I. Central Air Conditioning Noise Source Analysis
Central air conditioning is a mechanical equipment used in a circulating water supply system to lower water temperature (usually 4℃-6℃, with industrial high-temperature central air conditioning, the water temperature can be raised to 10℃-15℃). Its working principle is that the cooling water in the bottom collection pool of the central air conditioning flows down by gravity, then it is pumped into the condenser to absorb the heat released during the condensation of the refrigerant. This hot water is then discharged from the condenser and sent to the top of the central air conditioning, where it is sprinkled into droplets and flows down through the packing. As the hot water falls, it comes into contact with cooler air currents, undergoing heat exchange. At this point, some of the water evaporates, while the majority cools and returns to the collection pool.
With the development of the economy, factories, restaurants, hotels, office buildings, and entertainment venues have sprung up like bamboo shoots after a spring rain. Particularly in the southern regions, where the hot weather lasts for a long time, central air conditioning is a must for temperature regulation. In some concentrated areas, it's not uncommon to see a building equipped with a dozen or even twenty central air conditioning units. In mixed commercial-residential zones, businesses are unable to install units on the rooftop or at the same level, so they are placed on the ground, where the strong noise and heat from the exhaust vents often disturb the peace of residents. Consequently, the noise issue of central air conditioning has become a hot topic of environmental complaints. Analysis and spectral testing have identified that central air conditioning noise originates from several aspects:
1 Fan Noise
It is the main noise source of central air conditioning, which is an aerodynamic noise, including turbulent noise and rotational noise. According to the theoretical analysis of aerodynamic noise sources, the sound intensity of the full-flow noise is related to the relative airflow.
The speed squared to the sixth power is proportional and also related to blade shape, possessing continuous frequency characteristics. The rotational noise is formed by pulsations generated during blade rotation, and it is related to the number of blades, gas flow, static pressure, etc. Its frequency...
The spectrum exhibits a narrowband low-mid frequency characteristic.
2 Motor Noise
Motor noise consists of electromagnetic and mechanical noise; both of these noise sources generally have a negligible impact on the surrounding environment.
3. Pump Noise:
The pump is installed near the central air conditioning unit to circulate the medium water, often resonating with pipes and emitting high-frequency tuned noise. If the noise intensity is significant, it requires joint treatment.
4. Vibration and Noise:
Air conditioning unit operation vibration and piping water flow impact vibration.

Section 2: General measures for noise control are:
Control noise sources, sever transmission routes, and protect victims. The noise from central air conditioning affects residents' daily lives, with a wide range of victims and high mobility. Measures to protect the victims are infeasible; therefore, only control over noise sources and the severing of transmission routes can be implemented. In response to the noise characteristics of central air conditioning, the following remedial measures are taken:
1. Replace standard motor blades with low-noise blades to fundamentally reduce noise levels at the source.
2. The exhaust port noise exhibits a continuous frequency spectrum characteristic; acoustic absorption treatment is considered. A waterproof acoustic body is used to create a silencing channel, achieving the purpose of noise reduction.
3. To prevent noise caused by mechanical resonance, the central air conditioning is rigidly connected with vibration-reduction treatment.
4. Increase rapid filtration media in the water collection dish to reduce dripping noise.
5. Surround the recirculating pump with a waterproof and sound-absorbing barrier to increase the soft pipe connection and cut off the noise transmission path.