KNX weather stations: Selection criteria

The building type is an important starting point when selecting a KNX weather station. A detached house typically has only a few shading zones and relatively straightforward automation requirements. Office buildings, hotels and public buildings, on the other hand, often require multiple façades to be controlled independently, different occupancy schedules to be taken into account and more sophisticated shading strategies to be implemented. As a result, the requirements for sensor technology, control functions and the number of independently controlled façades vary considerably.

The shading concept determines which weather data is required for the building automation system and how it is evaluated. It is influenced not only by the type of shading systems used, but also by how they are to be controlled. For example, if individual façades are to respond independently, the sun's position is to be taken into account, or different shading strategies are required for office, residential or communal areas, the demands placed on the weather station increase.

The more sophisticated the shading automation, the greater the requirements for sensor technology, control functions and weather data evaluation. The shading concept is therefore one of the most important selection criteria when planning a KNX weather station.

The number of façades that need to be controlled independently is one of the key selection criteria when choosing a KNX weather station. Depending on their orientation, façades can be exposed to significantly different levels of sunlight, wind and shading. To ensure that each façade is controlled according to its actual weather conditions, these differences must be taken into account when evaluating the weather data.

Not every weather station supports the same number of independently controlled façades. It is therefore advisable to define at an early planning stage which façades require separate control and whether the building may be extended or additional shading zones added in the future. This makes it easier to select a weather station that meets both the current and future requirements of the project.

The weather data a KNX weather station needs to provide depends on the automation functions planned for the building. In addition to standard measurements such as wind speed, precipitation, brightness and outdoor temperature, other parameters such as wind direction, humidity, air pressure and the sun's position may also be relevant, depending on the application.

What matters is not the number of available sensors, but whether the weather station provides all the weather data required for the project. For example, if shading is to be controlled according to the sun's position, or if individual façades are to respond differently depending on the wind direction, the corresponding weather data must be available for evaluation. The required weather data should therefore be defined during the planning phase, as it has a significant influence on the choice of the most suitable weather station.

Whether GPS-based sun position calculation is required depends on how precisely the shading system is to be controlled. For straightforward applications, a single brightness sensor or – for direction-specific control – three brightness sensors are usually sufficient. GPS-based sun position calculation additionally takes the current position of the sun into account, enabling highly accurate shading control based on both the sun's position and the orientation of each façade.

The sun's position is calculated using the date, time and geographical location. This allows each façade to be controlled according to its orientation and the current position of the sun. GPS-based sun position calculation offers significant advantages in terms of comfort, daylight utilisation and energy efficiency, particularly in buildings with multiple façades and where blinds or external venetian blinds feature slat tracking.

The surrounding environment has a significant impact on the conditions under which a weather station operates. While measurements at free-standing buildings are generally straightforward, hillside locations, tall buildings or dense urban development can create updraughts and wind turbulence. Trees and neighbouring buildings may also affect solar exposure. Choosing the appropriate wind measurement technology and GPS-based shading control helps to account for these conditions.

The installation position of the weather station is equally important. Only when installed in a suitable location can wind, precipitation and solar radiation be measured reliably. The surrounding environment should therefore be taken into account when selecting a weather station.

Not every project has the same requirements for wind measurement. Depending on the type of building, the installation conditions and the local wind conditions, different measurement technologies are appropriate.

Mechanical wind measurement is particularly suitable for free-standing detached houses as well as smaller residential and commercial buildings where wind approaches the building horizontally.

Electronic wind measurement offers advantages in more complex building situations, such as hillside locations or conservatories, where wind can rise along the façade.

Ultrasonic wind measurement is recommended when wind conditions for a complex project are to be monitored centrally from a single weather station installed on the roof. In addition to wind speed, it also measures wind direction. Evaluating the wind direction is particularly beneficial for protecting buildings with complex façade layouts.

The choice of the most suitable wind measurement technology therefore depends not only on the size of the building, but above all on the local conditions and the requirements of the shading system.

The cost-effective solution for standard applications

Suitable for:

• Free-standing buildings with predominantly horizontal wind exposure
• Detached houses and small residential or commercial buildings
• Conventional façade layouts and standard shading solutions

Typical features:

• Cup anemometer for wind measurement
• Integrated sensors for sun, wind, rain and temperature
• Reliable automation for typical residential buildings
• GPS-based sun position calculation (depending on model)
• Integrated logic, time scheduling and calendar functions

Greater flexibility for high-end residential and commercial projects

Suitable for:

• Buildings where updraughts and/or air turbulence occur along the façades
• Apartment buildings and larger residential properties
• Commercial buildings
• Projects with higher requirements for comfort and shading automation

Typical features:

• Electronic wind measurement
• Shading control for up to eight façades (depending on model)
• Advanced automation functions for sophisticated KNX projects
• GPS-based sun position calculation (depending on model)
• Integrated logic, time scheduling and calendar functions

Maximum performance for sophisticated building automation

Suitable for:

• Office, commercial and public buildings
• Projects requiring centralised weather data acquisition and complex façade layouts
• Complex KNX installations

Typical features:

• Ultrasonic wind measurement with wind direction detection
• Measurement of humidity and air pressure
• Shading control for up to 12 façades
• Comprehensive automation functions for demanding building designs and user requirements
• GPS-based sun position calculation
• Integrated logic, time scheduling and calendar functions

More features do not automatically mean a better solution. Nor can the right weather station be selected based on building size alone. Only by considering the project requirements, shading concept, required weather data and installation conditions together can you determine which weather station will perform reliably. That is why it makes sense to start with the project rather than the product.