CFD Boundary Conditions Editor

The CFD Boundary Conditions Editor allows you to view and edit all of the boundary conditions in the selected domain in one place. In particular you can:

• Check and set the airflow rate through each supply and extract boundary condition and also through each window, vent, door and hole in the selected domain.
• Check that total flow in balances with total flow out (a key requirement for the CFD calculations). If flows do not balance there are options to automatically apply a correction flow to one of the existing openings to ensure balance.
• Check and set the temperatures of each boundary condition where temperature is defined (surfaces, supply flow, windows, temperature boundary conditions).
• Import surface and opening boundary conditions for a specific time/date from a previous EnergyPlus simulation.
  
  

CFD Analysis Domain

You can select the CFD Analysis domain from previously defined CFD Analyses - this defines the extent of the model that is displayed and checked for flow balance. If you have more than one analysis then you must make sure to select the correct one here before starting. Alternatively you can select the whole building or the current block or zone. This selection does not limit the EnergyPlus simulation data that is imported, it only defines the boundary condition data that is displayed on the dialog and the domain for airflow balance checks.

Group

The Group options allows you to group boundary condition data by one of:

• 1-None - each boundary condition is displayed in a simple list without any grouping.
• 2-Boundary types - boundary conditions are displayed groups according to type (extract, supply, temperature, window etc). See screenshot above.
• 3-Zones and surfaces - the boundary conditions are grouped by zone and then by surface.

Under some circumstances the display can be erratic when using the 2-Boundary type grouping and in this case you may find it better to use one of the other grouping options.

You can edit the flow in and flow out airflow rates and temperatures as appropriate on the dialog and the changes are only saved to the model when you press the OK button. No changes are made if you press Cancel.

Edit Boundary Conditions

Airflow

The Zone, Surface, Boundary and Boundary Type columns indicate the local of the boundary condition and it's type. You can edit the flow rates in the Flow In and Flow Out columns for windows, vents, doors and holes and the Flow In for supply diffusers and Flow Out for extracts.

If flows do not already balance this will be indicated in red on the Info panel to the right and you can select one of the openings in the dialog and click on the Correct balance using selected opening link. A flow is added or subtracted as appropriate to get flows to balance.

Temperature

You can edit the temperature for all temperature-related boundary conditions. There are 2 temperature columns, one for surface temperatures and the other for air temperature. The air temperature column is only relevant for openings and supply diffusers and is the temperature of the air entering the space. Openings such as windows, vents and doors can have different surface and air temperatures defined. If the airflow rate through the opening is zero then you will not be able to edit the data in the air temperature column.

Import EnergyPlus Boundary Conditions

You can import data that have been calculated in a previous EnergyPlus simulation as boundary conditions for the CFD simulation. The data that can be imported is:

• Surface inside temperatures of walls, floors, roofs, partitions, ceilings, windows, doors and sub-surfaces.
• Flow in and flow out of windows, vents, doors and holes (only when using the Calculated natural ventilation model option).

To import simulation data click on the Import button in the Boundary Conditions Editor (above). 

Import Dialog

The Import data dialog allows you to select boundary conditions for a particular snapshot in time from the simulation results.

Interval

Select Hourly or Sub-hourly interval depending on how the data was generated in the simulation.

Time, Day, Month

Select the time and date to use for the import. The date must lie between the simulation start and end periods for the last simulation carried our.

Press OK to import the results to the CFD Boundary Conditions Editor.

Note: all available opening airflow and inside surface temperature results from the most recent EnergyPlus simulation will be imported. That is the imported results are not restricted to the current CFD domain or zone (if this is a subset of the whole building).