Sharp JX-9400 Informations techniques télécharger pdf (Page 14)

Introduction

Why ventilate?

Without ventilation, a building’s occupants will initially be troubled by odours

and other possible contaminants and heat. Humidity may rise because of indoor

moisture sources such as the occupants, laund ry, cooking and plants; thus

enhancing moisture hazards (for example, mould growth and condensation).

Oxygen will nevertheless not be missed until much later. The purpose of venti-

lation is to eliminate airborne contaminants, which are generated both by

human activity and by the building itself. These are:

bad odours, to which people entering the room are very sensitive;

moisture, which increases the risk of mould growth;

carbon dioxide (CO

) gas, which may induce lethargy at high concentrations;

dust, aerosols and toxic gases resulting from human activity, as well as from

the building materials (in principle, ‘clean’ materials should be chosen for

internal use, but this is not always possible);

excessive heat.

The airﬂow rate required to ensure good indoor air quality depends upon the

contaminant sources’ strengths and on their maximum acceptable concentra-

tion: the larger the contaminant sources’ strengths or the smaller the maximum

acceptable concentration , the greater the required ventilation rate is.

During the heating season in well-designed and clean buildings, the

occupants are the main source of contaminants (mostly odours and water

vapour). The airﬂow rate should then be between 22 cubic metres per hour

/h) per person, which limits the CO

concentration to about 1000 parts

per million (ppm) above the outdoor concentration, and 54 m

/h per person,

which limits the CO

concentration to about 400 ppm above the outdoor

concentration – meaning that less than 10 per cent of people entering the

room will be dissatisﬁed by the odour (CEN, 2006). Airﬂow rates should be

much greater in poorly insulated buildings (where there is a risk of mould

growth and water vapou r condensation), or in spaces where there is a parti-

cular source of contamination, including spaces where smoking is allowed.

In summer, the minimum airﬂow rate may be much greater than the

hygienic airﬂow rate in order to evacuate heat or provide cooling draughts.

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Sharp JX-9400 Informations techniques Page 14