Basic Documentation

Chapter 1–Introduction
HVAC Sound Transmission
Ventilation system ductwork conducts or transmits sound in the same way that any conduit
can convey sound. We’re all familiar with how effectively a hose or pipe can conduct the
sound waves of the human voice. In the same way, ductwork conducts fan noise, and other
component sounds to the areas served. If the sound level is excessive or the sound pattern is
annoying, it can cause dissatisfaction with an HVAC system that otherwise does an excellent
job of maintaining comfort and providing the proper level of ventilation.
Background Sound
It is important to understand that the typical goal of a properly designed ventilation system is
not to obtain the least possible amount of sound, but to achieve a specific sound level and
profile. In most applications, a specific background sound level and sound profile are
desirable since it helps cover or mask other objectionable sounds. In the workplace, a good
ventilation system provides just enough background sound to prevent other sounds
(telephone conversations, keypad clicking, copy machines, etc.) from being excessively
annoying. This desirable background sound level and profile is sometimes termed white
noise and is usually very noticeable when not present. (Recall how much louder common
office sounds seem to be if the ventilation system is shut down and the white noise is not
present.) However, there is a sound level threshold that is dependent upon the room and its
activity, and when exceeded, results in excessive and objectionable sound.
Laboratory Applicability
Of the many HVAC applications where ambient sound level is an important design
component, laboratory applications are a particular challenge to the HVAC designer, due to
the necessity for providing high room ventilation rates to ensure the health and safety of the
occupants.
Computer Program Sound Analysis
Computer programs that assist the HVAC designer in producing optimum duct design layouts
often include a sound analysis capability that saves having to manually perform sound
analysis calculations. As with all such design aids, it is important that the user be
knowledgeable about the fundamentals of the subject in order to properly use the program. In
addition, having this background knowledge enables the user to recognize whether a specific
program incorporates an acceptable analytical approach.
2 Siemens Building Technologies, Inc.