BREEAM Daylight Factor Criteria
Terms and Definitions
Average Daylight Factor
The average daylight factor is the average indoor illuminance (from daylight) on the working plane within a room,
expressed as a percentage of the simultaneous outdoor illuminance on a horizontal plane under an unobstructed CIE Standard Overcast Sky.
Point Daylight Factor
A point daylight factor is the ratio between the illuminance (from daylight) at a specific point on the working plane within a room, expressed as a percentage of the illuminance received on an outdoor unobstructed horizontal plane. The minimum point daylight factor is the lowest value of the daylight factor on the working plane at a point that is not within 0.5m of a wall.
Uniformity
The uniformity is the ratio between the minimum illuminance (from daylight) on the working plane within a room (or minimum daylight factor) and the average illuminance (from daylight) on the same working plane (or average daylight factor).
Daylight Factor Criteria
BREEAM 2018
The relevant building areas must meet
1. Minimum value of average daylight factors required
2. Daylighting uniformity criteria
BS EN17037 Daylight Factor Criteria
Daylight Factor Criteria
UK National Annex
The UK Annex is intended for “hard to light” dwellings.
The targets for DF is linked to the lux targets defined for BS EN17037 SDA (This can be accessed via Project Settings Climate Daylighting tab). The target DF is calculated based on the target illuminance and the median external diffuse illuminance. e.g. For London Gatwick, median illuminance is 14100. The equivalent target DF for 100 lux is (100 / 14100) % 100 % i.e. 0.7%
The target DF is to be met for 50% of the time over 50% of the space
EN17037 Daylight Factor Criteria
Daylight Factor Criteria
The targets for DF is linked to the lux targets defined for EN17037 SDA. (This can be accessed via Project Settings Climate Daylighting tab). The target DF is calculated based on the target illuminance and the median external diffuse illuminance. e.g. For London Gatwick, median illuminance is 14100. The equivalent target DF for 300 lux is (300 / 14100) % 100 % i.e. 2.1%
The target DF is to be met for 50% of the time over 50% of the space. The min target DF is to be met for 50% of the time over 95% of the space.
Setting Pass Criteria
Assessment Criteria are set per project in Project Settings dialogue > Climate Daylighting tab.
Select the regulation first and then Press the … button next to the regulation to open the Climate Criteria dialog for the regulation.
DF BS EN17037 Criteria
The criteria is set according to BS EN17037 regulation. The DF criteria are derived from the SDA criteria based on the room type and the Median diffuse horizontal illuminance for the location.
For e.g. Median diffuse horizontal illuminance for London Gatwick based on the energy plus epw file is 14100. So the equivalent DF target for Living Room will be (150/14100)*100 = 1.1
DF EN17037 Criteria
The criteria is set according to EN17037 regulation. The DF criteria are derived from the SDA criteria based on the selected space type targets and the Median diffuse horizontal illuminance for the location.
For e.g. Median diffuse horizontal illuminance for London Gatwick based on the energy plus epw file is 14100. So the equivalent DF target for 300 Lux will be (300/14100)*100 = 2.1
BREEAM DF Criteria
All the entries on BREEAM Regulations Table 5.1 are predefined based on the BREEAM New Construction 2018 and loaded as default in Criteria table dialogue.
Each property and room type pair in BREEAM Regulations Table 5.1 is translated into one or two rows(based on number of credits, target lux, occupied hours) in the dialogue.
If a property, room type pair has different credits or target DF, one row is added for each credit in the table dialog.
For example, Higher education occupied space can achieve 1 credit with 60% area with 2% and 2 credits with 80% area with 2%
Two records are added to the table with the corresponding values for credit value and target DF.
The first entry for higher credit is selected for calculation.
– To Delete an existing criterion select the row on the table and press the Delete Selected Row button.
To Add new criterion fill in the text boxes with corresponding criterion and press the New Row button. Note that the AreaToComply column takes value between 0 – 1.
– To Update an existing criterion simply change the values on the table.
The Selected column displays the criteria that are set for calculation. The DF calculation uses the
registered property and space type of a room to query its assessment criteria from the above table. If more than one records exists for this property and room type, the Selected is returned from the table. If no records exists the default “Other Building Types” and Occupied Space criterion is used.
Notes for All DF Criteria
Note 1: The output report displays criteria that has been set prior to running the calculation.
In other words the selected criteria record is saved against the room on calculation time and same criteria is queried at report time.
Note 2: Changing the Selected criteria, changes to Target DF, Target DF Min requires re-running the calculation.
“Area To Comply” and “Credit For Area To Comply” does not require rerun.
Steps to run Daylight Factor Calculation
- Put the objects in the model in specific layers. e.g. walls in “wall” layer, any external obstructions in “external” layer and so on.
- The registered windows will automatically get Glass material based on their properties set during the registration time.
However the registered windows must be added to relevant group before conversion.
For more details on how to setup the model for running Daylight Factor, utility commands that automate the process and questions on Window Glazing Transmittance,
please refer to the topic How to prepare a model for Assigning the Materials? in Materials knowledge base section. - Open the Material dialog and assign a material for each layer. Material Library has a predefined list of most of the common materials. Yet you can define your own or customize them.
For more details on how the material dialogue works please refer to the About Material Dialog topic in Materials knowledge base section. - Set the Ray tracing Method and its options on Application Settings > Calculation tab > Ray Tracing section.
- The Sky distribution used for Daylight Factor is CIE Overcast Sky. However this can be changed to Uniform Sky on Project Settings dialogue > Calculation tab for experimental purpose.
- Tick Convert to Radiance format or Convert to GPU format before Converting the model.
- Set climate regulation to BREEAM, BS EN17037 or EN17037
- Finally run the calculation using the CPU or GPU rendering method
