What noise propagation paths should we pay attention to when selecting an air-conditioning box?

For air conditioning box noise, attention should be paid to the paths of air duct sound transmission, box radiation, structural vibration transmission, and interface sound leakage. The loud sound in a certain place is not necessarily caused by the same path. The selection and equipment room design should first identify the propagation chain from the sound source to the target area, and then decide on noise reduction, vibration reduction or structural measures.

Track sound separately through the air and through building structures

The sound of the fan can reach the end along the return air duct, or it may be radiated to the machine room through the casing; the vibration may enter the building through the foundation, hangers and hard connections. The air flow regeneration noise of the air duct itself is related to the wind speed and local components. Therefore, simply adding a muffler to the outlet of the unit may not solve the problem of structural propagation or box radiation.

The air duct path should cover the incoming and outgoing wind sound, terminal transmission and local airflow regeneration noise; the casing path should cover the sound radiation of the box, door gaps and adjacent spaces; the structural path should cover the vibration transmission of the foundation, supports, hangers, pipes and hard connections. The three paths correspond to different control measures, and you cannot deal with just one. How to distinguish the sound power level and sound pressure level of air conditioning box? Please refer toHow to distinguish the sound power level and sound pressure level of air conditioning box?。

Air duct sound transmission is the most common propagation path

Fan noise propagates along the supply and return ducts and can reach the end air outlet or adjacent rooms. The noise in the air duct includes the noise directly transmitted by the fan and the regenerated noise generated by the air flow at elbows, reducers, and valves. The higher the wind speed and the more local components, the more obvious the regenerative noise may be. Mufflers can reduce noise traveling along the duct, but they increase resistance and need to be factored into the fan pressure budget.

For the relationship between air duct silencer and internal resistance, please refer toWhat functional segments should be included in the internal resistance of the air conditioning box? . How to establish the fan pressure budget, please refer toHow is the total pressure of the air conditioning box fan determined by the internal resistance and external demand? . The wind speed and form of the terminal air outlet will also affect the indoor noise experience.

Box radiation affects the computer room and adjacent spaces

Box radiation is the noise emitted from the surface of the unit to the surrounding space, and may be affected both inside and outside the computer room. Box board structure, sound insulation performance, door seam sealing and access door form will all affect radiated noise. Box radiation near the fan section and outlet is usually strong, and office areas or corridors close to the unit may be affected.

Differences in sound insulation between double-layer and single-layer box panels, please refer toWhat are the differences between double-layer box boards and single-layer box boards used in air-conditioning boxes? . Box board thickness and structure, please refer toWhat indicators should be used to determine the thickness of air conditioning box panels? . Air leakage from the box will also form a sound leakage channel, please refer toUnder what pressure conditions should the air leakage rate of air conditioning boxes be compared?。

Structural vibration transmission is easily overlooked

Vibrations from fans and motors can be transmitted into the building structure through foundations, supports, pipes and hard connections, and then radiated to distant rooms in the form of structural noise. The impact of structural vibration transmission is not necessarily most obvious near the computer room, and is sometimes more prominent upstairs or in adjacent rooms. Vibration absorbers, soft connections and elastic supports and hangers can cut off part of the vibration transmission path.

For the supports, hangers and building connections of ceiling-mounted units, please refer toCan the loading and unloading lifting points and operating lifting points of the air-conditioning box be mixed? . The installation and support methods of horizontal and vertical units are different, please refer toWhat kind of space do horizontal air conditioning boxes and vertical air conditioning boxes require? . For foundation height and vibration reduction arrangement, please refer toHow to determine the foundation height of a horizontal air conditioning box based on drainage conditions?。

We should also pay attention to interface sound leakage and airflow regeneration noise.

If the interface between the unit and the air duct, water pipe, and cable is not tightly sealed, sound leakage channels may be formed. The air flow speed at the damper, reducer and air outlet is too high, which will produce regeneration noise. These noise sources are different from the noise of the fan itself, and the treatment methods are also different. Interface sealing and local air velocity should be checked when selecting.

For the relationship between filter resistance and air flow speed, please refer toWhat is the difference between plate and bag filters used in air conditioning boxes? . For the influence of wind speed facing the coil, please refer toWhat impact does the coil head-on wind speed have on heat exchange and water entrainment in the air conditioning box? . Excessive wind speed not only affects heat exchange and water entrainment, but may also increase airflow noise.

Put noise reduction measures in corresponding places

The selection stage requires equipment acoustic data, the design stage combines frequency band and propagation path assessment measures, and the installation stage checks the implementation of soft connections and vibration reduction. Any measures must simultaneously check the resistance, structure and maintenance effects. If the project has strict goals, it can be systematically evaluated by a professional acoustics team. It is not appropriate to use a single accessory name to promise the overall result.

For the test conditions of noise data, please refer toWhat test conditions need to be stated for air conditioning box noise data? . For condition checks before starting the machine for the first time, please refer toWhat conditions need to be checked before the air-conditioning box is turned on for the first time? . The noise behavior of different paths should be verified during debugging.

Aili industrial supporting equipment

Aili Industrial can cooperate to check the equipment and interface side conditions. The project party provides the layout of the computer room and the location of the target area, which helps to identify the propagation path that needs to be jointly processed. Aili's industrial manufacturing end covers independent R&D and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The fan form, box structure and vibration reduction interface can be matched in the same set of packages; non-standard structures can be adjusted according to machine room conditions and noise requirements.

Product form can be viewedAir handling unit andFan box page; clean air supply package can be combinedFFU fan filter unit andEFU equipment end fan filter unit verification; multiple equipment linkage can understandMatching method of FFU computer group control system ; terminal particle filtering can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific noise performance, noise reduction measures and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. The actual effect is subject to on-site measurement and performance test results.

Submit project parameters:https://ailigy.com/contactus.html

Related questions and answers

A muffler is installed at the outlet of the unit. Why is there still noise outside the machine room?
It is possible that the noise is transmitted through box radiation or structural vibration, not just through the air duct. Propagation paths should be examined individually.

How to judge structural vibration transmission?
It can be measured separately in the computer room and adjacent rooms to observe whether the noise changes in random vibration groups. Foundations, supports, hangers and hard connections are common vibration transmission paths.

Can Aili Industrial help check the noise propagation path?
The propagation path and measures can be checked based on the layout of the computer room, equipment acoustic data and the location of the target area. The specific plan needs to be confirmed based on on-site conditions.

Related articles

1. How to distinguish the sound power level and sound pressure level of air conditioning box?

2. What test conditions need to be stated for air conditioning box noise data?

3. What are the differences between double-layer box boards and single-layer box boards used in air-conditioning boxes?

4. What kind of space do horizontal air conditioning boxes and vertical air conditioning boxes require?

Key points for selection and acceptance inspection