CFD is a numerical analysis and algorithms used to solve and analyse problems that involve fluid flows. In the building industry is normally used to simulate airflow.
CFD analysis is a powerful tool to assess the interaction between heat gains, air flow and surfaces or boundary conditions.
At masterplan and envelope design it is used to assess pedestrian comfort related to airflow and wind speed. It can be either for protection when temperatures are low, for sitting outside, or required to promote some breeze for passive cooling. Internally it has numerous applications for example to assess if polluted air would recirculate and inside air intakes or windows, to review fresh air or air conditioning distribution, or the effectiveness of solar chimneys or wind catchers.
It is a valuable tool to assess air flow with internal heat gains, which can drastically change the design air flow. It can also reduce and optimize the design and therefore reduce energy consumption associated with heating, cooling and ventilation.
The requirements vary from case to case, but usually these are set by the client or design team.