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Ventilation system: what is important in planning

3. What ventilation systems are there? Can a system be retrofitted?

Depending on the building, needs and individual wishes, there are different systems or combinations of different systems. Some ventilation systems recover heat from the exhaust air and thus save heating energy. Many existing ventilation systems can be retrofitted. Professional planners who specialize in ventilation technology or building renovation can advise you individually. We will show you an initial overview of systems that are mainly installed:

Exhaust system

Exhaust systems are simple ventilation systems that can be found in many houses and apartments. A fan usually sucks in the air in an indoor bathroom without a window or in the kitchen. The negative pressure generated in this way ensures that air also flows in from other rooms via door slits or other openings. Adjustable outside air outlets in the house wall or in the window frames of the living rooms and bedrooms ensure that fresh outside air flows in continuously. A filter protects the lines and the system from becoming dirty. You should also open the windows of all rooms if necessary.

Since the amount of air transported is small, there is no unpleasant draft. If there are radiators nearby, they can warm up the air quickly. The output of the exhaust air fan can be set in stages and regulated, for example, using the light switch or humidity sensors.

Central supply and exhaust air system

With a central supply and exhaust air system, the controlled living space ventilation is controlled for the whole house. Since the air flows through shared pipes, there are only a few outlets in the house walls. With heat recovery, the thermal energy contained in the exhaust air is used to preheat the incoming outside air. Central supply and exhaust air systems can be retrofitted if the room layout and ceiling height are suitable, for example in a hallway.

The polluted air in the living space is extracted through exhaust air openings with filters and transported to the outside through the ventilation unit via pipes. Fresh air is sucked in from the outside and filtered through the ventilation unit via supply air lines into the living space. This is usually done using jet nozzles in the upper area of ​​the walls without creating drafts.

A heat exchanger in the ventilation unit ensures that up to 90 percent of the thermal energy from the exhaust air is retained in the building. The heated supply air can even be used to replace space heating in a very well insulated building, such as a passive house.

The air volume can be regulated manually or via sensors, for example depending on the temperature, the CO2 content or the desired humidity.

In order for the system to function smoothly and efficiently, the following must be taken into account during planning:

  1. the indoor air requirement,
  2. the size of the apartment,
  3. the number of residents as well
  4. the possibility of cleaning all system parts and lines via sufficient inspection openings.

Decentralized supply and exhaust air system

Decentralized air supply and exhaust air systems with heat recovery are compact ventilation systems that do not require complex lines. Passages are installed in the outer walls through which air is drawn in and out. They can therefore easily be retrofitted in existing buildings. They can also be used as a solution for individual, particularly stressed or poorly located rooms, such as living rooms and bedrooms on busy streets. The ventilation units require at least one masonry opening (core drilling) and a power connection. Since no cables are required in the house, they are easy to maintain. Decentralized ventilation devices are a cost-effective alternative to the central supply and exhaust air system, depending on the floor plan or apartment situation.

4. How does a ventilation system with heat recovery work?

Ventilation systems with heat recovery reduce energy losses. They ensure that sufficient preheated air comes into the house. In this way, you help to avoid structural damage and health problems.

With heat recovery, the thermal energy contained in the exhaust air is extracted and used to supply the building with energy, for example for room heating via the supply air or for hot water heating. This increases the efficiency of a ventilation system and reduces the overall energy requirement of the building. The efficiency of the system should be over 80 percent. Check the manufacturer's information for this.

The following techniques are available:

  1. Counterflow heat exchanger (Air-to-air heat exchanger): The warm exhaust air duct is routed past the cold supply air duct using the counterflow principle and thereby transfers the heat to the air flowing into the room (supply air).
  2. Regenerative heat exchangers: With decentralized supply and exhaust air systems, the air exchange takes place within a single device that is built into an external wall. The heat exchanger stores the heat of the room air (exhaust air) during extraction and transfers it directly to the incoming air flowing into the room. The air escaping to the outside (exhaust air) is cooled down in the process.
  3. Heat pump: As an alternative to the heat exchanger, the exhaust air is cooled with the help of a heat pump before it is discharged outside. The heat extracted in this way can be used, for example, to heat the drinking water for the bathroom. The excess heat can, however, also be fed into the heating system and, in combination with an electric or gas heater, help cover the entire heating energy requirement.
  4. Geothermal heat exchanger: The air supply lines can be laid in the ground to protect the heat exchanger from icing. Another advantage can be used in summer when the supply air is led into the house with pleasant soil temperatures. But be careful: To protect against bacteria and mold formation, the air ducts must be laid on a slope so that condensation moisture can be drained away. This requires careful planning and technical implementation so that the room air is not contaminated by germs.
  5. Ground-brine heat exchanger: If the property is large enough, a ground-to-brine heat exchanger can be an alternative. The geothermal energy is only transferred in a downstream brine-air heat exchanger. In this way, the supply air is not impaired.

5. What is part of planning a mechanical ventilation system?

Include a home ventilation system in the considerations and planning for your new building or renovation at an early stage. In order for the system to achieve the desired level of comfort and to work economically and efficiently, you must consider the following:

  • Airtight building envelope: A ventilation system can only work efficiently if the building is well sealed. The building's tightness should be checked with an airtightness measurement. In this way it can be ensured that the incoming air is filtered through the ventilation ducts and not uncontrolled through building joints.
  • Exhaust air zones: The rooms from which the air is extracted (bathroom, toilet, kitchen) should be as close to one another as possible within the building or apartment in order to avoid additional risers or long horizontal pipes. This reduces the cost of materials and costs.
  • Electric consumption: The fans are responsible for the electricity consumption of the ventilation system. For residential ventilation systems, the lowest level of the specific fan output (SFP 1) is usually sufficient. In a single-family house, depending on the system and size of the residential unit, an annual electricity consumption of around 200 to 400 kilowatt hours can be expected.
  • Energy label: Like household appliances, decentralized and centralized ventilation devices have an energy efficiency label. Devices currently to be purchased are divided into energy efficiency classes A + to D. In addition to the electricity consumption, the label evaluates the theoretical energy savings in kilowatt hours per square meter and year compared to classic window ventilation. This saving must amount to at least 20 kilowatt hours per year. The only exception to this are pure exhaust air devices that have less than 30 watts of power - such as simple toilet fans.

  • Ambient air-dependent fireplaces: Fireplace stoves, atmospheric boilers / thermal baths or gas stoves are so-called open-air-dependent fireplaces. They need air from the room they are in. If these fireplaces are to be operated together with a ventilation system, the chimney sweep responsible must be included in the system planning at an early stage. Depending on the system, flaps and circuits can ensure that both systems can be operated in parallel.
  • Think about maintenance: A ventilation system as well as its components and lines must be planned, implemented, installed and maintained in such a way that they remain permanently in a clean condition. For this, sufficient maintenance openings must be planned and ventilation lines must be protected from dust and dirt during the construction phase.

6. In operation: How should the ventilation system be set? How often does it need to be cleaned and serviced?

Adjustment: Before the ventilation system goes into operation, it must be correctly set and the ventilation flows must be correctly adapted to the planned valve opening and the desired use.

use: Have the function and mode of operation of the ventilation system explained to you in detail. With simple exhaust systems that are switched on with a toggle switch, you don't need to know much. On the other hand, you can set the basic ventilation for a central ventilation system on one device; also adjust the performance in the individual rooms. You can also monitor the optimal air quality with CO2 sensors and humidity meters (hygrometers) and thus regulate it automatically.

Maintenance and cleaning: You or a specialist company should maintain and clean the ventilation system once a year. The filters in particular need to be replaced regularly.

Because fine dust filters from class F7 remove over 90 percent of suspended matter such as pollen or dust from the supply air. Depending on the air pollution (inside / outside), you should change or have the supply air filter changed after three to six months for reasons of hygiene; but at the latest after one year.

We also recommend that the exhaust air filter be checked regularly and replaced if necessary. Depending on the amount of dust and pollen count, the filters clog more or less quickly. It is best to have an installed automatic filter monitoring system in which the condition of the filters is checked and a message is sent to the residents. Time-dependent filter monitoring integrated by many manufacturers is only sufficient. If the filter is changed correctly, the lines will remain clean for years and the system will remain effective.

Inspection openings and the shortest possible air lines should be provided at a suitable location for cleaning the air lines. Here, too, it is advisable to commission a specialist company with the cleaning and maintenance after about 10 years.