Sun protection: basic principles and definitions

Lamella setpoint tracing

A louvered blind that can be adjusted offers the option of intelligent sun protection here. The position of the slats is cyclically adapted to the current position of the sun, so that no direct daylight enters through the blinds, but as much diffuse daylight can be utilized as possible.

The illustration shows that diffuse light can still enter from underneath, whereas no further direct daylight, or theoretically only a single ray, can enter. The following parameters are necessary for the calculation of the slat angle:

• the current sun elevation (angle of elevation)
• the position of the sun, i.e. the azimuth angle
• the facade orientation
• the slat width
• the slat spacing

The effective angle of elevation is calculated from the first three of the parameters listed above:

If the facade orientation and the position of the sun (azimuth) are equal, then the effective angle is equal to the current angle of elevation.

However, if the sunlight falls at an angle onto the facade as seen from the sun direction, the effective angle is larger for the same angle of elevation.

The following three pictures illustrate the relationship between the effective angle of elevation and the dimensions of the blind and how the resulting slat angle λ changes:

Height adjustment

With a high position of the sun at midday, the direct rays of sunlight do not penetrate into the full depth of the room. If direct rays of sunlight in the area of the window sill are regarded as uncritical, the height of the sun protection can be adapted automatically in such a way that the rays of sunlight only ever penetrate into the room up to an uncritical depth.

In order to be able to calculate at any time the appropriate blind height that guarantees that the incidence of sunlight does not exceed a certain value, the following values are necessary.

Required for the calculation of the respective blind height:

• Sun elevation
• Window height
• Distance between the window and the floor

The following illustration shows where these parameters are to be classified:

Influence of the facade inclination

In both of the methods of sun protection described, it was assumed that the facade and thus the windows are perpendicular to the ground. In the case of an inclined facade, however, the incidence of light changes such that this influence will also be taken into account. The facade inclination is defined as follows: