Window Operation

Openings tab in model data under External Glazing, Internal Glazing and Roof Glazing headers


Note this data is only shown if Natural ventilation is activated on the HVAC tab at the current level.


The operation of windows can be defined by entering data under Operation headers. The data will depend on the Natural ventilation model option set:

Calculated Natural Ventilation

The % Glazing area opens slider allows you to define the openable window area as a percentage of the total window area. For example enter '20' if 20% of the window area can open.


The air flow opening is assumed to be a gap in the side of the window which takes on the full height of the window.


Note: if modulation is switched on (it isn't by default) the glazing opening areas defined here are multiplied by a factor to account for external conditions.


You can also enter a schedule to define the timing of the window operation. The schedule should have values of 0 and 1 only and intermediate fractional values do not indicate partial opening.


The windows are 'open' when:


Tzone_air > Tsetpoint AND Tzone_air > Toutside_air AND the schedule value = 1


The ventilation rate is calculated based on the pressure difference across the opening calculated from wind and stack pressure effects using equations described in Natural Ventilation Modelling.

Scheduled Natural Ventilation

Airflow through external windows, vents, doors and holes are not modelled with Scheduled natural ventilation because the natural ventilation airflow from outside is explicitly defined using the total natural ventilation flow rate and operation on the HVAC tab. No operation data is entered on the Openings tab for external windows in this case.


Note: Natural Ventilation can be overridden to be off on the HVAC tab for both Calculated and Scheduled model options.