CLIMATE BASED DAYLIGHT MODELLING (CBDM)
What is it?
Is a different and new detailed way of assessing daylight taking into account specific climate conditions, quality and quantity of sunlight and daylight.
What is it for?
Provides more detail about light distribution and intensity enabling the design of the building to be developed to maximize the use of both daylight and sunlight.
This modelling enables compliance with Priority School Building Programme (PSBP).
The EFA Output Specification established two criteria to assess compliance:
Spatial Daylight Autonomy (DA) or (sDA)
sDA is the amount of time a space can expect to reach a target illuminance level on the working plane. This criterion is aimed at delivering an energy efficient space. The output specification sets a minimum target sDA of 50% for each learning space, sports hall and exam area.
Useful Daylight Indicator (UDI)
UDI is defined as the annual occurrence of illuminances across the work-plane that is within a range considered “useful” by occupants – 100 to 3000 lux. This is subdivided:
UDI-a (100 to 3000 lux) where electric lighting is acceptable and electric lighting wouldn’t be needed for the majority of the day. Achieving a high UDI-a percentage signifies the space is predominantly daylit throughout and glare is controlled.
UDI-e (above 3000 lux) where the amount of light would be considered excessive and a source of glare and the blinds would be closed.
UDI-s (below 100 lux) where the light would be considered insufficient without electric lighting.
The output specification sets a minimum target of 80% UDI-a for each learning space, sports hall and exam area.