Calculated natural ventilation checklist

Modified on Fri, 12 Jul at 9:52 AM

Here is a checklist to work through when setting up a Calculated natural ventilation model:

Switch the Natural ventilation Model option to Calculated.
If you are not modelling daylight you may want to speed simulations up using 'Lump similar windows on surface' on the Advanced tab of the Model options dialog. This makes a big difference in Natural ventilation simulations because each window also has cracks and Large Vertical Opening airflow paths and reducing the number of windows simplifies the airflow network as well as the solar distribution calculations.
Determine if you need to include infiltration in your model. Incorporating infiltration can enhance accuracy and may be essential for fully connecting all zones in the airflow network. However, simulations without infiltration might run faster without significantly impacting accuracy. Be aware that models lacking infiltration may fail if the AirflowNetwork has insufficient nodes. If you choose to include infiltration, adjust the relevant settings in the Airtightness section of the Constructions tab.
Make sure that the 'HVAC + natural ventilation operates with occupancy' model option is unchecked (Timing model option Typical workday only)
Switch Natural ventilation on (HVAC tab).
On the Openings tab under External glazing under the Operation header enter the percentage area of glazing that opens.
Likewise for Internal glazing.
Set door opening frequency and area.
Set vent type, if any. Note that you do not have to check 'Vents fitted' for vents you have drawn manually to operate. The 'Vents fitted' data is used to include default vents in the automatic facade generation if the surface has default openings.
Set operation schedules to define the operation of external/internal windows, vents, and doors. Schedule values of 1 mean the window/vent/door can operate, a value of 0 means it cannot.
Check for natural ventilation setpoint temperatures below heating setpoint temperatures. If this occurs make sure that operation schedules don't allow natural ventilation operation during the heating season.
Set the appropriate natural ventilation setpoint temperature on the Activity tab under 'Environmental Control'. When the air temperature in the zone is above the setpoint the ventilation can operate. Holes have no operation schedule or temperature setpoint control.
Check that the Natural ventilation 'modulation according to inside-outside air temperature' settings on the Advanced tab of the Model options are set correctly to avoid cold draughts being introduced.
Important: Check hourly air change rate and airflow heat gain/loss simulation output for summer and winter conditions before using monthly and annual results. Hourly results can reveal errors in the model much more easily than daily, monthly or annual data.
Look at hourly/sub-hourly airflows through individual windows, vents, holes and doors to ensure that flows are as you expect.