Guidelines for natural ventilation

Ventilation may be described as the supply of fresh air from outside into an enclosed area, or the removal of inside air from the enclosed space. Ventilating is the process of “changing” or replacing air in any space to provide high indoor air quality (i.e. to control temperature, replenish oxygen, or remove moisture, odors, smoke, heat, dust, airborne bacteria, and carbon dioxide).

Ventilation is used to remove unpleasant smells and excessive moisture, introduce outside air, to keep interior building air circulating, and to prevent stagnation of the interior air. Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types.

“Mechanical” or “forced” ventilation is used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates much energy is required to remove excess moisture from ventilation air.

Ventilation increases the energy needed for heating or cooling, however heat recovery ventilation can be used to mitigate the energy consumption. This involves heat exchange between incoming and outgoing air. Energy recovery ventilation additionally includes exchange of humidity.

Need for ventilation

  • Creation of air movements
  • Prevention of undue carbon di oxide, flammable gas vapour, dust and bacteria carrying particles
  • Removal of odours, decomposing building materials and smoke.
  • Prevention of condensation or deposition of moisture on the wall surfaces

Types of ventilation systems

  • Natural ventilation
  • Mechanical/artificial ventilation

Natural ventilation is the ventilation of a building with outside air without the use of a fan or other mechanical system. It can be achieved with open able windows or trickle vents when the spaces to ventilate are small and the architecture permits. In more complex systems warm air in the building can be allowed to rise and flow out upper openings to the outside (stack effect) thus forcing cool outside air to be drawn into the building naturally through openings in the lower areas.

These systems use very little energy but care must be taken to ensure the occupants’ comfort. In warm or humid months, in many climates, maintaining thermal comfort solely via natural ventilation may not be possible so conventional air conditioning systems are used as backups. Air-side economizers perform the same function as natural ventilation, but use mechanical systems’ fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.

Natural ventilation uses the elaborated use of doors, windows, ventilators and skylights. In natural ventilation usually the concept of cross ventilation is relied on to achieve air movement.

Guidelines according to IS : 3362-1965 are as

  • Inlet openings in the building should be well distributed and should be located at the windward side at the low levels and the outlet openings should be located at the leeward side at the top levels.
  • Inlet openings should not be obstructed by structures such as buildings, Trees, signboards, partitions, etc.
  • Greatest flow per unit area is achieved by using inlet and outlet openings of approximately same areas.
  • When the direction of the wind is quite constant and dependable the inlet openings can be so placed so as to achieve full advantage of the force of the wind. When the direction of the wind is variable the openings may be arranged in such a manner so that there is approximately same area on all sides of the building.
  • Natural ventilation occurs only when the air temperature inside the building is different from the air temperature outside the building. Ventilators may be provided at the top levels or roofs.
  • Windows of living rooms must open either directly to an open space or to an unobstructed facing an open space. In places where open spaces are restricted or inadequate artificial space can be created by provision of ample number of courtyards.
Mechanical ventilation

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