Functional requirements of ventilation

Ventilation is the supply of fresh outdoor air to a space and the removal of stale air, without causing discomfort. Its functional requirements are:

1. Supply of oxygen: Each occupant uses only about 0.02 to 0.03 m³/h of oxygen at rest; fresh air keeps the oxygen level near 21 %.
2. Removal of carbon dioxide: CO₂ from breathing (about 0.02 m³/h per person) must be kept below about 0.1 %.
3. Control of odour, smoke and gases: Kitchen, toilet and body smells, fumes and dust are carried out.
4. Control of humidity: Removes vapour from cooking, bathing and breathing, and so prevents condensation, dampness and mould.
5. Heat removal: Removes excess heat from bodies, appliances and the sun, and air movement gives a cooling effect on the body.
6. Thermal comfort: Gives air movement of 0.1 to 0.5 m/s without draught.
7. Prevention of airborne infection: Dilutes the load of bacteria and viruses.
8. Adequate air change: The rate is fixed by use, such as 6 to 8 air changes per hour (ACH) for a living room and 15 to 20 ACH for a kitchen. Standards are given in the National Building Code.

Ventilation openings should be placed to give cross flow, with inlets low on the windward side and outlets high on the leeward side.