What is the multiplicity of air exchange? Construction Norms and Regulations (construction norms and rules) pays much attention to this moment. The energy efficiency requirements of modern windows, which allow for a high degree of tightness, should not lead to a refusal from the influx of fresh air into the room. Proper organization of the exchange implies the provision of the necessary controlled level of ventilation.
Introductory information
If we touch on housing construction, then in this case the same ventilation scheme usually operates. Namely, the exhaust air is removed from the zone of greatest pollution. Such are the kitchens and sanitary facilities. This is realized through the creation of natural exhaust duct ventilation. Replacement in this case is carried out by supplying external air, which is supplied due to leaks in the external fencing. As a rule, this refers to window fillings. Another way is to air the premises of the home. But there is an important technical solution, without which almost no room can do. This is the use of air ducts.
Technical information
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 trimmed, which reduces aerodynamic drag in the closed position. For example, the norm of the rate of air exchange is made on the basis 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. He clearly indicates that there must be natural ventilation in such buildings. You can also find the calculated parameters of the 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 all these moments are not always accountable! How to be, for example, private traders? In this case, you can use a purely mathematical approach, which involves the use of formulas. In order to get 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.
Determination of the volume of the room
Always calculated in cubic meters. For this, a simple formula is used, which provides for the multiplication of 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 the tables of the recommended air exchange rate, the values of 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 frequency of air exchange shows that safely in an enclosed space of this type you can work only a little more than an hour and a half. But these are far from all formulas.
What calculations are still needed?
For example, the detection of air exchange in case of moisture. It looks as follows: B / ((U-P) * Pl).
B is the amount of fluid released.
U - moisture content of the removed air. Measured in grams of water per kilogram of air.
P - moisture content of the supply air. Also measured in grams of water per kilogram of air.
Pl - air density. Measured in kilograms per cubic meter. If the temperature is 20 degrees Celsius, then this value is 1.205 kg / m 3 .
You should also mention the calculation of air exchange in cases where it is necessary to remove excess heat. This formula looks like this: W / (Pl * T * (U-P). Some of the values are already known.
W is the heat generated in a room.
T is the heat capacity of air. At 20 degrees Celsius is 1.005 kJ / (kg * K). These are far from all formulas, but perhaps the most used.
What values are considered the minimum necessary?
We already know how to calculate air norms and the rate of air exchange. Now let's turn to state standards. This will help us with a table in which an excerpt will be given for some areas:
Room | Air exchange rate |
Living room | Three cubic meters per hour per 1 m 3 of the room itself |
Kitchen | From 6 m 3 |
Restroom | From 8 m 3 |
Cellar | From 4 m 3 |
Office space | From 5 m 3 |
Bank | From 2 m 3 |
Swimming pool | From 10 m 3 |
Classroom | From 3 m 3 |
How to determine air exchange?
The rates of multiplicity, as it is not difficult to notice, depend on the intended purpose of the room. Domestic, commercial and industrial facilities have different requirements that must be met. More advanced values are affected by time and hours of work, labor intensity, and more. In addition, the equipment that is supposed to be used also makes its contribution. For example:
- Fan performance.
- The air pressure that is created by it.
- The length, as well as the cross section of the ventilation system.
- Type of system used. Allocate recirculation, recovery and supply and exhaust ventilation.
- Applicable climate systems.
What should you pay special attention to?
There is such an important fact, which, for some reason, they like to ignore. Namely - how air exchange will be carried out. For example, it is possible to provide a direct air discharge through the wall to the street using an axial fan. Or provide a branched duct system that uses ducted devices / centrifugal coils. All this directly affects what equipment you have to choose.
In addition to all this, the duct capacity deserves attention. It is influenced by several factors. First of all, this is the diameter of the duct. It is also necessary to take into account the pressure losses that occur per meter.
For example, it is necessary to provide 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 ensure 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 ensure a satisfactory multiplicity of air that allows you to comfortably stay in a particular place, the above parameters must be taken into account.
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 rate of air exchange for industrial premises should provide a margin of a quarter of the regulatory requirements. Another important role is played by the speed of air movement.
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, this will provide about 65-70 m 3 per hour. While increasing this value to 1 m will allow you to multiply the effectiveness. If you need even more - then the natural movement is clearly not enough. In addition, the use of various equipment will be required - such as fans, valves and other devices to increase productivity.