Page 19 - Fall_DTF

1—mm Unaccupiad L,” (Mechanical system on)
u, I
12- I
E I Limitations of Aimarican Natiiunal _
11' I Standards Institute/Acoustical Society
uf America 51 2.6::
% 5 I Many investigations have shown that although the
E i I reverberation time recommendations given in ANSI/ASA
5 I S12.60 are attainable, there are few classrooms that meet
5- the unoccupied background noise level requirements
(Knecht et al., 2002; Nelson et al., 2008; Sato and Bradley,
“,7 Ii 4: A: :: 9: 2008). Observations of the 220 classrooms in our study are
I 91% bim:|La‘s‘§ilbBt:lrns do not meet ANSI Consmmt Wm‘ “"53 findings (Figure 2)‘
Fecflmmend-W0"! Most of the K-12 classrooms that we visited have acoustical
ceiling tile covering the entire ceiling surface, with a ceiling
hei ht at or less than 11 feet 3.3 meters . These room
;nl,ReVeme'atl°nfrme U20) Mlmlfreq uency average chafacteristics lead to acceptable ileverberatioh times. Figure
45 i 3 shows examples of typical classroom conditions observed
I in our study. if a classroom is excessively reverberant,
a
n D I adding absorptive materials in the space is a relatively easy
g 35 I 15% of c|a55mom5 task postdesign. Major renovations, however, are typically
% 30 ’ I do not meet AN5| ' required to decrease background noise levels significantly,
Q 25 recommendations particularly those produced by building mechanical systems
g in _ I _ for heating, ventilation, and air conditioning (HVAC).
E I: r I The best way to ensure quiet background noise levels from
in building mechanical systems is to design for them and not
‘ rely on postdesign solutions because the cost of replacing
: L i noisy mechanical systems is far greater than designing quiet
"D ; ,3 3 D .. 3 3 D 5 D r a 5 D 5 systemsinthe first place. Designinga loud mechanical system
Tzorr , I5} is easier and less expensive than designing a quiet system,
but the financial cost should not be the only cost considered
$9“ 2- 5“’"Pl_95 ‘if the d‘““ m9“5"f3df"”" 220 K_’12 ‘l“55fW’"5 when it comes to our educational facilities. There is a cost
in five sehoez districts. Top: One—mmute urmeerepred A—weighted associated with designing and insiniiing niiiei nieciinnicni
equivalent levels (L i) were reeerrzerz to characterize the BNL m the
M . . . . systems, but the benefits experienced by the occupants of the
classruums due to ventrlatum noise. Nmet}/—:me percent ofclussmoms _ _
do not meet the American Nutirmul Standards Institute (ANSI) rec— C]**55f°°m fa! °“‘W=l8h these Increased Costs‘
'”"me"d;d "_"”‘i'"”m f-f?5 'iB(2i)':'gt”im}:;i""b:'“"-0" ti": W“: Routine approaches to mechanical systems frequently
mmsum usmgaswep {me me D. ' fly oft ussmoms om utilized in classrooms are often inconsistent with the best
meet the ANSI recommended maximum uf0.6 second. _ _ _ _
acoustical practices. It can be challenging to disregard
routine practices in favor of less utilized, more creative
and unoccupied Condifionsi They found “mi iower English design solutions. Coupling this with the fact that there are
. _ not easily enforceable acoustics requirements means that
test scores were more strongly related to higher occupied _ _ _ _
b d . 1 i tha _ d b d appropriate classroom sound levels are not always prioritized
ackgroun noise eves n to unoccupie ackgroun in the building design indusiry
noise levels. It is therefore necessary to diminish the ‘
background noise level in actively occupied classrooms In the United States, the ANSI classroom acoustics standard
to mitigate this effect. One other study has found that provides a guideline for background noise levels but
backgroundnoiselevelsinunoccupied classrooms correlated does not prescribe enforceable requirements. The United
to student achievement scores in reading and language States Green Building Council (USGBC) introduced the
subject areas (Ronsse and Wang, 2013). That study did not Leadership in Energy and Environmental Design (LEED)
measure levels in the occupied active classrooms though. green building certification system in 2000. LEED certifies
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