Noise Control of Air Conditioning System in Radio and Television Technology Room

Radio and television technology room refers to the studio (hall), recording room, live studio, reproduction room and control room and other functional rooms, is the place for radio and television program production. A good technical room should have comfortable air-conditioning environment besides standard sound decoration. But air-conditioning system will inevitably produce air noise such as airflow noise, equipment noise and solid sound transmission caused by vibration, destroy sound insulation wall and affect architectural acoustics. In practical use, many studios are often affected by air-conditioning noise. Therefore, how to deal with the noise problem of air conditioning system is extremely important, which is the difficulty and key of the project.

Characteristics of air conditioning system in technical rooms and standards issued by the Ministry of China

1. Characteristics of Air Conditioning System in Technical Rooms

Technology room is different from general office, it has very high acoustic requirements. On the one hand, it can not be affected by the external environment, on the other hand, it can not affect the external environment, so it is usually a closed space, walls, ceiling to do sound insulation, sound absorption treatment, flotation on the ground, but also set up sound gates, sound doors. Sound-proof windows, so that the room in line with the requirements of the acoustic environment. Its air-conditioning system usually adopts all-air system. Compared with the general air-conditioning system, it has the following characteristics:

(1) Because of the different nature of the buildings, different heat dissipation and different working hours, reasonable zoning is required for energy conservation and management convenience.

(2) The studio (hall) with large heat dissipation is equipped with a large number of stage lights, the general capacity is 0.6-1.0kW/m, and most of them are heat sources, which have a large heat dissipation.

(3) In order to minimize the re-pinning noise of airflow, improve the muffler's silencing effect and reduce the duct resistance, it is necessary to select low wind speed. Low wind speed results in huge wind pipes, which makes it more difficult to coordinate with other installation types.

(4) High noise requirement is a big difference from general air-conditioning system. Common air-conditioning is usually based on subjective evaluation of human beings. In the case of large environmental noise, air-conditioning noise is not obvious. In the technical rooms with standard acoustics requirements, air-conditioning noise has become almost the only source of noise. Noise not only affects people's working mood and interferes with the monitoring work of programs, but also records them on tape at the same time with programs, which reduces their signal-to-noise ratio. Therefore, the Ministry of Radio and Television has a set of perfect and strict standards for air-conditioning noise.

1.2 Permissible Noise Standards of the State Ministry of Radio and Television

 The noise evaluation curves mainly include NR curve, NC curve and PCN curve. NR curve is an indoor noise evaluation curve recommended by ISO in 1959. It is a comprehensive index for evaluating noise interference to conversation, noise annoyance and hearing protection (Fig. 1). It is also a widely used evaluation curve in China. After a long period of practical experience in China, the Ministry of Radio, Film and Television promulgated in 1989 the Standard for Allowable Noise in Technical Housing of Radio and Television Center GYJ42-89 (Table 1).

Technical Measures for Controlling Noise of Air Conditioning in Technical Room

For technical rooms with standard acoustic requirements, noise interference of air conditioning systems must be isolated or reduced to a large extent.

1. The way to form noise interference in air conditioning system Analysis technology Room air conditioning system uses the whole air system, the air volume is large, the noise is high, mainly through the following forms, to form noise interference in technical room.

(1) Equipment noise: The noise generated by the rotation of the fan and motor is transmitted through the air duct to produce direct noise interference.

(2) Rebooming noise: Because of the large air volume, if the air velocity is too high, especially the air velocity of the tuyere, it will cause the interference of re-booming noise in the system.

(3) Solid sound transmission: due to the vibration of air duct caused by equipment and airflow, solid sound transmission interference is produced by contacting with floor and wall.

(4) Crosstalk: In an air conditioning system with multiple rooms in the same partition, air ducts virtually connect these rooms. The working sound of one room, transmitted through the air duct to another room, will become noise, which is crosstalk interference.

2 Technical measures to control the interference of air conditioning system noise to technical buildings

(1) When the system is properly partitioned in the air-conditioning design, it is necessary to fully consider the function and use time of the technical room, to carry out reasonable partitioning, to try to convert the rooms with the same function or similar into a unified system, and to make the TV studio with loud sound, Rooms requiring higher radio drama studios are classified as separate systems, objectively reducing the chance of crosstalk, and different noise requirements, using different muffling measures, can save investment. Guangdong Broadcasting Center's technical buildings are mainly concentrated on several floors. The air-conditioning design adopts the all-air system, and the reasonable division (a total of 7 zones) is carried out according to the function, floor, area and comprehensive consideration of the reasonable direction of the air duct and the installation of the equipment room to reduce the difficulty of noise reduction. This paper takes one of the areas (Figure 2) as a representative for noise accounting and measurement.

(2) Strict noise reduction design calculation according to the literature In the design calculation, the transmission and return air ducts must be subjected to strict noise reduction calculation. Table 2 is the result of calculating the noise of the air supply duct of the 1# technical room shown in Fig. 2 according to the method in the literature.

(3) Reasonable selection of wind speed to avoid the occurrence of noise

 When designing, if the wind speed is too high, the airflow will pass through the muffler, damper, reducer, tuyere and other components, and then the noise will be generated again, especially the wind speed of the tuyere should be controlled. In the construction and commissioning of some studios in the past, it was found that when the surface wind speed was >1.8m/s, the noise was generated from the diffuser, which could not reach the noise standard of the room, and the system's noise elimination measures were abandoned. In this regard, combined with the literature and some practical experience, the tuyere wind speed is controlled below 1.5m / s, and the recording studio is lower (1.2m / s or less).

 According to the measurement results (Table 3), the wind speed of the tuyere is between 0.8 and 1.3 m/s, and the wind speed of each tuyere is relatively uniform, meeting the design requirements. In addition, the traditional diffuser tuyere is changed to a grid tuyere, which increases the effective ventilation area and greatly reduces the chance of re-squeaking noise.

(4) The indoor air duct uses a muffler duct, and the branch pipe is provided with a muffler to eliminate the generation of crosstalk. Reasonable partitioning reduces the transmission of the working sound of the tweeter through the duct to another room (ie, crosstalk). At the same time, a 3LD muffler is arranged on the branch pipe, and the indoor air duct is made into a silencer duct lined with 50mm and 32kg/m fine glass wool, which effectively eliminates the generation of crosstalk. On the other hand, it has also increased the system of noise reduction design.

(5) The installation process using flexible contact prevents the solid sound transmission of the solid sound transmission duct from occurring mainly in the wall through the duct and through the hanger and the floor. The air duct and the wall, the air duct and the hanger can not be in rigid contact. The project is processed according to the methods in Figure 3 and Figure 4 respectively. In addition, the design should also consider the location of the machine room, the vibration damping foundation of the air conditioner and the sound absorption treatment of the engine room.

RESULTS AND ANALYSIS

In the later stage of construction, we tested the engineering effect of the technical room, mainly measuring the wind speed of the tuyere and the noise of the room when the air conditioning was opened. The measuring instruments used include Japanese KANOMAX24-6111 anemometer, Danish B&amp, K company 2231 precision modular sound level meter, 1625 filter bank and 2318 printer, etc. Tables 3 and 4 are shown.

Fig. 5 - 8 is a comparison of the engineering effects of several technical houses tested with the standards issued by the Ministry of Radio and Television. From Fig. 5 to Figure 8, it can be seen that the noise measurements are all below the NR15 curve, and the effect is very good. It proves that the technical measures adopted in this project to control the noise of air-conditioning system in technical rooms are very successful and can meet the standards issued by the Ministry. As for the measurement value, compared with the calculated value, the low and high frequencies are close to each other, and the intermediate frequencies are quite different. This should be the reason of the influence of the noise of the measuring environment, that is, the background noise. Architectural acoustics design also has relatively perfect standards, but as long as it can meet the requirements of sound insulation and absorption, and meet the requirements of use, it is not in favor of blind standards from the economic point of view. As can be seen from Table 4, 1 # and 4 # are control rooms, 2 # and 3 # are live studios. Acoustic requirements and measurement results are different. Moreover, the whole project has not yet been completed and is still in the construction stage. A lot of construction noise affects the results. From the calculation process, it can be seen that mufflers have good muffling effect in Mid-frequency band, but poor muffling effect in low-frequency band and short-frequency band, but the natural attenuation of pipeline and room attenuation of low-frequency noise are obvious. Thus, in order to eliminate the noise in high-frequency band, low-resistance mufflers 4LD and 3LD are used to make the calculation results in mid-frequency band. Negative values appeared.

conclusion

Radio and television technology room is the technical room required by standard acoustics, and the noise of air conditioning system has become the only noise source. Engineering practice has proved that the following technical measures can effectively control the impact of these noises.

(1) Reasonable partition of the system.

(2) Strict noise reduction design according to literature.

(3) Reasonably reduce the wind speed, especially the wind speed of the tuyere, to avoid the "re-Sheng noise".

(4) Indoor ducts use anechoic ducts, and branch ducts are equipped with mufflers to eliminate crosstalk.

(5) Use flexible contact installation process to prevent the emergence of "solid sound transmission".