Air exchange is characterized by ventilation volume and multiplicity.
The volume of ventilation is the amount of air introduced (or supplied) into the room within one hour. It is possible to determine both the required ventilation volume (required) and the actual one.
Determination of the required ventilation volume. The amount of air that must be introduced into the room within one hour depends on its cubic capacity, the number of people and the nature of the work carried out in it.
The calculation is carried out according to the formula:
L = K / (P – P 1 )
where L is the desired volume of air in m 3 per person per hour; 53
K is the number of liters of carbon dioxide exhaled by an adult per hour;
P – permissible carbon dioxide content in the air of residential premises – equal to 0.1% (in 100 ml of air) or 1 ‰ (ppm – in 1000 ml of air, that is, in 1 liter).
P 1 – the carbon dioxide content in the atmospheric air is 0.04% or 0.4 ‰.
Under normal conditions, an adult, with light physical work (on average), emits 22.6 liters of carbon dioxide per hour. The atmospheric air introduced into the room already contains 0.4 ‰ of carbon dioxide, or 0.4 ml per 1000 ml (1 l) of air. Each liter can take it, without exceeding the permissible concentration (1 ‰), another 1 – 0.4 = 0.6 ml of carbon dioxide; in other words, each liter of fresh air can take away 0.6 ml of carbon dioxide from 22.6 liters of carbon dioxide emitted by a person per hour. It remains to be determined how much liters of fresh air must be introduced per hour in order to dilute 22.6 liters of carbon dioxide to a concentration of 1 ‰. Obviously, it is necessary to introduce as many liters as the number of times 0.6 ml is contained in 22.6 liters, or else 22600 ml. Substituting the corresponding values of the quantities in the formula, we obtain:
L = 22600 / (1.0–0.4) = 37 666 or 37.7 m 3 (~ 40 m 3 )
This amount of air must be introduced into the room per person per hour. The minimum normative value of the required ventilation volume in m 3 / hour per person should be considered: 40 – for residential premises; 16 – for school classes; 80 – for hospital wards.
Based on the indicated norms of the volume of ventilation air, the dimensions of the air cube for various rooms are established and the air exchange rate is determined , that is, the air exchange rate for an hour, necessary to completely remove the spoiled air and replace it with clean atmospheric air . The multiplicity of air exchange is expressed in multiple numbers relative to the volume of the room and is determined by the ratio of the ventilation volume to the cubic capacity of the room. For example, if it is said that the air exchange rate in a room is 2, this means that in one hour the air in it exchanges 2 times.
To clarify the above provisions, we indicate that, if, for example, for residential premises, the air cube norm is 25 m 3 (per 1 person), then with a 1.5-fold exchange
Of air with external air, the introduction of 37.7 m 3 of fresh air per hour is achieved , which, according to the previous one, is sufficient to maintain proper sanitary air condition in the room. For smaller values of the air cube, for example, in a 4-patient ward, with an air cube volume per patient of 20-21 m 3 , more intensive ventilation is required, however, within the permissible values that do not cause a strong wind blow (draft )