Ventilation is required for hygienic reasons in order to provide for the ongoing supply of quality, fresh air and to remove from a building the humidity produced by its occupants (breathing and perspiration) and their activities (cooking, laundry washing, drying and bathing) as well as other harmful substances and odors, including the matters released into the environment by furniture, plastics, paints, cleansers, combustion products generated when cooking and baking on a gas stove. In some cases, these materials can also include radon that penetrates into buildings from their subsoil.
Ventilation should ensure hygienically minimal intensity of air exchange. The minimum hygienic amount is tied with the volume of the inhabited area; strictly considered, it derives from the number of its occupants and their activities.
The ventilation of houses used to be a commonplace activity, regardless of whether it was done purposefully or subconsciously. If individual rooms were locally heated by a stove, the stove and a chimney formed a ventilation system, which was due to the imperfect tightness or intentionally poor tightness of a stove door also at the time when the rooms were not heated. The supply of the air was secured by poorly sealed windows and doors. This ‘unintentional’ ventilation was often complemented by ‘intentional’ ventilation consisting of an ‘adjustable’ ventilation rose fitted in a chimney draught way. Such ventilation was of great importance in old buildings because their humidity insulation was rather imperfect. Ventilation could thus provide the more or less successful removal of humidity penetrating intp the building through its structures.
The changeover from local heating with solid fuels to central heating eliminated chimney outlets in individual rooms, putting thus an end to the simplest ventilation system. Even after the changeover to central heating with a boiler burning solid, liquid, or gaseous fuels, the operation of the boiler always induced at least some ‘ventilation’ within the entire residential area. The boiler was placed in a cellar or in an independent boiler room (in the case of so-called central heating) or directly in a flat (so-called ‘single-story heating system’), i.e. in rooms that were more or less connected with a heated area through hallways and doors. The ‘more tighter’ separation of the boiler from the residential area and especially further changeover to electric heating has eliminated this type of ‘unintentional’ ventilation as well. Windows began to be sealed ‘to reduce thermal loss’ making thus well-sealed windows and doors responsible for the further reduction in the amount of the air exchanged naturally – i.e. by. infiltration and exfiltration. This situation has resulted - and in many cases continues to result – in many buildings being unable to breathe spontaneously.
The above-specified development of heating was accompanied with the development of construction materials and external cladding structures. Humidity insulation has reduced or prevented the penetration of humidity into the building and improved thermal resistance has increased the surface temperature of walls. Nevertheless, problems may occur due to insufficient ventilation in both reconstructed old buildings and new houses. Condensation of humidity followed by creation of moulds in critical rooms and in critical places (cold corners and thermal bridges), especially in bathrooms and kitchens, but also in bedrooms (that are usually heated to lower temperatures), i.e. in rooms with greater occurrence of humidity. It is surprising how high is the number of both old and new houses in which this problem develops.
Buildings in which natural gas is used not only for heating but also for cooking can witness even worse situations because the combustion of gas during cooking does not produce only combustion by-products but also water steam. The poor removal of combustion materials therefore leads to the insufficient removal of humidity.
At present it is usually assumed that necessary ventilation can be secured in natural ways: by infiltration – i.e. the spontaneous penetration of the fresh air into the building interior and by exfiltration – i.e. the spontaneous penetration of the utilized air into the outside. Natural ventilation is affected by several factors, especially by the penetration of the air in joints, i.e. by the poor tightness of windows and doors and by the situation of a building, or rather by wind influence.
If ventilation is not intensive enough, we found ourselves in a ‘stale air’ situation, which we try to remedy by opening windows. Naturally, the air exchanged by infiltration or by the random opening of windows must be heated to reach the temperature of the heated area. Therefore, ventilation increases requirements for the need for heating heat. In it, these requirements depend on the intensity of ventilation.
The natural ventilation as described above does not give us any guarantee of meeting the requirements imposed on ventilation in general. It can be said ‘it is not under control’. On the one hand, it does not necessarily have to secure the required intensity of ventilation (if doors and windows are ‘sealed’), on the other hand, this ventilation can be quite energetically demanding due to greater-than-necessary intensity (when doors and windows are not sealed properly or when windows are opened too often).
From the above information it implies that ventilation affects not only the hygienic environment in a building, but also its demand of energy. Providing the optimal intensity of ventilation and reduction in its energetic demands can be secured by replacing natural ventilation by forced ventilation.
Requirements for ventilation derive from hygienic needs. Subsequently, they define energetic requirements and, depending on a selected ventilation system, the energetic demands of ventilation.
In older buildings (with worse thermally-technical properties) the need for heat for ventilation represents about 15% of the total need for heating heat. In new buildings whose thermally-technical properties correspond with the current requirements stipulated by construction standards, the need for heat for ventilation represents up to 40% and more. It is obvious that insufficient ventilation ‘leads to the saving of heat for heating’, yet these savings are accompanied with all negative hygienic consequences affecting both a building (mould) and its occupants (mould spores are harmful).
With regard to new buildings it should be emphasized that it is mainly during the first years after their construction when it is necessary to remove humidity introduced to such buildings through construction procedures and – in many cases – by construction materials that may contain a sizeable amount of humidity due to production-technological reasons (but also due to inappropriate storage).
