How the parameters of ventilation systems are calculated. Calculation of ventilation systems Calculation of ventilation air volume

Do you dream that the house has a healthy microclimate and that no room smells musty and damp? In order for the house to be truly comfortable, even at the design stage, it is necessary to carry out a competent calculation of ventilation.

If this important point is missed during the construction of the house, in the future you will have to solve a number of problems: from removing mold in the bathroom to new repairs and installing an air duct system. Agree, it’s not very pleasant to see black mold nurseries in the kitchen on the windowsill or in the corners of the children’s room, and even plunge into repair work again.

The article presented by us contains useful materials on the calculation of ventilation systems, reference tables. Formulas, illustrative illustrations and a real example for premises for various purposes and a certain area, shown in the video, are given.

With correct calculations and proper installation, the ventilation of the house is carried out in a suitable mode. This means that the air in the premises will be fresh, with normal humidity and without unpleasant odors.

If the opposite picture is observed, for example, constant stuffiness in the bathroom or other negative phenomena, then you need to check the condition of the ventilation system.

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Conclusions and useful video on the topic

Roller #1. Useful information on the principles of operation of the ventilation system:

Roller #2. Together with the exhaust air, heat also leaves the home. Here, the calculations of heat losses associated with the operation of the ventilation system are clearly demonstrated:

The correct calculation of ventilation is the basis for its successful functioning and the guarantee of a favorable microclimate in a house or apartment. Knowing the basic parameters on which such calculations are based will allow not only to correctly design the ventilation system during construction, but also to correct its condition if circumstances change.

Ventilation in a room, especially in a residential or industrial one, must function at 100%. Of course, many may say that you can simply open a window or door to ventilate. But this option can only work in summer or spring. But what to do in winter when it's cold outside?

The need for ventilation

Firstly, it is immediately worth noting that without fresh air, a person’s lungs begin to function worse. It is also possible the appearance of a variety of diseases, which with a high percentage of probability will develop into chronic ones. Secondly, if the building is a residential building in which there are children, then the need for ventilation increases even more, since some ailments that can infect a child are likely to remain with him for life. In order to avoid such problems, it is best to deal with the arrangement of ventilation. It is worth considering several options. For example, you can do the calculation of the supply ventilation system and its installation. It is also worth adding that diseases are not all problems.

In a room or building where there is no constant exchange of air, all furniture and walls will be coated with any substance that is sprayed into the air. Suppose, if this is a kitchen, then everything that is fried, boiled, etc., will give its sediment. In addition, dust is a terrible enemy. Even cleaning products that are designed to clean will still leave their residue, which will negatively affect the residents.

Type of ventilation system

Of course, before proceeding with the design, calculation of the ventilation system or its installation, it is necessary to determine the type of network that is best suited. Currently, there are three fundamentally different types, the main difference between which is in their functioning.

The second group is the exhaust. In other words, this is an ordinary hood, which is most often installed in the kitchen areas of the building. The main task of ventilation is to extract air from the room to the outside.

Recirculation. Such a system is perhaps the most effective, since it simultaneously pumps air out of the room, and at the same time supplies fresh air from the street.

The only question that arises for everyone further is how the ventilation system works, why does the air move in one direction or another? For this, two types of air mass awakening source are used. They can be natural or mechanical, that is, artificial. To ensure their normal operation, it is necessary to carry out a correct calculation of the ventilation system.

General network calculation

As mentioned above, just choosing and installing a specific type will not be enough. It is necessary to clearly determine how much air needs to be removed from the room and how much needs to be pumped back. Experts call this air exchange, which must be calculated. Depending on the data obtained when calculating the ventilation system, it is necessary to start when choosing the type of device.

To date, a large number of different calculation methods are known. They are aimed at defining various parameters. For some systems, calculations are carried out to find out how much warm air or fumes need to be removed. Some are carried out in order to find out how much air is needed to dilute the pollution if it is an industrial building. However, the minus of all these methods is the requirement of professional knowledge and skills.

What to do if it is necessary to calculate the ventilation system, but there is no such experience? The very first thing that is recommended to do is to familiarize yourself with the various regulatory documents available for each state or even region (GOST, SNiP, etc.) These papers contain all the indications that any type of system must comply with.

Multiple calculation

One example of ventilation can be a multiplicity calculation. This method is rather complicated. However, it is quite feasible and will give good results.

The first thing to understand is what multiplicity is. A similar term describes how many times the air in a room is replaced by fresh air in 1 hour. This parameter depends on two components - this is the specificity of the structure and its area. For a visual demonstration, the calculation according to the formula for a building with a single air exchange will be shown. This indicates that a certain amount of air was removed from the room and at the same time fresh air was introduced in such an amount that corresponded to the volume of the same building.

The formula for calculation is as follows: L = n * V.

The measurement is carried out in cubic meters / hour. V is the volume of the room, and n is the multiplicity value, which is taken from the table.

If a system with several rooms is being calculated, then the volume of the entire building without walls must be taken into account in the formula. In other words, you must first calculate the volume of each room, then add up all the available results, and substitute the final value into the formula.

Ventilation with a mechanical type of device

The calculation of the mechanical ventilation system, and its installation must take place according to a specific plan.

The first stage is the determination of the numerical value of air exchange. It is necessary to determine the amount of substance that must enter the building in order to meet the requirements.

The second stage is the determination of the minimum dimensions of the air duct. It is very important to choose the correct section of the device, since such things as the purity and freshness of the incoming air depend on it.

The third stage is the choice of the type of system for installation. This is an important point.

The fourth stage is the design of the ventilation system. It is important to clearly draw up a plan-scheme according to which the installation will be carried out.

The need for mechanical ventilation arises only if the natural inflow cannot cope. Any of the networks is calculated on parameters such as its own air volume and the speed of this flow. For mechanical systems, this figure can reach 5 m 3 / h.

For example, if it is necessary to provide natural ventilation with an area of ​​​​300 m 3 / h, then it will be needed with a caliber of 350 mm. If a mechanical system is mounted, then the volume can be reduced by 1.5-2 times.

Exhaust ventilation

The calculation, like any other, must begin with the fact that performance is determined. The units of this parameter for the network are m 3 / h.

To make an effective calculation, you need to know three things: the height and area of ​​​​the rooms, the main purpose of each room, the average number of people who will be in each room at the same time.

In order to begin to calculate the ventilation and air conditioning system of this type, it is necessary to determine the multiplicity. The numerical value of this parameter is set by SNiP. Here it is important to know that the parameter for a residential, commercial or industrial premises will be different.

If the calculations are carried out for a residential building, then the multiplicity is 1. If we are talking about installing ventilation in an administrative building, then the indicator is 2-3. It depends on some other conditions. To successfully carry out the calculation, you need to know the value of the exchange by the multiplicity, as well as by the number of people. It is necessary to take the highest flow rate in order to determine the required power of the system.

To find out the air exchange rate, it is necessary to multiply the area of ​​​​the room by its height, and then by the multiplicity value (1 for household, 2-3 for others).

In order to calculate the ventilation and air conditioning system per person, you need to know the amount of air consumed by one person and multiply this value by the number of people. On average, with minimal activity, one person consumes about 20 m 3 / h, with average activity, the indicator increases to 40 m 3 / h, with intense physical exertion, the volume increases to 60 m 3 / h.

Acoustic calculation of the ventilation system

Acoustic calculation is a mandatory operation that is attached to the calculation of any room ventilation system. Such an operation is carried out in order to perform several specific tasks:

• determine the octave spectrum of airborne and structural ventilation noise at the calculated points;
• compare the existing noise with the permissible noise according to hygienic standards;
• determine how to reduce noise.

All calculations must be carried out at strictly established calculation points.

After all measures have been selected according to building and acoustic standards, which are designed to eliminate excessive noise in the room, a verification calculation of the entire system is carried out at the same points that were previously determined. However, the effective values ​​obtained during this noise reduction measure must also be added here.

To carry out calculations, certain initial data are needed. They were the noise characteristics of the equipment, which were called sound power levels (SPL). For the calculation, geometric mean frequencies in Hz are used. If an approximate calculation is carried out, then correction noise levels in dBA can be used.

If we talk about design points, then they are located in human habitats, as well as in the places where the fan is installed.

Aerodynamic calculation of the ventilation system

Such a calculation process is performed only after the air exchange for the building has already been calculated, and a decision has been made on the routing of air ducts and channels. In order to successfully carry out these calculations, it is necessary to compose a ventilation system in which it is necessary to highlight such parts as the fittings of all air ducts.

Using information and plans, it is necessary to determine the length of individual branches of the ventilation network. Here it is important to understand that the calculation of such a system can be carried out in order to solve two different problems - direct or inverse. The purpose of the calculations depends on the type of the task:

• straight line - it is necessary to determine the dimensions of the sections for all sections of the system, while setting a certain level of air flow that will pass through them;
• the reverse is to determine the air flow by setting a certain cross section for all ventilation sections.

In order to perform calculations of this type, it is necessary to break the entire system into several separate sections. The main characteristic of each selected fragment is a constant air flow.

Programs for calculation

Since it is a very time-consuming and time-consuming process to carry out calculations and build a ventilation scheme manually, simple programs have been developed that are able to do all the actions on their own. Let's consider a few. One such program for calculating the ventilation system is Vent-Clac. Why is she so good?

Such a program for calculating and designing networks is considered one of the most convenient and effective. The algorithm of this application is based on the use of the Altshul formula. The peculiarity of the program is that it copes well with both the calculation of natural ventilation and mechanical ventilation.

Since the software is constantly updated, it is worth noting that the latest version of the application is able to carry out such work as aerodynamic calculations of the resistance of the entire ventilation system. It can also effectively calculate other additional parameters that will help in the selection of preliminary equipment. In order to make these calculations, the program will need data such as the air flow at the beginning and end of the system, as well as the length of the main room duct.

Since it takes a long time to manually calculate all this and you have to break the calculations into stages, this application will provide significant support and save a lot of time.

Sanitary standards

Another option for calculating ventilation is according to sanitary standards. Similar calculations are carried out for public and administrative facilities. In order to make correct calculations, it is necessary to know the average number of people who will constantly be inside the building. If we talk about permanent consumers of air inside, then they need about 60 cubic meters per hour per one. But since temporary persons also visit public facilities, they must also be taken into account. The amount of air consumed by such a person is about 20 cubic meters per hour.

If all calculations are carried out based on the initial data from the tables, then when the final results are obtained, it will become clearly visible that the amount of air coming from the street is much greater than that consumed inside the building. In such situations, most often they resort to the simplest solution - hoods of about 195 cubic meters per hour. In most cases, adding such a network will create an acceptable balance for the existence of the entire ventilation system.

The quality of the air environment in the workshops is regulated by law, the standards are set in SNiP and TB. In most facilities, effective air exchange cannot be generated by a natural system, and equipment must be installed. It is important to achieve standards. For this, the calculation of the supply and exhaust ventilation of the production premises is performed.

The regulations provide for various types of pollution:

• excess heat from the operation of machines and mechanisms;
• fumes containing harmful substances;
• excess moisture;
• various gases;
• human secretions.

The calculation method offers an analysis for each type of pollution. The results are not summarized, and the largest value is taken into work. So, if in production the maximum volume is needed to remove excess heat, this indicator is taken to calculate the technical parameters of the structure. Let us give an example of calculating the ventilation of a production facility with an area of ​​100 m 2.

Air exchange at an industrial site with an area of ​​100 m 2

In production, it must perform the following functions:

1. remove harmful substances;
2. clean the environment from pollution;
3. remove excess moisture;
4. remove harmful emissions from the building;
5. regulate the temperature;
6. form an inflow of a clean stream;
7. depending on the characteristics of the site and weather conditions, heat, humidify or cool the incoming air.

Since each function requires additional power from the ventilation structure, therefore, the choice of equipment should be made taking into account all indicators.

Local exhaust

If emissions of harmful substances occur in the production processes at one of the sites, then, according to the regulations, a local exhaust must be installed next to the source. So the removal will be more effective.

Most often, such a source is technological tanks. For such objects, special installations are used - suction in the form of umbrellas. Its dimensions and power are calculated using the following parameters:

• source dimensions depending on the shape: side length (a*b) or diameter (d);
• flow velocity in the source zone (vv);
• suction speed of the unit (vz);
• suction height above the tank (z).

The sides of a rectangular suction are calculated by the formula:
A \u003d a + 0.8z,
where A is the suction side, a is the tank side, z is the distance between the source and the device.

The sides of a circular device are calculated using the formula:
D=d+0.8z,
where D is the diameter of the device, d is the diameter of the source, z is the distance between the suction and the reservoir.

Predominantly has the shape of a cone, the angle of which should not exceed 60 degrees. If the speed of the masses in the workshop is more than 0.4 m/s, then the device should be equipped with an apron. The amount of extract air is determined by the formula:
L=3600vz*Sa,
where L– air consumption in m3/h, vz – flow rate in the hood, Sa – suction working area.

Expert opinion

The result must be taken into account in the design and calculations of the general exchange system.

General ventilation

When the calculation of the local exhaust, types and volumes of pollution, it is possible to do a mathematical analysis of the required volume of air exchange. The simplest option is when there are no technological pollution on the site, and only human emissions are taken into account.

In this case, the task is to achieve sanitary standards and cleanliness of production processes. The required volume for employees is calculated by the formula:
L=N*m,
where L is the amount of air in m 3 / hour, N is the number of employees, m is the volume of air per person per hour. The last parameter is normalized by SNiP and is 30 m 3 / hour - in a ventilated workshop, 60 m 3 / hour - in a closed one.

If harmful sources exist, then the task of the ventilation system is to reduce pollution to the maximum standards (MAC). Mathematical analysis is performed according to the formula:
O \u003d Mv \ (Ko - Kp),
where O is the air flow rate, Mw is the mass of harmful substances emitted into the air in 1 hour, Ko is the concentration of harmful substances, Kp is the number of pollutants in the inflow.

The influx of pollution is also calculated, for this I use the following formula:
L \u003d Mv / (ypom - yp),
where L is the volume of inflow in m3/h, Mw is the weight value of harmful substances emitted in the workshop in mg/h, yp is the specific concentration of pollutants in m3/h, yp is the concentration of pollutants from the supply air.

The calculation of general ventilation of industrial premises does not depend on its area, other factors are important here. Mathematical analysis for a particular object is complex, it needs to take into account a lot of data and variables, you should use special literature and tables.

Forced ventilation

It is advisable to calculate industrial premises according to aggregated indicators, which express the flow of incoming air per unit volume of the room, per 1 person or 1 source of pollution. The standards set their own standards for various industries.

The formula is:
L=Vk
where L is the volume of supply masses in m 3 / hour, V is the volume of the room in m 3, k is the frequency of air exchange.
For a room with an area of ​​100 m 3 and a height of 3 meters for a 3-fold air change, you will need: 100 * 3 * 3 + = 900 m 3 / hour.

The calculation of exhaust ventilation of industrial premises is carried out after determining the required volumes of supply masses. Their parameters should be similar, so for an object with an area of ​​100 m 3 with a ceiling height of 3 meters and a three-fold exchange, the exhaust system should pump out the same 900 m 3 / hour.

Design includes many aspects. It all starts with the preparation of the terms of reference, which determines the orientation of the object to the cardinal points, purpose, layout, materials of building structures, features of the technologies used and the mode of operation.

Computing volumes are large:

• climatic indicators;
• air exchange rate;
• distribution of air masses inside the building;
• determination of air ducts, including their shapes, location, capacities and other parameters.

Then a general scheme is drawn up, and the calculations continue. At this stage, the nominal pressure in the system and its loss, the noise level in production, the length of the duct system, the number of bends and other aspects are taken into account.

Summarizing

The correct mathematical analysis for determining the parameters of air exchange in production can only be done by a specialist using various data, variables and formulas.

Independent work will lead to errors, and as a result: violation of sanitary standards and technological processes. Therefore, if your company does not have a specialist with the proper level of qualifications, it is better to use the services of a specialized company.

One of the conditions for creating a comfortable microclimate in residential and industrial premises is the presence of an engineering system, through which air is circulated. To ensure its effective functioning, it is necessary to correctly calculate the length and diameter of the ventilation pipe. For this, several methods are used, depending on the characteristics of the engineering system.

Ventilation scheme of a private house

Consequences of poor ventilation

If the fresh air supply system is not properly organized in the premises, there will be a lack of oxygen and increased humidity. Mistakes in the design of the hood are fraught with the appearance of soot on the walls of the kitchen, fogging of windows and the appearance of fungus on the surface of the walls.

Fogging windows due to insufficient ventilation

It should be borne in mind that pipes of round or square section can be used for the installation of the ventilation system. When removing air without the use of special devices, it is advisable to install round air ducts, as they are stronger, tighter and have good aerodynamic characteristics. Square pipes are best used for forced ventilation.

Calculation of the ventilation system

Normative supply air volume

Typically, natural ventilation systems are used in residential buildings. In this case, outside air enters the premises through transoms, vents and special valves, and it is removed using ventilation ducts. They can be attached or located in the internal walls. The construction of ventilation ducts in the external enclosing structures is not allowed due to the possible formation of condensate on the surface and subsequent damage to the structures. In addition, cooling can reduce the rate of air exchange.

Ensuring natural air flow through ventilation

The determination of the parameters of ventilation pipes for residential buildings is carried out on the basis of the requirements regulated by SNiP and other regulatory documents. In addition, the indicator of the multiplicity of exchange is also important, which reflects the efficiency of the ventilation system. According to him, the volume of air flow into the room depends on its purpose and is:

• For residential buildings -3 m 3 / hour per 1 m 2 of area, regardless of the number of people staying on the territory. According to sanitary standards, 20 m 3 / hour is enough for temporary residents, and 60 m 3 / hour for permanent residents.
• For auxiliary buildings (garage, etc.) - at least 180 m 3 / hour.

To calculate the diameter, a system with natural air flow is taken as the basis, without the installation of special devices. The easiest option is to use the ratio of the area of ​​\u200b\u200bthe room and the cross section of the ventilation hole.

In residential buildings, 1 m 2 requires 5.4 m 2 of an air duct section, and in ancillary buildings - about 17.6 m 2. However, its diameter cannot be less than 15 m 2, otherwise air circulation is not provided. More accurate data are obtained using complex calculations.

Algorithm for determining the diameter of the ventilation pipe

Based on the table given in the SNiP, the parameters of the ventilation pipe are determined based on the air exchange rate. It is a value that shows how many times during an hour the air in the room is replaced, and depends on its volume. Before determining the diameter of the pipe for ventilation, do the following:

Diagram for determining the diameter of the ventilation pipe

Features of determining the length of ventilation pipes

Another important parameter in the design of ventilation systems is the length of the outer pipe. It combines all the channels in the house through which air is circulated, and serves to bring it out.

Table calculation

The height of the ventilation pipe depends on its diameter and is determined from the table. Its cells indicate the cross section of the ducts, and in the column on the left - the width of the pipes. Their height is indicated in the top line and is indicated in mm.

Selection of the height of the ventilation pipe according to the table

In this case, you need to take into account:

• If the ventilation pipe is next to, then their height must match in order to avoid the penetration of smoke into the premises during the heating season.
• If the duct is located from the ridge or parapet at a distance that does not exceed 1.5 m, its height must be more than 0.5 m. If the pipe is within 1.5 to 3 m from the roof ridge, then it cannot be lower than his.
• The height of the ventilation pipe above the flat roof cannot be less than 0.5 m.

The location of the ventilation pipes relative to the roof ridge

When choosing a pipe for the construction of ventilation and determining its location, it is necessary to provide sufficient wind resistance. It must withstand a storm of 10 points, which is 40-60 kg per 1 m 2 of surface.

Software use

An example of calculating natural ventilation using special programs

The calculation of natural ventilation is less laborious if you use a special program for this. To do this, the optimal volume of air flow is first determined, depending on the purpose of the room. Then, based on the data obtained and the features of the designed system, the calculation of the ventilation pipe is made. At the same time, the program allows you to take into account:

• average temperature inside and outside;
• the geometric shape of the ducts;
• roughness of the inner surface, which depends on the pipe material;
• resistance to air movement.

Ventilation system with round pipes

As a result, the necessary dimensions of the ventilation pipes are obtained for the construction of an engineering system, which must ensure air circulation under certain conditions.

In the process of calculating the parameters of the ventilation pipe, attention should also be paid to the local resistance during air circulation. It can occur due to the presence of grids, gratings, bends and other design features.

The correct calculation of the parameters of the ventilation pipes will allow you to design and build an effective system that will make it possible to control the level of humidity in the premises and provide comfortable living conditions.

Proper ventilation in the house significantly improves the quality of human life. With the wrong calculation of supply and exhaust ventilation there are a lot of problems - for a person with health, for a building with destruction.

Before starting construction, it is imperative and necessary to make calculations and, accordingly, apply them in the project.

PHYSICAL COMPONENTS OF CALCULATIONS

According to the method of operation, at present, ventilation schemes are divided into:

1. Exhaust. To remove used air.
2. Supply. For clean air intake.
3. Recovery. Supply and exhaust. Remove the used one and let in the clean one.

In the modern world, ventilation schemes include various additional equipment:

1. Devices for heating or cooling the supplied air.
2. Filters for cleaning odors and impurities.
3. Devices for humidification and air distribution in rooms.

When calculating ventilation, the following quantities are taken into account:

1. Air consumption in cubic meters / hour.
2. Pressure in air channels in atmospheres.
3. Heater power in kWh.
4. Cross-sectional area of ​​​​air channels in sq.cm.

Exhaust ventilation calculation example

Before the beginning exhaust ventilation calculation it is necessary to study the SN and P (System of Norms and Rules) devices of ventilation systems. According to CH and P, the amount of air needed for one person depends on his activity.

Little activity - 20 cubic meters / hour. Average - 40 kb.m./h. High - 60 kb.m./h. Next, we take into account the number of people and the volume of the room.

In addition, you need to know the multiplicity - a complete exchange of air for an hour. For a bedroom, it is equal to one, for household rooms - 2, for kitchens, bathrooms and utility rooms - 3.

For example - calculation of exhaust ventilation rooms 20 sq.m.

Suppose two people live in a house, then:

V (volume) of the room is equal to: SxH, where H is the height of the room (standard 2.5 meters).

V \u003d S x H \u003d 20 x 2.5 \u003d 50 cubic meters.

In the same order, we calculate the performance of exhaust ventilation of the whole house.

Calculation of exhaust ventilation of industrial premises

At calculation of exhaust ventilation of the production room the multiplicity is 3.

Example: garage 6 x 4 x 2.5 = 60 cubic meters. 2 people work.

High activity - 60 cubic meters / hour x 2 \u003d 120 cubic meters / hour.

V - 60 cubic meters. x 3 (multiplicity) = 180 kb.m./h.

We choose more - 180 cubic meters / hour.

As a rule, unified ventilation systems, for ease of installation, are divided into:

• 100 - 500 cubic meters / hour. - apartment.
• 1000 - 2000 cubic meters / hour. - for houses and estates.
• 1000 - 10000 cubic meters / hour. – for factory and industrial facilities.

Calculation of supply and exhaust ventilation

AIR HEATER

In the climate of the middle lane, the air entering the room must be heated. For this, supply ventilation with heating of the incoming air is installed.

Heating of the coolant is carried out in various ways - an electric heater, the inlet of air masses near battery or stove heating. According to SN and P, the temperature of the incoming air must be at least 18 degrees. celsius.

Accordingly, the power of the air heater is calculated depending on the lowest (in the given region) outdoor temperature. The formula for calculating the maximum temperature for heating a room with an air heater:

N / V x 2.98 where 2.98 is a constant.

Example: air consumption - 180 cubic meters / hour. (garage). N = 2 kW.

Thus, the garage can be heated up to 18 degrees. At outside temperature minus 15 degrees.

PRESSURE AND SECTION

The pressure and, accordingly, the speed of movement of air masses are affected by the cross-sectional area of ​​the channels, as well as their configuration, the power of the electric fan and the number of transitions.

When calculating the channel diameter, the following values ​​are empirically taken:

• For residential premises - 5.5 sq.cm. per 1 sq.m. area.
• For a garage and other industrial premises - 17.5 sq.cm. per 1 sq.m.

At the same time, flow rates of 2.4 - 4.2 m / s are achieved.

ABOUT ELECTRICITY CONSUMPTION

Electricity consumption directly depends on the duration of the electric heater operation, and the time is a function of the ambient temperature. Usually, the air needs to be heated in the cold season, sometimes in the summer on cool nights. For the calculation, the formula is used:

S = (T1 x L x d x c x 16 + T2 x L x c x n x 8) x N/1000

In this formula:

S is the amount of electricity.

T1 is the maximum daily temperature.

T2 is the minimum night temperature.

L - performance cubic meters / hour.

c - volumetric heat capacity of air - 0.336 W x hour / kb.m. / deg.c. The parameter depends on pressure, humidity and air temperature.

d is the price of electricity during the day.

n is the price of electricity at night.

N is the number of days in a month.

Thus, if you adhere to sanitary standards, the cost of ventilation increases significantly, but the comfort of residents improves. Therefore, when installing a ventilation system, it is advisable to find a compromise between price and quality.