Ventilation and Air Conditioning Systems

Air movement is coused by pressure differences, i.e., disturbances to state of equilibrium. Resulting from:

  1. Temperature differences
  2. Natural wind
  3. Ventilators

arrangement of ventilation and air conditioning systems

Room ventilation systems are used to guarantee a specific room climate. In fulfilling this objective, the following requirements must be satisfied, depending on the application:

  1. Removal from rooms of impurities in the air including smoke and other harmful substances, and suspended particles
  2. Removal of perceptible heat from rooms: unwanted quantities of both hot and cold air
  3. Removal of latent heat from rooms: enthalpy flows of humidifying air and dehumidifying air
  4. Protective pressure maintenance: pressure maintenance in buildings for protection against unwanted air exchange.

Most of the requirements under (1) are solved through continuous replacement of air (ventilation) and/or suitable air treatment (filtering). Requirements of type (2) and (3) are usually met by appropriate thermodynamic treatment of the air, and, to a limited degree, by air replacement. Requirements of type (4) are solved by various types of mechanical control of supply and extraction air.


Natural ventilation
Uncontrolled air is admitted through joints and gaps in window frames, doors and shutters (as a result of the effects of wind) rather than through the walls. However, the increased use of thermal insulation measures in buildings means that the natural sources of ventilation through gaps in windows and doors may no longer be adequate. It may therefore be necessary to provide controlled ventilation in living accommodation, using mechanical ventilation systems and, if necessary, to replace the heat lost as a consequence.

Window ventilation is generally adequate for living rooms. Sash windows are favourable, where the outside air is admitted at the bottom and internal air flows out above.

Intensive ventilation is brought about by mechanical ventilation systems. In accordance with the building regulations, this is a requirement for windowless bathrooms and WCs, with the removal of air to the outside via ducting. Allowance should be made for the requirement of a flow of replenishment air through ventilator grills, windows and/or gaps in the fabric of the building. Furthermore, as far as is possible, draught-free admission of the outside air must be provided.

The installation of simple ventilator grills in outside walls for inflow and outflow of air leads to the danger of draughts in the winter. Mechanical ventilation systems are better.


Humidity of room air
For comfort, the upper limit for the moisture content of the air is 11.5 kg of water per kg of dry air. A relative humidity of 65% should not be exceeded. The minimum flow of fresh air per person for cinemas, banqueting halls, reading rooms, exhibition halls, sale rooms, museums and sports halls is 20 m3/h. The value for individual offices, canteens, conference rooms, rest rooms, lecture halls and hotel rooms is 30 m3/h; it is 40 m3/h for restaurants, and 50 m3/h for open plan offices.


Taken from: Architects’ Data by Ernst and Peter Neufert


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