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 virtual partitions as standard partitions.

Calculated natural ventilation option

Wind Factor

When carrying out conservative design simulations you may prefer to exclude (or reduce) the effects of wind from Calculated natural ventilation. To exclude wind-driven airflow from the analysis altogether set the Wind factor to 0. For full treatment of wind effects set it to 1 and for intermediate treatment of wind set to a number between 0 and 1.

Modulation of Openings

You can modulate the window/door openings when Calculated natural ventilation is being used by making appropriate settings to:

• Limit value of opening modulation factor - gives the reduction on opening area for low outside air temperatures.

• Lower value of Tin-Tout  - lower value on inside/outside temperature difference for modulating the venting open factor.    

• Upper value of Tin-Tout  - upper value on inside/outside temperature difference for modulating the venting open factor (defines 'low outside air temperatures')

Note: if Modulate calculated opening sizes is switched on then airflow will be switched off if the difference between inside and outside air temperatures is greater than Upper value of Tin-Tout

This data is used within EnergyPlus/AIRNET to calculate a factor between 0 and 1 that multiplies the opening factor of each window and door in the building. Modulation of the openings can reduce the large temperature swings that can occur if the windows/doors are too far open when they are venting, especially when there is a large inside-outside temperature difference.

For example if the Lower value of Tin - Tout is 0, the Upper value is 15 and the Limit value of opening modulation factor is 0.05, the windows and doors are only opened 5% of their full opening area when the outside air is 15 degC or more colder than inside.

Scheduled natural ventilation option

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 selecting the Airflow through internal openings  option and entering the Airflow rate per opening area.

Technical note: this airflow is modelled using the EnergyPlus Mixing option.

Warning: In EnergyPlus v.2.1.0 there is a bug in internal airflow reports for zones having 2 or more internal openings. In such zones Internal Natural ventilation typically has very large values.