Consulting Sound absorption and insulation measures in the air conditioning ventilation system

HOW TO APPLY SOUND ABSORPTION AND HEAT INSULATION INSIDE THE AIR CONDITIONING VENTILATION SYSTEM The scope of duct work includes all necessary ducts to meet the ventilation and air conditioning needs of the project. Wind mouths on standard accessories popular in Vietnam. Ensure noise cancellation and insulation requirements in the air conditioning ventilation system Method […]


The scope of duct work includes all necessary ducts to meet the ventilation and air conditioning needs of the project. Wind mouths on standard accessories popular in Vietnam. Ensure noise cancellation and insulation requirements in the air conditioning ventilation system

Method 1: Sound absorption and insulation inside corrugated iron air ducts with 2 layers: 

1- Rockwool cotton layer density 60kg/m3 thickness 25mm 

2-The inner layer is thick glass fabric (dustproof from rockwool cotton) the outermost is fabric and cotton fixing splints.

Method 2: Sound absorption and heat insulation inside the corrugated iron air duct with 3 layers: 

1 -Rockwool cotton layer density 40 to 60kg/m3

2-Inner layer is thin glass fabric (dustproof from rockwool cotton)

3-The innermost layer is corrugated iron, shot rive fixed fabric and cotton.


Nano flex specializes in the production of various types of insulation materials that meet the requirements of noise cancellation and heat insulation in air conditioning ventilation systems


To cancel noise in air conditioning duct systems, many different measures are used for each source of noise. In this section, Nanoflex would like to introduce noise protection measures commonly used in air conditioning systems:



Sound absorption in air conditioning duct systems – Nanoflex specializes in supplying and manufacturing the cheapest duction boxes nationwide

1.1. Noise cancellation for engines and devices
To reduce the noise level generated by the motors and equipment it is customary to use the following measures:

a. Choose devices (FCU, AHU, fan, air conditioning assembly) with a small noise level to install in the room. This is the first job that designers need to take care of. The noise level of most air conditioning units is given by manufacturers in catalogues. However, it is necessary to check and adjust before installation.

b. Install assemblies of machines and equipment in separate rooms isolated from the work area. This solution is usually applied to large machine clusters, such as ACCs, large capacity chiller clusters, often installed in private rooms, these rooms can be soundproofed or not depending on the specific project.

c. Regular maintenance of equipment: lubrication of moving parts, bearings, adjustment of drive belts of devices, dynamic balancing of rotating mechanisms, etc.

d. Local sound absorption wrapping of equipment: In case of force majeure, when a cluster or equipment with a large noise level must be installed in the room, in this case it is necessary to carry out local soundproofing of such devices. For example, AHUs, FCUs and large-capacity ventilation fans are installed just above the false ceiling of the room. In this case the noise capacity of the devices is quite large, in many cases exceeding the permissible level, to fix the local wrapping of such devices

1.2. Anti-noise generated by air flow aerodynamics

Air flow has great speed when moving on pipes, especially through auxiliary equipment of the wind tunnel such as regulating valves, branch segments, turning lines, extension or narrowing of the line, etc. often produces significant noise. To overcome the noise caused by the aerodynamics of the moving air flow, it is necessary to:

a. Choose the right speed of movement of air flow on the pipe. That speed is said in professional literature, depending on the features of the office and related to the noise level. Rooms that require low speed are bedrooms, recording studios, radio rooms, film studios, etc. In contrast, in factories, restaurants, supermarkets, you can choose a higher speed.

b. The design and installation of piping equipment (numbness, quail, stall, taper, etc.) must comply with technical standards. Such standards are strictly regulated in the documents on the DW/142 and SMACNA wind tunnel design standards. For branched sections of ducts, do not design suddenly cheap, but must wind according to prescribed standards, or use wind glider blades 

1.3. Prevent noise transmitted from external sources into the room

a. The source of noise travels with the flow of air into the room

One of the sources of noise for rooms is the transmission of sound from external noise sources, emitted from appliances, machines, fans and air conditioning assemblies according to the flow of air moving across the air channels into the room. To eliminate noise from these sources people use measures:

Install sound absorbers on suction lines and push lines. There are many different types of sound boxes, but the most common are rectangular, circular, and plate-type sound absorber boxes. 
Wrap insulation inside the pipe:One of the quite effective and commonly used measures today is insulation wrap inside the pipes. These layers of insulation are clamped tightly under layers of fabric and iron mesh, which has a very good negative suction effect. However, due to the difficulty of wrapping the insulation inside and the large cost, it is usually only a few meters close to the device (AHU, FCU and fan) including the suction and push side. The internally insulated sleeve segments are actually sound boxes.

Placing the equipment away from the building: Obviously, if you place the equipment right next to the works with a very short section of air ducts, the sound absorption is also very difficult and not as desired. In many cases it is imperative to stretch the wind pipe and place the equipment away from the construction site.

b. Noise source transmitted according to the construction structure

Sound transmission according to the construction structure is quite complex and relatively difficult to handle, these works belong to the designer of the construction structure of the building. Sound transmission according to the construction structure includes: Transmission by wall and or by floor.

As for the source of noise transmitted through the walls, most masonry walls meet sound insulation under normal conditions, for special rooms that require small noise levels such as recording studios, radio and film studios of radio and television stations it is necessary to carry out soundproofing inside these rooms.

For the source of noise transmitted by shocks transmitted by construction structures, it is common to transmit the shocks of machinery and equipment clusters to the floor when installed on high-rise floors. To eliminate such shocks, assemblies and equipment were installed on inertial platforms and damping springs (figure 4a, b).The inertial platform must have a mass suitable for the shock generated by the assembly, generally having as much mass as possible. It is also possible to use the method of completely separating the construction structure of the working room from rooms capable of making loud noise, avoiding impacts on walls and foundations.

c. Sources of noise caused by transmission of wind pipe materials and water pipes into the room

Fans and pumps of air conditioning equipment systems during work often generate vibrations. Those vibrations can produce sound and travel through water pipes and especially windpipes. 

To eliminate shocks transmitted from assemblies of machinery and equipment by pipeline, between assemblies of machines, pumps, fans with pipes, fabric hoses, specialized hoses or rubber hose segments are installed. In addition, when connecting to output devices such as blowing mouths and suction mouths, people also use hose segments.

d. Noise transmitted from the outside follows the openings into the room 

The source of external noise transmitted by the air environment according to the openings into the room is the most difficult to identify, prevent and spontaneous source of noise. For these sources of noise one takes the following measures:

For normal working rooms, the source of external noise is not frequent and constantly negative, special measures are not required, because air-conditioned rooms often have a minimum fixable tightness.
For special rooms requiring small noise levels or cases near frequent, continuous and high-intensity noise sources, it is necessary to seal the room by wrapping the soundproofing inside and using rubber cushions and foams to seal doors and windows.

1.4. Noise cancellation of airflow output of blowing mouths

When the speed of entering and exiting the suction mouths and large blowing mouths can create secondary sounds that affect certain constructions. 
To reduce the noise generated at the blowing and suction mouths it is necessary to:

Choose a low-noise mouth and suction mouth. Diffuser-type blowing mouths usually have a low noise level.
Reduce the wind speed in and out or increase the size of the wind feed mouths.



Methods for applying insulation in the air conditioning ventilation system

1. Positioning accessories

– Standard: As required by the investor
– Quick clamp: The round needle has a surface not less than 25 mm circle, the task of clamping tightly and quickly, surrounding the surface of the insulation.
– Protection: apply film tape to the outer surface of the insulation, cut off excess residues to avoid danger to people when using.

2. Stack the insulation layer

Perform a 300-foot-long eyelid stack when converting from internal insulation to outer insulation. Insulation near dew stagnant devices:Use external insulation only.

Metal cover: only done in places where the design drawings require

Location: Place the moisture barrier layer on the side where the temperature is warmer during refrigeration.

Use masking tape: Wipe the surface before applying, tape length> 100 mm


System Description

– Insulation Type:Elastic batts or soft covers.
– Surface coating: Aluminum film produced at the factory.


– General: Wrap the insulation around the outside of the duct in places where insulation is required. Minimize splices
– Joints: Cut perpendicularly and join head-to-head for the edges of the adjacent insulation plate.

– Moist sealing wedges: Seal moisture barriers with aluminum tape placed right in the center along the seams. Places pierced by pins seal moisture partitions with round pieces of aluminum or silver tape.
– Flaps and joints: Maintain the thickness of the insulation when passing through the flap, hardened tendon, or joint.

Fixed method

Non-polyolefin foam materials: Choose the following ways:
– Stick pins to the sides of the duct as follows:
. Horizontal air ducts < 380 mm wide: No nails are required. . . Horizontal air ducts > 380, < 760 mm: Glue a row of nails along the center and bottom of the duct with a maximum nail center distance of 380 mm. . . Horizontal air ducts > width 760 mm: Glue pins with a maximum nail center distance of 380 mm.

Vertical surface air duct < 610 mm wide: No nail paste required. . . Vertical surface air duct > 610 mm wide: Pinned with a maximum nail center distance of 380 mm.
– Method of using pins and ligaments:
. Horizontal air duct > 600 mm wide: Apply insulation on the bottom with a row of pins the maximum distance of 400 mm for the face of the duct

Vertical surface air duct > 600 mm wide: Glue pins with a maximum center distance of 380 mm for the side of the duct.
Polyolefin foam: use pins 50 mm from the edge and about 200 to 300 mm apart in all directions.

4. Installation of duct fittings
Wind mouthshot box

– Type with insulation: The internal insulation must be accompanied by a tole sheet and black paint. External insulation is the same as insulation for straight pipes.

– Install insulation: Turn upside down the rough edge surface of the insulation at least 75 mm and glue this side to the insulation before installation, using pins at a maximum distance of 250 mm with at least one row of pins on the side of the air duct. Glue the insulation around the neck of the tape stranglehold.

Air valves

– Inside: Leave a space between the insulation and the splitter or manual air valve fin.
– External: Air valve adjusted by moto or manually adjusted, use tole plate with insulation as the shooting part to insulate the air valve.

Visiting door

Insulate the visiting door and waiting areas to ensure that there is no surface dew.

5. Hose insulation


Perform insulation of the hose if the temperature inside the hose may cause external dew stagnation.

Construction methods

When the outer insulation of both connectors of the hose hose is:

The outer thin film surface layer is insulated in accordance with the requirements of the type of insulation of the outer surface edema layer and the outer metal coating.
– Metal coating on the outside or inside, depending on the insulation material prescribed, has an appropriate implementation.

6. Installation of the duct mouth


Keep the protective cover intact until installation.

Hanging method

General: On the floating ceiling, divide the back hole to minimize not cutting the ceiling frame, there must be a frame to cover the gaps in the wind mouth and around, adjust the air mouth surface to seal the gaps and unevenness with the surroundings.
– Appearance: Adjust the position of the wind mouth perpendicular to other structures

Positioning accessories

– Unseen capability: Use the installation accessory and select the positioning position so that it is not visible.
– Accessibility: choose an installation option so that it is easy to disassemble without damaging other parts of the system involved
– Padding: add padding to the underside of the wind mouth or stand if necessary.

Wind mouthshot box

General: Use the air box to take the air in according to the side of the air box, to easily install the hose
Price of the wind mouth capture box:
– For ceiling-mounted wind mouths: independent of the top.
Soft duct joining: Use a round neck or oval neck mounted on the mouthshot box.

Internal insulation:

– Insulated speaker: glass cotton, thickness 25 mm.

– Install the tole layer.

– Ensure that the noise level of the insulation soft duct is according to technical requirements.

Paint: Paint the inside of the wind mouth capture boxes to avoid seeing the inside of the wind mouth.

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Consulting Sound absorption and insulation measures in the air conditioning ventilation system - Nanoflex High Quality Insulation