Priority School Building Programme

CBDM03

CLIMATE BASED DAYLIGHT MODELLING (CBDM) – A DIFFERENT APPROACH TO DAYLIGHT DESIGN IN SCHOOLS.

The PSBP Output Specification takes a new approach to daylight design in schools. Historically, designing daylight within the learning environment has been a numerical process focused on the adequacy of illumination under a static overcast sky – daylight factor (DF%). The ambition was to deliver a certain percentage of diffuse light into the space and to achieve a degree of uniformity.

The latest guidance requires Climate Based Daylight Modelling (CBDM) to be used in place of the more traditional methods. Using CBDM in place of daylight factors provides far greater detailed information regarding the illuminance present within the space, throughout the year, under varying sky conditions. It therefore aims to more accurately predict likely interior illuminance levels, helps to reduce potential visual comfort issues (glare) and maximise potential energy savings from the electric lighting system, when used in conjunction with daylight-liked controls.

For the PSBP, the Education Funding Agency (EFA) Daylight Design Guide Rev2 2014 and the Facilities Output Specification (FOS) define two; Useful

Daylight Illuminance (UDI) and Daylight Autonomy (DA).

DAYLIGHT AUTONOMY – DA OF MORE THAN 50% FOR MORE THAN 50% OF THE WORKING PLANE FOR THE TARGET ILLUMINATION (TYPICALLY 300 LUX IN TEACHING SPACES),

USEFUL DAYLIGHT ILLUMINANCE - UDI-A (100 LUX ~ 3000 LUX) WILL BE ACHIEVED FOR AT LEAST AN AVERAGE OF 80% OF THE TIME OVER THE WORKING PLANE.

BOTH DA & UDI-A ARE TO BE PROVIDE IN 80% OF TEACHING AND LEARNING SPACES DURING CORE HOURS OF OPERATION, TYPICALLY FROM 8.30AM TO 4.00PM.