Central ventilation system: function, planning & installation

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Many modern building projects are already equipped with mechanical ventilation systems. On the one hand, this requires a high level of energy insulation in order to regulate indoor air humidity as effectively and safely as possible. On the other hand, it is considered a comfort feature adding value to a property.

Viessmann central ventilation systems are extremely energy efficient. A powerful heat exchanger recovers up to 98 percent of the latent heat in the extract air and uses it to heat incoming fresh air. This reduces household expenditure perceptibly thanks to a significantly lower energy demand. In addition, CO₂ emissions are reduced, which means that the use of central mechanical ventilation also reduces the burden on the environment. Further features of central ventilation are explained in the section Benefits of mechanical ventilation.

How central ventilation systems work

The characteristic difference between a central and a decentralised ventilation system lies in its design. Central ventilation systems have a central ventilation unit that directs fresh air to the rooms via an air distribution system. Decentralised ventilation units, on the other hand, are installed entirely within a wall. From there, they supply the building with the required volume of fresh air.

Depending on the type of construction, central ventilation systems operate in different ways

Central ventilation can be divided into three groups:

  • Simple extract air systems
  • Combined extract and supply air systems
  • Systems with heat recovery

In their most simple configuration, stale air is actively drawn in by a fan and discharged to the outside. The air diffusers of such systems are usually located in extract air areas. These include the kitchen, bathroom and WC, which have more moisture and unpleasant odours compared to living spaces such as living rooms or studies. Fresh air, on the other hand, only enters the house passively through air diffusers in the building envelope, window gaps and door slits.

In practice, mechanical ventilation systems that actively draw in supply air as well as extract air are often used. These combined extract and supply air systems have a central ventilation unit and an air distribution system. Not only stale air is actively drawn in and removed. Fresh air also enters the house actively. To prevent unwanted particles from the air as well as noise from entering, most systems are equipped with filters.

A central supply and extract air system with heat recovery consists of a ventilation unit with an air distribution system as well. The ventilation unit has two fans and a heat exchanger. The two fans are used to convey both the air flowing into the building and the air being removed from the building. On one side, the outdoor air/supply air flow draws fresh air into the building. On the other side, the extract air/exhaust air flow transports stale air out of the building.

Both flows are passed through a heat exchanger inside the ventilation unit. In the cooler months, heat from the extract air is transferred to the supply air. This operating mode ensures that as little heat as possible is transported out of the building by the ventilation system. All Viessmann central ventilation units operate in this way. Central mechanical ventilation with heat recovery thus operates in an identical manner to central mechanical ventilation with extract and supply air diffusers. The section on controlled mechanical ventilation explains whether and for which property central ventilation units are suitable.

Operating principle of central mechanical ventilation with a ventilation system

Planning a central ventilation system in older and new buildings

If homeowners want to buy a central mechanical ventilation system, they should research thoroughly in advance and clarify the requirements. The first question regarding a central mechanical ventilation system should be about one's own requirements. After all, this serves as the basis for the subsequent investment. To make thing simpler, buildings are divided into three types:

  • Older buildings
  • Modernised older buildings
  • New buildings

For a more accurate calculation of demand, the number of rooms and occupants as well as their usage patterns must be taken into account. Regardless of the area of application, homeowners should therefore always leave the planning and implementation of a mechanical ventilation system to a contractor. This is because they can estimate exactly how large the ventilation system must be so that it operates as efficiently as possible. In the following section, you can read what else homeowners and modernisers should look out for when selecting the right ventilation system.

In unmodernised existing buildings, fresh air enters the house passively through the leaky building envelope, door slits and through window gaps. The use of a ventilation system in such buildings is nevertheless a good idea, as the risk of mould formation is still very high. However, central ventilation is only rarely an option in unmodernised older buildings. This is because it requires a great deal of planning effort, which is mostly only worthwhile as part of a construction or modernisation phase. Basically, it is important to note: In older buildings, the use of a central ventilation system is possible, but its installation will be more difficult. This is because it requires alterations to the fabric of the building. In addition, the air ducts must be clad.

A central ventilation system is often used in new buildings. It is installed at an early stage in the unfinished building. After completion of the building, it is no longer visible. A central ventilation system in a new build should therefore always be planned in advance. For residential buildings, a ventilation concept according to DIN 1946-6 is prepared for this purpose. A ventilation system is used there to ensure the minimum health-related air change rate and to protect the building. Most building owners opt for central ventilation during the construction phase. This is usually sensible, but not always necessary. With optimal planning and implementation, decentralised mechanical ventilation could also efficiently supply new buildings with fresh air.

Heating system in combination with a Vitoair FS ventilation system

Installation options for the air distribution system

The operating principle of the central mechanical ventilation also involves the installation of air ducts. There are several options to choose from for installation. The best-known methods are:

  • Installation in the floor structure
  • Installation in concrete
  • Installation in a suspended ceiling

This type of installation is often used in new buildings. Here, flat air ducts are initially laid directly on the unfinished floor, followed by the installation of insulation. If necessary, underfloor heating pipes are installed on top of this before a screed is applied as the final layer. The air ducts are no longer visible afterwards. Only floor or ceiling diffusers show that a ventilation system is installed underneath.

An alternative to installing air ducts on an unfinished floor is installation in concrete. For this purpose, round air ducts are usually placed inside the steel reinforcement of ceilings during the initial construction phase. Only then is the concrete poured. This installation method is suitable for both partially pre-cast ceilings and concrete ceilings poured in-situ. The advantage of this installation is that no additional floor construction is required. However, detailed planning with the structural engineer is required in advance.

Depending on the room height, ventilation systems may also fit into a suspended ceiling. Vitovent  200-C and Vitovent  300-C flat ceiling units are particularly suitable here. These units can be mounted directly to the ceiling. The air ducts to individual rooms are integrated into the suspended ceiling so that they are no longer visible.

What central ventilation systems does Viessmann offer?

A central mechanical ventilation system in a building consists of a ventilation unit and an air distribution system. The air distribution system is concealed in the floor or integrated into the wall. Air diffusers are all that remain visible. The air exchange rate is controlled independently by the central ventilation unit.  

Different ventilation systems are available

Depending on the building characteristics and personal requirements, different systems for central ventilation should be considered. Ceiling units such as the Vitovent  200-C and Vitovent  300-C are designed to have a very low installation height and can be integrated into a suspended ceiling. A wall mounted unit such as the Vitovent  300-W is somewhat larger in size and can deliver an air flow rate of 300  m³/h to 400  m³/h.

All Viessmann central ventilation units can be controlled via both the ViCare and VitoGuide apps. This requires the control system to be integrated with the respective heat generator and connectivity via a Vitoconnect  box. The ventilation system and heat generator thus form a central building services unit, both visually and technically. An example of this is the Vitoair FS ventilation system which can be flexibly installed: under the ceiling, on the wall or lying on the attic.

All Viessmann central ventilation systems feature heat recovery. This means they remove heat from the extract air and then transfer it to the supply air. This increases efficiency and saves heating costs.

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