Shading according to the position of the sun: Efficient control of blinds, shutters and awnings

Step by step.

Various systems are offered for controlling blinds, shutters or awnings. Modern systems with extensive comfort functions should already have a sun-guided control. In some systems, the sun-guided control is carried out via a weather station. The use of shading according to the position of the sun to reduce the cooling load of a house and save energy is generally known.

Retrofitting the sun-guided shading system

Anyone who has already equipped blinds, shutters or awnings with drives can retrofit sun-guided shading relatively easily. This uses location-based geostationary data that is output by an astro-clock, for example. In our example, however, we use a logic group template that calculates the position of the sun based on azimuth (cardinal direction) and solar altitude (angle above the 0 horizon) for the location.

Determining the angular ranges for shading

First, based on the geographic orientation of our windows for shading, we need to determine the angular ranges in which the blinds, shutters or awnings should operate. The height of the sun determines the angle of incidence at which a roller shutter, for example, must be positioned in order to shade and still allow light into the room.

For east-facing windows, the angular ranges for azimuth should be from 90 to 155°, for south-facing from 135 to 220° and for west-facing from 210 to 280°. These values are only examples and can be influenced by various factors, such as the position of the house in relation to the horizon (e.g. in a valley, on an elevation or on which floor it is located) as well as the structural environment (hills, vegetation, other buildings, etc.). Due to the inclination of the earth to the sun and its distance, the visibility of the sun changes, which changes the values for shading.

Switching values for shading
Depending on the desired functionality of the shading, there are different approaches.

Solution 1: Fixed value for azimuth

A simple solution is to assign a fixed switching value to an azimuth value in order to approach the shading position. This assumes that this fixed value is transmitted correctly. If the value is not detected, no shading takes place.

Solution 2: Azimuth value range

In our example, we use a safer method and use a range of values for the azimuth for shading. As soon as a valid value is recorded within the range, the release to move to the shading position takes place. When leaving the range, the release is reset. The release can be triggered by pulses of the azimuth value. However, it should be sufficient to send only changes of the releases to the BUS. A filter has been implemented for this purpose.

With this, it would now be possible to use the releases to carry out the shading according to the cardinal directions. For moving to a position, e.g. a blind, a fixed value, e.g. 60%, is specified. However, the height of the sun is not taken into account. This means that shading may be carried out even though the sun has not even crossed the horizon.

Solution 3: Combination of sun elevation and azimuth value range

The sun height (angle of the sun above the horizon) determines at which position blinds, shutters or awnings should move. A minimum value is also set to ensure that the sun has crossed the horizon. For vertical shading (blinds or shutters), this value applies equally to all windows. Depending on the compass direction, the release for the corresponding front for shading is given. Value ranges can also be defined so that the shading can also be tracked at sunrise or sunset.

Activation of the shading

Finally, in our example, it is manually determined when the shading should be active at all. A recommended combination for this is brightness and temperature, as the sun is an additional heat source on cold, sunny days. The functions of the weather query can also be used to activate the shading.