Ventilation

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Ventilation of a building describes the process of exchanging indoor air with outdoor air. There are numerous ways to achieve this.

Ventilation serves three major purposes: It is first used to renew indoor air and remove the air pollutants, in order to insure appropriate air quality

for the health and comfort of the occupants. Secondly, it also prevents excessive accumulation of condensation indoors (as long as interior humidity is higher than exterior humidity. Thirdly, it acts on thermal comfort (almost like "free" air conditioning).

Natural ventilation is based on two driving forces: wind pressure and temperature difference. Air flows in and out through open windows and doors, imperfect seals throughout the building envelope and louvers and other openings for the purpose of ventilation. This type of ventilation only may perform adequately if they are carefully designed. Typically, in harsher climates (especially hot climates) it does not work too well.

Mechanical ventilation typically relies on the use of electric fans to extract or introduce air into the building. Mechanical systems allow controlled ventilation of a building.The air flow rate is managed in some fashion. It may be a simple on/off device or automated. Mechanical systems are particularly adapted to severe climates and are then often combined with heat recovery (process by which thermal energy is recovered from exhaust air for re-use within the building).

Air infiltration: in both ventilation strategies, air also enters and leaves a building involuntarily, through cracks and gaps in the building envelope, duct leakage, fire places, and so on.

Insulation Science