By Mark Warburton, Ivory Egg.
In our constant strive to keep the Ivory Egg office up to date, we have just installed a weather station. The one we chose is the Gira Weather Station Plus (also available from INSTA and Jung). Now, this isn’t just any KNX weather station, as it has over 15 different sensors, allowing all manner of environmental conditions to be read. Even a basic version, however, will still offer a wide range of data on the external environmental conditions.
Although providing visualisation of the weather outside is a common use of weather stations, on its own, this is little justification for adding a weather station to a project. When considered as part of the wider building control system, there a numerous ways in which the weather station can be used in order to increase the automation and performance of the building.
Some room-temperature controllers have the option to use the external temperature to influence the demand variable. This ensures that a sudden drop in temperature will be compensated for before the room temperature decreases.
Alternatively, the external temperature can be used by the boiler or central plant equipment to increase the flow temperature of the heating circuits. This has the same effect as influencing the room control, but it will benefit the entire system at once.
If you don’t have this level of control, by using the limiting threshold that is integral to most weather stations, you could change the heating mode when the external temperature drops below a predefined threshold. For example, to change from night to standby mode when the temperature drops below 0°c.
Brightness and Shading
Using the external brightness level to activate internal lighting and close blinds provides a more accurate level of automation than just using sunset/sunrise times, particularly in winter when bad weather can have a big effect on the light levels.
If the weather station has integrated shading control and multiple, directional brightness sensors, you can intelligently control internal and external shading in order to prevent, for example, solar gain, manage the light levels internally or protect delicate pieces of art or furniture. To achieve this functionality, GPS is used for an accurate position of the installation, allowing the weather station to determine the position and angle of the sun. By using parameters to define the direction of the façade, the angle at which to begin shading, and the rate of shading, you can realise extremely accurate shading control.
Wind Speed and Direction
If you have external shutters, then using the wind speed for protection can be a requirement – not just a nice feature! On the other hand, if you have wide-opening windows, then restricting the opening based on wind speed helps to create a more comfortable internal environment.
A wind direction sensor can be used as part of a natural ventilation solution that uses fresh air to heat, cool and ventilate a building. When paired with the wind speed, temperature and humidity sensors, this can be used to achieve the kind of functionality usually reserved for much more complex and expensive systems.
When skylights are installed and automated, closing them automatically when it rains is an expected feature. You could also use the rain sensor as a warning for the household – perhaps when the washing has been put out to dry. It can also be used as an input for irrigation control, although using a soil moisture probe will provide a far better indication of the amount of rain that has fallen.
Humidity – Absolute and Relative
Increasingly, humidity is being controlled as part of the environmental controls, as it has such a big impact on our comfort levels. When combined with temperature, it is possible to provide a much more relevant temperature that takes into consideration the oppressiveness and comfort. The Gira weather station makes these calculations available on specific objects, allowing you to display and track the local conditions more accurately.
The air pressure tells us a lot about the weather, particularly when it drops suddenly. This can allow the heating system to pre-empt a sudden drop in temperature or give the solar system time to work before using other forms of energy generation.
Knowing the strength of the sun will allow you to check the efficacy of the solar installation, particularly as the installation begins to age. It could be an indication of a fault in the system or that the solar units should be cleaned earlier than the usual maintenance period.
With so many sensors and logic, it not surprising to find additional logic functions in most weather stations. The Gira unit is one of the few that allows more than 2 inputs on each logic gate. This increases the likelihood of you not needing a separate logic unit on the project – particularly as the input can be from the bus, not just internal from the weather station.
Now, I’d like to pretend our office has all the functions and devices listed above, but other than the external temperature, our weather station will mainly be providing the data for visualisation so we can show what is possible. However, by archiving the data from the weather station, we can build a historical record of the weather in our specific location. This can be useful in the future, particularly if we want to look at energy generation from solar or wind. Having a clearer picture of the environment would allow us to make a more informed decision about the efficacy and payback of these systems.
Using a weather station in a project will give you another dimension of control and data that can be used to make the building more comfortable, efficient and create a wider range of solutions than were previously possible.
Mark Warburton is the Technical Director of Ivory Egg (UK) Ltd, a supplier of leading KNX products and provider of KNX training courses.