Basic Documentation

Commentary on HVAC System Sound
Laboratory Room Ambient Sound
Aside from the sound caused by the supply system serving a laboratory room, the major
source of a chemical laboratory’s HVAC ambient sound is often due to the exhaust side of
the ventilation system particularly chemical fume hood exhaust. As a result, a laboratory
room sound analysis should also address the exhaust side of the ventilation system. The
principles that apply to HVAC supply side produced sound (airflow’s through duct fittings,
terminal units, etc.) also apply to the exhaust side and are calculated in the same manner.
Figure 19 shows a portion of a chemical laboratory room with potential HVAC sound sources
identified. Note that because of the probable high airflow rates, the radiated sound potential
of the SUPPLY VAV TERMINAL and the EXHAUST TERMINALS should be part of the
room’s sound analysis.
Fume Hood Sound
Since a fume hood will typically exhaust at least 100 cfm for each square foot of sash
opening, it follows that the large exhaust airflow’s that leave by means of the fume hood will
be a very significant potential source of sound in a laboratory.
Figure 19. Chemical Laboratory - Sources of Ventilation System Sound.
To make a proper system analysis, NC factors that apply to a particular fume hood operating
at specific exhaust airflow’s would need to be provided by the manufacturer. However, since
fume hood manufacturers do not normally test their product for sound, a precise means of
analyzing the resulting sound at varying sash openings does not (as of this time) exist.
It is recommended that particular attention be given to the sound level ratings of VAV fume
hood exhaust terminals, especially the radiated component, since, in many cases, these
components are located in the laboratory room directly atop the fume hood.
Siemens Building Technologies, Inc. 89