Ventilation (architecture)

Under air change is understood in the physics of the exchange of the air in closed spaces.

The air exchange in rooms necessary for:

• Discharge of exhaled carbon dioxide. The supply of oxygen plays a rather subordinate role ( unless a set imputed in the living room stove oxygen consumed ).
• Transfer of odors and air pollutants (eg fumes from the facility )
• Removal of humidity, which is released inside the apartment. Can the air absorb any more moisture ( such as cooking ), the result is haze or fog in the room condenses on the cold window surfaces or walls to water.
• (Known from tropical areas ) Humidity too high can prevent the human body dissipates heat through sweat evaporation. You feel weak and overheated (see also thermoregulation and heat exhaustion ).

Of air changes per hour is referred to as the air exchange rate, the unit 1 / h. An air change rate of 1 / h means that the entire air volume of the enclosed space is exchanged within an hour exactly once. This is the calculated value, which results from the following equation:

Due to the mixing of the fresh air with the present air is not completely renewed in one hour in an air moving from the ambient air 1. The ratio of "effective air renewal" and the air exchange rate is a characteristic parameter for the selected ventilation concept and is referred to as ventilation effectiveness.

In living rooms, an air change rate of 0.5 / h (DIN 4108-2 of 2011, Section 4.2.3) is required. If there are no noticeable odors in the home, an inadequate air exchange often manifests itself through excessive humidity.

Uncontrolled air exchange

The air exchange can be done in unregulated manner by the building envelope is leaking intentionally or unintentionally. Typically, these are the joints of windows and doors, with lightweight construction and joints in the walls and ceilings. In this form, the air exchange rate is heavily dependent on the weather, especially depending on the wind. Are the joints in the outer shell of the building, it is called professionally by infiltration.

Controlled ventilation

If the building envelope almost airtight as it provides a modern design, it can no longer take place an uncontrolled air exchange. The air exchange, i.e. open by the so-called airing all the windows for a few minutes completely, to accomplish, or it is incorporated a mechanical ventilation system.

Calculation example

A 4-person family uses about 10 liters of water per day free through the breath, sweat, cooking, bathing or showering and houseplants. This water is distributed at 100 m² of living space on approximately 250 cubic meters of air. Thus, this water must be dissipated by the air exchange.

At an air temperature of 20 ° C 1 cubic meter of air can hold a maximum of 17.3 g. At a relative humidity of 50 %, these are 8.7 g airing and at 4 ° C and assumed 80% rel. Humidity, the fresh air, 6.4 g / m³ at saturation and 5.1 g / m³ at the assumed humidity.

One cubic meter of fresh air should therefore take with the assumed numbers of water. Thus for dissipating 10 liters of water have 2833 m³ (10,000 / 3.5 = 2,857 m³) of air per day through the apartment, according to 11.3 air changes or an air exchange rate of about one air change every two hours.

In a fully sealed joint house would be 11 times shock aired on the day. Assuming for the airing of an air exchange rate of 9-15, therefore, an hour a shock- ventilated, with cross ventilation ( air exchange rate 40) corresponding to approximately 17 minutes.

This number is reduced to 7 Ventilation operations under otherwise identical conditions, if one accepts a humidity of 65 %. This can lead to mold growth. Because at 65 % room air that is 65/50 * 8.7 = 11.3 grams of water vapor can absorb. It may therefore 11.3 to 8.7 = 2.6 grams of water vapor can be transported during release more out per cubic meter than at 50 % rel. Humidity.