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A Review of Thermal Acoustical and Special Project Requirements Data in Designing a Duct System
Abstract
The primary foci in designing a duct system is:
1) Delivery of the correct amount of air; 2) Delivery
of air at an acceptable temperature with minimum
temperature drop; 3) Delivery of air quietly; and,
4) A system which is applicable to the project conditions. The Sheet Metal and Air Conditioning Association (SMACNA) and the Thermal Insulation Manufacturers Association (TIMA), have done considerable
testing on air loss and temperature drop on operating
HVAC systems.
It is important to note that these tests show
that air leakage through unsealed joints is the most
significant factor in heat loss. No amount of insulation can make up for a 24 percent air leakage rate
in an unsealed, rectangular sheet metal system.
Acoustical data is not as readily available. ASHRAE
is currently testing acoustical companies; however.
this information is not yet available. Based on
testing by Owens/Corning Fiberglas, duct attenuation
in dB's per lineal foot at 500 HZ of various insulating materials can range from 2.9 dB's t o 3.7 dB's.
The last area to consider in designing a duct
system is project conditions. This area is not as
technically oriented as the other three; however.
it is crucial in designing a duct operable system.
Items to consider are susceptibility to abuse, concealed
or exposed duct, how critical the acoustics
are, duct clean out requirements, climate conditions.
residential versus commercial construction, and new
versus retrofit construction. Without revealing the
properties of each system, a failure or a less than
acceptable environment for occupants could occur.
Citation
Lebens, A. F. (1986). A Review of Thermal Acoustical and Special Project Requirements Data in Designing a Duct System. Energy Systems Laboratory (http://esl.tamu.edu); Texas A&M University (http://www.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /6868.