Presence detectors in the Smart Building

When they hear the words "motion detector" or "presence detector", many people still think of the automatic switching on and off of the light. But with modern, networked building technology, so many more processes can be controlled based on presence. An important topic here is the keyword "energy saving". Today, we want to live in a way that conserves resources, but at the same time we don't want to sacrifice comfort. This is precisely where presence detectors can help. Properly integrated into the building's individual room control system, they greatly reduce energy consumption in rooms. They are thus also an important part of load management.

A prerequisite for this is the networking of all building services, as can be achieved with KNX, for example. A presence detector with several output channels can then influence several functions in the room, for example light brightness-dependent with a decade specification (light requirement 30%), temperature control with two states assigned to the modes "present" and "briefly absent", etc.

For lighting control, information on presence is combined with room brightness. A light sensor is therefore integrated in most presence detectors. In both commercial and private buildings, the lights are usually not only switched on or off, but also dimmed. The current room brightness is measured and artificial light is added in a well-dosed manner. Ideally, this constant light control also includes control of the overall brightness and the light colour temperature during the course of the day.

Biodynamic lighting control or Human Centric Lighting is the name given to this type of lighting, which adjusts the light to suit the rhythm of the day. It supports waking up in the morning and the activity phase during the day with bright, cool lighting similar to daylight. Towards evening, the illuminance is reduced and the light is set warmer so that all users can come to rest.

This support of the biorhythm by light can not only provide more well-being in social facilities and at home, but also support a healthy daily rhythm at the workplace. The presence detector is now the energy-saving plan behind this feel-good concept, which also simply switches off the light sometimes when no one is in the room. If you pursue this goal further, you will quickly come up with other areas of application for the presence detector.

There are also different scenarios for ventilation, depending on whether a room is occupied or not. This applies equally to central ventilation with ventilation units and to natural ventilation via windows. The needs are very different. Some users want more ventilation in meeting rooms during meetings, while others want to avoid draughts and prevent ventilation for that long.

So a separate motion detector channel should also be created for ventilation, which is independent of light or air conditioning. For ventilation control, an actuating variable comparator is helpful independent of the presence detector. Since ventilation can be triggered by too high a temperature just as much as by humidity or CO2, the comparator filters out the value relevant for ventilation from the commands. For example, the maximum, minimum or average value.

For sun protection, the presence detector can also help to find the balance between user needs and energy saving. In winter, the sun should often shine in deliberately to heat up the room. There is no shading until the desired room temperature is reached. This saves a lot of energy on the heating side.

However, this goal contradicts the user's desire for glare protection, for example at office workplaces. So when work is being done in the room, the indoor temperature block must be lifted so that the shading moves down and does its job as glare protection. Here, a channel of the motion detector is linked to the indoor temperature block and blocks it.