Daylighting Calculation Options - General

General Simulation Options

Perform annual simulation

If you would like one or more of the annual Climate Based Daylighting Method annual simulations to be run tick this checkbox.

Perform point in time simulation

If you would like one or more of the point in time illuminance simulations to be run tick this checkbox.

Annual Options

Window shading

This setting allows any window blinds selected on the Openings tab to be applied for daylighting calculations as well, or LM-83-12 rules for dynamic blinds can be applied.

 

Note: Local shading model data settings are always applied to Radiance simulations.

Dynamic shading method

This setting allows you to control the algorithm used to simulated the dynamic blinds. Two methods are provided, 1-Standard and 2-Detailed. The 2-Detailed option allows dynamic shading to be fully optimised for buildings where light is transferred through internal windows that connect zones with different occupancy schedules. However, these optimised calculations can take a long time to run in large buildings with many internal windows due to the ray tracing method used to identify the dependency of each room on every other. So a second 1-Standard option is also provided which introduces some simplifying assumptions which help it to run much more quickly in such buildings without significantly impacting the accuracy of the sDA results. If all rooms in the building have the same occupancy or if there are no internal windows then the issue doesn’t arise and either method can be used.

 

Override zone occupancy schedule

By default the occupancy schedule used for each zone in the Annual simulations are based on the zone Occupancy schedule defined on the Activity tab, however you can override this to use the same occupancy schedule for each zone by selecting this option and selecting the schedule in the browse control below.

Occupancy schedule

When the above Override zone occupancy schedule option is selected, you can select the occupancy schedule to be used to define when zones are occupied for all zones in the simulation. Values in the schedule greater than 0 indicate occupancy.

 

The default occupancy schedule provided by DesignBuilder does not include daylight saving time (DST). DST has to be added manually to the schedule. For example for the Northern Hemisphere you can use a schedule like the following:


Schedule:Compact,

8:00 - 18:00 Every day (DST Northern Hemisphere),

Fraction,

Through: 03/30,

For: AllDays,

Until: 08:00, 0,

Until: 18:00, 1,

Until: 24:00, 0,

Through: 10/26,

For: AllDays,

Until: 07:00, 0,

Until: 17:00, 1,

Until: 24:00, 0,

Through: 12/31,

For: AllDays,

Until: 08:00, 0,

Until: 18:00, 1,

Until: 24:00, 0;

Exclude unlit hours

You can exclude hours where no light is received in a zone from results by checking this checkbox. This option is only available when the 1-Custom Simulation type is selected. For all other Simulation type settings the calculations are carried out as if this option is unchecked.

sDA Thresholds

sDA lower illuminance threshold

When annual results are being generated you can enter the lower illuminance threshold, the minimum level of illuminance (in lux or fc) below which lighting levels are considered to be inadequate. A typical lower threshold value for sDA calculations is 300 lux.

ASE Thesholds

ASE illuminance threshold

When annual results are being generated you can enter the maximum level of illuminance (in lux or fc) above which lighting levels are considered to be likely to lead to visual discomfort, i.e. glare. A typical upper threshold for ASE calculations is 1,000 lux.

UDI Thresholds

UDI lower illuminance threshold

When annual results are being generated you can enter the minimum level of illuminance (in lux or fc) below which lighting levels are considered to be inadequate. A typical lower threshold value for UDI calculations is 300 lux.

UDI upper illuminance threshold

When annual results are being generated you can enter the maximum level of illuminance (in lux or fc) above which lighting levels are considered to be excessive and lead to visual discomfort, i.e. glare. A typical upper value for UDI calculations is 3,000 lux.

Point-in-time Options

Window shading

This setting allows any window blinds selected on the Openings tab to be applied for daylighting calculations as well.

 

Note: Local shading model data settings are always applied to Radiance simulations.

Sky method

There are 2 methods for generating the sky illuminance distribution for the Radiance calculation:

 

Perez method

When the Sky method is set to 2-Perez all weather there are 4 methods to choose from depending on the data you have available. In all cases the time, day and month of the analysis must be set to define the location of the sun in the sky.

 

Sky clearness (Epsilon)

Perez sky clearness (ε). Enter a value from 1.0 to 12.0.

 

Available only when using the 2-Perez all weather Sky method and the 1-Brightness and clearness Perez method

 

See: Perez, R., R. Seals, and J. Michalsky, 1993. All-weather model for sky luminance distribution—Preliminary configuration and validation

Sky brightness (Delta)

Perez sky brightness (Δ). Enter a value from 0.01 to 0.6.

 

Available only when using the 2-Perez all weather Sky method and the 1-Brightness and clearness Perez method

 

See: Perez, R., R. Seals, and J. Michalsky, 1993. All-weather model for sky luminance distribution—Preliminary configuration and validation

Direct normal irradiance

The direct normal solar broad spectrum irradiance (in W/m2 or W/ft2). This value can be found from the site level hourly weather data.

 

Available only when using the 2-Perez all weather Sky method and the 2-Direct normal irradiance Perez method.

Diffuse horizontal irradiance

The diffuse horizontal solar broad spectrum irradiance (in W/m2 or W/ft2). This value can be found from the site level hourly weather data.

 

Available only when using the 2-Perez all weather Sky method and the 2-Direct normal irradiance or 3-Direct horizontal irradiance Perez method have been selected.

Direct normal illuminance

The direct normal illuminance (visible spectrum) (in lux or fc).

 

Available only when using the 2-Perez all weather Sky method and the 4-Direct normal illuminance Perez method

Diffuse horizontal illuminance

The diffuse horizontal illuminance (visible spectrum) (in lux or fc).

 

Available only when using the 2-Perez all weather Sky method and the 4-Direct normal illuminance Perez method

Sky model

When using the 1-Standard sky Sky method, select the sky model to be used for the daylighting calculations. Select from:

 

Sky luminance profiles for 3 sky models (Source Rendering with Radiance: A Practical Tool for Global Illumination)

Solar position

When using the 1-Standard sky Sky method and one of the sunny or intermediate Sky models (options 1-4), you must define the position of the sun by entering the Month, Day of the month and Hour.

 

Zenith illuminance

When the Sky model (above) is set to 6-CIE overcast day (scaled) you can define the scaling illuminance at the Zenith (in lux or fc). The default is 10,000 lux which allows daylight factors to be calculated simply as working plane illuminance values divided by 100.