B - room constant in the considered octave band in m 2, taken in accordance with paragraphs. 3.4 or 3.5;

AZ-i - an amendment that takes into account the distribution of sound power levels of ceiling lamps and gratings in octave bands, taken according to Table. 6, in dB;

D - correction for the location of the noise source; when the source is located in the working area (not higher than 2 m from the floor), A = 3 dB; if the source is above this zone, A *■ 0;

0.7 - safety factor;

F, B - the designations are the same as in paragraph 2.9, formula (5).

Note. The determination of the allowable air speed is carried out only for one frequency, which is equal to VNIIGS 250 Shch for ceiling lamps, 500 Hz for disk ceiling lamps, and 2000 Hz for anemostats and gratings.

2.14. In order to reduce the sound power level of the noise generated by bends and tees of air ducts, areas of a sharp change in the cross-sectional area, etc., it is necessary to limit the speed of air movement in the main air ducts of public buildings and auxiliary buildings of industrial enterprises to 5-6 m / s, and on branches up to 2-4 m/sec. For industrial buildings, these speeds can be respectively doubled, if this is permissible according to technological and other requirements.

3. CALCULATION OF OCTAVE SOUND PRESSURE LEVELS AT CALCULATED POINTS

3.1. Octave levels of sound pressure at permanent workplaces or in rooms (at design points) should not exceed the established norms.

(Notes: 1. If the regulatory requirements for sound pressure levels are different during the day, then the acoustic calculation of the installations should be made for the lowest permissible sound pressure levels.

2. Sound pressure levels at permanent workplaces or in rooms (at design points) depend on the sound power and location of noise sources and the sound-absorbing qualities of the room in question.

3.2. When determining the octave levels of sound pressure, the calculation should be made for permanent workplaces or settlement points in rooms closest to noise sources (heating and ventilation units, air distribution or air intake devices, air or air curtains, etc.). In the adjacent territory, the design points should be taken as the points closest to noise sources (fans located openly on the territory, exhaust or air intake shafts, exhaust devices of ventilation installations, etc.), for which sound pressure levels are normalized.

a - noise sources (autonomous air conditioner and ceiling) and the calculated point are in the same room; b - noise sources (fan and installation elements) and the calculated point are located in different rooms; c - source of noise - the fan is located in the room, the calculated point is on the arrival side of the territory; 1 - autonomous air conditioner; 2 - calculated point; 3 - noise-generating ceiling; 4 - vibration-isolated fan; 5 - flexible insert; in - the central muffler; 7 - sudden narrowing of the duct section; 8 - branching of the duct; 9 - rectangular turn with guide vanes; 10 - smooth turn of the air duct; 11 - rectangular turn of the duct; 12 - lattice; /

3.3. Octave/Sound pressure levels at design points should be determined as follows.

Case 1. The noise source (noise-generating grille, ceiling lamp, autonomous air conditioner, etc.) is located in the room under consideration (Fig. 3). Octave sound pressure levels generated at the calculated point by one noise source should be determined by the formula

L-L, + I0! g (-£-+--i-l (8)

Oct \ 4 I g g W t )

N o t e. For ordinary rooms that do not have special requirements for acoustics, according to the formula

L \u003d Lp - 10 lg H w -4- D - (- 6, (9)

where Lp okt is the octave sound power level of the noise source (determined according to Section 2) in dB\

B w - room constant with a noise source in the considered octave band (determined according to paragraphs 3.4 or 3.5) in g 2;

D - correction for the location of the noise source If the noise source is located in the working area, then for all frequencies D \u003d 3 dB; if above the working area, - D=0;

Ф - radiation directivity factor of the noise source (determined from the curves in Fig. 4), dimensionless; d - distance from the geometric center of the noise source to the calculated point in g.

The graphical solution of equation (8) is shown in fig. 5.

Case 2. The calculated points are located in a room isolated from noise. Noise from a fan or an installation element propagates through the air ducts and is radiated into the room through an air distribution or air intake device (grille). Octave sound pressure levels generated at design points should be determined by the formula

L \u003d L P -DL p + 101g (-% + -V (10)

Note. For ordinary rooms, for which there are no special requirements for acoustics, - according to the formula

L - L p -A Lp -10 lgiJ H ~b A -f- 6, (11)

where L p in is the octave level of the sound power of the fan or installation element radiated into the duct in the considered octave band in dB (determined in accordance with paragraphs 2.5 or 2.10);

AL r in - the total reduction in the level (loss) of the sound power of the noise of the fan or electric

installation time in the octave band under consideration along the sound propagation path in dB (determined in accordance with clause 4.1); D - correction for the location of the noise source; if the air distribution or air intake device is located in the working area, A \u003d 3 dB, if it is higher, - D \u003d 0; Ф and - directivity factor of the installation element (hole, grate, etc.) emitting noise into the isolated room, dimensionless (determined from the graphs in Fig. 4); rn is the distance from the installation element emitting noise into the isolated room to the calculated point in m

B and - the constant of the room isolated from noise in the considered octave band in m 2 (determined according to paragraphs 3.4 or 3.5).

Case 3. The calculated points are located on the territory adjacent to the building. Fan noise propagates through the duct and is radiated to the atmosphere through the grate or shaft (Fig. 6). Octave levels of sound pressure generated at design points should be determined by the formula

I = L p -AL p -201gr a -i^- + A-8, (12)

where g a is the distance from the installation element (grid, hole) emitting noise into the atmosphere to the design point in m \ p a - sound attenuation in the atmosphere, taken according to Table. 7 in dB/km

A is the correction in dB, taking into account the location of the calculated point relative to the axis of the installation element emitting noise (for all frequencies, it is taken according to Fig. 6).

1 - ventilation shaft; 2 - louvre

The remaining quantities are the same as in formulas (10)

3.4. The room constant B should be determined from the graphs in fig. 7 or according to table. 9, using the table. 8 to determine the characteristics of the room.

3.5. For rooms with special requirements for acoustics (unique

halls, etc.), the constant of the room should be determined in accordance with the instructions for acoustic calculation for these rooms.

3.6. If the design point receives noise from several noise sources (for example, supply and recirculation grilles, an autonomous air conditioner, etc.), then for the considered design point, according to the corresponding formulas in clause 3.2, the octave sound pressure levels generated by each of the noise sources separately should be determined , and the total level in

These "Instructions on the acoustic calculation of ventilation units" were developed by the Research Institute of Building Physics of the USSR State Construction Committee together with the institutes Santekhproekt of the USSR State Construction Committee and Giproniiaviaprom of Minaviaprom.

The instructions were developed in development of the requirements of the chapter SNiP I-G.7-62 “Heating, ventilation and air conditioning. Design Standards” and “Sanitary Design Standards for Industrial Enterprises” (SN 245-63), which establish the need to reduce the noise of ventilation, air conditioning and air heating installations for buildings and structures for various purposes when it exceeds the sound pressure levels allowed by the standards.

Editors: A. No. 1. Koshkin (Gosstroy of the USSR), Doctor of Engineering. sciences, prof. E. Ya. Yudin and candidates of tech. Sciences E. A. Leskov and G. L. Osipov (Research Institute of Building Physics), Ph.D. tech. Sciences I. D. Rassadi

The Guidelines set out the general principles of acoustic calculations for mechanically driven ventilation, air conditioning and air heating installations. Methods for reducing sound pressure levels at permanent workplaces and in rooms (at design points) to the values ​​established by the norms are considered.

at (Giproniiaviaprom) and eng. | g. A. Katsnelson / (GPI Santekhproekt)

1. General Provisions............ - . . , 3

2. Noise sources of installations and their noise characteristics 5

3. Calculation of octave levels of sound pressure in the calculated

points................. 13

4. Reducing the levels (losses) of the sound power of noise in

various elements of air ducts ........ 23

5. Determining the required reduction in sound pressure levels. . . *. ............... 28

6. Measures to reduce sound pressure levels. 31

Application. Examples of acoustic calculation of ventilation, air conditioning and air heating installations with mechanical stimulation...... 39

Plan I quarter. 1970, No. 3

3.7. If the calculated points are located in a room through which a “noisy” duct passes, and noise enters the room through the walls of the duct, then the octave sound pressure levels should be determined by the formula

L - L p -AL p + 101g --R B - 101gB „-J-3, (13)

where Lp 9 is the octave level of the sound power of the noise source radiated into the duct, in dB (determined in accordance with paragraphs 2 5 and 2.10);

ALp b is the total reduction in sound power levels (losses) along the sound propagation path from the noise source (fan, throttle, etc.) to the beginning of the considered section of the duct that emits noise into the room, in dB (determined in accordance with Section 4);

State Committee of the Council of Ministers of the USSR for Construction Affairs (Gosstroy of the USSR)

1. GENERAL PROVISIONS

1.1. These Guidelines are developed in development of the requirements of the chapter SNiP I-G.7-62 “Heating, ventilation and air conditioning. Design Standards” and “Sanitary Design Standards for Industrial Enterprises” (SN 245-63), which established the need to reduce the noise of mechanically driven ventilation, air conditioning and air heating installations to sound pressure levels acceptable by the standards.

1.2. The requirements of these Guidelines apply to acoustic calculations of airborne (aerodynamic) noise generated during the operation of the installations listed in clause 1.1.

Note. These Guidelines do not consider calculations of vibration isolation of fans and electric motors (isolation of shocks and sound vibrations transmitted to building structures), as well as calculations of sound insulation of enclosing structures of ventilation chambers.

1.3. The method for calculating airborne (aerodynamic) noise is based on determining the sound pressure levels of noise generated during the operation of the installations specified in clause 1.1 at permanent workplaces or in rooms (at design points), determining the need to reduce these noise levels and measures to reduce sound levels pressure to the values ​​allowed by the standards.

Notes: 1. Acoustic calculation should be included in the design of mechanically driven ventilation, air conditioning and air heating installations for buildings and structures for various purposes.

Acoustic calculation should be done only for rooms with normalized noise levels.

2. Air (aerodynamic) fan noise and noise generated by air flow in air ducts have broadband spectra.

3. In these Guidelines, noise should be understood to mean all kinds of sounds that interfere with the perception of useful sounds or break silence, as well as sounds that have a harmful or irritating effect on the human body.

1.4. When acoustically calculating a central ventilation, air conditioning and hot air heating installation, the shortest duct run should be considered. If the central unit serves several rooms, for which the normative noise requirements are different, then an additional calculation should be made for the duct branch serving the room with the lowest noise level.

Separate calculations should be made for autonomous heating and ventilation units, autonomous air conditioners, units of air or air curtains, local exhausts, units of air shower installations, which are closest to the calculated points or have the highest performance and sound power.

Separately, it is necessary to carry out an acoustic calculation of the branches of the air ducts that exit into the atmosphere (suction and exhaust of air by installations).

If there are throttling devices (diaphragms, throttle valves, dampers), air distribution and air intake devices (grilles, shades, anemostats, etc.) between the fan and the serviced room, sudden changes in the cross section of air ducts, turns and tees, acoustic calculation of these devices should be made and plant elements.

1.5. Acoustic calculation should be made for each of the eight octave bands of the auditory range (for which noise levels are normalized) with the geometric mean frequencies of the octave bands 63, 125, 250, 500, 1000, 2000, 4000 and 8000 Hz.

Notes: 1. For central air heating, ventilation and air conditioning systems in the presence of an extensive network of air ducts, it is allowed to calculate only for frequencies of 125 and 250 Hz.

2. All intermediate acoustic calculations are performed with an accuracy of 0.5 dB. The final result is rounded to the nearest whole number of decibels.

1.6. Required measures to reduce noise generated by ventilation, air conditioning and air heating installations, if necessary, should be determined for each source separately.

2. SOURCES OF NOISE IN INSTALLATIONS AND THEIR NOISE CHARACTERISTICS

2.1. Acoustic calculations to determine the sound pressure level of air (aerodynamic) noise should be made taking into account the noise generated by:

a) a fan

b) when the air flow moves in the elements of the installations (diaphragms, chokes, dampers, turns of air ducts, tees, grilles, shades, etc.).

In addition, the noise transmitted through the ventilation ducts from one room to another should be taken into account.

2.2. Noise characteristics (octave sound power levels) of noise sources (fans, heating units, room air conditioners, throttling, air distribution and air intake devices, etc.) should be taken from the passports for this equipment or from catalog data

In the absence of noise characteristics, they should be determined experimentally on the instructions of the customer or by calculation, guided by the data given in these Guidelines.

2.3. The total sound power level of the fan noise should be determined by the formula

L p =Z+251g#+l01gQ-K (1)

where 1^P is the total sound power level of vein noise

tilator in dB re 10“ 12 W;

L-noise criterion, depending on the type and design of the fan, in dB; should be taken according to the table. one;

I is the total pressure created by the fan, in kg / m 2;

Q - fan performance in m^/s;

5 - correction for the fan operation mode in dB.

Table 1

Notes: 1. The value of 6 when the deviation of the fan operation mode is not more than 20% of the maximum efficiency mode should be taken equal to 2 dB. In the fan operation mode with maximum efficiency 6=0.

2. To facilitate the calculations in fig. 1 shows a graph for determining the value of 251gtf+101gQ.

3. The value obtained by formula (1) characterizes the sound power radiated by an open inlet or outlet pipe of the fan in one direction into the free atmosphere or into the room in the presence of a smooth air supply to the inlet pipe.

4. When the air supply to the inlet pipe is not smooth or the throttle is installed in the inlet pipe to the values ​​specified in

tab. 1, should be added for axial fans 8 dB, for centrifugal fans 4 dB

2.4. The octave sound power levels of fan noise emitted by an open inlet or outlet of the fan L p a, into the free atmosphere or into the room, should be determined by the formula

(2)

where is the total sound power level of the fan in dB;

ALi is a correction that takes into account the distribution of the sound power of the fan in octave bands in dB, taken depending on the type of fan and the number of revolutions according to table. 2.

table 2

Amendments ALu taking into account the distribution of the sound power of the fan in octave bands, in dB

Notes: 1. Given in Table. 2 data without brackets are valid when the fan speed is in the range of 700-1400 rpm.

2. At a fan speed of 1410-2800 rpm, the entire spectrum should be shifted an octave down, and at a speed of 350-690 rpm, an octave up, taking the values ​​\u200b\u200bfor the extreme octaves indicated in brackets for frequencies of 32 and 16000 Hz.

3. When the fan speed is more than 2800 rpm, the entire spectrum should be shifted two octaves down.

2.5. Octave sound power levels of fan noise radiated into the ventilation network should be determined by the formula

Lp - L p ■- A L-± -|~ L i-2,

where AL 2 is the correction that takes into account the effect of connecting the fan to the duct network in dB, determined from the table. 3.

2.6. The total sound power level of the noise radiated by the fan through the walls of the casing (housing) into the ventilation chamber room should be determined by formula (1), provided that the value of the noise criterion L is taken from Table. 1 as its average value for the suction and discharge sides.

The octave levels of the sound power of the noise emitted by the fan into the room of the ventilation chamber should be determined by the formula (2) and Table. 2.

2.7. If several fans operate simultaneously in the ventilation chamber, then for each octave band it is necessary to determine the total level

sound power of the noise emitted by all fans.

The total noise sound power level L cyu during operation of n identical fans should be determined by the formula

£sum = Z.J + 10 Ign, (4)

where Li is the sound power level of the noise of one fan in dB-, n is the number of identical fans.

Table four.

2.8. Octave sound power levels of noise radiated into the room by autonomous air conditioners, heating and ventilation units, air shower units (without air duct networks) with axial fans should be determined by formula (2) and Table. 2 with a 3dB up-correction.

For autonomous units with centrifugal fans, the octave sound power levels of the noise emitted by the suction and discharge pipes of the fan should be determined by formula (2) and table. 2, and the total noise level - according to table. four.

Note. When air is taken from outside by installations, it is not necessary to take a higher correction.

2.9. The total sound power level of noise generated by throttling, air distribution and air intake devices (throttle valves.

Engineering and construction magazine, N 5, 2010
Category: Technology

Doctor of Technical Sciences, Professor I.I. Bogolepov

GOU St. Petersburg State Polytechnic University
and GOU St. Petersburg State Marine Technical University;
master A.A. Gladkikh,
GOU St. Petersburg State Polytechnic University

The ventilation and air conditioning system (VVKV) is the most important system for modern buildings and structures. However, in addition to the necessary quality air, the system transports noise into the premises. It comes from the fan and other sources, spreads through the duct and radiates into the ventilated room. Noise is incompatible with normal sleep, educational process, creative work, high-performance work, good rest, treatment, obtaining high-quality information. In the building codes and regulations of Russia, such a situation has developed. The method of acoustic calculation of the SVKV of buildings, used in the old SNiP II-12-77 "Protection from noise", is outdated and therefore was not included in the new SNiP 23-03-2003 "Protection from noise". So, the old method is outdated, and there is no new generally accepted one yet. The following is a simple approximate method for the acoustic calculation of TSWH in modern buildings, developed using the best manufacturing practices, in particular, on marine vessels.

The proposed acoustic calculation is based on the theory of long sound propagation lines in an acoustically narrow pipe and on the theory of sound in rooms with an almost diffuse sound field. It is carried out in order to assess sound pressure levels (hereinafter referred to as SPL) and the compliance of their values ​​​​with the current permissible noise standards. It provides for the determination of SPL from SVKV due to the operation of the fan (hereinafter referred to as the "machine") for the following typical groups of premises:

1) in the room where the machine is located;

2) in rooms through which air ducts pass in transit;

3) in the premises serviced by the system.

Initial data and requirements

Calculation, design and control of people protection from noise are proposed to be performed for the most important octave frequency bands for human perception, namely: 125 Hz, 500 Hz and 2000 Hz. An octave frequency band of 500 Hz is a geometric mean value in the range of noise-normalized octave frequency bands of 31.5 Hz - 8000 Hz. For constant noise, the calculation involves determining the SPL in octave bands from the sound power levels (SPL) in the system. The SPL and SPL values ​​are related by the general relationship = - 10, where SPL is relative to the threshold value of 2·10 N/m; - USM relative to the threshold value of 10 W; - area of ​​propagation of the front of sound waves, m.

SPL must be determined at the design points of noise-rated rooms using the formula = + , where is the SPL of the noise source. The value that takes into account the influence of the room on the noise in it is calculated by the formula:

where is the coefficient taking into account the influence of the near field; - spatial angle of emission of the noise source, rad.; - radiation directivity coefficient, taken according to experimental data (in the first approximation it is equal to one); - distance from the center of the noise emitter to the calculated point in m; = - acoustic constant of the room, m; - the average coefficient of sound absorption of the internal surfaces of the room; - total area of ​​these surfaces, m; - coefficient that takes into account the violation of the diffuse sound field in the room.

The indicated values, design points and norms of permissible noise are regulated for the premises of various buildings by SNiP 23-03-2003 "Protection from noise". If the calculated SPL values ​​exceed the permissible noise level in at least one of the three frequency bands indicated, then it is necessary to design measures and means to reduce noise.

The initial data for acoustic calculation and design of UHCS are:

- layout schemes used in the construction of the structure; dimensions of machines, air ducts, control valves, elbows, tees and air distributors;

- speed of air movement in the mains and branches - according to the terms of reference and aerodynamic calculation;

- drawings of the general arrangement of the premises serviced by the SVKV - according to the construction design of the structure;

- noise characteristics of machines, control valves and air distributors SVKV - according to the technical documentation for these products.

The noise characteristics of the machine are the following levels of SPL airborne noise in octave frequency bands in dB: - SPL of noise propagating from the machine into the suction duct; - USM noise propagating from the machine to the discharge duct; - USM noise emitted by the machine body into the surrounding space. All machine noise characteristics are currently determined based on acoustic measurements in accordance with relevant national or international standards and other regulations.

The noise characteristics of silencers, air ducts, adjustable fittings and air distributors are presented by the airborne noise SMU in octave frequency bands in dB:

- USM noise generated by the elements of the system when the air flow passes through them (noise generation); - USM of noise dissipated or absorbed in the elements of the system when the flow of sound energy passes through them (noise reduction).

Efficiency of noise generation and noise reduction by UHCS elements is determined on the basis of acoustic measurements. We emphasize that the values ​​of and must be specified in the relevant technical documentation.

At the same time, due attention is paid to the accuracy and reliability of the acoustic calculation, which are included in the error of the result by the values ​​and .

Calculation for the premises where the machine is installed

Let there be a fan in room 1 where the machine is installed, the sound power level of which, radiated into the suction, discharge pipeline and through the machine body, is the values ​​in dB , and . Let the fan on the side of the discharge pipeline have a silencer with a silencer efficiency in dB (). The workplace is located at a distance from the machine. The wall separating room 1 and room 2 is at a distance from the machine. Room sound absorption constant 1: = .

For room 1, the calculation provides for the solution of three problems.

1st task. Compliance with the norm of permissible noise.

If the suction and discharge pipes are removed from the machine room, then the SPL calculation in the room where it is located is made according to the following formulas.

Octave SPL at the design point of the room are determined in dB by the formula:

where - USM noise emitted by the machine body, taking into account accuracy and reliability using . The value indicated above is determined by the formula:

If the premises are placed n noise sources, SPL from each of which at the calculated point is equal to , then the total SPL from all of them is determined by the formula:

As a result of the acoustic calculation and design of the SVKV for room 1, where the machine is installed, it must be ensured that the permissible noise standards are met at the design points.

2nd task. Calculation of the SPL value in the discharge air duct from room 1 to room 2 (the room through which the air duct passes in transit), namely, the value in dB is made according to the formula

3rd task. Calculation of the SPL value radiated by the wall with the soundproofed area of ​​room 1 to room 2, namely the value in dB, is performed by the formula

Thus, the result of the calculation in room 1 is the fulfillment of the noise standards in this room and the receipt of the initial data for the calculation in room 2.

Calculation for rooms through which the duct passes in transit

For room 2 (for rooms through which the air duct passes), the calculation provides for the solution of the following five problems.

1st task. Calculation of the sound power radiated by the walls of the air duct into room 2, namely, the determination of the value in dB according to the formula:

In this formula: - see above the 2nd task for room 1;

\u003d 1.12 - equivalent diameter of the duct section with a cross-sectional area ;

- room length 2.

The sound insulation of the walls of a cylindrical duct in dB is calculated by the formula:

where is the dynamic modulus of elasticity of the duct wall material, N/m;

- internal diameter of the duct in m;

- duct wall thickness in m;


The sound insulation of the walls of rectangular ducts is calculated according to the following formula in DB:

where = is the mass of a unit surface of the duct wall (the product of the density of the material in kg/m and the wall thickness in m);

- geometric mean frequency of octave bands in Hz.

2nd task. Calculation of SPL at the design point of room 2, located at a distance from the first noise source (air duct) is performed according to the formula, dB:

3rd task. Calculation of SPL at the design point of room 2 from the second noise source (the SPL radiated by the wall of room 1 to room 2 - the value in dB) is performed according to the formula, dB:

4th task. Compliance with the norm of permissible noise.

The calculation is carried out according to the formula in dB:

As a result of the acoustic calculation and design of the SVKV for room 2, through which the air duct passes in transit, it must be ensured that the permissible noise standards are met at the design points. This is the first result.

5th task. Calculation of the SPL value in the discharge duct from room 2 to room 3 (the room serviced by the system), namely the value in dB according to the formula:

The value of losses due to the emission of noise sound power by the walls of air ducts on straight sections of air ducts of a unit length in dB/m is presented in Table 2. The second result of the calculation in room 2 is to obtain the initial data for the acoustic calculation of the ventilation system in room 3.

Calculation for rooms served by the system

In rooms 3 serviced by SVKV (for which the system is ultimately intended), the design points and norms of permissible noise are adopted in accordance with SNiP 23-03-2003 "Protection from noise" and the terms of reference.

For room 3, the calculation involves solving two problems.

1st task. The calculation of the sound power radiated by the air duct through the outlet air distribution opening into the room 3, namely the determination of the value in dB, is proposed to be performed as follows.

Private problem 1 for low speed system with air speed v<< 10 м/с и = 0 и трех типовых помещений (см. ниже пример акустического расчета) решается с помощью формулы в дБ:

Here



() - losses in the silencer in room 3;

() - losses in the tee in room 3 (see the formula below);

- loss due to reflection from the end of the duct (see table 1).

General task 1 consists of solving for many of the three typical rooms using the following formula in dB:



Here - SLM of noise propagating from the machine into the discharge duct in dB, taking into account the accuracy and reliability of the value (accepted according to the technical documentation for the machines);

- SLM of the noise generated by the air flow in all elements of the system in dB (accepted according to the technical documentation for these elements);

- USM of noise absorbed and dissipated during the passage of the flow of sound energy through all elements of the system in dB (accepted according to the technical documentation for these elements);

- the value that takes into account the reflection of sound energy from the end outlet of the air duct in dB, is taken from Table 1 (this value is zero if it already includes );

- a value equal to 5 dB for low-speed UACS (air speed in the mains is less than 15 m/s), equal to 10 dB for medium-speed UACS (air speed in the mains is less than 20 m/s) and equal to 15 dB for high-speed UACS (velocity in the mains is less than 25 m/s).

Table 1. Value in dB. Octave bands

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 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. 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 the general case, sound pressure levels in a room depend on the sound power of the source and the directivity factor of noise radiation, the number of noise sources, the location of the design point relative to the source and building envelopes, 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.

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

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.

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.

The acoustic calculation of the UHVAC is carried out in order to optimally select all the necessary means of noise reduction and determine 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.

Now, in the building codes and regulations 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 "Noise Protection", the method of acoustic calculation of the SVKV of buildings is outdated and therefore was not included in the new SNiP 23-03-2003 "Noise Protection" (instead of SNiP II-12-77), where it is still at all missing.

So the old method is deprecated and the new one is not. The time has come to create a modern method of 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. Let's consider three possible methods of acoustic calculation, as applied to UHCS.

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 a rectangular pipe, the side must be less than half the wavelength, and for a round pipe, the 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 side of the section 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. A typical diagram of a long line of a 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 R1 soundproof inlet, R2 soundproof active muffler, R3 soundproof tee, R4 soundproof jet silencer, R5 soundproof damper and R6 soundproof 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 greater than the above n = 6. Let us apply the theory of long lines to the above characteristic elements of the air ventilation system to calculate the values ​​of R i .

Inlet and outlet openings of the ventilation system with R 1 and R 6 . The junction of two narrow pipes with different cross-sectional areas S 1 and S 2 according to the theory of long lines is an analogue of 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 improve 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 r j is the distance from the jth 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 radiation angle of the source, Φ is the factor directivity of the source, κ is the coefficient of violation of the diffuseness of the sound field).

If m air diffusers are placed in the room of a modern building, the noise level from each of them at the calculated point is equal to 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 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 to reduce 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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2. Isakovich M.A. General acoustics // M .: Publishing house "Nauka", 1973.
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4. Khoroshev G.A., Petrov Yu.I., Egorov N.F. Fighting fan noise // M .: Energoizdat, 1981.
5. 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.
6. Bogolepov I.I. Industrial soundproofing. Foreword by acad. I.A. Glebov. Theory, research, design, manufacture, control // Leningrad, Shipbuilding, 1986.
7. Aviation acoustics. Part 2. Ed. A.G. Munin. - M.: "Engineering", 1986.
8. Izak G.D., Gomzikov E.A. Noise on ships and methods of its reduction // M.: "Transport", 1987.
9. Noise reduction in buildings and residential areas. Ed. G.L. Osipova and E.Ya. Yudin. - M.: Stroyizdat, 1987.
10. 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.
11. 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.
12. 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.
13. 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.
14. 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.
15. 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.
16. Bogolepov I.I. Building acoustics. Foreword by acad. Yu.S. Vasilyeva // St. Petersburg. Polytechnic University Press, 2006.
17. 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.
18. 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.
19. 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.
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23. Federal Law of May 1, 2007 No. 65-FZ “On Amendments to the Federal Law “On Technical Regulation”.

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

The need for ventilation

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

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

Type of ventilation system

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

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

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

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

General network calculation

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

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

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

Multiple calculation

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

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

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

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

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

Ventilation with a mechanical type of device

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

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

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

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

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

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

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

Exhaust ventilation

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

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

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

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

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

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

Acoustic calculation of the ventilation system

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

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

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

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

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

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

Aerodynamic calculation of the ventilation system

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

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

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

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

Programs for calculation

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

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

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

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

Sanitary standards

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

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