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℃, while high-temperature central air conditioning in industry can lower the water temperature to 10-15℃). Its working principle is as follows: the cooling water in the bottom collection pool of the central air conditioning flows down by gravity, and the pump sends it to the condenser, absorbing the heat released when the refrigerant condenses. This hot water is then discharged from the condenser and sent to the top of the central air conditioning, where it sprinkles down as droplets 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 economic development, factories, restaurants, hotels, office buildings, and entertainment venues have sprouted like bamboo after a spring rain. Especially in the southern regions with long hot seasons, central air conditioning is a must for temperature regulation. In some concentrated areas, it's not uncommon to find a building equipped with a dozen or even twenty central air conditioning units. In mixed commercial-residential zones, companies cannot install units on rooftops or at their own level, so they are placed on the ground. The strong noise and heat from the exhaust outlets often disturb residents, making the central air conditioning noise a hot topic for environmental complaints. Analysis and spectral testing have identified several sources of central air conditioning noise:
Fan noise
It is the primary source of noise in central air conditioning, with the noise being aerodynamic in nature, including turbulent and rotational noise. Theoretical analysis of aerodynamic noise sources indicates that the sound intensity of turbulent noise is proportional to the sixth power of the relative airspeed and is also related to the blade shape, exhibiting continuous spectral characteristics. Rotational noise is generated by pulsations formed during blade rotation and is related to the number of blades, gas flow rate, static pressure, etc., with its spectrum showing narrowband low to medium frequency characteristics.
2. Motor Noise
Motor noise is typically electromagnetic and mechanical, and both 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 to produce high-frequency modulated noise. If the noise intensity is significant, it requires joint treatment.
4. Vibration Noise:
Air conditioning unit operation vibration and piping water flow impact vibration.
Section II: General Measures for Noise Control:
Control noise sources, interrupt transmission routes, and protect the 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 interruption 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; consider sound absorption treatment. Use waterproof sound-absorbing materials to create a silencing channel, achieving the purpose of noise reduction.
3. To prevent noise caused by mechanical resonance, the central air conditioning is hard-wired with vibration reduction treatment.
4. Add rapid filtration media to the water collection tray to reduce dripping noise.
5. Surround the circulating water pump with a waterproof and sound-absorbing barrier to increase the soft pipe connection and cut off the noise transmission path.
