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Cooling tower noise control and prevention

Author：Trlon Views: Time:2020-10-22

Noise Control Measures for Large Air Conditioning Cooling Towers

Large-scale air-conditioning cooling towers bring huge noises, causing air-conditioning cooling towers to become a new focus of disputes between owners and developers. How to control the noise of the cooling tower of the air conditioner to cause interference to the surrounding residents? Who can effectively provide noise control solutions for air conditioning cooling towers? Where is the cooling tower built so that it will not produce noise and disturb the people? It has become the most concerned issue for everyone.

Noise Control Measures for Air Conditioning Cooling Tower

1. Add a layer of sound insulation cotton to the existing cooling tower, which not only prevents noise generation, but also serves as a filter.
2, install a silencer on the top of the air outlet of the cooling tower to prevent noise from being transmitted to the outside.
3. Add a soundproof cover outside the cooling tower operating unit to control most of the noise inside the cooling tower.
Wait until the air-conditioning cooling tower produces noise, and then it will have an impact on the surrounding residents. It is a way to make up for it. We should put an end to the air-conditioning cooling tower noise before it occurs. This involves the location of the cooling tower. Hanks Soundproofing puts forward the following opinions on the location of air conditioning cooling towers for the reference of real estate developers.
1. In the building group, this will have a great impact on the owners and should not be adopted;
2. At the top of the building, the building load and vibration will increase on the top of the building, and it will be used when there is no alternative;
3. On the ground far away from the main building.
After many considerations, the third option is more practical and feasible. At the same time, it is recommended to take sound insulation measures while building the cooling tower to prevent noise from disturbing surrounding residents.

Noise Control of Air Conditioning Cooling Tower in Data Center Computer Room

There are mainly three types of cooling towers: natural ventilation, mechanical ventilation and jet ventilation. Most of them are countercurrent mechanical ventilation cooling towers. The above-mentioned coffee shop uses the standard countercurrent mechanical ventilation cooling tower. Countercurrent mechanical ventilation cooling tower includes fan, reducer, water distributor, tower body, filler and other parts. The cooling tower fan is placed on the top of the tower for exhaust, including motors and blades. The reducer reduces the high-speed rotation of the blades to low-speed rotation to increase the heat exchange time between cold air and hot water. The water distributor is a drilled alloy tube, which rotates with the blades to make the hot water fall evenly. The tower body is usually made of FRP, light in texture and corrosion resistant. The filler in the tower is a PVC inclined wave plate, which increases the contact surface and improves the water cooling efficiency.
There are many types of cooling towers. According to the noise level, they can be divided into low noise type (A sound level 62～7ZdB) and ultra-low noise type (8～10dB lower than low noise type).

(1) The content and content of noise control of cooling tower

1, the purpose of cooling tower noise control
(1) Prevent the noise of the cooling tower from interfering with the building (or group of buildings) of the unit.
(2) Control the noise of the cooling tower to reach the allowable noise range of the area where the building is located, that is, prevent noise interference to surrounding buildings.

2, cooling tower noise control

(1) Reasonably determine the location of the cooling tower.
(2) Design and select low-noise cooling towers.
(3) Take sound insulation and silencing measures.

(2) The main source of cooling tower noise

1, fan noise

It is the main noise source of mechanically ventilated cooling towers. The noise is aerodynamic noise, including turbulence noise and rotating noise. According to the theoretical analysis of aerodynamic noise sources, it can be seen that the sound intensity of turbulent noise is proportional to the sixth power of the relative velocity of the airflow, and is also related to the shape of the blade. Rotational noise is generated by the pulsation formed when the blades rotate. It is related to the number of blades, gas flow, static pressure, etc., and its frequency spectrum shows low-mid frequency characteristics.

2, water splashing noise (ie water falling noise)

It is caused by the impact of the water spray device of the cooling tower with the accumulated water in the lower tower chassis when the water is falling. Its noise level is related to the falling water height and the water flow per unit time. It is generally second only to the fan noise and has high frequency characteristics. The water falling noise of the cooling tower is usually the second component of the cooling tower noise to the fan. When the fan noise is reduced, the water splashing noise is dominant. Depending on the type and size of the cooling tower, sometimes the noise of this fan is even louder, generally depending on the tower height, water volume and the spacing of the packing in the tower.
In cross-flow cooling towers, the filler used has changed from drop-point type to thin-film type, so its water falling noise is relatively low, but the convection cooling tower water drops directly into the pool, so that the water droplets hit the water surface in the pool and make a sound .
The water falling noise of a forced ventilation cooling tower is related to the size of the cooling tower, which is also related to the amount of water.

3, reducer and motor noise

The noise of the reducer is mainly the noise generated when the gear is meshed. Generally, if the processing accuracy is high, the noise is not large. The noise of the reducer has little effect on the total noise of the cooling tower. Therefore, in addition to the need to reduce the noise near the cooling tower and reduce the total noise, these noises are negligible.
In addition, for the base of the reducer, it is best to use anti-vibration materials to isolate possible noise.
Motor noise is electromagnetic noise and mechanical noise. The impact of these two types of noise sources on the surrounding environment can generally be ignored. The noise of the fan motor is lower than the noise of the reducer, so it is not necessary to pay special attention. In the occasions that require high-power and low-noise motors, water-cooled low-noise motors can be used to solve the problem.

4, water pump noise

Industrial cooling towers are often equipped with circulating water pumps near the tower, and its noise is also very large compared with other sound sources. In addition, the water pump is generally driven by an electric motor or a steam turbine, which is also a strong source of noise. The water pump is placed near the cooling tower to circulate the cooling water, and it often resonates with the water pipe to produce high-frequency noise. If the noise intensity is high, it needs to be treated together.

5, noise from cooling tower accessories

This kind of noise has no impact on the environment in actual use. It only produces harsh turbulence when the water volume of the pipe is insufficient or the valve is not properly throttled when it is in operation. For example, the cooling tower of Anqing Fertilizer Plant is The high-pressure steam piping of the steam turbine leaks gas, which produces higher sound level noise. Generally, it can be solved by adjusting the operating conditions.

(3) Governance plan and technical measures

The general measures of noise control are: control the noise source, cut off the transmission route, and protect the victims. The noise of the cooling tower affects the health and daily life of operators and residents. The victims are widespread and mobile. Measures to protect the victims are not feasible. Only measures to control the noise source and cut off the transmission route can be taken. The principle of the sound insulation screen is to use sound wave diffraction to make sensitive buildings in the sound shadow area to achieve the purpose of reducing the sound level.
According to the noise characteristics of cooling towers, the following measures are often taken.
(1) Replace ordinary motor blades with low-noise blades to reduce the noise level from the source.
(2) The exhaust vent noise has continuous spectrum characteristics, so consider sound absorption treatment. Use waterproof sound-absorbing body to make noise reduction channel to achieve the purpose of noise reduction.
(3) Avoid mechanical resonance to generate noise, and hard-connect the cooling tower for vibration reduction.
(4) Add quick filter packing in the drip tray to reduce water splashing noise.
(5) Surround the tower body and the pump with a waterproof sound-absorbing barrier to cut off the noise transmission path.
When designing and manufacturing cooling towers, the recommendations are as follows.
(1) When the noise-sensitive area is higher than the cooling tower, the sound insulation effect of the sound barrier is limited; installing mufflers at the top wind W, outlet and bottom air inlet of the cooling tower will increase the pressure loss and reduce the cooling effect, and the muffler The sound-absorbing material used for long-term exposure to water vapor will seriously reduce the sound-absorbing performance; although the sound-insulation room has a significant noise reduction effect, the cost is relatively high. Therefore, in the process of noise control, it is necessary to adapt measures to local conditions, fully consider various complex situations, and select an appropriate control plan.
(2) In view of the fact that there is no supply of fan cooling towers on the market, and the noise level of such cooling towers is below 60dB, users have generally responded well after use. Therefore, it is recommended to promote the use of new environmentally friendly cooling towers.
(3) Reasonably determine the location of the cooling tower. In the specified building land, the location of the cooling tower should be as far away as possible from the buildings that require quietness (including the building of the unit and the surrounding buildings). Because the noise attenuates with the increase of the distance from the sound source, in free space, when the distance doubles, the noise level decreases by 6dB (when the sound source is a point source and the surrounding silent reflection conditions), it is actually due to the sound of the surrounding buildings. Reflection, and the cooling tower is not a point sound source, so when the distance is doubled, the attenuation is about 3-4dB.
It is generally easy to do in factory buildings. At the same time, turn the side with the strong sound source of the cooling tower toward the side that does not need to be quiet, and configure warehouses and commercial buildings between the cooling tower and the area in front of the factory that need to be quiet. It can effectively control the noise interference of the cooling tower.
In civil buildings, especially in large and medium-sized cities where construction land is greatly restricted, it is difficult, or even impossible, to keep the cooling tower away from the unit’s building or building complex. In high-rise buildings, such as hotels, apartments and office buildings, even if it is possible to stay far away from the cooling tower, the cooling requirements of the tower cannot be ensured. Therefore, the cooling tower is usually arranged on the roof of the building. In this case, only low-noise cooling towers and sound insulation measures can be used.
(4) Design and select low-noise cooling tower. The noise sources of cooling towers include fan noise, water falling noise, reducer noise, motor noise, valve noise and cooling pump noise, but the main ones are fan and water falling (water splashing) noise.
Reducing fan noise is an active measure to reduce the noise of cooling towers. For example, the use of low speed, large diameter, new leaf shape, broad blades, small leaf angles, belt transmission and other measures can effectively reduce the noise of the fan unit and reduce the amount of noise. Usually it can reach A sound level around 10dB.
In addition, a two-speed motor is used according to the temperature difference between day and night or the operating load. When the temperature is high during the day and the production is full, the fan of the cooling tower runs at full speed; and when the temperature is low at night, the capacity of the cooling tower can be reduced, so that the motor runs at 2/3 or 1/2 speed. In this way, the noise of the fan can be reduced correspondingly, which is suitable for the low allowable value of urban areas at night.
Although the location, floor space, sound source distribution, and functional areas of the large-scale cooling towers of each unit are not the same, as long as you have a good grasp of the noise control design principles, analyze the mechanism and characteristics of the sound source based on the specific situation, and select the corresponding The treatment measures can effectively solve the noise pollution problems of various large cooling towers.

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