Daylighting Calculation Options - BREEAM

This topic describes the BREEAM-specific Daylighting Calculation options which can be accessed when the Simulation type is set to 3-BREEAM.

BREEAM Simulation Options

Perform BREEAM HEA option 4b (annual) simulation

Check this checkbox if you would like to run an annual daylighting simulation suitable for assessing credits for BREEAM Health and Wellbeing Credit HEA 01 option 4b .

Perform BREEAM HEA option 4a (point in time) simulation

Check this checkbox if you would like to run a point in time illuminance daylighting simulation suitable for assessing credits for BREEAM Health and Wellbeing Credit HEA 01 option 4a .

Option 4b (Annual) Options

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;

Min illuminance threshold

For BREEAM HEA 01 Option 4b, you can to enter a minimum illuminance threshold value from Table 12 based on the area type of the zones being analysed.

Avg illuminance threshold

For BREEAM HEA 01 Option 4b, you can enter an average illuminance threshold value from Table 12 based on the area type of the zones being analysed.

Shading

BREEAM annual daylighting calculations do not apply LM-83-12 dynamic shading or any other window shading algorithms. Any Window shading settings on the Openings tab are ignored.

Option 4a (Point-in-time) Options

In general you should make the following settings for BREEAM point in time daylighting calculations.

• Sky method: 1-Standard sky

• Sky model: 6-CIE overcast day (specify illuminance)

• Zenith illuminance: 10000

Sky method

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

• 1-Standard sky - the default method where one of the predefined standard sky distributions are applied using the Radiance gensky tool.
• 2-Perez all weather - an alternative method suitable for all weather types based on the Perez sky clearness (ε) and sky brightness (Δ) parameters and using the Radiance gendaylit tool. There are 3 Perez methods to choose from as described below.

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.

• 1-Brightness and clearness - if you know the Perez sky clearness (ε) and sky brightness (Δ) parameters of the sky to be analysed choose this option.
• 2-Direct normal irradiance for when measured direct normal and diffuse horizontal irradiance data is available. This option can be useful since it allows readily available solar data in W/m2 from the EnergyPlus weather file to be used to define sky illuminance. Go to the Simulation tab, navigate to site level and select hourly data to see solar data suitable for the location of your building for any hour of the year. Note that using full spectrum solar data to define illuminance is seen by daylighting purists as less accurate than using measured values of actual illuminance (see option 4).

• 3-Direct horizontal irradiance for when measured (or calculated) direct horizontal and diffuse horizontal irradiance data is available. Such data can usually be found in EnergyPlus epw files in W/m2.

• 4-Direct normal illuminance for when measured (or calculated) direct normal and diffuse horizontal illuminance data is available. Such data can often be found in EnergyPlus epw files but DesignBuilder does not provide access to it directly. This is considered to provide the most accurate method if the required illuminance data is available.

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:

• 1-CIE sunny clear day, the sky distribution corresponds to the standard CIE clear sky condition with additional direct illumination from the sun included. Expect very bright patches due to direct illumination from the sun with relatively dark areas where direct sunlight does not fall.
• 2-CIE clear day, the standard CIE clear sky distribution without direct illumination from the sun.
• 3-CIE sunny intermediate day, sky with intermediate conditions between the overcast and clear skies (see graph below) with direct illuminance from the sun included.
• 4-CIE intermediate day, the CIE standard intermediate sky with illuminance distribution conditions between the overcast and clear skies (see graph below). Direct illuminance from the sun is not included.
• 5-CIE overcast day, The CIE Standard Overcast Sky, originally known as the Moon and Spencer Sky, was devised to represent the luminance distribution observed for overcast skies. Adopted as a standard by the CIE in 1955, this description is the one most frequently used for illuminance modelling. In this model, the sky brightness increases gradually with altitude from the horizon to the zenith, but it does not vary with azimuth.

• 6-CIE overcast day (specify illuminance) This default option is similar to 5-CIE overcast day described above but is scaled using a standard sky illuminance at the zenith. By default the zenith illuminance is set to 10,000 lux so that daylight factors can be calculated simply as working plane illuminance values divided by 100. This option is frequently used for daylight factor calculations. Other zenith illuminance values can be entered though.
• 7-Uniform cloudy sky where the sky illumination is completely uniform.

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.