Types of ventilation . By the method of supplying air to the room, natural and artificial (mechanical) ventilation are distinguished , and depending on the method of organizing air exchange, local, general and combined (local + general).
Ventilation systems . The air entering the room is called the supply air, and the exhaust air is called the exhaust air.
A ventilation system that provides only clean air is called a supply system , and one that only removes polluted air is called an exhaust system ; in addition, it is possible to simultaneously receive clean and remove contaminated air – the so-called. supply and exhaust ventilation system .
Natural ventilation
Natural ventilation is the movement of air in an indoor environment, which occurs due to the difference in temperatures (and therefore volumes) of the external and internal air (heat pressure, gravity pressure) and the effect of wind (wind pressure).
Natural air exchange in buildings arises by infiltrating (seeping) outside air through cracks and leaks in window and door openings, as well as through pores in building materials of building structures (the so-called “wall breathing”). The greater the temperature difference and wind force, the more intensive the air exchange. Promotes enhanced air infiltration and an open type of development, remoteness from other buildings. The air heated in the room rises and leaves it through the upper part of the walls, window and
doorways; in its place, cold air flows into the lower zones of the premises.
With closed windows and doors, natural ventilation is negligible – the air exchange rate is 0.5-1 and a maximum of 1.5 times in the winter. In this regard, means of enhancing natural ventilation are used: windows that open or special devices – windows and transoms. Such controlled organized natural ventilation is called aeration, and when designing inhabited premises (excluding rooms requiring special cleanliness and sterility regimen), the so-called normalization is normalized. window coefficient or aeration coefficient – which is the ratio of the area of the active window to the floor area of the room (its permissible value is 1:50, the optimal one is 1:40 ). In winter, it is enough to open the vents for 5-10 minutes 4 times a day or more, it is better to do this in the absence of people in the room. The transom located at the top of the window and opening at an angle of 45o to its surface is a more advanced design, since the air coming through it from the outside rises and mixes with the warm air of the room, which reduces the possibility of cooling people and allows you to keep the transom open for a long time. The best airing effect is achieved by simultaneously opening the room’s windows (or windows) from two opposite sides of it (or through the corridor) – the so-called. through ventilation , in which the air exchange rate reaches 25-100 times. Good aeration results are also possible with angular ventilation. In typical construction, fanless windows with a narrow side flap are also used, which ensure sufficient air exchange in the room. However, the full opening of the sash is accompanied by a strong blow, which limits their use in the cold periods of the year.
The means of enhancing natural ventilation in multi-story buildings also include individual exhaust ventilation ducts located in the walls of the buildings and facing the roof, where their openings are equipped with special nozzles-deflectors that suck air through wind energy; In summer, due to a small difference in the temperature of the outdoor and indoor air, the efficiency of this system may be zero. In the southern regions of the country, additional window aeration supply devices are additionally arranged.
It should be borne in mind that in multi-storey hospital buildings as a result of the interaction of wind and air lift, uncontrolled air flows occur inside the building (especially in the shafts of staircase elevators), which contributes to the spread of microorganisms. Therefore, it is advisable to comply with the following laws when ventilating the premises of a health facility :
1. You can ventilate through windows only those rooms where the transfer of microbes is not possible;
2. The air exchange between rooms with varying degrees of purity is reduced if the doors are tightly closed;
3. It is preferable to create neutral gateway zones and mechanical ventilation where hazardous air flows are not ruled out (see below, hygiene requirements for ventilation in health facilities).
The main disadvantages of natural ventilation are its inconsistency and variability associated with weather conditions, especially the direction and strength of the wind, so artificial ventilation is necessary for many rooms.