Vents and Holes

Openings tab in model data

Vents

DesignBuilder vents are used for modelling airflow through openings and can be easily added to the model by navigating to the appropriate surface and checking the Vents fitted option. This adds a single vent under each of the windows (if the vent spacing is the same as the window spacing). Alternatively, for more control over the placement position of the vents, you can go to surface level and draw the vents using the Draw vent command.  On surfaces where custom openings have been defined, any changes to vent layout model data on the Opening tab is ignored.

• Vent Placement
• Vent Operation

Note: if you have drawn custom vents at the surface level then these will be used even if the Vents fitted checkbox is not checked. The Vents fitted checkbox only controls the automatic generation of vents, not their use in the calculations.

The properties of the vent are defined by the selection of the vent type:

Holes

Holes are modelled in a similar way to vents with some exceptions:

• Holes must be drawn at surface level
• Airflow through holes is uncontrolled, i.e. the airflow path is active all the time.
• Drawing holes can be used as a way to merge two zones when the Merge zones connected by holes Model option is set.
• Holes are used internally with DesignBuilder to model the heat transfer and airflow through Virtual partitions.
• The discharge coefficient to be used for all holes (and doors) in the model is defined on the Advanced tab of the Model options dialog under the Natural Ventilation header. The default discharge coefficient is 0.65 is used. For vents the vent component defines the discharge coefficient.

Vent modelling

Calculated Natural Ventilation (Simulations only)

Each vent is modelled using:

• An EnergyPlus Door. The heat conduction through the vent Door component is displayed in results as Internal Natural vent and External Natural vent.
• An EnergyPlus AirflowNetwork:MultiZone:Component:DetailedOpening and other associated AirflowNetwork components, providing a controllable flow path. You can define Vent operation.

Scheduled Natural Ventilation (and Heating and Cooling Design Calculations)

Each vent is modelled using:

• An EnergyPlus Door. The heat conduction through the vent Door component is displayed in results as Internal Natural vent and External Natural vent.
• Internal vents also have an EnergyPlus ZoneMixing object using parameters set in the Model options dialog. External vents do not exchange air explicitly with Scheduled natural ventilation.

Hole modelling

Calculated Natural Ventilation (Simulations only)

Each hole is modelled using an EnergyPlus sub-surface and an airflow connection:

• Sub-surface:
• When using the 1-Minimum shadowing or 2-Full exterior solar distribution Model options external holes are modelled using 'perfectly clear' windows which transmit all solar radiation and visible light, while internal holes are modelled using EnergyPlus Doors and an Infrared Transparent construction.
• When using 3-Full interior and exterior solar distribution, all holes are represented using 'perfectly clear' windows which transmit all solar radiation and visible light. In this case heat conduction through window components are displayed in results as Internal Natural vent and External Natural vent as appropriate.

 

• EnergyPlus AirflowNetwork:MultiZone:Component:DetailedOpening and other associated AirflowNetwork components, providing a non-controllable flow path.

Scheduled Natural Ventilation (and Heating and Cooling Design Calculations)

Each hole is modelled using an EnergyPlus sub-surface as follows:

• External holes are represented using 'perfectly clear' windows which transmit all solar radiation and visible light. In this case the heat conduction through windows is displayed in results as External Natural vent. External holes do not exchange air explicitly with Scheduled natural ventilation.
• Internal holes are modelled using an internal door between the 2 zones and, if the Airflow through internal openings Model option is selected, an EnergyPlus ZoneMixing object is also included using parameters set in the Model options dialog.