ASHRAE Journal - January 2021 - 53

COLUMN ENGINEER'S NOTEBOOK

" dB " is not a " dBA. "
Only later in a design are duct noise abatement strategies considered. These are based on sources (such as a
fan, flow rate, connection to a radiating building member) and for HVAC housing, case or duct radiating noise
(Table 2). This may include regenerated noise from tight
bends and downstream VAV devices that add more noise
later in the path. While an isolated fan inside an AHU
offers reduced noise, air turbulence still generates case
radiated noise that occurs after the internal fan isolation. So internally isolated fans do not always address
noise. This leads to adding isolation for case radiated
noise when the AHU is hard coupled to a deck. After the
above items are addressed, silencers can be considered.
But this also means a good design may not need add-on
silencers.
Next, the room reflection time (RT60) is considered. The reverberation time of any room depends on
its cubic volume and is driven by room surfaces and
ceiling height. All room surfaces are acoustical surfaces, with each assigned an attribute for absorption

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duct entrances above an accessible ceiling. Door bottom
thresholds are classic shortcomings. Further, a hotel
using a local room HVAC with packaged terminal air
conditioner (PTAC) may be an open hole to a highway
with truck brakes outside and people sleeping inside.
These holes and openings are the first sources of noise to
treat.
After the weakest barrier or open leaks are assessed,
further design can acoustically protect where
people reside, sleep and work. In this process, the
A-weighted decibel (dBA) (Table 1) and noise criteria
(NC) are used to determine how quiet it must be. To
determine the appropriate NC value, HVAC decibel
values are identified from noise sources in octave
center bands. (Figure 1 in last month's column shows
an NC graph.) If sound power is cited, it must be converted to sound pressure level because sound power
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ASHRAE JOURNAL

53


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ASHRAE Journal - January 2021

Table of Contents for the Digital Edition of ASHRAE Journal - January 2021

Contents
ASHRAE Journal - January 2021 - Intro
ASHRAE Journal - January 2021 - Cover1
ASHRAE Journal - January 2021 - Cover2
ASHRAE Journal - January 2021 - 1
ASHRAE Journal - January 2021 - 1a
ASHRAE Journal - January 2021 - 1b
ASHRAE Journal - January 2021 - Contents
ASHRAE Journal - January 2021 - 3
ASHRAE Journal - January 2021 - 4
ASHRAE Journal - January 2021 - 5
ASHRAE Journal - January 2021 - 6
ASHRAE Journal - January 2021 - 7
ASHRAE Journal - January 2021 - 8
ASHRAE Journal - January 2021 - 9
ASHRAE Journal - January 2021 - 10
ASHRAE Journal - January 2021 - 11
ASHRAE Journal - January 2021 - 12
ASHRAE Journal - January 2021 - 13
ASHRAE Journal - January 2021 - 14
ASHRAE Journal - January 2021 - 15
ASHRAE Journal - January 2021 - 16
ASHRAE Journal - January 2021 - 17
ASHRAE Journal - January 2021 - 18
ASHRAE Journal - January 2021 - 19
ASHRAE Journal - January 2021 - 20
ASHRAE Journal - January 2021 - 21
ASHRAE Journal - January 2021 - 22
ASHRAE Journal - January 2021 - 23
ASHRAE Journal - January 2021 - 24
ASHRAE Journal - January 2021 - 25
ASHRAE Journal - January 2021 - 26
ASHRAE Journal - January 2021 - 27
ASHRAE Journal - January 2021 - 28
ASHRAE Journal - January 2021 - 29
ASHRAE Journal - January 2021 - 30
ASHRAE Journal - January 2021 - 31
ASHRAE Journal - January 2021 - 32
ASHRAE Journal - January 2021 - 33
ASHRAE Journal - January 2021 - 34
ASHRAE Journal - January 2021 - 35
ASHRAE Journal - January 2021 - 36
ASHRAE Journal - January 2021 - 37
ASHRAE Journal - January 2021 - 38
ASHRAE Journal - January 2021 - 39
ASHRAE Journal - January 2021 - 40
ASHRAE Journal - January 2021 - 41
ASHRAE Journal - January 2021 - 42
ASHRAE Journal - January 2021 - 43
ASHRAE Journal - January 2021 - 44
ASHRAE Journal - January 2021 - 45
ASHRAE Journal - January 2021 - 46
ASHRAE Journal - January 2021 - 47
ASHRAE Journal - January 2021 - 48
ASHRAE Journal - January 2021 - 49
ASHRAE Journal - January 2021 - 50
ASHRAE Journal - January 2021 - 51
ASHRAE Journal - January 2021 - 52
ASHRAE Journal - January 2021 - 53
ASHRAE Journal - January 2021 - 54
ASHRAE Journal - January 2021 - 55
ASHRAE Journal - January 2021 - 56
ASHRAE Journal - January 2021 - 57
ASHRAE Journal - January 2021 - 58
ASHRAE Journal - January 2021 - 59
ASHRAE Journal - January 2021 - 60
ASHRAE Journal - January 2021 - 61
ASHRAE Journal - January 2021 - 62
ASHRAE Journal - January 2021 - 63
ASHRAE Journal - January 2021 - 64
ASHRAE Journal - January 2021 - 65
ASHRAE Journal - January 2021 - 66
ASHRAE Journal - January 2021 - 67
ASHRAE Journal - January 2021 - 68
ASHRAE Journal - January 2021 - 69
ASHRAE Journal - January 2021 - 70
ASHRAE Journal - January 2021 - 71
ASHRAE Journal - January 2021 - 72
ASHRAE Journal - January 2021 - 73
ASHRAE Journal - January 2021 - 74
ASHRAE Journal - January 2021 - 75
ASHRAE Journal - January 2021 - 76
ASHRAE Journal - January 2021 - 77
ASHRAE Journal - January 2021 - 78
ASHRAE Journal - January 2021 - 79
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ASHRAE Journal - January 2021 - 81
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ASHRAE Journal - January 2021 - 104
ASHRAE Journal - January 2021 - 105
ASHRAE Journal - January 2021 - 106
ASHRAE Journal - January 2021 - 107
ASHRAE Journal - January 2021 - 108
ASHRAE Journal - January 2021 - 109
ASHRAE Journal - January 2021 - 110
ASHRAE Journal - January 2021 - 111
ASHRAE Journal - January 2021 - 112
ASHRAE Journal - January 2021 - Cover3
ASHRAE Journal - January 2021 - Cover4
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