IDA ICE extensions

Daylight calculation

Simulation in the Daylight tab is done with Radiance as a calculation engine. It is included in the Expert version and offered as an extension to the Standard version of IDA ICE. Three simulation types are supported: Daylight factor, Illuminance (for selected points of time), and yearly climate-based daylight is an option. A simulation may be done with a controllable shading that is either on or off. For illuminance and whole year illuminance, there is a third option to consider shading for windwo integrated shadings according to the control signal. The level of precision can be chosen.

Measuring planes can be set up in selected zones by giving the height above the floor, the distance from the walls and the resolution for each zone. It is also possible to instead choose use “user defined measuring planes”, where measuring planes of arbitrary shape and location have been created manually.

Optical properties of the surfaces, except for the glazing, are shown in the Optical properties table. For glazing, the visual transmission for each pane or for the entire glazing is used as input.

Daylight factor

Daylight factor is calculated for the standard CIE overcast sky. It gives the ratio of the illuminance on the measuring plane in the zone compared to the unshaded illuminance on the ground. Usually, daylight factor is calculated without any controllable shadings. Daylight factor simulations are not influenced by orientation, location or point of time.

Illuminance

Illuminance in the measuring plane is calculated for chosen points of time. For an illuminance calculation it is possible to select any of the sky types that are available, i.e

• CIE overcast sky
• CIE clear sky
• Clear sky without sun
• Uniform cloudy sky
• Climate based sky (Perez)

Yearly climate-based daylight

For the yearly climate-based simulation the so-called Three-phase method is used.

It means that the flux transfer is divided into three phases (matrices) for separate calculation:

1. Sky to exterior of fenestration
2. Transmission through fenestration
3. Interior of fenestration into the simulated space

The glazing transmission matrix describes the transmission of light from different incident solid angles to different outgoing solid angles. This may be calculated with and without a window-integrated shading. The matrices are finally multiplied with each other and also with a matrix that contains sky luminance values for all parts of the sky and at all hours of the year. 

External shadings cannot be simulated as controllable “According to control signal” in climate-based daylight simulations, since they are not window integrated, and are therefore not part of the window matrix. For this case the external shading is disregarded (not drawn).

Only light coming from windows facing the outside that are in the same zone as the measurement plane or in adjacent zones (through an inner window or opening) is considered in climate-based daylight simulations. So light that passes through more than one inner window or opening is disregarded.