Central ventilation systems consist of a centrally installed ventilation unit that ensures air transport within a pipe system.

There are pure exhaust air systems that only extract the air, while supply and exhaust air systems usually have two separate duct systems with separate fans with which the air can be extracted and blown in. In contrast to decentralised systems, the air transport for supply and exhaust air in central ventilation systems is not carried out via the free air volume of the building, but via a closed pipe system.

More about central ventilation systems for residential buildings

In principle, there are central ventilation systems with and without heat recovery (heat recovery). The heat recovery is carried out via a heat exchanger and can be used either to heat fresh air or to heat the service water. Plants without heat recovery are not the subject of this bauwion knowledge page.

DIN 4108-7 prescribes an airtight construction method for new buildings in order to minimise ventilation heat losses due to leaks. This requirement also has an impact on the use of the building, because at the same time a hygienic minimum air exchange is required, which must be ensured over the periods of use. Due to the tightness of the building, there is no natural air exchange due to the leaks of the building (air exchange due to infiltration). Correct manual ventilation through the windows requires a corresponding, regular and conscientious activity on the part of the user.

Adequate ventilation of common rooms is important for the removal of moisture, odours and pollutants (e.g. CO2), and in summer also of heat. With the increased airtightness, the pollution of the indoor air also increases, especially in new buildings, because many pollutants are released from building materials and accumulate in the air, especially in the first few years of use.

Both the Energy Saving Ordinance (EnEV) and DIN 1946-6 contain regulations such as the minimum air exchange, which require the planner to draw up a ventilation concept. DIN 1946-6 asks for the characteristics of the building according to which the necessity of a ventilation system can be assessed: if, for example, there are internal exhaust air rooms, the air exchange rate via infiltration is not sufficient for moisture protection or there are special requirements for energy, sound insulation or hygiene, the use of a ventilation system is unavoidable.

Pre-tempering of the outside air: At particularly low outside temperatures, the outside air must be pre-heated to prevent icing of the heat exchanger. The simplest solution is an electric preheater that heats the temperature of the outside air to -2 to 0°C, but electricity is needed as auxiliary energy to heat up. Another solution is the brine geothermal collector, which uses near-surface geothermal energy below the frost-proof area for heating. Somewhat more cost-effective is the use of an air-guided geothermal heat collector (ground-to-air heat exchanger or "geothermal heat pipe"), through which the outside air flows before it is directed into the WT. In summer, a geothermal collector can also be used for cooling.

Distribution/cable routing: During planning, great attention must be paid to the cable routing in order to take into account as many recesses and cable penetrations as possible at an early stage.

The choice of piping system has a significant impact on sound insulation, cleaning and performance of the system. Optimal for low flow resistance, and thus the quietest and most efficient operation of the ventilation system, are large, round cross-sections with smooth and easy-to-clean surfaces, as well as as possible changes of direction within the pipe system. In practice, this requirement can only be achieved with compromises due to the often limited space available. There are pipe systems that only carry one supply and exhaust air pipe in the riser and then manage the splitting into the individual rooms floor by floor via a distribution box. Other systems lead all cables individually to the device, which results in advantages in terms of sound insulation between the rooms.

Infloor or on-floor systems are used in residential buildings when the cables cannot be routed in suspended ceilings.

Hygiene/cleaning/maintenance: The exhaust air ducts in the kitchen should be equipped with a grease filter on the room side and should not be in the immediate vicinity of the stove to avoid contamination. In addition, the use of a recirculating air extractor hood is recommended (see below).

In order to keep the ventilation system as clean as possible between cleaning intervals, it is important that the filters are regularly maintained and that the ventilation system also runs in summer, otherwise bacteria and mould can form in the pipes, which can only be removed with greater effort. Pipelines can be cleaned by special brushes, whereby supply air pipes have hardly any impurities if the filter is changed regularly.

Filtering: Most filters in ventilation systems are fine dust filters, but they can also be supplemented with finer filters such as pollen filters. The filters should be inspected by the user regularly by visual inspection and changed about 1 time a year. Most systems have filters that can be changed by the user. When selecting the device, it should be noted that not too short maintenance intervals are required, otherwise there is a risk of neglecting maintenance, which means that contamination of the system is inevitable. It is important that not only the fresh outside air is filtered, but also that a filter is used on the exhaust air side in front of the heat exchanger, otherwise the WT will be polluted by house dust entered. This can lead to hygiene problems, especially with enthalpy heat exchangers.

Extractor hoods: It is advisable to use a recirculating air extractor hood to collect grease vapours. Exhaust extractor hoods cannot be used in apartments with ventilation systems, as their powerful fans would interfere with the function of the ventilation system.

Parallel operation of ventilation systems and fireplaces: If a ventilation system and a fireplace for solid fuels (e.g. stoves) are operated at the same time, it must be ensured that the combustion air is not taken from the room air. At the same time, it must also be prevented that flue gases from the stove are introduced into the room. Leaks in the fireplace or its supply air duct can allow these smoke gases to enter the room and, in the worst case, lead to poisoning of the users.

Regulations on this can be found in §4 of the Model Combustion Ordinance (FeuVO), which have been adopted in the combustion ordinances of the individual federal states and can be looked up there for the respective building site.

One possibility isto use room-air-dependent fireplaces with an external combustion air supply. In these devices, the combustion air must be supplied directly from the outside via an on-site supply air duct and at the same time a safety device with general building authority approval from the DIBT (e.g. vacuum monitor) must be installed, which monitors the air pressure conditions in the room and switches off the ventilation system in the event of negative pressure. This device configuration must be coordinated with the ventilation system manufacturer and the local chimney sweep.

Alternatively, fireplaces that areindependent of indoor air can be used, which meet increased requirements for tightness and have a general building authority approval from the DIBT. These devices are marked with a so-called "Ü mark" (conformity mark). During installation, however, attention must also be paid to the tightness of the supply air duct and the transitions to the chimney. Although a safety device to monitor air pressure is not mandatory, the tightness of the furnace must be checked regularly, which results in maintenance costs. There is a certain residual risk that leaks will occur between test intervals that go unnoticed if there is no vacuum monitor.

Bypass: To renew the air, the ventilation system must also run in summer. The heat exchanger continues to work during this time and must be deactivated to prevent the rooms from overheating. Most manufacturers have a so-called bypass function, with which the air is guided past the heat exchanger. Other devices have a replaceable heat exchanger, which is replaced by a special duct piece in the warm season.

Sound insulation: Quiet operation of the ventilation system is crucial for user satisfaction, which is why the minimum building law requirements according to DIN 4109 are not sufficient. However, most devices fall well short of this minimum requirement, so that this does not automatically result in a restriction in the choice of product.

Protection of neighbouring residential units: DIN 4109 regulates minimum requirements for noise from third-party residential units, whereby a sound pressure level of up to 35 dB(A) is permissible for ventilation systems without conspicuous individual tones in living and recreation rooms. It should be noted that sound pressure levels from ventilation systems of 30 dB(A) and more are not accepted by a significant number of people, so it makes sense to agree on increased sound insulation levels for the sound insulation of noise from ventilation systems both in one's own and in other residential units.

Notes onsound insulation within the residential unit: For the protection of living and recreation rooms of one's own residential unit, a sound pressure level of about 25 dB(A) creates good conditions and can also be easily achieved technically. However, sound insulation is the interplay of several factors that play a different role depending on the system design. Outside the house, noise emissions must be limited to protect the neighbors, and the local municipalities provide information on this in addition to the VDI guideline 2058. It should be noted that the requirements in residential areas are much higher than in industrial areas. Of course, the sound from outside must also be limited into the building so that the interiors are not polluted by external noise sources such as busy roads.

Inside the house, there are sound emissions resulting from the movement of the fans and which are transmitted on the one hand as airborne sound into the pipe system and on the other hand in the form of vibration of the device as structure-borne noise on pipes and components. In order to contain the spread of structure-borne noise, soft bearings and sleeves should be used instead of force-fit connections when fastening the cables. Sound insulation can be improved by means of silencers, which are positioned directly between the ventilation unit and the pipe network, as well as by a "heavy" design of the unit and the sound-decoupled installation within the technical room. Depending on the prevailing air velocity, flow noise can occur at the air outlets themselves, which can be reduced by regulating the volume flows differently or by choosing other nozzles.

The sound transmission between the rooms, the so-called telephony sound, must also be reduced as far as possible. In in-floor systems, the cables are often routed to the device in a string with many individual cables. As a result, silencers against telephony sound are largely superfluous in the individual floors. If several rooms are supplied with several individual branches via a wiring harness, a telephony silencer must be installed between the neighbouring rooms.

uFire protection: Requirements for ventilation systems in this regard result from the Model Ventilation System Directive (M-LüAR) in conjunction with the respective state building code, which is usually derived from the Model Building Code (MBO) 2002 quoted below.

According to § 41 para. 2 of the Model Building Code, ventilation ducts as well as their cladding and insulating materials must be made of non-combustible building materials; combustible building materials are permissible if there is no reason to fear that the ventilation duct will contribute to the occurrence and propagation of fire. Ventilation ducts may only bridge room-enclosing components for which fire resistance is prescribed if there is no reason to fear the spread of fire for a sufficiently long period of time or if precautions have been taken against it."

However, this does not apply to

buildings of building classes 1 and 2,
within apartments and
within the same usage unit with no more than 400 m² on no more than two floors.

The preceding facts reflect the requirements set out in the model building code, the applicable state building code may deviate from this. In addition, depending on the project, it must be clarified whether the requirements for special buildings change due to applicable special building regulations (e.g. High-Rise Directive, Accommodation Facilities Ordinance, Restaurant Ordinance, Industrial Building Directive, Regulations for Temporary Structures, Ordinance on Places of Assembly, Places of Sale Ordinance, Guidelines for Kindergartens, Hospitals, Schools,) or corresponding alternative stipulations of the building supervisory authority.

In particular, the M-LüAR regulates when the use of combustible or flame-retardant building materials is permissible and what requirements exist for the installation of ventilation ducts and for their implementation by fire-resistant room-enclosing components.

Ventilation systems in apartment buildings: Decentralized devices are often used in apartment buildings. If central ventilation systems are used, this refers to central housing systems; this means that each apartment unit has its own device and its own piping system, otherwise the requirements for sound insulation and fire protection between the residential units would drive up the costs. Some manufacturers offer particularly compact devices for renovations, which are arranged in the hallway above a suspended ceiling and ventilate and ventilate the adjacent rooms via supply and exhaust air openings in the walls.

Pipeline routing: When laying the pipes, care must be taken to ensure that there are no other sound-emitting pipes or pipes in the immediate vicinity of supply air ducts. For example, pipes from central vacuum cleaner systems can transmit sound, but also unprotected sanitary pipes and downpipes. If ventilation pipes and sewage pipes are routed in a shaft, measures must be taken to prevent sound transmission.

Furthermore, care must be taken during the execution that the intake opening of the external air duct is not located near a source of odor (e.g. compost, garbage can container, etc.) or the exhaust opening of the exhaust air duct. Otherwise, odour emissions will be introduced into the building and the supply air will be polluted. It should also be avoided that the wind blows the used exhaust air to the outside air opening, which is why the outside air opening should be located on the windward side of the building, while the exhaust air opening should be located on the downwind side. An additional factor is solar radiation, which can heat the ventilation pipe so much in summer that the cooling function of the downstream geothermal pipe is eliminated. The ventilation tower of the outside air must also be protected against the entry of impurities and foreign bodies with fine-meshed grids.

Sound-decoupled bearing: If vibration noises are noticeable during the use of the system or already during the construction phase, which are difficult to locate and do not come directly from the ventilation opening, it should be checked whether the noise is due to insufficient sound decoupling during the storage of the device.

Adjustment: Both DIN and EnEV require the ventilation system to be adjusted by the executing specialist company in order to check the projected values and to be able to make any adjustments. The adjustment protocol is also an important proof of certification by the Passive House Institute.

Standards and literature

DIN 4108-7, Thermal insulation and energy saving in buildings, Part 7: Airtightness of buildings. Requirements, planning and implementation recommendations and examples

DIN V 18599-6, Calculation of the usable, final and primary energy requirements for heating, cooling, ventilation, domestic hot water and lighting

DIN EN 1946-6, Ventilation of apartments. Regulations and technical specifications for free ventilation, decentralised and centralised systems for exhaust air and supply and exhaust air systems.

DIN EN 12779, Ventilation of non-residential buildings - General principles and requirements for ventilation and air conditioning systems and room cooling systems; German version EN 13779:2007

DIN EN 13779, Ventilation of non-residential buildings – General principles and requirements for ventilation and air conditioning systems and room cooling systems.

EEWärmeG 2011, Renewable Energies Heat Act (EEWärmeG 2011)

VDI guideline 2081, noise generation and noise reduction in ventilation and air-conditioning systems.

Model Ventilation System Directive, Model Directive on Fire Protection Requirements for Ventilation Systems (M-LüAR), as of 29.09.2005

Source: bauwion