An important initial concept for CFD analyses is that of boundary conditions. Each of the dependent variable equations requires meaningful values at the boundary of the calculation domain in order for the calculations to generate meaningful values throughout the domain. These values are known as boundary conditions and can be specified in a number of ways.
The specification of boundary conditions for external analyses is relatively straightforward because it is an isothermal calculation and so it only requires the building exposure, wind velocity and wind direction to be set and this is done in the New CFD Analysis dialog box.
Internal analysis boundary conditions are more involved and can require the addition of zone surface boundaries such as supply diffusers, extract grilles, temperature and heat flux patches and also the incorporation of model assemblies representing occupants, radiators, fan-coil units, etc. DesignBuilder provides default wall and window boundary temperatures automatically but it is important that you check that these defaults are appropriate and that you correctly specify any additional boundary conditions required for your project.
Tip: The internal surface temperature for each surface in the domain can be calculated using EnergyPlus simulation by switching on the appropriate options. Airflow rates through open windows, vents, doors and holes can be calculated using the Calculated natural ventilation option.You can find a webinar recording demonstrating the process involved at: https://www.youtube.com/user/DesignBuilderUK.
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