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HVAC stands for heating, ventilating, and air conditioning. Basically, a HVAC system will feature a cooling or heating system for the fluid, a circulator to help that fluid circulate into the building, and terminals in the spaces of interest.


Boilers produce hot water or steam using a heat source. While small individual boilers are either electric or gas burning, larger boilers burn gas, fuel, or coal.

The noise can come from the pump bringing the fuel or from the coal dropping on the chute. The burner is the main contributor; in many cases, it is supplemented by a fan to increase combustion.

The overall sound power level of a boiler is given in [4] for either a small or a large boiler as follows:

where M is the quantity of steam produced, in kilograms.

where P is the power output, in MW.

AHU and Fans

Fans are used to either deliver or extract air from a space. The simplest to be found is the axial fan, in which the airflow is perpendicular to the wheel. Unfortunately, while it is pretty simple to implement (we have all seen such fans in a wall or even in a window of a workshop or kitchen), it does not accept a large pressure drop. In order to cope with pressure drops, one uses a centrifugal fan in which the airflow is tangent to the wheel.

The sound power level of a fan per octave band is given by the formula [4]

where Q is the flow rate, in m3/s, p is the pressure increment, in Pa, and Cor is a frequency correction in the range 7 to 26.

More detailed models (i.e., regarding sound power levels per octave band, injected in the ducts or radiated in the fan’s environment, according to type of fan unit) are available in [5, 6].

AHU stands for an air handling unit. Such units are used to circulate air inside a building, which is eventually electrically heated or water cooled prior to its circulation. Manufacturers normally provide at least the A-weighted sound power level of the ducted equipment plus the A-weighted sound power level radiated by the unit in its environment under a free field over reflective plane conditions.

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