Air Conditioner Noise

Noise is unwanted sound and needs to be considered when designing HVAC equipment. Air conditioner noise is unavoidable but it can be minimized with the use of insulator, rubber and other noise absorber materials. Good equipment design plays a big factor in the air conditioner noise emitted by the unit.

In mini split system, the typical sources of noise is the condenser which is located outside the house and the evaporator which is inside the house. The typical air-cooled condenser consists of the compressor, fan, coil and expansion valve.

The compressor emits the highest sound pressure and the sound pressure increases over time due to the wearing off of the vibration pads that are used to mount the compressor to the metal casing. Other factors include the wearing off of the components in the compressor such as the motor, valve and other mechanical component.

There are not much you can do to a hermetic compressor as you will not be able to access the internal mechanical parts. If the noise comes from the mounting problem, this can be solved else you will need to replace the compressor for good.

Sometimes, the noise can come from the leaves and other material that block the fan blades from rotating properly. Check also the bearings of the fan motor which can cause imbalance to the fan.

The indoor unit or evaporator consists of electronic control, cooling coil, air filters and blower. The noise usually comes from the fan. Over time, dirt and other materials may block the movement of the fan blades and the air. 

Hence it is always a good practise to clean the air filters regularly. Internal parts that are not easily accessible should be cleaned by qualified technicians. Check also the bearings of the fan motor.

Sound Measurement

Sound waves are generated due to a changing of air pressure and travels in all directions. The strength of the sound decrease with the distance from the source. The measurement of the sound pressure is usually taken from about 3 feet from the source. For most people, the sound frequencies from 1kHz to 4kHz are the easiest to hear.

The typical sound pressure is as shown in the table below.

Typical Sound Pressure 

Sound Source Sound Pressure
in Decibels or dB
Jet Engine
Subway Station Platform
Computer Room With Printing
Normal Speech
Window Air Conditioner
Quiet Residential Area
Hearing Threshold

The human ear hears the same loudness for sound pressure even though with different decibels for different frequencies. For example, the loudness at 93dB(50 Hz) is the same as 87dB(5 kHz).

The measurement unit usually used is dBA instead of dB. The dBA unit means that the sound pressure is measured using a standard "A" filter that has been placed in the microphone. This filter decreases the amplitude of the low frequencies but letting the higher frequencies pass through. Hence, the sound pressure using dBA scale for 93dB(50 Hz) is the same as 87dB(5 kHz) which is 87dBA.

Example of Wall Mounted Sound Level Specifications

When purchasing any air conditioner unit, make sure that you check the air conditioner noise level that is usually printed on the product specifications of the unit. Both the indoor and outdoor units will have this specifications. If not, you can always request from the technical personnel to provide you with the values.

An example of the noise level specifications of R410A Wall Mounted Inverter Single Split Systems from Mitsubishi Electric is as shown on the tables below. Take note that the higher the cooling capacity, the higher the noise level.

Model Cooling Capacity (BTU) Noise Level(dBA)
Indoor MSY-GE10VA 8,530 21-36
Outdoor MUY-GE10VA 3,752-11,942 46
Indoor MSY-GE24VA 22,519 37-45
Outdoor MUY-GE24VA 8,189-29,684 55

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