Acoustic calculation of the ventilation and air conditioning system 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 sound attenuation of ventilation and air conditioning systems is acoustic calculation - a mandatory application to the ventilation project of any object. The main tasks of such a calculation are: determination of the octave spectrum of airborne, structural ventilation noise at the calculated 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 design points is carried out, taking into account the effectiveness of these measures.

The initial data for 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, 1000, 2000, 4000, 8000 Hz. Corrected sound power levels of noise sources in dBA can be used for indicative calculations.

The calculated 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 pass in transit; in the area of the air intake or exhaust device, or only the air intake for recirculation.

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

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

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

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

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

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

Settlement points are located on the territory adjacent to the building

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

If the distance from the fan to the calculated point is much larger than its dimensions, the noise source can be considered as a point source.

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

where L Pocti is the octave level of the sound power of the noise source, dB;

∆L Pneti - total reduction of the sound power level along the path of sound propagation in the duct in the considered octave band, dB;

∆L ni - sound radiation directivity index, dB;

r - distance from the noise source to the calculated point, m;

W - spatial angle of sound emission;

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

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

First, it should be immediately noted that without fresh air human lungs begin to function worse. It is also possible the appearance of a variety of diseases, which, with a large percentage chances will become chronic. 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 calculate supply system ventilation and 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. At present, there are three main 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. Similar 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 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 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 made to find out how much to remove warm air or evaporation. 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 to do is to familiarize yourself with the various normative documents available in 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 correct section devices, 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 an area of 300 m 3 / h, you will need it 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 calculations are carried out for a residential building, then the multiplicity is 1. If we are talking on the installation of ventilation in the administrative building, 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 intensive physical activity volume increases up 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. It is important to understand here that the calculation of such a system can be carried out in order to solve two various tasks- direct or reverse. 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 doing calculations and building a ventilation scheme manually is a very laborious and lengthy process, we have developed simple programs who 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 last edition application is able to carry out such work as aerodynamic calculations 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, then this application will provide significant support and save a lot of time.

Sanitary standards

Another option for calculating ventilation - 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 resort to the most simple solution- extracts of approximately 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.

2008-04-14

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

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

Acoustic calculation of UHVH is carried out in order to optimal choice all necessary means of reducing noise and determining the expected noise level at the design points of the room. Traditionally, active and reactive silencers have been the main means of reducing system noise. Soundproofing and sound absorption of the system and premises is required to ensure compliance with the norms of permissible noise levels for humans - important environmental standards.

Right now in building codes and the rules of Russia (SNiP), which are mandatory for 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 "Protection from noise", the method of acoustic calculation of the SVKV of buildings is outdated and therefore was not included in the new SNiP 23-03-2003 "Protection from noise" (instead of SNiP II-12-77), where it is still at all missing.

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

The first method of acoustic calculation. This method, which is established purely on analytical dependencies, 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 made under the condition that the pipe diameter is much less than the sound wave length.

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

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

The long line contains the following characteristic elements. They are R 1 sound inlet, R 2 active silencer, R 3 sound insulated tee, R 4 sound insulated jet silencer, R 5 sound insulated butterfly valve, and R 6 sound insulated outlet. Sound insulation here refers to the difference in dB between the sound power in the waves incident on a given element and the sound power radiated by this element after the waves have passed through it further.

If the sound insulation of each of these elements does not depend on all others, then the sound insulation of the entire system can be estimated by calculation as follows. The wave equation for a narrow pipe 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, related to 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 duct over the period of sound vibrations T in W:

where T = 1/f is the period of sound vibrations, s; f is the oscillation frequency, Hz. Sound power in dB: L w \u003d 10lg (N / N 0), where N 0 \u003d 10 -12 W. Within the specified assumptions, the sound insulation of a long line of a ventilation system is calculated using the following formula:

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

Inlet and outlet openings of the ventilation system 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, are analogous to the interface between two media with 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 connection boundary, multiplied by the cross-sectional area of the pipes.

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

An analysis of this formula shows that at S 2 >> S 1 the properties of the second tube approach those of the free boundary. For example, a narrow pipe open into a semi-infinite space can be considered, from the point of view of the soundproofing 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 noise suppressor R2. 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 passage section, m; l is the silencer length, m; S is the cross-sectional area of the silencer channel, m 2 ; α eq is the 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

It follows from the formula that the sound insulation of the channel of the active silencer R 2 is the greater, the greater the absorption capacity of the walls α eq, the length of the silencer l and the ratio of the channel perimeter to its cross-sectional area П/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 R3. In ventilation systems, most often the first pipe with a cross-sectional area S 3 then branches into two pipes with cross-sectional areas S 3.1 and S 3.2. Such a branch is called a tee: through the first branch, sound enters, through the other two it passes further. In general, the first and second pipes may be comprised of a plurality of pipes. Then we have

The sound insulation of a tee from section S 3 to section S 3.i is determined by the formula

Note that due to aerohydrodynamic considerations in tees, they strive 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 suppressor R4. The chamber silencer is an acoustically narrow pipe with a cross section S 4 , which passes into another acoustically narrow pipe of large cross section S 4.1 with a length l, called a chamber, and then again passes into an acoustically narrow pipe with a cross section S 4 . Let us use the theory of the long line here as well. Replacing the characteristic impedance in the well-known formula for the sound insulation of a layer of arbitrary thickness at normal incidence of sound waves by the corresponding reciprocals of the pipe area, we obtain the formula for the sound insulation of a chamber silencer

where k is the wave number. The sound insulation of a chamber silencer reaches its greatest 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 silencer, then the sound reduction formula must be applied sequentially from chamber to chamber, and the total effect is calculated by applying, for example, the boundary conditions method. Efficient chamber silencers sometimes require large overall dimensions. But their advantage is that they can be effective at any frequency, including low frequencies, where active jammers are practically useless.

The zone of large sound insulation of chamber silencers covers repeating fairly wide frequency bands, but they also have periodic sound transmission zones that are very narrow in frequency. To increase efficiency and equalize the frequency response, a chamber silencer is often lined on the inside with a sound absorber.

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

where c is the speed of sound in air. In the first method, the main issue for us when developing a new method is the assessment of 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 entering the ventilated room - in this case, the values

Let us rewrite this expression in the following notation for the algebraic sum, namely

Note that the absolute maximum error of an approximate value is the maximum difference between its exact value y 0 and 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 adopted, 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 the 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. Let us define this quantity 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 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

At 2Φ(t), = 0.9973, we have t = 3 = α and the statistical estimate at almost 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 “ignorance margin”, which is proposed to be used in the acoustic calculation of the SVKV to ensure that the permissible noise standards are met in a ventilated room (this has not been done before).

But the probabilistic estimation of the result errors also indicates in this case that it is difficult to achieve high accuracy of the calculation results by the first method even for very simple circuits and a low-velocity ventilation system. For simple, complex, low- and high-speed UTCS circuits, 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. On ships, a calculation method has long been used, based partly on analytical dependencies, 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 UCS, R i is the sound insulation in the i-th element of the UCS, dB (see the first method),

a value that takes into account the influence of the room on the noise in it (in the construction literature, sometimes B is used instead of Q). Here rj is the distance from the jth air diffuser to the calculated 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 radiation angle of the source, Φ is directivity of the source, κ is the coefficient of violation of the diffuseness of the sound field).

If m air distributors are placed in the room of a modern building, the noise level from each of them at the calculated point is L j , then the total noise from all of them must be below the noise levels acceptable 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 UHCS, and the sound insulation R i that takes place in all these elements, for each of them is preliminarily determined experimentally. The fact is that over the past one and a half to two decades, the electronic technology of acoustic measurements, combined with a computer, has greatly progressed.

As a result, enterprises producing SVKV elements must indicate in 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 noise generation not only in the fan (as in the first method), but also in all other elements of the UHCS, which can be significant 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 standard measurements, which is now done for the second method. As a result, the second method, unlike the first one, covers almost all SVKV 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 \u200b\u200bof noise acceptable to a person according to 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 sound power of noise sources in watts, and the sound insulation of elements in decibels, according to the indicated formula for the acoustic calculation of UHCS, is valid only, at least, when there is no interference of sound waves in the system. And when there is interference in 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 been included in the textbook and guidelines for building acoustics course projects for senior students of St. Petersburg State Polytechnic University. Failure to take into account interference phenomena in pipelines increases the "margin for ignorance" or requires, in critical cases, experimental refinement of the result to the required degree of accuracy and reliability.

For the choice of "margin of ignorance", as shown above for the first method, the probabilistic error estimate is preferable, which is proposed to be used in the acoustic calculation of the SVKV of buildings to ensure that the permissible noise standards in the premises 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 Brekhovskikh L.M., 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 δ 2 , whose sound propagation constant γ 2 = β 2 + ik 2 and 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 the forward and reverse directions, with sound pressure

The input impedance of the entire layer system (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 pipe. And thus, with interference in narrow pipes, we have the formula for sound insulation in dB of a long line of a ventilation system:

The input impedances here can be obtained both, in simple cases, by calculation, and, in all cases, by measurement on a special installation with modern acoustic equipment. According to the third method, similarly to the first method, we have the sound power coming from the discharge air duct at the end of a long UHVAC line 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 obtain the following basic formula for the acoustic calculation of the ventilation and air conditioning system of buildings:

With the calculation reliability 2Φ(t)=0.9973 (practically the highest degree of reliability), we have t = 3 and the error values are 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 complex - 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. It, according to the author, can be proposed as a new method of acoustic calculation of the ventilation and air conditioning systems of buildings.

Summing up

The solution of urgent issues of developing a new method of acoustic calculation should take into account the best of the existing methods. A new method of acoustic calculation of the UTCS of buildings is proposed, which has a minimum "margin of ignorance" BB, due to the inclusion of errors by the methods of probability theory and mathematical statistics and the consideration of interference phenomena by the impedance method.

The information about the new calculation method presented in the article does not contain some of the necessary details obtained by additional research and work practice, and which constitute the author's "know-how". The ultimate goal of the new method is to provide a choice of a set of means for reducing the noise of the ventilation and air conditioning system of buildings, which increases, in comparison with the existing one, the efficiency, reducing the weight and cost of HVAC.

Technical regulations in the field of industrial and civil construction are not yet available, therefore, developments in the field, in particular, noise reduction in UHV buildings are relevant and should be continued at least until such regulations are adopted.

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Handbook of ship acoustics. Edited by I.I. Klyukin and I.I. Bogolepov. - Leningrad, "Shipbuilding", 1978.
Khoroshev G.A., Petrov Yu.I., Egorov N.F. Fighting 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 studying in the specialty "Electroacoustics and Ultrasonic Engineering" // Leningrad, "Shipbuilding", 1983.
Bogolepov I.I. Industrial soundproofing. Foreword by acad. I.A. Glebov. Theory, research, design, manufacture, control // Leningrad, Shipbuilding, 1986.
Aviation acoustics. Part 2. Ed. A.G. Munin. - M.: "Engineering", 1986.
Izak G.D., Gomzikov E.A. Noise on ships and methods of its reduction // M.: "Transport", 1987.
Noise reduction 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 Decree of the State Committee of the Council of Ministers of the USSR for Construction of June 14, 1977 No. 72. - M.: Gosstroy of Russia, 1997.
Guidance for the calculation and design of noise attenuation of ventilation installations. Developed for SNiPu 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 Gosstroy of the USSR // M.: Stroyizdat, 1988.
Construction norms and rules of the Russian Federation. Noise 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.
Soundproofing and sound absorption. A textbook for university students studying in the specialty "Industrial and civil engineering" and "Heat and gas supply and ventilation", ed. G.L. Osipov and V.N. Bobylev. - M.: AST-Astrel Publishing House, 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. SPbODZPP Publishing House, 2004.
Bogolepov I.I. Building acoustics. Foreword by acad. Yu.S. Vasilyeva // St. Petersburg. Polytechnic University Press, 2006.
Sotnikov A.G. Processes, devices and systems of air conditioning and ventilation. Theory, technology and design at the turn of the century // St. Petersburg, AT-Publishing, 2007.
www.integral.ru Firm "Integral". Calculation of the external noise level of ventilation systems according to: SNiP II-12-77 (part II) - "Guidelines for the calculation and design of noise attenuation of ventilation installations." St. Petersburg, 2007.
www.iso.org is an Internet site that contains complete information about the International Organization for Standardization ISO, a catalog and an online standards store through which you can purchase any currently valid ISO standard in electronic or printed form.
www.iec.ch is an Internet site that contains complete information about the International Electrotechnical Commission IEC, a catalog and an Internet store of its standards, through which it is possible to purchase the current IEC standard in electronic or printed form.
www.nitskd.ru.tc358 - a website on the Internet that contains complete information about the work of the technical committee TK 358 "Acoustics" of the Federal Agency for Technical Regulation, a catalog and an online store of national standards through which you can purchase the current required 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 No. 54 of the Gosgortekhnadzor of the Russian Federation dated March 27, 2003.
Federal Law of May 1, 2007 No. 65-FZ “On Amendments to the Federal Law “On Technical Regulation”.

Description:

The norms and regulations in force in the country stipulate that the projects must 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 of tech. sciences, head. noise protection laboratory for ventilation and engineering equipment (NIISF)

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

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 indicative calculations, corrected sound power levels of noise sources in dBA are sometimes used.

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

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

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

S is the area of an imaginary sphere or part thereof 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 the room adjacent to the room where the fan is installed

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

(3)

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

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

S - area of the building envelope, m 2 ;

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

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

The calculated point is located in the room served by the system

The noise from the fan propagates through the air duct (air duct), partially attenuates in its elements and penetrates into the serviced room through the air distribution and air intake grilles. Octave levels of sound pressure in a room depend on the amount of noise reduction in the air duct and the acoustic qualities of this 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 remember - the same as in formula (1) - formula (2).

Attenuation in the network (in the air channel) D L R network - the sum of the attenuation in its elements, sequentially located along the sound waves. The energy theory of sound propagation through pipes assumes that these elements do not influence each other. In fact, a sequence of shaped elements and straight sections form a single wave system, in which the principle of attenuation independence 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 compensate each other, and therefore the energy approach, which 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 air ducts made of sheet material is due to losses due to wall deformation and sound emission to the outside. The decrease in the sound power level D L R 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 can be seen, in rectangular air ducts, the attenuation (lowering SAM) decreases with increasing sound frequency, while that of a circular cross section increases. In the presence of thermal insulation on metal air ducts, shown in fig. 1 values should be approximately doubled.

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

(5)

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

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

Attenuation at bends (in elbows, 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 cross section of the channel increases due to the resulting non-uniformity of the velocity field. The rectangular turn acts like a low pass filter. The amount of noise reduction at a turn 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 the channel rotation. The maximum noise reduction is observed when the turning depth is approximately half the wavelength. The magnitude of the theoretical modulus of the sound transmission coefficient through rectangular turns can be judged from Fig. 2.

In real designs, according to the data of the 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 region of wavelengths close in magnitude to twice the channel width. Then it again smoothly increases at high frequencies, reaching 8-13 dB. On fig. Figure 3 shows the noise attenuation curves 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 noise reduction maximum at a = l /2 can be used to reduce noise with low-frequency discrete components by adjusting the channel sizes at turns to the frequency of interest.

Noise reduction on turns less than 90° is approximately proportional to the angle of the turn. For example, the noise reduction on a 45° turn is equal to half the noise reduction on a 90° turn. On curves with an angle of less than 45°, noise reduction is not taken into account. For smooth bends 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 branching channels, the transverse dimensions of which are less than half the wavelength of the sound wave, the physical causes of attenuation are similar to the causes of attenuation in bends and bends. This attenuation is determined as follows (Fig. 5).

Based on the medium continuity equation:

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

and the reduction in the sound power level at the cross-sectional area of the branch

	(11)
	(12)
	(13)

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

The reduction in sound power levels when the channel sizes are larger than the non-planar half-wavelengths due to 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 there is no reflection of waves with a length shorter than the channel dimensions.

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

Characteristics of directivity of sound emission by air distribution grilles are shown in fig. 8.

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

The attenuation of the noise level in the room is determined by formula (2). The calculated 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 created by several gratings, then the acoustic calculation is made taking into account their total impact.

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

(16)

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

D L' Рneti - attenuation in the network between the source and the transit section under consideration, dB;

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

S T - surface area of the transit section, which 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.

Settlement points are located on the territory adjacent to the building

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

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

(17)

where L Pocti is the octave level of the sound power of the noise source, dB;

D L Pseti - total reduction of the sound power level along the path of sound propagation in the duct in the considered octave band, dB;

D L ni - sound radiation directivity indicator, dB;

r - distance from the noise source to the calculated point, m;

W - spatial angle of sound emission;

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

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

Structural noise calculation

Structural noise in rooms adjacent to ventilation chambers occurs as a result of the transfer of dynamic forces from the fan to the ceiling. The octave sound pressure level in the adjacent isolated room is determined by the formula

For fans located in the technical room outside the ceiling above the isolated 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 the elements of vibration isolators, on which the refrigeration machine is installed, N s / m;

Z lane - input impedance of the ceiling - the carrier plate, in the absence of a floor on an elastic base, the floor plate - if available, N s / m;

S - conditional floor area of the technical room above the isolated room, m 2;

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

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

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

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

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

Determination of required noise reduction

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

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

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

In the total number of noise sources n, when determining D L tri the required reduction in octave sound pressure levels in urban areas, all noise sources that create sound pressure levels at the design point that differ by less than 10 dB should be included.

When determining D L tri for design points in a room protected from ventilation system noise, 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 considered ventilation system, - 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 noise reduction generated by shaped elements and air distribution devices of the considered branch, the number of shaped elements 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 at the design point the sound pressure level 10 dB lower than the permissible one, if their number is not more than 3 and 15 dB less than the permissible one, if their number is not more than 10.

As you can see, acoustic calculation is not an easy task. The necessary accuracy of its solution is provided by acoustic 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 laid directly into the project. So, only due to the installation of silencers, the length of which is 300-500 mm longer than required, additional costs for medium and large objects can amount to 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 // ABOK. 2004. No. 4.

4. Guidance for the calculation and design of noise attenuation of ventilation installations. Moscow: Stroyizdat, 1982.

5. Yudin E. Ya., Terekhin AS Fighting the noise of mine ventilation installations. Moscow: Nedra, 1985.

6. Noise reduction 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. Control of fan noise. Moscow: 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 conditions of the environment.

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

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

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

At the same time, in some large cities, where measures are being taken to improve the noise situation, noise levels are decreasing.

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, resulting from the oscillatory motion of particles in elastic media (solid, liquid, gaseous).

Non-acoustic noise - Radio-electronic noise - random fluctuations of currents and voltages in radio-electronic devices, arise as a result of uneven emission of electrons in electrovacuum devices (shot noise, flicker noise), uneven processes of 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. (cosmic noise).

Acoustic calculation, noise level calculation.

In the process of construction and operation of various facilities, noise control problems 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.

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

The objectives of the acoustic calculation are:

Identification of noise sources;

Determination of their noise characteristics;

Determination of the degree of influence of noise sources on normalized 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 need in any building (whether residential or administrative), acoustic calculation should be carried out for rooms of this type. So, if the noise level is not calculated, it may turn out that the room has a very low level of sound absorption, and this greatly complicates the process of communication between people in it.

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

Acoustic calculation is most often carried out for objects that have complex acoustics or have high requirements for sound quality.

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

The value of the hearing threshold depends on the frequency of perceived sounds and is equal to 10-12 W/m 2 at frequencies close to 1000 Hz. The upper limit is the pain threshold, which is less dependent on frequency and lies within 130 - 140 dB (at a frequency of 1000 Hz, intensity 10 W / m 2, sound pressure).

The ratio of intensity level and frequency determines the sensation of sound volume, i.e. sounds that have different frequencies and intensities can be assessed by a person as equally loud.

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

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

The procedure for performing acoustic calculation.

To perform an acoustic calculation, the following data will be required:

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;

Noise spectrum from the source;

Characteristics of the barrier;

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

In the calculation, the sources of noise and their characteristic properties are first determined. Next, on the object under study, points are selected at which calculations will be carried out. At selected points of the object, a preliminary sound pressure level is calculated. Based on the results obtained, a calculation is performed to reduce noise to the required standards. Having received all the necessary data, a project is carried out to develop measures that will reduce the noise level.

Properly 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;

* the 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 noise suppressors in ventilation and air conditioning systems.

Carrying out 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 area.

noise acoustic calculation measurement

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

The acoustic calculation process consists of the following main steps:

1. Collection of 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);

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

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

Geometric and soundproof parameters of weakened elements of enclosing structures;

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

Analysis of distances from external noise sources to normalized objects;

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

Analysis of weakened elements of enclosing structures (windows, doors, etc.), through which noise will penetrate into normalized premises, identification of their soundproofing ability.

2. Acoustic calculation is carried out on the basis of current guidelines and recommendations. Basically, these are “Methods of calculation, standards”.

At each calculated point, it is necessary to sum up 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 the equivalent value of the sound level (dBA) at the calculated point.

3. Analysis of the calculation results.

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

If necessary, the next step in the acoustic calculation can be the design of the necessary noise protection measures that will reduce the acoustic impact at the calculated 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.;

Carrying out measurements of noise levels for attestation of workplaces;

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

Carrying out work on instrumental measurement of noise levels as part of technical reports when approving the boundaries of the SPZ;

Implementation of any instrumental measurements of noise exposure.

Conducting instrumental measurements of noise levels is carried out by a specialized mobile laboratory using modern equipment.

Timing of acoustic calculation. Terms of performance of work depend on volume of calculations and measurements. If it is necessary to make an acoustic calculation for projects of residential developments or administrative facilities, then they are performed on average 1 - 3 weeks. Acoustic calculation for large or unique objects (theaters, organ halls) takes more time, based on the source materials provided. In addition, the number of studied noise sources, as well as external factors, largely affect the life.