconds for airflow versus hours for the annual energy balance)—concludes by demonstrating that simulating a building is not a matter of applying a single tool, but rather of selecting the specific computational scale required to answer each physical question.

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