Central air conditioning noise control

   1、 Analysis of Noise Sources in Central Air Conditioning:

Central air conditioning is a mechanical equipment used in a circulating water supply system to reduce water temperature (usually 4 ℃ -6 ℃, and in industrial high-temperature central air conditioning, the water temperature can be reduced to 10~C-15 ℃). Its working principle is that the cooling water in the bottom collection tank of the central air conditioning system flows down by gravity, and the water pump sends it to the condenser to absorb the heat released by the refrigerant during condensation. This hot water is discharged from the condenser and sent to the top of the central air conditioning system, where it is sprinkled into water droplets and flows down through the packing material. When hot water falls, it comes into contact with a cooler airflow for heat exchange. At this time, some of the water evaporates, and most of it is cooled and flows back to the collection tank.
With the development of the economy, factories, restaurants, hotels, office buildings, and dance halls have sprung up like mushrooms after rain. Especially in the south where the weather is hot for a long time, central air conditioning must be installed to regulate the air temperature. In some concentrated areas, there is a phenomenon where a building has more than ten or twenty central air conditioners. In some mixed use commercial and residential areas, enterprises cannot be placed on rooftops or in their own floor space, and can only be placed on the ground. The strong noise and heat from the air vents often disturb residents' peace. So the noise problem of central air conditioning has become a hot topic of environmental complaints. After analysis and spectrum testing, the noise of central air conditioning is generated in the following aspects:

1. Fan noise

It is the main source of noise for central air conditioning, which is aerodynamic noise, including turbulent noise and rotational noise. According to the theoretical analysis of aerodynamic noise sources, 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 blades, exhibiting continuous spectral characteristics. Rotating noise is generated by the pulsation of blades during rotation, which is related to the number of blades, gas flow rate, static pressure, etc. Its frequency spectrum exhibits narrowband low to medium frequency characteristics.

2. Motor noise

Motor noise is composed of electromagnetic noise and mechanical noise, and the impact of these two types of noise sources on the surrounding environment can generally be ignored.

3. Pump noise:
The water pump is installed near the central air conditioning unit for circulating medium water, and often resonates with the water pipe to produce high-frequency modulated noise. If the noise intensity is high, it needs to be treated together.

4. Vibration noise:

Vibration during the operation of the air conditioning unit and impact vibration from water flow in the water pipeline.

2、 The general measures for noise control are:

Control noise sources, cut off transmission routes, and protect victims. The noise from central air conditioning affects the daily lives of residents, with a wide range of victims and high mobility. Measures to protect victims are not feasible, and only measures to control noise sources and cut off transmission routes can be taken. The following measures are taken to address the noise characteristics of central air conditioning:

1. Replace the ordinary motor blades with low-noise blades to fundamentally reduce the noise level from the source.

2. The noise from the exhaust outlet has a continuous frequency spectrum characteristic, and sound absorption treatment should be considered. Using waterproof sound-absorbing materials to create sound-absorbing channels, achieving the goal of noise reduction.

3. Avoid mechanical resonance and noise, and perform vibration reduction treatment on the hard connection of central air conditioning.

4. Add a quick filter filler to the water receiving tray to reduce water spray noise.

5. Use waterproof and sound-absorbing barriers to surround the circulating water pump, and add flexible pipe connections to cut off the path of noise transmission.
 

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