Natural Ventilation Options

Advanced tab on Model Options dialog.

Model holes (including holes in virtual partitions)

You can optionally switch off all holes in the model including those holes generated by defining partitions as virtual partitions. In this case the building is modelled as if no holes were defined.

Tip: Unchecking this data can be a quick way to model all virtual partitions in the model as standard partitions.

Calculated Natural Ventilation

Discharge coefficient for open doors and holes

Enter the discharge coefficient for all open doors and holes. The default of 0.65 is a good general purpose setting.

The discharge coefficient for windows is defined in model data on the Openings tab.

The discharge coefficient for vents is defined on the Vent dialog.

Scheduled Natural Ventilation

Airflow through internal openings

When using Scheduled natural ventilation, windows, vents, doors and holes in internal partitions can be modelled by mixing a predefined amount of air from one zone with the adjacent zone by checking the Airflow through internal openings checkbox and entering the Airflow rate per opening area. This inter-zone airflow is transferred equally in both directions and is modelled using the EnergyPlus ZoneMixing option.

The mixing flow rate for internal openings is calculated as:

Airflow through internal openings x Opening area x Factor

The value of the Factor used in the above calculation depends on the type of opening as follows:

• Windows: % Glazing area opens / 100
• Vents: 0.9 (the rationale is that the vent is 90% free area with 10% obstruction by the vent slats)
• Doors: (% Time open / 100) * (% Area door opens) / 100
• Holes: 1

See also:

• Interzone Airflow

Note: An internal airflow path (IDF ZoneMixing object) will only be added if both zones are have the 1-Standard Zone type (1-Conditioned for ASHRAE 90.1 models) set.