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 noise generated by bends and tees of air ducts, areas of a sharp change in 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-thermal 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 unit element propagates through the air ducts and is radiated into the room through the air distribution or air inlet 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 r 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 cover 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 air (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, an 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 - 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 emitted 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 4.

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. 4.

Note. When air is taken in by installations outside, 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.

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 general, the sound pressure levels in a room depend on the sound power of the source and the directivity factor of the noise emission, the number of noise sources, the location of the calculated 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 casing or an open branch 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.

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 rail 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 combination 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 performed 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 to estimate the noise level generated by a noise source at a given design point with a set quality of 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 (window openings, 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.

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 noise levels permissible 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 absent.

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 analog 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 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 r j is the distance from the j-th air distributor to the design point of the room, Q is the sound absorption constant of the room, and the values ​​χ, Φ, Ω, κ are empirical coefficients (χ is the coefficient of influence of the near field, Ω is the spatial angle of the source radiation, 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 elements of SVKV 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 σ Li and σ Ri The third method, looking 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 for 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 of 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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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.
20. 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.
21. 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.
22. 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.
23. Federal Law of May 1, 2007 No. 65-FZ “On Amendments to the Federal Law “On Technical Regulation”.

Ventilation calculation

Depending on the method of air movement, ventilation can be natural and forced.

The parameters of the air entering the intake openings and openings of local exhausts of technological and other devices located in the working area should be taken in accordance with GOST 12.1.005-76. With a room size of 3 by 5 meters and a height of 3 meters, its volume is 45 cubic meters. Therefore, ventilation should provide an air flow rate of 90 cubic meters per hour. In the summer, it is necessary to provide for the installation of an air conditioner in order to avoid exceeding the temperature in the room for the stable operation of the equipment. It is necessary to pay due attention to the amount of dust in the air, as this directly affects the reliability and service life of the computer.

The power (more precisely, the cooling power) of the air conditioner is its main characteristic, it depends on what volume of the room it is designed for. For approximate calculations, 1 kW per 10 m 2 is taken with a ceiling height of 2.8 - 3 m (in accordance with SNiP 2.04.05-86 "Heating, ventilation and air conditioning").

To calculate the heat inflows of this room, a simplified method was used:

where: Q - Heat inflows

S - Room area

h - Room height

q - Coefficient equal to 30-40 W / m 3 (in this case 35 W / m 3)

For a room of 15 m 2 and a height of 3 m, the heat inflows will be:

Q=15 3 35=1575 W

In addition, heat dissipation from office equipment and people should be taken into account, it is considered (in accordance with SNiP 2.04.05-86 "Heating, ventilation and air conditioning") that in a calm state a person emits 0.1 kW of heat, a computer or a copier 0.3 kW, By adding these values ​​to the total heat inputs, the required cooling capacity can be obtained.

Q add \u003d (H S opera) + (С S comp) + (P S print) (4.9)

where: Q add - The sum of additional heat gains

C - Computer heat dissipation

H - Heat dissipation of the operator

D - Printer Heat Dissipation

S comp - Number of workstations

S print - Number of printers

S operas - Number of operators

Additional heat inflows of the room will be:

Q add1 \u003d (0.1 2) + (0.3 2) + (0.3 1) \u003d 1.1 (kW)

The total sum of heat gains is equal to:

Q total1 \u003d 1575 + 1100 \u003d 2675 (W)

In accordance with these calculations, it is necessary to choose the appropriate power and number of air conditioners.

For the room for which the calculation is carried out, air conditioners with a rated power of 3.0 kW should be used.

Noise calculation

One of the unfavorable factors of the production environment in the information and computing center is the high level of noise generated by printing devices, air conditioning equipment, fans of cooling systems in the computers themselves.

To address questions about the need and feasibility of noise reduction, it is necessary to know the noise levels at the operator's workplace.

The noise level arising from several incoherent sources operating simultaneously is calculated based on the principle of energy summation of radiation from individual sources:

L = 10 lg (Li n), (4.10)

where Li is the sound pressure level of the i-th noise source;

n is the number of noise sources.

The obtained calculation results are compared with the permissible value of the noise level for a given workplace. If the calculation results are above the permissible noise level, then special noise reduction measures are necessary. These include: lining the walls and ceiling of the hall with sound-absorbing materials, reducing noise at the source, proper equipment layout and rational organization of the operator's workplace.

The sound pressure levels of noise sources acting on the operator at his workplace are presented in Table. 4.6.

Table 4.6 - Sound pressure levels of various sources

Typically, the operator's workplace is equipped with the following equipment: hard drive in the system unit, fan(s) of PC cooling systems, monitor, keyboard, printer and scanner.

Substituting the values ​​of the sound pressure level for each type of equipment into formula (4.4), we get:

L=10 lg(104+104.5+101.7+101+104.5+104.2)=49.5 dB

The obtained value does not exceed the permissible noise level for the operator's workplace, equal to 65 dB (GOST 12.1.003-83). And if you consider that it is unlikely that such peripheral devices as a scanner and a printer will be used simultaneously, then this figure will be even lower. In addition, when the printer is working, the direct presence of the operator is not necessary, because. The printer is equipped with an automatic sheet feeder.