What is the air exchange rate? SNiP (building norms and rules) pays a lot of attention to this moment. The requirements for energy efficiency of modern windows, which allow for a high degree of tightness, should not lead to the rejection of the flow of fresh air into the room. The correct organization of the exchange implies the provision of the necessary controlled level of ventilation.
Introduction
When it comes to housing construction, the same ventilation scheme usually applies. Namely, the exhaust air is removed from the zone of greatest pollution. These are kitchens and sanitary facilities. This is realized through the creation of natural exhaust duct ventilation. Replacement in this case is carried out by supplying outside air, which enters due to leaks in external enclosures. As a rule, this means window fillings. One more way- ventilation of the premises of the dwelling. But there is an important technical solution, without which almost no room can do. This is the use of air ducts.
Technical info
An apartment from this position is considered as a single air volume, at any point of which there is the same pressure. In this case, it is assumed that the interior doors are open or made with a trimming of the leaf, which reduces the aerodynamic resistance in the closed position. For example, the rate of air exchange is made based on the fact that the gaps under the latrines and bathrooms will be at least two centimeters.
In general, all these points are regulated by a number of SNiP, as well as other documents. For example, 2.08.01-89 "Residential buildings" deals with places of residence. It clearly states that such buildings must necessarily have natural ventilation. You can also find the calculated parameters of air, and the frequency of its exchange in the room.
How is the data obtained?
On the basis of what information is formed, which builders are guided by. The amount of ventilation air is determined separately for each room, taking into account harmful impurities. As an alternative, this parameter is set based on the results of previous studies.
But it's not always that all these moments can be accounted for! How to be, for example, private traders? In this case, you can use a purely mathematical approach, which involves the use of formulas. Forin order to obtain the value of the ventilation air exchange rate for the optimal position, multiply the volume of the room by the minimum standard value, which is measured in cubic meters per hour. Let's look at all these formulas in more detail.
Determining the volume of a room
Always calculated in cubic meters. For this, a simple formula is used, which involves multiplying the length, width and height. Let's look at a small example. There is a room with a length of 10 meters, a width of 5 and a height of 2. To determine the volume of air that is in it, we multiply the available values: 10 x 5 x 2=100. That is, in such a room there are 100 cubic meters of air.
Then it is necessary to use tables of recommended air exchange rates, the values in which vary depending on the purpose of the room and the number of people in it. In this case, a formula is used that involves multiplying the norm by the number of people in the room.
So, if the conversation is about one person with minimal physical activity, then 25 cubic meters per hour is enough. When doing light work, this value rises to 45. Heavy physical activity requires 60 cubic meters per hour per person.
That is, the calculation of the air exchange rate shows that it is safe to work in this type of enclosed space for only a little more than an hour and a half. But these are not all formulas.
What other calculations are needed?
For example, detection of air exchange in case of moisture release. It looks like this: V/((U-P)Pl).
B is the amount of liquid released.
U - moisture content of the removed air. Measured in grams of water per kilogram of air.
П – supply air moisture content. Also measured in grams of water per kilogram of air.
Pl - air density. It is measured in kilograms per cubic meter. If the temperature is 20 degrees Celsius, then this value is 1.205 kg/m3.
It should also be mentioned about the calculation of air exchange in cases where it is necessary to remove excess heat. This formula looks like this: W / (PlT(U-P). Some of the values \u200b\u200bare already known.
W is the heat output in the room.
T is the heat capacity of air. At 20 degrees Celsius is 1.005 kJ/(kgK). These are not all formulas, but perhaps the most used ones.
What are the minimum required values?
We already know how to calculate air rates and air exchange rates. Now let's turn to state standards. A table will help us with this, in which an excerpt will be given for some areas:
| Room | Frequency of air exchange |
| Living room | Three cubic meters per hour per 1 m3 of the room itself |
| Kitchen | From 6 m3 |
| Toilet | From 8 m3 |
| Cellar | From 4 m3 |
| Office space | From 5 m3 |
| Bank | From 2 m3 |
| Pool | From 10 m3 |
| School class | From 3 m3 |
How to determine the air exchange?
The multiplicity norms, as it is not difficult to see, depend on the purpose of the room. Residential, commercial and industrial facilities have different requirements that must be met. More dative values are affected by the time and hours of work, the intensity of labor, and much more. In addition, the equipment that is supposed to be used also makes its contribution. For example:
- Fan performance.
- The air pressure that it creates.
- The length and sections of the ventilation system.
- The type of system you are using. Allocate recirculation, recovery and supply and exhaust ventilation.
- Applied climate systems.
What should I pay special attention to?
There is such an important fact that, for some reason, they like to ignore. Namely - how the air exchange will be carried out. For example, it is possible to provide direct air exhaustthrough the wall to the street using an axial fan. Or provide a system of branched air ducts that use duct devices / centrifugal volute. All this directly affects what equipment you have to choose.
Besides all this, the capacity of the air duct deserves attention. Several factors influence it. First of all, this is the diameter of the duct. It is also necessary to take into account the pressure losses that occur per linear meter.
For example, it is necessary to provide an air exchange of a thousand cubic meters per hour at a distance of 1000 mm. In this situation, an air duct with a diameter of 200 millimeters can cope with this task. But if it is necessary to provide a transmission of 10,000 millimeters, then it would be better to use 250 mm. In this case, there will be less resistance and loss of performance.
In order to provide a satisfactory air ratio that allows you to comfortably stay in a certain place, you must consider the above parameters.
Conclusion
But even these factors are not enough to fully assess all possible needs. Therefore, it will not be superfluous to take a certain reserve. For example, the air exchange rate for industrial premises should provide for a reserve of a quarter of the standard requirements. Air speed also plays an important role.
So, for example, if there is an air duct with a diameter of 160 mm and a length of 12 m, along which there is a movement of 0.5 meters, then thiswill provide about 65-70 m3 per hour. Whereas an increase in this value to 1 m will multiply the efficiency. If you need even more, then natural movement is clearly not enough. Additionally, the use of various equipment will be required - such as fans, valves and other devices to increase efficiency.
