Each human being produces their personal quota of heat, water vapour, carbon dioxide and body odour.
It is not sufficient merely to ensure an acceptable average freshness of atmosphere throughout the room; if people are crowded together by shortage of space the average odour concentration must be reduced. This means that the fresh air supply per person must increase with the number of people in a room, and consequently the air change rate must increase.
Recommended minimum fresh air supply
These rates should be increased by a third if smoking is permitted or if there are doubts about standards of personal hygiene. If minimum legal requirements are specified, they are generally about a third less. In contrast, as little as 1 litre/s will suffice to meet the strictly physiological needs of one person for oxygen supply and carbon dioxide limitation.
Consideration of dust and odours in a normal office or workroom ventilation job can usually be ignored when preparing the scheme, as the rate of ventilation needed to give comfortable conditions based on temperature, humidity and air movement – 6 to 10 ACH – would be considerably higher than that required to keep dust and odours down to a comfortable level – about 1 to 2 ACH.
Incidentally, it is always advisable when dealing with a fairly crowded space (e.g. auditoria, dance halls) to give a quick check for the minimum air volume required by allowing 28m3/h per person. This is to prevent body odours from becoming a nuisance. Also the carbon dioxide content of the air, gradually increasing due to the CO2 exhaled from the lungs, should be prevented from exceeding 10 parts per 10,000. This calculation is commonly used as the maximum CO2 concentration desirable in a closed occupied space.