Decentralized ventilation system – features, function and funding

Decentralised ventilation systems with continuous operation are also called permanent fans. They are a complete ventilation unit with a built-in cross-countercurrent heat exchanger. The units have two fans that convey air simultaneously. This results in two air flows. The outdoor and supply air flow brings fresh air into the room, while the extract and exhaust air flow removes stale air from the room to the outside. The cross-countercurrent heat exchanger is positioned between the two air flows. In it, the heat is recovered from the indoor air and transferred to the supply air. This means that a large part of the heat remains in the room despite continuous ventilation.

Due to integral filters and the corresponding design of the unit, neither dirt particles nor noise from outside can penetrate through to the rooms. Permanent fans can supply air to and vent individual rooms and can be installed in the external wall both in supply air areas (living room, bedrooms or children's rooms) and in extract air areas (kitchen, bathroom or WC). One appliance that uses this operating mode is the Vitovent 200-D decentralised ventilation system.

There are also other designations for decentralised ventilation systems in reversing operation. They are called push-pull units or pendulum fans. Unlike their continuous operation counterparts, pendulum fans have only one fan. Two constantly communicating units are responsible for the required air change rate. While one ensures the removal of stale air, the other ensures that fresh air flows in. A thermal store is used for heat recovery, which temporarily stores the heat from the extract air and transfers it to the supply air.

Other aspects of the operating principle of decentralised ventilation with reversing operation: both units are connected to each other via a controller. This ensures that the direction of rotation of the fans is reversed after approximately 70 seconds and the air flow is thus conveyed in the opposite direction. These units also have filters against dirt from outside and protect against road noise. With a pair of pendulum fans, two supply air areas can be supplied with air and vented simultaneously if there is an air connection between the two rooms. As a rule, these units are not installed in extract air areas. The Vitovent 100-D ventilation unit is a pendulum fan.

You can find more tips and information about this in the mechanical ventilation section on heizung.de.

When looking for the right ventilation system, the scope of the modernisation is a significant factor. After all, a core modernisation achieves very different results from a partial modernisation. Depending on the building characteristics, a central ventilation system may also be considered for a core modernisation. It is also possible to use a decentralised ventilation system in a new build. Which ventilation system ultimately suits which building depends on many factors. Among other things, the building characteristics of the living space, usage patterns and the number of occupants must be taken into account. 

As already mentioned, decentralised mechanical ventilation is primarily characterised by its room-related use. Each individual ventilation unit requires its own electrical connection. Depending on the ventilation unit, this may be a 230 volt connection, as with the Vitovent 200-D, or a data cable, as with the Vitovent 100-D. Since the units are installed in an external wall, homeowners must also take the building type into account when purchasing a decentralised mechanical ventilation unit. Finally, for use in a new build, there are special wall blocks into which ventilation units can be inserted. Retrofitting of the units, on the other hand, is done with the help of a drilled hole.

Since stale air accumulates at the top of the room, ventilation units should be positioned there if possible. Although the units are quiet, very sensitive people may feel disturbed by the airflow noise, especially in sleeping areas. To avoid this, positioning and design of ventilation units should be well planned in advance.

Compared to central mechanical ventilation, the planning effort for a decentralised ventilation system is lower. However, the expertise of a contractor is essential for efficient and quiet operation. An experienced installer quickly determines how to size the ventilation system and where the optimal placement for the air diffusers is. They will also help with the selection of the appropriate type of unit. Depending on the available space, either a ventilation unit with a built-in cross-countercurrent heat exchanger or one with a single fan and a ceramic thermal store should be considered.