Acoustic calculation of ventilation and air conditioning systems in modern buildings. Acoustic calculation as a basis for designing a low-noise ventilation (air conditioning) system Calculation of the noise level

The basis for the design of noise suppression of ventilation and air conditioning systems is the acoustic calculation - a mandatory attachment to the ventilation project of any object. The main tasks of such a calculation are: determination of the octave spectrum of air, structural ventilation noise at design points and its required reduction by comparing this spectrum with the permissible spectrum according to hygienic standards. After the selection of construction and acoustic measures to ensure the required noise reduction, a verification calculation of the expected sound pressure levels at the same calculated points is carried out, taking into account the effectiveness of these measures.

The initial data for the acoustic calculation are the noise characteristics of the equipment - sound power levels (SPL) in octave bands with geometric mean frequencies of 63, 125, 250, 500, 1,000, 2,000, 4,000, 8,000 Hz. For approximate calculations, the corrected sound power levels of noise sources in dBA can be used.

Design points are located in human habitats, in particular, at the place where the fan is installed (in the ventilation chamber); in rooms or in areas adjacent to the installation site of the fan; in rooms served by a ventilation system; in rooms where air ducts are in transit; in the area of the intake or exhaust device, or only intake air for recirculation.

The calculated point is in the room where the fan is installed

In general, the sound pressure levels in a room depend on the sound power of the source and the directivity factor of the noise emission, the number of noise sources, on the location of the design point relative to the source and enclosing building structures, on the size and acoustic qualities of the room.

The octave sound pressure levels generated by the fan (s) at the installation site (in the ventilation chamber) are:

where Фi is the directivity factor of the noise source (dimensionless);

S is the area of an imaginary sphere or its part surrounding the source and passing through the calculated point, m 2;

B is the acoustic constant of the room, m 2.

Design points are located in the area adjacent to the building

Fan noise propagates through the duct and is radiated into the surrounding space through a grill or shaft, directly through the walls of the fan casing or an open branch pipe when the fan is installed outside the building.

When the distance from the fan to the design point is much larger than its size, the noise source can be considered a point source.

In this case, the octave sound pressure levels at the calculated points are determined by the formula

where L Pokti - octave sound power level of the noise source, dB;

∆L Pnetworki is the total decrease in the sound power level along the path of sound propagation in the duct in the considered octave band, dB;

∆L ni - directivity index of sound radiation, dB;

r is the distance from the noise source to the design point, m;

W is the spatial angle of sound radiation;

b a - attenuation of sound in the atmosphere, dB / km.

Ventilation in a room, especially in a residential or industrial area, must be functioning at 100%. Of course, many might 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

First, it should be noted right away that without fresh air human lungs begin to function worse. The appearance of a wide variety of diseases is also possible, which with a large percentage the probabilities will develop into chronic ones. Secondly, if the building is a residential building in which children are located, 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 arrange ventilation. Several options are worth considering. For example, you can do the calculation supply system ventilation 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 covered with a coating from any substance that is sprayed into the air. For example, 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 up will still leave a residue that will negatively affect the occupants.

Type of ventilation system

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

The second group is exhaust. In other words, it is a conventional 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.

Recirculating. A similar system is, perhaps, the most effective, since it simultaneously pumps air from 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 sources are used. They can be natural or mechanical, that is, artificial. To provide them normal work, it is necessary to carry out the correct calculation of the ventilation system.

General network calculation

As mentioned above, just choosing and installing a certain type will not be enough. It is necessary to clearly define exactly how much air must be removed from the room and how much must 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 make a start when choosing the type of device.

Today, a large number of various calculation methods are known. They aim at defining various parameters. For some systems, calculations are made to find out how much to remove warm air or fumes. 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 it is recommended to do is to familiarize yourself with the various regulatory documents available to 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 of the examples of ventilation can be the calculation of the multiplicity. This method is quite 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 the room is replaced by fresh air in 1 hour. This parameter depends on two components - this is the specifics of the structure and its area. For a visual demonstration, the calculation by the formula for a building with a single air exchange will be shown. This suggests 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 the 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 calculated, then the formula must take into account the volume of the entire building without walls. 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 mechanical device type

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

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

The second stage is to determine the minimum dimensions of the air duct. It is very important to choose correct section devices, since things such as the cleanliness and freshness of the supplied 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-diagram according to which the installation will be carried out.

The need for mechanical ventilation only arises if the natural flow cannot cope. Any of the networks is calculated on such parameters 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 you need to provide natural ventilation an area of 300 m 3 / h, you will need it with a caliber of 350 mm. If a mechanical system is being installed, then the volume can be reduced by 1.5-2 times.

Exhaust ventilation

Calculation, like any other, must begin with the definition of performance. The unit of measurement for this parameter for the network is m 3 / h.

To carry out 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 start calculating the ventilation and air conditioning system of this type, it is necessary to determine the frequency. The numerical value of this parameter is set by SNiPom. It is important to know here that the parameter for a residential, commercial or industrial space will be different.

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

To find out the multiplicity of air exchange, 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, it is necessary 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 m3 / h, with average activity, the indicator rises to 40 m3 / h, with intensive physical activity 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. A similar operation is carried out in order to perform several specific tasks:

determine the octave spectrum of airborne and structural ventilation noise at design points;
compare the existing noise with the acceptable noise according to hygiene standards;
determine the path of noise reduction.

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

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

To carry out the calculations, certain initial data are needed. These are the noise characteristics of the equipment, which are called sound power levels (SPL). The geometric mean frequencies in Hz are used for the calculation. If a rough calculation is carried out, then the correction noise levels in dBA can be used.

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

Aerodynamic calculation of the ventilation system

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

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

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;
reverse - determine the air flow by setting a certain section for all ventilation sections.

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

Calculation programs

Since it is a very laborious and time-consuming process to carry out calculations and build a ventilation scheme manually, simple programs who are able to do all the actions on their own. Let's consider a few. One of such programs 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 ventilation of the natural type and of the mechanical type.

Since the software is constantly being updated, it should be noted that latest revision applications are able to carry out such work as aerodynamic calculations resistance of the entire ventilation system. It can also efficiently calculate other additional parameters that will help in the selection of preliminary equipment. In order to carry out these calculations, the program will need data such as the air flow at the beginning and at the end of the system, as well as the length of the main duct in the room.

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

Sanitary standards

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

If we carry out all the calculations based on the initial data from the tables, then when receiving the final results, 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 resort to the most simple solution- hoods for about 195 cubic meters per hour. In most cases, the addition of such a network will create an acceptable balance for the existence of the entire ventilation system.

2008-04-14

The ventilation and air conditioning system (VACS) is one of the main sources of noise in modern residential, public and industrial buildings, on ships, in sleeping cars of trains, in all kinds of salons and control cabins.

Noise in the SVKV comes from the fan (the main source of noise with its own tasks) and other sources, propagates through the duct together with the air flow and is radiated into the ventilated room. Noise and its reduction are influenced by: air conditioners, heating units, control and air distribution devices, construction, turns and branching of air ducts.

The acoustic calculation of the SVKV is made for the purpose of optimal choice all necessary means of noise reduction and determination of the expected noise level at the design points of the room. Traditionally, active and reactive silencers have been the primary means of noise reduction in a system. Sound insulation and sound absorption of the system and the room is required to ensure that the norms of noise levels permissible for humans - important environmental standards - are met.

Now in building codes and the rules of Russia (SNiP), mandatory in the design, construction and operation of buildings in order to protect people from noise, an emergency situation has developed. In the old SNiP II-12-77 "Noise protection", the method of acoustic calculation of UHCW buildings is outdated and therefore has not been included in the new SNiP 23-03-2003 "Noise protection" (instead of SNiP II-12-77), where it is still generally missing.

In this way, old method outdated, but not new. It's time to create modern method acoustic calculation of UHCW in buildings, as is already the case with its own specificity in other, previously more advanced in acoustics, areas of technology, for example, on sea vessels. Consider three possible ways acoustic calculation in relation to the SVKV.

The first method of acoustic calculation... This method, established purely on analytical dependences, uses the theory of long lines, known in electrical engineering and referred here to the propagation of sound in a gas filling a narrow pipe with rigid walls. The calculation is performed under the condition that the pipe diameter is much less than the sound wavelength.

For pipe rectangular section side should be less than half the wavelength, and for round pipe- radius. It is these pipes that are called narrow in acoustics. So, for air at a frequency of 100 Hz, a rectangular pipe will be considered narrow if the side of the section is less than 1.65 m. In a narrow curved pipe, the sound propagation will remain the same as in a straight pipe.

This is known from the practice of using negotiating pipes, for example, for a long time on steamships. Typical scheme a long line of the ventilation system has two determining values: L wH is the sound power entering the discharge line from the fan at the beginning of the long line, and L wK is the sound power coming from the discharge line at the end of the long line and entering the ventilated room.

The long line contains the following characteristic elements. We list them: soundproofed inlet R 1, soundproofed active silencer R 2, soundproofed tee R 3, soundproofed jet silencer R 4, soundproofed butterfly valve R 5 and soundproofed outlet R 6. Sound insulation here means the difference in dB between the sound power in the waves incident on a given element and the sound power emitted by this element after the waves pass through it further.

If the sound insulation of each of these elements does not depend on all the others, then the sound insulation of the entire system can be estimated by calculation as follows. The wave equation for a narrow tube has the following form of the equation for plane sound waves in an unbounded medium:

where c is the speed of sound in air, and p is the sound pressure in the pipe associated with the vibrational speed in the pipe according to Newton's second law by the relation

where ρ is the air density. The sound power for plane harmonic waves is equal to the integral over the cross-sectional area S of the air duct for the period of sound oscillations T in W:

where T = 1 / f is the period of sound vibrations, s; f - vibration frequency, Hz. Sound power in dB: L w = 10lg (N / N 0), where N 0 = 10 -12 W. Within the specified assumptions, the sound insulation of a long line of the ventilation system is calculated using the following formula:

The number of elements n for a particular UHCW can, of course, be greater than the above n = 6. Let us apply the theory of long lines to the above characteristic elements air ventilation systems.

Ventilation inlet and outlet with R 1 and R 6. The junction of two narrow pipes with different areas cross-sections S 1 and S 2, according to the theory of long lines, is an analogue of the interface between two media at normal incidence of sound waves on the interface. The boundary conditions at the junction of two pipes are determined by the equality of sound pressures and vibrational velocities on both sides of the junction, multiplied by the cross-sectional area of the pipes.

Solving the equations obtained in this way, we obtain the energy transmission coefficient and sound insulation of the junction of two pipes with the above sections:

Analysis of this formula shows that at S 2 >> S 1 the properties of the second pipe approach the properties of the free boundary. For example, a narrow pipe opened into a semi-infinite space can be considered from the point of view of sound insulating effect as bordering on a vacuum. For S 1<< S 2 свойства второй трубы приближаются к свойствам жесткой границы. В обоих случаях звукоизоляция максимальна. При равенстве площадей сечений первой и второй трубы отражение от границы отсутствует и звукоизоляция равна нулю независимо от вида сечения границы.

Active silencer R 2. Sound insulation in this case can be approximately and quickly estimated in dB, for example, according to the well-known formula of engineer A.I. Belova:

where P is the perimeter of the flow area, m; l is the length of the muffler, m; S is the cross-sectional area of the muffler channel, m 2; α eq - equivalent sound absorption coefficient of the lining, depending on the actual absorption coefficient α, for example, as follows:

α 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

α eq 0.1 0.2 0.4 0.5 0.6 0.9 1.2 1.6 2.0 4.0

From the formula it follows that the sound insulation of the channel of the active muffler R 2 is the greater, the greater the absorption capacity of the walls α eq, the length of the muffler l and the ratio of the channel perimeter to its cross-sectional area P / S. For the best sound-absorbing materials, for example, the PPU-ET, BZM and ATM-1 brands, as well as other widely used sound absorbers, the actual sound absorption coefficient α is presented in.

Tee R 3. In ventilation systems, most often, the first pipe with a cross-sectional area S 3 then branches into two pipes with a cross-sectional area S 3.1 and S 3.2. Such a branch is called a tee: sound enters through the first branch, and passes through the other two. In general, the first and second tubes can be composed of a plurality of tubes. Then we have

Sound insulation of the tee from section S 3 to section S 3.i is determined by the formula

Note that due to aerohydrodynamic considerations, tees tend to ensure that the cross-sectional area of the first pipe is equal to the sum of the cross-sectional area in the branches.

Reactive (chamber) noise damper R 4. A chamber silencer is an acoustically narrow pipe with a cross section S 4, which passes into another acoustically narrow pipe of a large cross section S 4.1 of length l, called a chamber, and then again passes into an acoustically narrow pipe with a cross section S 4. We will use the long line theory here as well. Replacing the characteristic impedance in the well-known formula for sound insulation of a layer of arbitrary thickness at normal incidence of sound waves by the corresponding reciprocal values of the pipe area, we obtain the formula for sound insulation of a chamber silencer

where k is the wavenumber. The sound insulation of the chamber silencer reaches the highest value at sin (kl) = 1, i.e. at

where n = 1, 2, 3, ... Frequency of maximum sound insulation

where c is the speed of sound in air. If several chambers are used in such a muffler, then the sound insulation formula must be applied sequentially from chamber to chamber, and the total effect is calculated using, for example, the boundary condition method. Effective chamber silencers sometimes require large dimensions. But their advantage is that they can be effective at any frequency, including low frequencies, where active mufflers are practically useless.

The zone of great soundproofing of chamber noise mufflers covers repeating rather wide frequency bands, but they also have periodic sound transmission zones that are very narrow in frequency. To improve efficiency and equalize the frequency response, a chamber muffler is often lined with a sound absorber from the inside.

Damper R 5. The damper is structurally a thin plate with an area S 5 and a thickness of δ 5, clamped between the pipeline flanges, the hole in which with an area of S 5.1 is less than the internal diameter of the pipe (or other characteristic size). Soundproofing such a throttle

where c is the speed of sound in air. In the first method, the main question for us when developing a new method is to assess the accuracy and reliability of the result of the acoustic calculation of the system. Let us determine the accuracy and reliability of the result of calculating the sound power supplied to the ventilated room - in this case, the values

We rewrite this expression in the following notation of the algebraic sum, namely

Note that the absolute maximum error of the approximate value is the maximum difference between its exact value y 0 and the approximate y, that is, ± ε = y 0 - y. The absolute maximum error of the algebraic sum of several approximate values y i is equal to the sum of the absolute values of the absolute errors of the terms:

Here, the least favorable case is accepted, when the absolute errors of all terms have the same sign. In reality, partial errors can have different signs and be distributed according to different laws. Most often, in practice, the errors of an algebraic sum are distributed according to the normal law (Gaussian distribution). Let us consider these errors and compare them with the corresponding value of the absolute maximum error. We define this value under the assumption that each algebraic term y 0i of the sum is distributed according to the normal law with the center M (y 0i) and the standard

Then the sum also follows the normal distribution law with the mathematical expectation

The error of the algebraic sum is defined as:

Then it can be argued that with a reliability equal to the probability 2Φ (t), the error of the sum will not exceed the value

For 2Φ (t), = 0.9973, we have t = 3 = α and the statistical estimate with practically maximum reliability is the error of the sum (formula) The absolute maximum error in this case

Thus ε 2Φ (t)<< ε. Проиллюстрируем это на примере результатов расчета по первому способу. Если для всех элементов имеем ε i = ε= ±3 дБ (удовлетворительная точность исходных данных) и n = 7, то получим ε= ε n = ±21 дБ, а (формула). Результат имеет совершенно неудовлетворительную точность, он неприемлем. Если для всех характерных элементов системы вентиляции воздуха имеем ε i = ε= ±1 дБ (очень высокая точность расчета каждого из элементов n) и тоже n = 7, то получим ε= ε n = ±7 дБ, а (формула).

Here, the result in the probabilistic estimation of errors in the first approximation can be more or less acceptable. So, the probabilistic estimation of errors is preferable and it should be used to select the “margin of ignorance”, which is suggested to be necessarily used in the acoustic calculation of the UHCS to ensure that the permissible noise standards in a ventilated room are met (this has not been done before).

But the probabilistic assessment of the errors of the result also indicates in this case that it is difficult to achieve high accuracy of the calculation results using the first method, even for very simple circuits and a low-speed ventilation system. For simple, complex, low- and high-speed SVKV schemes, satisfactory accuracy and reliability of such a calculation can be achieved in many cases only by the second method.

The second method of acoustic calculation... For a long time, ships have used a calculation method based in part on analytical dependences, but decisively on experimental data. We use the experience of such calculations on ships for modern buildings. Then, in a ventilated room served by one j-th air distributor, the noise levels L j, dB, at the design point should be determined by the following formula:

where L wi is the sound power, dB, generated in the i-th element of the UHCW, R i is the sound insulation in the i-th element of the UHCW, dB (see the first method),

a value that takes into account the effect of a room on noise in it (in construction literature, sometimes B is used instead of Q). Here rj is the distance from the j-th air distributor to the design point of the room, Q is the sound absorption constant of the room, and the values χ, Φ, Ω, κ are empirical coefficients (χ is the near-field influence coefficient, Ω is the spatial angle of radiation of the source, Φ is the factor directionality of the source, κ is the coefficient of disturbance of the diffuseness of the sound field).

If there are m air distributors in the room of a modern building, the noise level from each of which at the design point is equal to L j, then the total noise from all of them must be lower than the noise levels permissible for a person, namely:

where L H is the sanitary noise standard. According to the second method of acoustic calculation, the sound power L wi, generated in all elements of the UHCW, and the sound insulation R i, which takes place in all these elements, for each of them is preliminarily found experimentally. The fact is that over the past one and a half to two decades, the electronic technique of acoustic measurements, combined with a computer, has progressed.

As a result, enterprises producing UHCW elements must indicate in their passports and catalogs the characteristics L wi and R i, measured in accordance with national and international standards. Thus, the second method takes into account the generation of noise not only in the fan (as in the first method), but also in all other elements of the HVAC, which can be of significant importance for medium- and high-speed systems.

In addition, since it is impossible to calculate the sound insulation R i of such system elements as air conditioners, heating units, control and air distribution devices, therefore they are not in the first method. But it can be determined with the required accuracy by means of standard measurements, which is now being done for the second method. As a result, the second method, in contrast to the first, covers almost all UHCW schemes.

And finally, the second method takes into account the influence of the properties of the room on the noise in it, as well as the values of noise permissible for a person in accordance with the current building codes and regulations in this case. The main disadvantage of the second method is that it does not take into account the acoustic interaction between the elements of the system - interference phenomena in pipelines.

The summation of the acoustic power of the noise sources in watts, and the sound insulation of elements in decibels, is valid only, at least when there is no interference of sound waves in the system, according to the specified formula for the acoustic calculation of the UHCW. And when there is interference in the pipelines, then it can be a source of powerful sound, on which, for example, the sound of some wind musical instruments is based.

The second method has already entered the textbook and methodological guidelines for course projects in building acoustics for senior students of the St. Petersburg State Polytechnic University. Failure to take into account interference phenomena in pipelines increases the “margin of ignorance” or, in critical cases, requires experimental refinement of the result to the required degree of accuracy and reliability.

For the choice of “margin of ignorance”, it is preferable, as shown above for the first method, a probabilistic estimation of errors, which is proposed to be necessarily applied in the acoustic calculation of UHCW buildings to ensure that the permissible noise standards in rooms are met when designing modern buildings.

The third method of acoustic calculation... This method takes into account interference processes in a narrow pipeline of a long line. Such accounting can dramatically improve the accuracy and reliability of the result. For this purpose, it is proposed to apply for narrow pipes the "method of impedances" of Academician of the Academy of Sciences of the USSR and the Russian Academy of Sciences LM Brekhovskikh, which he used when calculating the sound insulation of an arbitrary number of plane-parallel layers.

So, let us first determine the input impedance of a plane-parallel layer with a thickness of δ 2, the sound propagation constant of which is γ 2 = β 2 + ik 2 and the acoustic impedance Z 2 = ρ 2 c 2. Let us denote the acoustic resistance in the medium in front of the layer, from where the waves fall, Z 1 = ρ 1 c 1, and in the medium behind the layer we have Z 3 = ρ 3 c 3. Then the sound field in the layer, with the omission of the factor i ωt, will be a superposition of waves traveling in forward and backward directions with sound pressure

The input impedance of the entire system of layers (formula) can be obtained by a simple (n - 1) -fold application of the previous formula, then we have

Let us now apply, as in the first method, the theory of long lines to a cylindrical tube. And thus, with interference in narrow pipes, we have the formula for sound insulation in dB of a long line of the ventilation system:

The input impedances here can be obtained both, in simple cases, by calculation, and, in all cases, by measuring on a special installation with modern acoustic equipment. According to the third method, similar to the first method, we have the sound power emanating from the discharge duct at the end of the long line of the SVKV and entering the ventilated room according to the scheme:

Next comes the evaluation of the result, as in the first method with a "margin of ignorance", and the sound pressure level of the room L, as in the second method. Finally, we get the following basic formula for the acoustic calculation of the ventilation and air conditioning system of buildings:

With the reliability of the calculation 2Φ (t) = 0.9973 (practically the highest degree of reliability), we have t = 3 and the error values are equal to 3σ Li and 3σ Ri. With reliability 2Φ (t) = 0.95 (high degree of reliability), we have t = 1.96 and the error values are approximately 2σ Li and 2σ Ri, With reliability 2Φ (t) = 0.6827 (engineering reliability assessment), we have t = 1.0 and the error values are equal to σ Li and σ Ri The third method, directed to the future, is more accurate and reliable, but also more complicated - it requires high qualifications in the fields of building acoustics, probability theory and mathematical statistics, and modern measuring technology.

It is convenient to use it in engineering calculations using computer technology. According to the author, it can be proposed as a new method for acoustic calculation of ventilation and air conditioning systems in buildings.

Summing up

The solution of urgent questions of the development of a new method of acoustic calculation should take into account the best of the existing methods. A new method of acoustic calculation of UHCW of buildings is proposed, which has a minimum "margin of ignorance" BB, thanks to the accounting of errors by methods of probability theory and mathematical statistics and accounting for interference phenomena by the method of impedances.

The information on the new calculation method presented in the article does not contain some of the necessary details obtained by additional research and practice, and which constitute the author's "know-how". The ultimate goal of the new method is to ensure the selection of a complex of means for noise reduction of ventilation and air conditioning systems of buildings, which increases, in comparison with the existing one, efficiency, reducing the weight and cost of the UHCS.

There are still no technical regulations in the field of industrial and civil construction, therefore, developments in the field, in particular, of noise reduction of UHCW buildings are relevant and should be continued, at least until such regulations are adopted.

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Isakovich M.A. General acoustics // M .: Publishing house "Science", 1973.
Handbook on ship acoustics. Edited by I.I. Klyukin and I.I. Bogolepova. - Leningrad, "Shipbuilding", 1978.
Horoshev G.A., Petrov Yu.I., Egorov N.F. Fight against fan noise // M .: Energoizdat, 1981.
Kolesnikov A.E. Acoustic measurements. Approved by the Ministry of Higher and Secondary Specialized Education of the USSR as a textbook for university students enrolled in the specialty "Electroacoustics and Ultrasonic Engineering" // Leningrad, "Shipbuilding", 1983.
Bogolepov I.I. Industrial soundproofing. Preface by Acad. I.A. Glebova. Theory, research, design, manufacture, control // Leningrad, "Shipbuilding", 1986.
Aviation acoustics. Part 2. Ed. A.G. Munina. - M .: "Mechanical engineering", 1986.
Izak G.D., Gomzikov E.A. Noise on ships and methods of its reduction // M .: "Transport", 1987.
Reducing noise in buildings and residential areas. Ed. G.L. Osipova and E. Ya. Yudin. - M .: Stroyizdat, 1987.
Building regulations. Noise protection. SNiP II-12-77. Approved by the Resolution of the State Committee of the Council of Ministers of the USSR for Construction Affairs of June 14, 1977, No. 72. - M .: Gosstroy of Russia, 1997.
Guidelines for the calculation and design of sound attenuation of ventilation units. Developed for SNiP II-12–77 by organizations of the Research Institute of Building Physics, GPI Santekhpoekt, NIISK. - M .: Stroyizdat, 1982.
Catalog of noise characteristics of technological equipment (to SNiP II-12–77). Research Institute of Construction Physics of the USSR State Construction Committee // Moscow: Stroyizdat, 1988.
Building codes and regulations of the Russian Federation. Sound protection. SNiP 23-03-2003. Adopted and put into effect by the Resolution of the Gosstroy of Russia dated June 30, 2003 No. 136. Date of introduction 2004-04-01.
Sound insulation and sound absorption. Textbook for university students enrolled in the specialty "Industrial and civil construction" and "Heat and gas supply and ventilation", ed. G.L. Osipov and V.N. Bobylev. - M .: Publishing house AST-Astrel, 2004.
Bogolepov I.I. Acoustic calculation and design of ventilation and air conditioning systems. Methodical instructions for course projects. St. Petersburg State Polytechnic University // St. Petersburg. Publishing house SPbODZPP, 2004.
Bogolepov I.I. Construction acoustics. Preface by Acad. Yu.S. Vasilyeva // St. Petersburg. Polytechnic University Press, 2006.
Sotnikov A.G. Processes, apparatus and systems of air conditioning and ventilation. Theory, technique and design at the turn of the century // St. Petersburg, AT-Publishing, 2007.
www.integral.ru. Firm "Integral". Calculation of the level of external noise of ventilation systems according to: SNiPu II-12–77 (part II) - "Guidelines for the calculation and design of noise suppression of ventilation units." St. Petersburg, 2007.
www.iso.org is an Internet site that provides complete information about the International Organization for Standardization ISO, a catalog and an online standards store where you can purchase any currently valid ISO standard in electronic or print form.
www.iec.ch is an Internet site that provides complete information about the International Electrotechnical Commission IEC, a catalog and an online store of its standards, through which you can purchase the currently valid IEC standard in electronic or printed form.
www.nitskd.ru.tc358 - a website on the Internet, which contains complete information about the work of the technical committee TC 358 "Acoustics" of the Federal Agency for Technical Regulation, a catalog and an online store of national standards, through which you can purchase the currently valid Russian standard in electronic or printed form.
Federal Law of December 27, 2002 No. 184-FZ "On Technical Regulation" (as amended on May 9, 2005). Adopted by the State Duma on December 15, 2002. Approved by the Federation Council on December 18, 2002. For the implementation of this Federal Law, see order of the RF Gosgortekhnadzor No. 54 of March 27, 2003.
Federal Law No. 65-FZ of May 1, 2007 “On Amendments to the Federal Law“ On Technical Regulation ”.

Description:

The norms and rules in force in the country prescribe that the projects should provide for measures to protect against noise of equipment used for human life support. Such equipment includes ventilation and air conditioning systems.

Acoustic calculation as a basis for designing a low-noise ventilation (air conditioning) system

V.P. Gusev, doctor tech. sciences, head. laboratory of noise protection of ventilation and engineering-technological equipment (NIISF)

The materials below do not pretend to be a complete presentation of the methodology for acoustic calculation of ventilation systems (installations). They contain information that clarifies, supplements or reveals in a new way various aspects of this methodology using the example of the acoustic calculation of the fan as the main source of noise in the ventilation system. The materials will be used in the preparation of a set of rules for the calculation and design of noise suppression of ventilation units for the new SNiP.

The calculated point is in the room where the fan is installed

The octave sound pressure levels generated by the fan (s) at the installation site (in the ventilation chamber) are:

where Фi is the directivity factor of the noise source (dimensionless);

S is the area of an imaginary sphere or its part surrounding the source and passing through the calculated point, m 2;

B is the acoustic constant of the room, m 2.

The calculated point is located in a room adjacent to the room where the fan is installed

The octave levels of airborne noise penetrating through the fence into the insulated room adjacent to the room where the fan is installed are determined by the soundproofing ability of the fences in a noisy room and the acoustic qualities of the protected room, which is expressed by the formula:

(3)

where L w is the octave sound pressure level in a room with a noise source, dB;

R - insulation from airborne noise by the enclosing structure through which noise penetrates, dB;

S is the area of the enclosing structure, m 2;

B u - acoustic constant of the insulated room, m 2;

k is a coefficient that takes into account the violation of the diffuseness of the sound field in the room.

The design point is located in a room served by the system

The noise from the fan spreads through the air duct (air duct), partially attenuates in its elements and through the air distribution and air intake grilles penetrates into the served room. The octave sound pressure levels in a room depend on the amount of noise reduction in the air duct and the acoustic qualities of that room:

(4)

where L Pi is the sound power level in the i-th octave radiated by the fan into the air duct;

D L networki - attenuation in the air channel (in the network) between the noise source and the room;

D L with i - the same as in formula (1) - formula (2).

Attenuation in the network (in the air channel) D L P network - the sum of attenuation in its elements, sequentially located along the course of sound waves. The energy theory of sound propagation through pipes assumes that these elements do not affect each other. In fact, the sequence of shaped elements and straight sections form a single wave system, in which the principle of independence of damping in the general case cannot be justified on pure sinusoidal tones. At the same time, in octave (wide) frequency bands, standing waves created by individual sinusoidal components cancel each other out, and therefore an energy approach that does not take into account the wave pattern in air ducts and considers the flow of sound energy can be considered justified.

Attenuation in straight sections of ducts made of sheet material is due to losses due to deformation of the walls and radiation of sound outward. The decrease in the sound power level D L P per 1 m of the length of straight sections of metal air ducts, depending on the frequency, can be judged from the data in Fig. one.

As you can see, in air ducts of rectangular cross-section, the attenuation (decrease in USM) decreases with increasing frequency of sound, and increases in circular cross-section. In the presence of thermal insulation on metal air ducts, shown in Fig. 1, the values should be approximately doubled.

The concept of attenuation (decrease) of the level of the sound energy flow cannot be equated with the concept of change in the level of sound pressure in the air duct. As a sound wave moves through a channel, the total amount of energy it carries decreases, but this is not necessarily associated with a decrease in the sound pressure level. In a narrowing channel, despite the attenuation of the total energy flux, the sound pressure level can increase due to an increase in the sound energy density. Conversely, in an expanding duct, the energy density (and sound pressure level) can decrease faster than the total sound power. The sound attenuation in a section with a variable cross-section is equal to:

(5)

where L 1 and L 2 are the average levels of sound pressure in the initial and final sections of the channel section along the course of sound waves;

F 1 and F 2 - cross-sectional areas, respectively, at the beginning and end of the channel section.

Attenuation at bends (in bends, bends) with smooth walls, the cross-section of which is less than the wavelength, is determined by the reactance of the additional mass type and the appearance of higher-order modes. The kinetic energy of the flow at the turn without changing the channel cross-section increases due to the resulting non-uniformity of the velocity field. The square rotation acts like a low pass filter. Cornering noise reduction in the plane wave range is given by an exact theoretical solution:

(6)

where K is the modulus of the sound transmission coefficient.

For a ≥ l / 2, the value of K is equal to zero and the incident plane sound wave is theoretically completely reflected by turning the channel. The maximum noise reduction occurs when the turning depth is approximately half the wavelength. The value of the theoretical modulus of the coefficient of sound transmission through rectangular bends can be judged from Fig. 2.

In real structures, according to the data of works, the maximum attenuation is 8-10 dB, when half the wavelength fits in the channel width. With increasing frequency, the attenuation decreases to 3-6 dB in the range of wavelengths close in magnitude to the doubled channel width. Then it smoothly increases again at high frequencies, reaching 8-13 dB. In fig. 3 shows the curves of noise attenuation at channel turns for plane waves (curve 1) and for random, diffuse sound incidence (curve 2). These curves are obtained on the basis of theoretical and experimental data. The presence of a maximum noise reduction at a = l / 2 can be used to reduce noise with low-frequency discrete components by adjusting the channel sizes at bends to the frequency of interest.

Noise reduction on bends less than 90 ° is roughly proportional to the steering angle. For example, the noise reduction in a 45 ° corner is equal to half the noise reduction in a 90 ° corner. Noise reduction is not taken into account when cornering less than 45 °. For smooth turns and straight bends of air ducts with guide vanes, the noise reduction (sound power level) can be determined using the curves in Fig. 4.

In channel branchings, the transverse dimensions of which are less than half the wavelength of the sound wave, the physical causes of attenuation are similar to those of attenuation in the elbows and branches. This attenuation is determined as follows (Fig. 5).

Based on the equation of continuity of the medium:

From the condition of pressure continuity (r p + r 0 = r pr) and equation (7), the transmitted sound power can be represented by the expression

and the decrease in the sound power level with a branch cross-sectional area

	(11)
	(12)
	(13)

With a sudden change in the cross-section of a channel with transverse dimensions less than half-wavelengths (Fig. 6 a), the decrease in the sound power level can be determined in the same way as in the case of branching.

The calculation formula for such a change in the channel cross-section has the form

(14)

where m is the ratio of the larger channel cross-sectional area to the smaller one.

The decrease in sound power levels when the channel sizes are larger than the half-wavelength of non-planar waves with a sudden narrowing of the channel is

If the channel expands or gradually narrows (Fig. 6 b and 6 d), then the decrease in the sound power level is equal to zero, since the reflection of waves with a length less than the channel dimensions does not occur.

In simple elements of ventilation systems, the following reduction values are taken at all frequencies: heaters and air coolers 1.5 dB, central air conditioners 10 dB, mesh filters 0 dB, the place where the fan is adjacent to the air duct network is 2 dB.

Reflection of sound from the end of the duct occurs if the transverse dimension of the duct is less than the length of the sound wave (Fig. 7).

If a plane wave propagates, then there is no reflection in the large duct, and we can assume that there are no reflection losses. However, if the opening connects a large room and an open space, then only diffuse sound waves, directed towards the opening, enter the opening, the energy of which is equal to a quarter of the energy of the diffuse field. Therefore, in this case, the sound intensity level is attenuated by 6 dB.

Directional characteristics of sound emission by air distribution grilles are shown in Fig. eight.

When a noise source is located in space (for example, on a column in a large room) S = 4p r 2 (radiation into the full sphere); in the middle part of the wall, floors S = 2p r 2 (radiation into the hemisphere); in the dihedral angle (radiation in 1/4 of the sphere) S = p r 2; in a triangular corner S = p r 2/2.

The attenuation of the noise level in the room is determined by the formula (2). The design point is selected at the place of permanent residence of people closest to the noise source, at a distance of 1.5 m from the floor. If the noise at the design point is generated by several gratings, then the acoustic calculation is performed taking into account their total impact.

When the source of noise is a section of a transit air duct passing through a room, the octave levels of sound power of the noise emitted by it, determined by the approximate formula, serve as the initial data for the calculation using formula (1):

(16)

where L pi is the sound power level of the source in the i-th octave frequency band, dB;

D L 'Pseti - attenuation in the network between the source and the considered transit section, dB;

R Ti - sound insulation of the structure of the transit section of the air duct, dB;

S T is the surface area of the transit section that goes into the room, m 2;

F T - cross-sectional area of the duct section, m 2.

Formula (16) does not take into account the increase in the density of sound energy in the duct due to reflections; the conditions for the incidence and passage of sound through the duct structure are significantly different from the passage of diffuse sound through the enclosures of the room.

Design points are located in the area adjacent to the building

When the distance from the fan to the design point is much larger than its size, the noise source can be considered a point source.

In this case, the octave sound pressure levels at the calculated points are determined by the formula

(17)

where L Pokti - octave sound power level of the noise source, dB;

D L Pnetsi is the total decrease in the sound power level along the path of sound propagation in the duct in the considered octave band, dB;

D L ni - directivity index of sound radiation, dB;

r is the distance from the noise source to the design point, m;

W is the spatial angle of sound radiation;

b a - attenuation of sound in the atmosphere, dB / km.

If there is a row of several fans, grilles or other extended noise source of limited dimensions, then the third term in formula (17) is taken equal to 15 lgr.

Structure-borne noise calculation

Structure-borne noise in rooms adjacent to ventilation chambers results from the transfer of dynamic forces from the fan to the ceiling. The octave sound pressure level in the adjacent insulated room is determined by the formula

For fans located in a technical room outside the overlap above the insulated room:

(20)

where L Pi is the octave sound power level of airborne noise emitted by the fan into the ventilation chamber, dB;

Z c - total wave resistance of vibration isolator elements on which the refrigerating machine is installed, N s / m;

Z lane - the input impedance of the floor - the bearing slab, in the absence of a floor on an elastic foundation, the floor slab - if available, N s / m;

S is the conditional overlap area of the technical room above the insulated room, m 2;

S = S 1 for S 1> S u / 4; S = S u / 4; at S 1 ≤ S u / 4, or if the technical room is not located above the insulated room, but has one common wall with it;

S 1 - the area of the technical room above the insulated room, m 2;

S u - area of the insulated room, m 2;

S in - the total area of the technical room, m 2;

R - own insulation of airborne noise by overlap, dB.

Determining the required noise reduction

The required reduction in octave sound pressure levels is calculated separately for each noise source (fan, fittings, fittings), but this takes into account the number of noise sources of the same type in the sound power spectrum and the sound pressure levels generated by each of them at the design point. In general, the required noise reduction for each source should be such that the total levels in all octave bands from all noise sources do not exceed the permissible sound pressure levels.

In the presence of one noise source, the required octave sound pressure level reduction is determined by the formula

where n is the total number of noise sources taken into account.

The total number of noise sources n in determining D L tri of the required octave sound pressure level reduction in the urban area should include all noise sources that create sound pressure levels at the design point that differ by less than 10 dB.

When determining D L tri for design points in a room protected from the noise of the ventilation system, the total number of noise sources should include:

When calculating the required fan noise reduction - the number of systems serving the room; noise generated by air distribution devices and fittings is not taken into account;

When calculating the required noise reduction generated by the air distribution devices of the ventilation system under consideration, - the number of ventilation systems serving the room; the noise of the fan, air distribution devices and fittings is not taken into account;

When calculating the required reduction of noise generated by fittings and air distribution devices of the considered branch, - the number of fittings and chokes, the noise levels of which differ from one another by less than 10 dB; the noise of the fan and grilles is not taken into account.

At the same time, the total number of noise sources taken into account does not take into account noise sources that create a sound pressure level at the design point by 10 dB less than the permissible one, with their number not exceeding 3 and 15 dB less than the permissible one with their number not exceeding 10.

As you can see, acoustic calculation is not an easy task. The required accuracy of its solution is provided by acoustics specialists. The efficiency of noise suppression and the cost of its implementation depend on the accuracy of the performed acoustic calculation. If the value of the calculated required noise reduction is underestimated, then the measures will not be effective enough. In this case, it will be necessary to eliminate the shortcomings at the operating facility, which is inevitably associated with significant material costs. If the required noise reduction is overestimated, unjustified costs are incorporated directly into the project. So, just by installing mufflers, the length of which is 300-500 mm longer than the required one, additional costs for medium and large objects can be 100-400 thousand rubles or more.

Literature

1. SNiP II-12-77. Noise protection. Moscow: Stroyizdat, 1978.

2. SNiP 23-03-2003. Noise protection. Gosstroy of Russia, 2004.

3. Gusev V.P., Acoustic requirements and design rules for low-noise ventilation systems, AVOK, no. 2004. No. 4.

4. Guidelines for the calculation and design of sound attenuation of ventilation units. Moscow: Stroyizdat, 1982.

5. Yudin E. Ya., Terekhin A.S. The fight against the noise of mine ventilation units. Moscow: Nedra, 1985.

6. Reducing noise in buildings and residential areas. Ed. G. L. Osipova, E. Ya. Yudina. Moscow: Stroyizdat, 1987.

7. Khoroshev S. A., Petrov Yu. I., Egorov P. F. Fight against fan noise. M .: Energoizdat, 1981.

Acoustic calculations

Among the problems of improving the environment, the fight against noise is one of the most urgent. In large cities, noise is one of the main physical factors that shape the living environment.

The growth of industrial and residential construction, the rapid development of various types of transport, the increasing use of plumbing and engineering equipment in residential and public buildings, have led to the fact that the noise levels in residential areas of the city have become comparable to the noise levels at work.

The noise regime of large cities is formed mainly by road and rail transport, which makes up 60-70% of all noise.

An increase in the intensity of air traffic, the emergence of new powerful aircraft and helicopters, as well as railway transport, open metro and shallow metro lines have a noticeable effect on the noise level.

At the same time, in some large cities, where measures are being taken to improve the noise environment, a decrease in noise levels is observed.

There are acoustic and non-acoustic noises, what is the difference between them?

Acoustic noise is defined as a set of sounds of different strength and frequency, arising from the vibrational motion of particles in elastic media (solid, liquid, gaseous).

Non-acoustic noise - Radio-electronic noise - random fluctuations of currents and voltages in electronic devices, arise as a result of uneven emission of electrons in vacuum devices (shot noise, flicker noise), irregularities in the generation and recombination of charge carriers (conduction electrons and holes) in semiconductor devices, thermal motion of current carriers in conductors (thermal noise), thermal radiation of the Earth and the Earth's atmosphere, as well as planets, the Sun, stars, the interstellar medium, etc. (space noise).

Acoustic calculation, noise level calculation.

In the process of construction and operation of various objects, the problems of noise control are an integral part of labor protection and protection of public health. Machines, vehicles, mechanisms and other equipment can act as sources. Noise, its magnitude of impact and vibration on a person depends on the level of sound pressure, frequency characteristics.

The standardization of noise characteristics is understood as the establishment of restrictions on the values of these characteristics, at which the noise affecting people should not exceed the permissible levels regulated by the current sanitary norms and rules.

The objectives of the acoustic design are:

Identification of sources of noise;

Determination of their noise characteristics;

Determination of the degree of influence of noise sources on standardized objects;

Calculation and construction of individual zones of acoustic discomfort of noise sources;

Development of special noise protection measures that provide the required acoustic comfort.

The installation of ventilation and air conditioning systems is already considered a natural requirement in any building (be it residential or administrative), the acoustic calculation should also be performed for premises of this type. So, if the calculation of the noise level is not carried out, it may turn out that the level of sound absorption in the room is very low, and this greatly complicates the process of communication between people in it.

Therefore, before installing ventilation systems in the room, it is imperative to carry out an acoustic calculation. If it turns out that the room is characterized by poor acoustic properties, it is necessary to propose to carry out a number of measures to improve the acoustic environment in the room. Therefore, acoustic calculations are performed for the installation of household air conditioners.

The acoustic calculation is most often carried out for objects that have complex acoustics or have increased requirements for sound quality.

Sound sensations arise in the organs of hearing when they are exposed to sound waves in the range from 16 Hz to 22 thousand Hz. The sound propagates in the air at a speed of 344 m / s, in 3 seconds. 1 km.

The value of the hearing threshold depends on the frequency of the perceived sounds and is equal to 10-12 W / m2 at frequencies close to 1000 Hz. The upper limit is the pain threshold, which is less dependent on frequency and lies in the range of 130 - 140 dB (at a frequency of 1000 Hz in intensity 10 W / m2, in sound pressure).

The ratio of the level of intensity and frequency determines the perception of the loudness of the sound, i.e. sounds of different frequency and intensity can be assessed by a person as equally loud.

When sound signals are perceived against a certain acoustic background, the signal masking effect can be observed.

The masking effect can negatively affect acoustic indicators and can be used to improve the acoustic environment, i.e. in the case of masking the high-frequency tone with a low-frequency one, which is less harmful to humans.

The procedure for performing an acoustic calculation.

To perform the acoustic calculation, the following data is required:

The dimensions of the room for which the calculation of the noise level will be carried out;

The main characteristics of the premises and its properties;

Source noise spectrum;

Description of the obstacle;

Distance data from the center of the noise source to the point of acoustic calculation.

When calculating, for a start, the sources of noise and their characteristic properties are determined. Further, on the object under study, points are selected at which calculations will be carried out. At the selected points of the object, a preliminary sound pressure level is calculated. Based on the results obtained, a calculation is made to reduce the noise to the required standards. Having received all the necessary data, a project is being carried out to develop measures, thanks to which the noise level will be reduced.

A correctly performed acoustic calculation is the key to excellent acoustics and comfort in a room of any size and design.

Based on the performed acoustic calculation, the following measures can be proposed to reduce the noise level:

* installation of soundproof structures;

* use of seals in windows, doors, gates;

* the use of structures and screens that absorb sound;

* implementation of planning and development of the residential area in accordance with SNiP;

* the use of silencers in ventilation and air conditioning systems.

Acoustic calculation.

Work on the calculation of noise levels, assessment of acoustic (noise) impact, as well as the design of specialized noise protection measures should be carried out by a specialized organization with a relevant field.

noise acoustic calculation measurement

In the simplest definition, the main task of acoustic calculation is to estimate the level of noise generated by a noise source at a given design point with a specified quality of acoustic impact.

The acoustic calculation process consists of the following main stages:

1. Collecting the necessary initial data:

The nature of noise sources, their mode of operation;

Acoustic characteristics of noise sources (in the range of geometric mean frequencies 63-8000 Hz);

Geometrical parameters of the room in which the noise sources are located;

Analysis of weakened elements of the enclosing structure, through which noise will penetrate into the environment;

Geometric and soundproofing parameters of weakened elements of enclosing structures;

Analysis of nearby objects with the established quality of acoustic impact, definitions of permissible sound levels for each object;

Analysis of distances from external noise sources to standardized objects;

Analysis of possible shielding elements on the path of sound wave propagation (buildings, green spaces, etc.);

Analysis of weakened elements of enclosing structures (window openings, doors, etc.) through which noise will penetrate into the standardized premises, identifying their sound insulation capacity.

2. The acoustic calculation is carried out on the basis of the current guidelines and recommendations. Basically, these are "Calculation methods, standards".

At each calculated point, it is necessary to summarize all available noise sources.

The result of the acoustic calculation are certain values (dB) in octave bands with geometric mean frequencies of 63-8000 Hz and an equivalent sound level (dBA) at the calculated point.

3. Analysis of the calculation results.

The analysis of the results obtained is carried out by comparing the values obtained at the calculated point with the established Sanitary Standards.

If necessary, the next stage of the acoustic calculation can be the design of the necessary noise protection measures that will reduce the acoustic impact at the design points to an acceptable level.

Carrying out instrumental measurements.

In addition to acoustic calculations, it is possible to calculate instrumental measurements of noise levels of any complexity, including:

Measurement of noise impact of existing ventilation and air conditioning systems for office buildings, private apartments, etc .;

Measurement of noise levels for certification of workplaces;

Carrying out work on instrumental measurement of noise levels within the project;

Carrying out works on instrumental measurement of noise levels within the framework of technical reports when approving the boundaries of the SPZ;

Carrying out any instrumental measurements of noise exposure.

Instrumental measurements of noise levels are carried out by a specialized mobile laboratory using modern equipment.

The timing of the acoustic calculation. The timing of the work depends on the volume of calculations and measurements. If it is necessary to make an acoustic calculation for projects of residential buildings or administrative buildings, then they are carried out on average 1 - 3 weeks. Acoustic design for large or unique objects (theaters, organ halls) takes more time based on the source materials provided. In addition, the number of noise sources investigated, as well as external factors, greatly affect the operating life.