Set Ventilation

Understanding how air moves through a building is essential for designing spaces that are comfortable, healthy and energy efficient. Modelling natural and mechanical ventilation helps predict airflow patterns, indoor air quality and thermal comfort under different conditions. By adjusting factors like window openings, wind speeds, temperature differences and fan performance, designers can simulate how ventilation systems behave throughout the year.

Set Ventilation Type

To set Ventilation Type, select 'Set Ventilation' and either 'Select from Template' or 'Create Custom'. 'Select from Template' allows you to quickly apply predefined settings that match common design scenarios. 'Create Custom' gives you full control to define your own settings from scratch. Use this option when you need a tailored setup that doesn't fit standard templates, allowing you to fine-tune all inputs to match your specific design goals.

Select From Template

Where a template exists for Ventilation, such as in H1/VM1 were ventilation is prescribed in the building code, it will be automatically populated. Input options to adjust ventilation include openability, temp difference, min and max outdoor temperatures, as per the following definitions.

Openability (%)

Defines how much of the total available opening area is operable for ventilation, expressed as a percentage. A value of 50% means only half the opening area is available to allow airflow, simulating partially open windows or vents.

Temp. Difference (°C)

Sets the minimum temperature difference required between indoor and outdoor air before ventilation occurs. A positive value means the outdoor air must be warmer than indoor; a negative value means it must be cooler. This prevents unwanted heat loss or gain.

Minimum Indoor Temperature' (°C)

The lower indoor temperature limit for allowing natural ventilation. If the indoor temperature drops below this threshold, ventilation is disabled to avoid overcooling the space.

Maximum Indoor Temperature' (°C)

The upper indoor temperature limit for natural ventilation. If the indoor temperature exceeds this value, ventilation is turned off to prevent bringing in hot air that could worsen comfort conditions.

Where additional control is required, these can be found by left-clicking 'Settings' to reveal more detailed control options for operation method & threshold, opening effectivness, discharge coefficients, max wind speeds an dhigh difference. See the additional definitions below:

Operation Method

Specifies how the opening operates during the simulation. When set to 'Scheduled', the degree of opening is controlled by a user-defined schedule, allowing timed or conditional operation of natural ventilation openings throughout the simulation period.

Opening Effectiveness Method

Determines how efficiently an opening contributes to airflow. Selecting 'Automatic' allows the software to assign a value based on typical flow behaviours and the geometry of the opening, simplifying setup while ensuring realistic airflow modelling.

Discharge Coefficient for Opening Method

Sets the discharge coefficient, which influences the calculated airflow rate through the opening. Choosing 'Automatic' uses standard values based on typical opening conditions and shapes, representing the pressure loss due to flow resistance.

Maximum Wind Speed (m/s)

Defines the highest wind speed at which an opening remains fully effective. If outdoor wind speeds exceed this value, the opening's effectiveness may be reduced to reflect real-world safety or performance limits. The input is measured in metres per second, with a typical range from 0 to 40 m/s.

Height Difference Method

Controls how the height difference for stack ventilation is calculated. When set to 'Custom', users manually enter a vertical distance between inlet and outlet openings, allowing precise control over the buoyancy-driven airflow input.

Height Difference (m)

The vertical distance between the lower and upper openings used in stack effect calculations. A greater height difference increases the potential for natural ventilation due to thermal buoyancy. The input is specified in metres.

Create Custom

Where a custom Ventilation is required, these are set as either a 'Design Flow Rate' or via 'Wind and Stack Ventilation'.

Set Design Flow Rate

To adjust ventilation for a 'Design Flow Rate' the following inputs are applicable.

Fan Design Pressure Rise (Pa)

This value represents the total pressure rise across the fan, in pascals (Pa). It reflects the resistance the fan must overcome to move air through the system. For natural ventilation systems, this is typically set to zero.

Fan Total Efficiency (%)

The total efficiency of the fan, expressed as a percentage. It accounts for the motor and drive efficiency, and is used when calculating fan energy consumption. For natural ventilation, this is usually 100% to indicate no mechanical input.

Ventilation Type

Specifies the type of ventilation system applied. Options typically include Natural, Exhaust, Intake, or Balanced, with Natural used for airflow driven by natural forces like wind and buoyancy.

Maximum Wind Speed (m/s)

Sets the upper wind speed limit at which natural ventilation remains effective. If outdoor wind speeds exceed this threshold, the model assumes reduced airflow or closes the openings for safety or realism. Measured in metres per second (m/s).

Constant Coefficient (A)

This is the base flow rate coefficient used in the ventilation equation. It defines a constant airflow component (in m³/s) that is always present regardless of temperature or wind conditions.

Temperature Coefficient (B)

A multiplier applied to the indoor–outdoor temperature difference. This coefficient adjusts ventilation rates based on buoyancy effects from temperature-driven pressure differences.

Velocity Coefficient (C)

This coefficient scales the ventilation rate in proportion to outdoor wind speed, representing the linear wind-driven contribution to airflow through openings.

Velocity Squared Coefficient (D)

A multiplier for the square of the wind speed, accounting for the non-linear relationship between wind pressure and ventilation rate. This is useful when simulating stronger wind-driven effects.

Set Wind and Stack Ventilation