senso s
A icle
Analysis o Impac o Na u al Ven ila ion S a egies in
Ven ila ion Ra es and Indoo En i onmen al Acous ics Using
Senso Measu emen Da a in Educa ional Buildings
Ma ía L. de la Hoz-To es 1, An onio J. Aguila 1, Diego P. Ruiz 1and Ma ía Dolo es Ma ínez-Ai es 2,*


Ci a ion: de la Hoz-To es, M.L.;
Aguila , A.J.; Ruiz, D.P.;
Ma ínez-Ai es, M.D. Analysis o
Impac o Na u al Ven ila ion
S a egies in Ven ila ion Ra es and
Indoo En i onmen al Acous ics
Using Senso Measu emen Da a in
Educa ional Buildings. Senso s 2021,
21, 6122. h ps://doi.o g/10.3390/
s21186122
Academic Edi o : Hossam A. Gabba
Recei ed: 1 Augus 2021
Accep ed: 9 Sep embe 2021
Published: 12 Sep embe 2021
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Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
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A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
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1Depa men o Applied Physics, Uni e si y o G anada, A . Se e o Ochoa s/n, 18071 G anada, Spain;
mlhoz@ug .es (M.L.d.l.H.-T.); an ojes@ug .es (A.J.A.); d uiz@ug .es (D.P.R.)
2Depa men o Building Cons uc ion, Uni e si y o G anada, A . Se e o Ochoa s/n, 18071 G anada, Spain
*Co espondence: ai es@ug .es
Abs ac :
Indoo en i onmen al condi ions can signi ican ly a ec occupan s’ heal h and com o .
These condi ions a e especially impo an in educa ional buildings, whe e s uden s, eache s and
s a spend long pe iods o he day and a e ulne able o hese ac o s. Recen ly, indoo ai quali y
has been a ocus o a en ion o ensu e ha disease ansmission in hese spaces is minimised. In
o de o inc ease he knowledge in his ield, expe imen al es s ha e been ca ied ou o cha ac e ise
he impac o na u al en ila ion s a egies on indoo ai quali y and he acous ic en i onmen .
This s udy has e alua ed h ee en ila ion scena ios in ou di e en class ooms in buildings o he
Uni e si y o G anada, conside ing di e en window and doo opening con igu a ions. Ven ila ion
a es we e es ima ed using he CO
2
Decay Me hod, and backg ound noise eco dings we e made
in each class oom o acous ic es s. Resul s show ha speci ic na u al en ila ion s a egies ha e a
ele an impac ha is wo h conside ing on he backg ound noise in indoo spaces. In his sense
en ila ion a es p o ided by he di e en con igu a ions a ied be ween 3.7 and 39.8 ai changes
pe hou (ACH) and he acous ic es s show a backg ound noise anging om 43 o 54 dBA in hese
scena ios. Consequen ly, manage s and eache s should ake in o accoun no only he ACH, bu also
o he colla e al impac s on he indoo en i onmen al condi ions such as he he mal com o o he
acous ic en i onmen .
Keywo ds: buildings; en ila ion a e; indoo ai quali y; na u al en ila ion; COVID-19
1. In oduc ion
Since people spend mo e han 80% o hei ime in indoo en i onmen s [
1
], i he
indoo condi ions a e de icien , he heal h and com o o he occupan s may be a ec ed [
2
].
Building design and i s cha ac e is ics a e impo an ac o s o indoo condi ions and,
hence, he sa is ac ion le els o he occupan s [
3
]. Indoo en i onmen al quali y (IEQ) is
de ined as an indica ion ha ela es he heal h and well-being o he occupan s o in e io
spaces wi h he quali y o he building’s en i onmen [4].
The IEQ is essen ial in educa ional buildings, which a e ypically designed o high
occupancy o long pe iods o he day [
5
,
6
]. In pa icula , a good indoo ai quali y (IAQ)
is c ucial o p o ide a heal hy, sa e, p oduc i e and com o able en i onmen [
7
]. S uden s,
eache s and o he school s a a e ulne able o he impac o poo IAQ in hese spaces,
whe e concen a ion and in ellec ual wo k is equi ed. Indoo ai pollu an s (i.e., ino -
ganic/o ganic gases and biological and non-biological pa icles) accumula e mo e easily
in indoo en i onmen s as a esul o he building en elopes which in en ionally sepa a e
occupan s om he ou side [
8
]. Exposu e o ai pollu an s may cause a isk o sho - and
long- e m heal h p oblems, such as se e al espi a o y diseases [9,10], ca dio ascula dis-
ease [
11
], i i a ed eyes o nose, blocked nose, headaches and so o h [
12
]. In addi ion, poo
Senso s 2021,21, 6122. h ps://doi.o g/10.3390/s21186122 h ps://www.mdpi.com/jou nal/senso s
Senso s 2021,21, 6122 2 o 21
IAQ may a ec he com o , p oduc i i y and academic achie emen o
s uden s [6,13,14]
.
The e o e, IAQ is o pa icula conce n in eaching-lea ning spaces.
These ci cums ances de e mine ha one o he mos demanding challenges acing ed-
uca ional building adminis a o s is IAQ managing [
15
]. An adequa e en ila ion
a e (VR)
is one o he key elemen s o a oid comp omising he IAQ since p o iding ou doo ai
en ila ion dilu es in e nally gene a ed con aminan s o le els ha do no cause heal h
and com o p oblems [
16
]. The analysis o he VR based on measu ed s udies and he
adequa ely cha ac e ised en ila ion design o buildings a e c i ical o assessing and in e -
p e ing IAQ [
17
,
18
]. Selec ing an app op ia e en ila ion s a egy is essen ial o mee ing
he equi emen s o good IAQ. In e na ional guidelines, s anda ds and building codes
s a e a minimum VR in buildings [
19
–
22
]. Howe e , i should be no ed ha p e ious
esea ch sugges s ha in o de o subs an ially dec ease illness absence and he e o e
p oduce economic bene i s, one o he measu es ha can be aken is o inc ease class oom
VRs abo e he S a e s anda d [23].
This ac has been highligh ed by he COVID-19 pandemic. Acco ding o he Wo ld
Heal h O ganiza ion, as o 7 July 2021, he e had been 3,997,640 dea hs and 184,572,371
con i med cases o COVID-19 epo ed globally [
24
]. T ansmission o SARS-CoV-2 occu s
when unin ec ed people a e exposed o in ec ious espi a o y luids a e con ac wi h
in ec ed people [
25
]. Fac o s con ibu ing o inc eased ansmission include: loud speech
olume; in ense physical ac i i y; lack o well- i ing ace masks; la ge numbe s o people
in he same space; dec eased in e pe sonal dis ance; inc eased emission and exposu e ime
and poo indoo VR [
26
]. Mo eo e , ecen esea ch has shown ha ansmission can be
agg a a ed in con ined and poo ly en ila ed spaces. Indeed, Nishiu a e al. [
27
] s a e ha
COVID-19 ansmission can be up o 18.7 imes highe in con ined spaces han in open
ai spaces. Pa k e al. [
28
] sugges ed ha c oss- en ila ion is mo e e icien compa ed o
single-sided en ila ion, and ecommend c oss- en ila ion o minimise he possibili y o
in ec ion in high-densi y public buildings. Acco ding o Dai and Zhao [
29
], o a class oom
wi h a olume o 348 m
3
and o an exposu e pe iod o 2 h, o keep he p obabili y o
in ec ion below 1%, a VR o wo Ai Changes pe Hou (ACH) wi h masks and se en ACH
wi hou masks is necessa y.
Since s uden s and eache s spend long pe iods each day in class ooms, hese indoo
spaces a e isk en i onmen s o he ai bo ne ansmission o SARS-CoV-2 [
30
]. Con-
sequen ly, measu es adop ed by go e nmen s o minimise he possibili y o con agion
included he closu e o educa ional buildings. As a esul , nea ly hal o he wo ld’s s u-
den s a e s ill a ec ed by his measu e and mo e han 100 million addi ional child en will
all below he minimum le el o eading p o iciency [
31
]. The Uni ed Na ions Educa ional,
Scien i ic and Cul u al O ganiza ion (UNESCO) wa ns ha i is c ucial o p io i ise ed-
uca ion eco e y in o de o a oid a gene a ional ca as ophe [
31
]. Adop ing e ec i e
mi iga ion s a egies o con ol he isk o ai bo ne in ec ion and adap ing educa ional-
lea ning spaces a e essen ial p ocesses o mi iga e he impac o educa ional building
closu es. The eopening o educa ional buildings has had many socio-economic implica-
ions in all coun ies, and he e o e coun ies a e aking ac ions o ensu e ha educa ional
buildings a e sa e spaces. In his ega d, he Spanish Go e nmen ’s p e en ion guidelines
equi e he use o well- i ed acemasks (a su gical mask is a minimum), educing he
olume o he oice in con e sa ion, inc eased in e pe sonal dis ance and educed con ac
ime (e.g., educing he occupa ion o indoo spaces) and imp o ed en ila ion in indoo
spaces. Ven ila ion s a egies a e a key aspec o indoo spaces managemen in his con ex .
In he case o na u al en ila ion, c oss- en ila ion (opening doo s and/o windows on
opposi e sides) is ecommended [
26
]. Fo mechanical en ila ion, a en ion should be paid
o he con igu a ion o he sys em, o educe he eci cula ion o ai and inc ease/maximise
ou side ai . The VR is measu ed by ACH. The ecommended VR in indoo spaces o good
ai quali y is 12.5 li es/second pe pe son (L/s/p), which co esponds o app oxima ely
5–6 ACH.
Senso s 2021,21, 6122 3 o 21
Howe e , while hese en ila ion s a egies ensu e an op imal concen a ion o CO
2
and o he pollu an s, hey also ha e an impac on o he impo an indoo a iables in
indoo en i onmen s. One o he mos impo an in eaching-lea ning spaces is he indoo
acous ic en i onmen , which is in luenced by he na u al and/o mechanical en ila ion
s a egy selec ed [
32
]. In ecen yea s, pe cei ed acous ic quali y in indoo en i onmen s
has gained momen um and ecen esea ch has ocused on indoo soundscapes [
33
,
34
]
Acous ic design and s a egies should include noise con ol and pe cep ual app oach o he
use s in o de o enhance people’s heal h and well-being [
35
,
36
]. In his sense, Tang [
37
]
analysed a ailable açade noise con ol s a egies o in oducing de ices while imp o ing
na u al en ila ion in buildings. The indings o his s udy show ha , in conges ed ci ies,
p o usi e de ices such as balconies, lin els and ins a e no e ec i e noise sc eening
de ices o high- ise buildings (e en wi h sound abso be s and/o e lec o s). Ac i e
con ol ins alla ion and esonance-based de ices o en esul in bulky sys ems, a ec ing
he açade design and he e ec i eness o na u al en ila ion s a egies. Sys ems such as
plenum windows and double-wall plenum s uc u es a e o en use ul as na u al en ila ion
and noise con ol de ices. In addi ion, esea ch is being conduc ed on he de elopmen
o new window de ices. Fusa o e . al. [
38
,
39
] p oposed a new me acage window which
allows na u al en ila ion and noise educ ion based on he p inciple o Snell’s Law. The
used o his no el p o o ype showed an o e all mean sound educ ion o 15 dB wi hin a
bandwid h o 380 o 5000 Hz.
In his con ex , he managemen o na u al en ila ion s a egies and hei impac in
he indoo acous ic en i onmen is essen ial in he eaching-lea ning spaces. Poo acous ic
en i onmen s in class ooms a ec lea ning achie emen s [
40
,
41
] as well as he academic,
psychosocial and psychoeduca ional pe o mance o s uden s [
42
]. Mo eo e , hese may
cause oice p oblems [
43
] and physical s ess in eache s [
44
], and ha e signi ican e ec s on
wo d iden i ica ion and in elligibili y [
45
]. Ex e nal noise sou ces o educa ional buildings
as well as sou ces wi hin he building (e.g., in acili ies ooms, con iguous spaces, e c.)
in luence he backg ound noise inside he eaching-lea ning spaces. In o de o achie e an
adequa e acous ic com o and speech in elligibili y o ensu e he quali y o educa ional
p ocesses he backg ound noise le el should no exceed he sound le el o 35 dBA [
46
,
47
].
The e o e, acous ic com o is c i ical in de e mining he quali y o educa ional p ocesses.
This ac makes i necessa y o e alua e he impac o he en ila ion s a egies on IEQ
pa ame e s such as IAQ and acous ic pe o mance. This is he main gene al pu pose o
his esea ch.
In his con ex , and gi en he 6 ACH alues ecommended in cu en Spanish public
policies o p e en he ansmission o COVID-19, he aim o his s udy was o cha ac e ise
hei impac on he a iables condi ioning IAQ and he indoo acous ic en i onmen . The
s udy assesses he need o de ine heal h p o ocols o en ila ion in educa ional buildings
ha , in addi ion o iden i ying na u al en ila ion s a egies wi h a VR alue as close as
possible o he equi ed ACH alue, ake in o accoun he backg ound noise le el. This
will he e o e ensu e he quali y o eaching and lea ning p ocesses while main aining he
equi ed en ila ion p o ocols.
2. Me hodology and Da a Collec ion
Wi h he aim o cha ac e ising he impac o na u al en ila ion s a egies on he
a iables condi ioning IAQ and he indoo acous ic en i onmen , na u al en ila ion
e iciency was checked in h ee en ila ion scena ios wi h di e en window and doo
opening con igu a ions. Backg ound equi alen con inuous sound pP essu e le el (Leq) in
dBA was also calcula ed om sound p essu e le els measu ed in he con igu a ion ha
p o ided su icien VR h ough na u al en ila ion acco ding o he cu en egula o y limi .
This alue was compa ed wi h he backg ound equi alen con inuous sound p essu e le el,
measu ed in he closed doo s and windows scena io. This sec ion desc ibes he s udy a ea,
he da a-collec ion me hodology and he senso s used in he p ocess. Figu e 1shows an
o e iew o he s udy’s me hodological app oach.
Senso s 2021,21, 6122 4 o 21
Senso s 2021, 21, 6122 4 o 22
Figu e 1. Diag am o he s udy’s me hodological app oach.
2.1. S udy A ea and Building Desc ip ion
The s udy comp ises educa ional buildings om he Fuen enue a Campus o he
Uni e si y o G anada, loca ed in G anada (Spain). The ield measu emen s we e con-
duc ed be ween Ma ch and Ap il 2021 (sp ing season) in he Ad anced Technical School
o Building Enginee ing (buil in 1972) and he Ad anced Technical School o Ci il En-
ginee ing (buil in 2000) (Figu e 2).
Figu e 2. Loca ion o he senso s du ing he expe imen al es s pe o med in each class oom; (a) B1-
A1 class oom; (b) B1-A2 class oom; (c) B2-A1 class oom. (d) B2-A2 class oom; Blue dimensions in-
dica e size o he openings; Black dimensions indica e sizes o he oom; G een sphe es indica e he
posi ion o he acous ic senso s; G ey sphe es indica e he posi ion o CO
2
senso s (dimensions in
me e s).
Face- o- ace eaching was suspended a he Uni e si y o G anada om Oc obe o
Janua y in esponse o COVID-19. The es s we e ca ied ou be o e he adap a ion o he
eaching spaces o he e u n o ace- o- ace eaching ac i i ies. Fo his pu pose, en ila-
ion and acous ic measu emen s we e ca ied ou in he newly adap ed spaces. G anada
is classi ied as a C3 zone by he Spanish Technical Building code CTE [48]. This zone is
Figu e 1. Diag am o he s udy’s me hodological app oach.
2.1. S udy A ea and Building Desc ip ion
The s udy comp ises educa ional buildings om he Fuen enue a Campus o he Uni-
e si y o G anada, loca ed in G anada (Spain). The ield measu emen s we e conduc ed
be ween Ma ch and Ap il 2021 (sp ing season) in he Ad anced Technical School o Build-
ing Enginee ing (buil in 1972) and he Ad anced Technical School o Ci il Enginee ing
(buil in 2000) (Figu e 2).
Senso s 2021, 21, 6122 4 o 22
Figu e 1. Diag am o he s udy’s me hodological app oach.
2.1. S udy A ea and Building Desc ip ion
The s udy comp ises educa ional buildings om he Fuen enue a Campus o he
Uni e si y o G anada, loca ed in G anada (Spain). The ield measu emen s we e con-
duc ed be ween Ma ch and Ap il 2021 (sp ing season) in he Ad anced Technical School
o Building Enginee ing (buil in 1972) and he Ad anced Technical School o Ci il En-
ginee ing (buil in 2000) (Figu e 2).
Figu e 2. Loca ion o he senso s du ing he expe imen al es s pe o med in each class oom; (a) B1-
A1 class oom; (b) B1-A2 class oom; (c) B2-A1 class oom. (d) B2-A2 class oom; Blue dimensions in-
dica e size o he openings; Black dimensions indica e sizes o he oom; G een sphe es indica e he
posi ion o he acous ic senso s; G ey sphe es indica e he posi ion o CO
2
senso s (dimensions in
me e s).
Face- o- ace eaching was suspended a he Uni e si y o G anada om Oc obe o
Janua y in esponse o COVID-19. The es s we e ca ied ou be o e he adap a ion o he
eaching spaces o he e u n o ace- o- ace eaching ac i i ies. Fo his pu pose, en ila-
ion and acous ic measu emen s we e ca ied ou in he newly adap ed spaces. G anada
is classi ied as a C3 zone by he Spanish Technical Building code CTE [48]. This zone is
Figu e 2.
Loca ion o he senso s du ing he expe imen al es s pe o med in each class oom; (
a
) B1-A1 class oom; (
b
) B1-A2
class oom; (
c
) B2-A1 class oom. (
d
) B2-A2 class oom; Blue dimensions indica e size o he openings; Black dimensions
indica e sizes o he oom; G een sphe es indica e he posi ion o he acous ic senso s; G ey sphe es indica e he posi ion o
CO2senso s (dimensions in me e s).
Face- o- ace eaching was suspended a he Uni e si y o G anada om Oc obe o
Janua y in esponse o COVID-19. The es s we e ca ied ou be o e he adap a ion o he
eaching spaces o he e u n o ace- o- ace eaching ac i i ies. Fo his pu pose, en ila ion
and acous ic measu emen s we e ca ied ou in he newly adap ed spaces. G anada is
classi ied as a C3 zone by he Spanish Technical Building code CTE [
48
]. This zone is
cha ac e ised by sho , e y ho and mos ly clea summe s and long, cold and pa ly
Senso s 2021,21, 6122 5 o 21
cloudy win e s. Du ing he cou se o he yea , he empe a u e gene ally a ies om 0
◦
C
o 34 ◦C and a ely d ops below −4◦C o ises abo e 38 ◦C.
Two ep esen a i e class ooms we e selec ed o each building based on he da a
p o ided by he COVID-19 Ac ion Plan de eloped by he Uni e si y o G anada [
49
]. This
plan de ines ins i u ional policies and guidance on occupa ional heal h and sa e y, which
include: manda o y masks indoo s, 50% occupancy, physical dis ancing (a leas 1.5 m)
and ha indoo spaces mus be en ila ed na u ally h ough open windows and doo s.
Wi hin his amewo k, and in o de o adap he gene al measu es es ablished by he
gene al ac ion plan, he Academic Di ec ion o each Technical School d ew up an ac ion
plan adap ed o hei needs and o he cha ac e is ics o hei spaces. The selec ion o hese
spaces ook in o accoun all he measu es de eloped in his con ex .
Table 1shows he cha ac e is ics o he class ooms. The p ocess o cha ac e isa ion
and analysis s a s wi h he selec ion o ep esen a i e class ooms om he buildings o he
campus. I should be no ed ha each selec ed class oom has a di e en o ien a ion and
ha hei geome y allows hem o mee he equi emen s se ou in he COVID-19 Ac ion
Plan. In addi ion, hei di e en cha ac e is ics allow di e en en ila ion s a egies o be
analysed: Class oom B1-A1 has windows on opposi e sides, so na u al c oss- en ila ion
s a egies can be assessed; Class oom B1-A2 is accessed h ough a co ido wi h windows,
so c oss- en ila ion h ough co ido s can be assessed; Class ooms B2–A1 and B2–A2 ha e
iden ical geome ies bu a e loca ed on opposi e sides o he building, such ha en ila ion
s a egies can be compa ed acco ding o he loca ion o he oom.
Table 1. Cha ac e is ics o he class ooms.
Building Id Class A ea
[m2]
Volume
[m3]O ien a ion
Occupa ion
P e-Co id-19
[Sea s]
Occupa ion
Ra io
[m2/S uden ]
Occupa ion
Co id-19
[Sea s]
Occupa ion
Ra io
[m2/S uden ]
Building 1
(ETSIE)
B1-A1 175 524 Eas 96 1.82 48 3.27
B1-A2 167 500 Wes 61 2.73 35 4.77
Building 2
(ETSICCP)
B2-A1 172 518 No h 156 1.10 78 2.20
B2-A2 174 522 Sou h 156 1.12 78 2.24
2.2. Decay Me hod o De e mine Ai Change in Na u al Ven ila ion in Class oom
The decay me hod can be used in unoccupied spaces using a ace gas such as CO
2
.
The aim o his me hod is o de e mine he ACH. In ac , he decay me hod consis s o
inc easing he CO
2
concen a ion by using a CO
2
gene a ion sou ce (e.g., d y ice) [
50
] in he
class oom un il a homogeneous and well-mixed mix u e is eached [
16
,
51
,
52
]. Subsequen ly
(wi hou sou ce and unoccupied) he a e o dec ease o he CO
2
concen a ion unde he
di e en con igu a ions is de e mined. The expe imen al es ends when he CO
2
le el
app oaches 37% o i s o iginal peak concen a ion abo e he backg ound [
51
,
52
]. Fo his
pu pose, he CO
2
concen a ion is measu ed a known imes and he ACH can be es ima ed
using Equa ion (1):
ACH =
−1∗lnCend−Cou doo
Cs a −Cou doo 
end − s a (1)
whe e C
end
is he measu ed CO
2
concen a ion a he end o he decay cu e,
end
is he
end ime o he decay cu e, C
s a
is he measu ed CO
2
concen a ion a he s a o he
decay cu e,
s a
is he end ime o he decay cu e and C
ou doo
is he measu ed CO
2
concen a ion ou side he building.
O he wise, in o de o i a solu ion o he decay concen a ion p ocess using a eg es-
sion o o he means, a sequence o CO
2
concen a ions o e a po ion o he decay pe iod,
C , is used as shown in Equa ion (2) [16]:
C =(CS a −Cou doo )exp(−ACH ∗ )+Cou doo (2)

Senso s 2021,21, 6122 6 o 21
whe e
is he measu emen ime in hou s. In addi ion, Equa ion (2) can be ea anged o
be linea in ime as (Equa ion (3)):
ln(C −Cou doo )=−ACH ∗ +ln(CS a −Cou doo )(3)
whe e
CS a
is he s eady-s a e CO
2
concen a ion a he s a o he es . The es ima ed
ACH is he slope o he eg ession o ln(C −Cou doo ) agains ime .
In his s udy, his me hod was applied o he VR cha ac e isa ion o h ee con igu a-
ions o each class oom. The alues ob ained we e used o compa e he ACH p o ided by
each con igu a ion. In addi ion, and gi en ha he e-opening guidelines [
26
] ecommend
a en ila ion a e o 12.5 li es pe second and pe son o achie e good ai quali y (co e-
sponding o app oxima ely 5–6 ACH), he con igu a ion p o iding he equi ed ACH alue
was selec ed.
2.3. Backg ound Noise Indoo Da a Collec ion
In o de o cha ac e ise he indoo acous ic en i onmen in di e en con igu a ions
o na u al en ila ion s a egies, he sound p essu e le el o he backg ound noise was
measu ed in he di e en con igu a ions. Fo his pu pose, a wo-phase me hodology was
ollowed: in he i s phase, he backg ound noise was measu ed in he class oom wi h
all doo s and windows closed. Subsequen ly, in phase wo, he backg ound noise was
measu ed wi h he na u al en ila ion con igu a ion selec ed based on he expe imen al
esul s o he decay me hod p e iously ob ained (i.e., he con igu a ion ha p o ided he
equi ed ACH alue).
Du ing he ield measu emen pe iod, h ee acous ical measu emen s we e made a
h ee sea loca ions in he class oom ( on , middle and back) in bo h phases, esul ing in
nine measu emen s in each phase. The loca ions we e selec ed because hey we e ypical
lis ene posi ions inside he class oom. The measu emen s we e eco ded a leas 1.2 m
away om he g ound, 0.7 m be ween measu emen posi ions and a 0.5 m. away om
any wall, ceiling o g ound su ace, in compliance wi h he UNE-ISO 1996-2:2020 [
53
]
ecommenda ions (de ails abou he ins umen and posi ions a e shown in Sec ion 2.4
and Figu e 2). Each measu emen consis s o a binau al eco dings signal, which con ains
backg ound noise and has a du a ion abo e 15 min. This minimum measu emen ime
in e al was selec ed because p e ious s udies ha e iden i ied ha ac i i y backg ound
noise le el measu ed o a long ime (4 h) was no ound o be s a ically di e en om he
alues ob ained o e 15 min [54,55]. The measu emen s we e eco ded a he ea posi ion
using a head- o so manikin (heigh : 1.30 m) loca ed in he lis ene posi ions p e iously
selec ed. The manikin was s ably ixed o pe o m he eco dings in a s a iona y condi ion
in o de o a oid addi ional noise. The manikin’s head was o ien ed owa ds he ypical
eache ’s posi ion in he class oom.
The con inuous equi alen sound p essu e le el (Leq) o each acous ical measu emen
was calcula ed as he a e aged equi alen -ene gy o he sound p essu e le els om he le
and igh channels du ing he measu ing ime. Based on hese measu emen s, an ene gy
a e aging o he acous ic measu emen in each con igu a ion was pe o med wi h he aim
o ob aining a sound-le el alue (dBA) ep esen a i e o each con igu a ion.
The ob ained alues we e hen compa ed wi h he limi s o he ambien noise le el
o eaching-lea ning spaces ecommended by he Wo ld Human O ganiza ion (WHO) [
46
]
and ANSI/ASA S12.60-2010/Pa 1 [
47
]. Bo h o ganisa ions ecommend sound-le el alues
below 35 dBA.
2.4. Senso s and Da a Collec ion
The HOBO
®
MX1102 logge was used o measu e he CO
2
concen a ions in he class-
oom. The ins umen has a measu emen ange om 0 o 5000 ppm (
accu acy ±50 ppm ±5%
o eading a 25
◦
C, less han 90% RH non-condensing and 1.013 mba ). The sensing me hod
is non-dispe si e in a ed (NDIR) abso p ion. Rega ding he acous ical signals eco dings,
hese we e made using a Squad iga I eco de and BHS I headse /mic ophone uni . The
Senso s 2021,21, 6122 7 o 21
sampling a e o he ex e nal mic ophones was 48 kHz. Maximum sound p essu e le el o
130 dBSPL and equency esponse o 4 Hz o 20 kHz.
Figu e 2shows he posi ion o he senso s in he expe imen al es s o each class oom.
Se en HOBO
®
MX1102 senso s we e used du ing he decay me hod expe imen al es s,
numbe ed in Figu e 2as senso S1-CO
2
o senso S7-CO
2
. Wi h ega d o he acous ic
measu emen s, hey we e pe o med in he loca ions P1-Ac, P2-Ac and P3-Ac ( on , middle
and back posi ion in he audience espec i ely).
One o he undamen al equi emen s es ablished in he COVID-19 Ac ion Plan elab-
o a ed by he Uni e si y o G anada was o es ablish na u al en ila ion h ough open
windows and doo s, e en in ad e se wea he condi ions [49].
Fo his eason, di e en scena ios o window and doo opening combina ions we e
selec ed o gene a e each con igu a ion. Th ee ypes o con igu a ions we e de ined o
each o he ou selec ed class ooms (Table 2). Expe imen al es s we e ca ied ou in o de
o e alua e he con igu a ion ha p o ides su icien en ila ion acco ding o he COVID-19
s anda ds. In addi ion, he impac o he selec ed con igu a ion on he acous ic com o
was e alua ed.
Table 2. Con igu a ions o na u al en ila ion s a egic es s.
Class oom Con igu a ion Doo s and Windows Opening Combina ions
B1-A1
C-1 All windows opened and main doo opened.
C-2 End windows opened and main doo opened.
C-3
Only windows a he end in wes açade opened, he cen e windows in eas açade opened (“Y”
con igu a ion) and he main doo opened.
B1-A2
C-1 All windows opened, main doo opened and he co ido windows opened.
C-2 All windows opened, main doo opened and he co ido windows closed.
C-3
Only he windows a he end opened and main doo opened, and he co ido windows opened.
B2-A1
C-1 All windows opened and wo doo s opened.
C-2 All windows opened and main doo opened.
C-3 Only windows a he end opened and main doo opened.
B2-A2
C-1 All windows opened and he wo doo s opened.
C-2 All windows opened and he main doo opened.
C-3 Only windows a he end and he main doo opened.
3. Resul s
In he nex sec ions, esul s a e p esen ed o he h ee con igu a ion scena ios o he
ou class ooms p e iously desc ibed. Fi s ly, each sec ion shows he da a ob ained om
he expe imen al es s o he decay me hod and he a e age ACH esul s. Subsequen ly, he
backg ound noise sound p essu e le els Leq ob ained in wo di e en en ila ion scena ios
a e shown: (1) doo s and windows closed; and (2) he na u al en ila ion con igu a ion
ha p o ides he ACH alue equi ed (based on he decay me hod expe imen al esul s
p e iously ob ained).
3.1. Building 1—Class oom A-1 (B1-A1): Windows-Based Na u al C oss-Ven ila ion
S a egies—Eas O ien a ion
Figu e 3shows he decay me hods esul s ob ained o he h ee di e en con igu a-
ions selec ed o he class oom B1-A1. In addi ion, he eg ession o ln(C1-CR) agains
ime is shown in Table A1 in Appendix A. Di e ences be ween he da a eco ded by each
senso a e obse ed o he h ee es ed scena ios. These a e mainly due o he di e en
ela i e posi ions o he senso s om he windows and doo s, and may also de i e om he
indoo ai cu en s. This ac is applicable also o all he es ed na u al en ila ion scena ios
shown in he ollowing sec ions.
Senso s 2021,21, 6122 8 o 21
Senso s 2021, 21, 6122 8 o 22
om he indoo ai cu en s. This ac is applicable also o all he es ed na u al en ila ion
scena ios shown in he ollowing sec ions.
Figu e 3. Con igu a ion schemes and decay cu es in Class oom B1-A1; (a) Con igu a ion 1; (b)
Con igu a ion 2; (c) Con igu a ion 3.
Based on he alues shown in Table A1, he slope alue ob ained in he i ing cu e
o each case indica es he ACH alue o he con igu a ion measu ed a each poin . As can
be seen in Figu e 4, which shows he ACH ob ained in each con igu a ion, he ACH alues
ob ained a e homogeneous. I should be no ed ha C-1 con igu a ion is he one ha p o-
ides he highes numbe o ACH. The ACH alues in C-1 a ied om 7.4 o 9.4 wi h a
mean o 8.3 ± 0.6 pe hou , whe eas con igu a ion C-3 shows he lowes en ila ion a es,
om 4.3 o 5.1 wi h a mean o 4.6 ± 0.3 pe hou . Following he ecommenda ions o he
Spanish Minis y o Heal h [26], he ecommended en ila ion a e o indoo spaces (such
as class ooms) is a minimum o 6 ACH. As we can see in Figu e 4, he con igu a ion ha
sa is ies his p emise is con igu a ion C-1 (all windows opened and main doo opened),
in which he en ila ion a e is highe han he 6 ACH alue o all senso s.
Figu e 3.
Con igu a ion schemes and decay cu es in Class oom B1-A1; (
a
) Con igu a ion 1;
(b) Con igu a ion 2; (c) Con igu a ion 3.
Based on he alues shown in Table A1, he slope alue ob ained in he i ing cu e
o each case indica es he ACH alue o he con igu a ion measu ed a each poin . As
can be seen in Figu e 4, which shows he ACH ob ained in each con igu a ion, he ACH
alues ob ained a e homogeneous. I should be no ed ha C-1 con igu a ion is he one ha
p o ides he highes numbe o ACH. The ACH alues in C-1 a ied om 7.4 o 9.4 wi h a
mean o 8.3
±
0.6 pe hou , whe eas con igu a ion C-3 shows he lowes en ila ion a es,
om 4.3 o 5.1 wi h a mean o 4.6
±
0.3 pe hou . Following he ecommenda ions o he
Spanish Minis y o Heal h [
26
], he ecommended en ila ion a e o indoo spaces (such
as class ooms) is a minimum o 6 ACH. As we can see in Figu e 4, he con igu a ion ha
sa is ies his p emise is con igu a ion C-1 (all windows opened and main doo opened), in
which he en ila ion a e is highe han he 6 ACH alue o all senso s.
Since con igu a ion C-1 p o ides an ACH alue abo e 6, i was selec ed in o de o
e alua e he backg ound noise in his scena io. Hence, he backg ound noise was measu ed
in he ollowing wo con igu a ions: (1) windows and doo closed and (2) con igu a ion
C-1. As shown in Figu e 5, he backg ound Leq in he C-1 con igu a ion is 12 dBA abo e
he Leq measu ed in he same class oom wi h windows and doo closed.
Senso s 2021,21, 6122 9 o 21
Senso s 2021, 21, 6122 9 o 22
Figu e 4. Ven ila ion a e (ACH) in Class oom B1-A1.
Since con igu a ion C-1 p o ides an ACH alue abo e 6, i was selec ed in o de o
e alua e he backg ound noise in his scena io. Hence, he backg ound noise was meas-
u ed in he ollowing wo con igu a ions: (1) windows and doo closed and (2) con igu a-
ion C-1. As shown in Figu e 5, he backg ound Leq in he C-1 con igu a ion is 12 dBA
abo e he Leq measu ed in he same class oom wi h windows and doo closed.
Figu e 5. Backg ound noise le els in class oom B1-A1.
The backg ound noise Leq o he C-1 was 54.1 dBA. This alue is abo e he back-
g ound noise Leq wi h windows and doo closed (41.5 dBA) and he alue ecommended
by WHO (35dBA). Exposu e o a ic noise is he main p oblem in his class oom, since i
is loca ed in he eas açade o building 1, close o he main s ee o his dis ic . The a ic
noise has a high impac on he backg ound noise o he class oom, since in o de o achie e
an adequa e VR i is necessa y o open all windows and he main doo .
3.2. Building 1—Class oom A-2 (B1-A2): C oss-Ven ila ion h ough Co ido s S a egies—Wes
O ien a ion
Figu e 4. Ven ila ion a e (ACH) in Class oom B1-A1.
Senso s 2021, 21, 6122 9 o 22
Figu e 4. Ven ila ion a e (ACH) in Class oom B1-A1.
Since con igu a ion C-1 p o ides an ACH alue abo e 6, i was selec ed in o de o
e alua e he backg ound noise in his scena io. Hence, he backg ound noise was meas-
u ed in he ollowing wo con igu a ions: (1) windows and doo closed and (2) con igu a-
ion C-1. As shown in Figu e 5, he backg ound Leq in he C-1 con igu a ion is 12 dBA
abo e he Leq measu ed in he same class oom wi h windows and doo closed.
Figu e 5. Backg ound noise le els in class oom B1-A1.
The backg ound noise Leq o he C-1 was 54.1 dBA. This alue is abo e he back-
g ound noise Leq wi h windows and doo closed (41.5 dBA) and he alue ecommended
by WHO (35dBA). Exposu e o a ic noise is he main p oblem in his class oom, since i
is loca ed in he eas açade o building 1, close o he main s ee o his dis ic . The a ic
noise has a high impac on he backg ound noise o he class oom, since in o de o achie e
an adequa e VR i is necessa y o open all windows and he main doo .
3.2. Building 1—Class oom A-2 (B1-A2): C oss-Ven ila ion h ough Co ido s S a egies—Wes
O ien a ion
Figu e 5. Backg ound noise le els in class oom B1-A1.
The backg ound noise Leq o he C-1 was 54.1 dBA. This alue is abo e he back-
g ound noise Leq wi h windows and doo closed (41.5 dBA) and he alue ecommended
by WHO (35dBA). Exposu e o a ic noise is he main p oblem in his class oom, since i
is loca ed in he eas açade o building 1, close o he main s ee o his dis ic . The a ic
noise has a high impac on he backg ound noise o he class oom, since in o de o achie e
an adequa e VR i is necessa y o open all windows and he main doo .
3.2. Building 1—Class oom A-2 (B1-A2): C oss-Ven ila ion h ough Co ido s
S a egies—Wes O ien a ion
The expe imen al esul s ob ained in he es s pe o med in he class oom B1-A2 a e
shown in his sec ion. This class oom is cha ac e ised by he ac ha i can only gene a e
na u al en ila ion h ough he windows loca ed on i s wes side and he main doo on i s
eas side. In his espec , he di e en na u al en ila ion s a egies ha e been analysed,
aking in o accoun scena ios wi h di e en opening con igu a ions o hese windows,
he opening o he doo and he possibili y o opening he co ido windows. The decay
Senso s 2021,21, 6122 16 o 21
C-3 p o ides he lowes mean ACH alue (8.4) and con igu a ion C-1 p o ides he highes
mean ACH alue (24.9). In he case o class oom B2-A2, he con igu a ion p o iding he
lowes a e age ACH alue is con igu a ion C-3 (6.1) and he highes a e age ACH alue is
con igu a ion C-1 (15.5).
As can be seen, he VR depends on he local and pa icula condi ions o each in-
doo space. In his con ex , he con igu a ion chosen among he h ee analysed in each
class oom was he one ha mee s he minimum en ila ion equi emen s. The con igu a-
ions selec ed o class ooms B1-A1, B1-A2, B2-A1 and B2-A2 we e con igu a ions C-1 (all
windows opened and main doo opened), C-1 (all windows opened, main doo opened
and he co ido windows opened), C-3 (only windows a he end opened and main doo
opened) and C-2 (all windows opened and he main doo opened) espec i ely. This
decision is based on ensu ing ha he ACH alue is su icien o gua an ee ha he space
is sa e, al hough he e may be a iabili y in he ACH alue due o possible a ia ions in
en i onmen al condi ions.
Once he na u al en ila ion con igu a ion was selec ed o each class oom, an acous ic
s udy was ca ied ou o compa e he no mal class oom scena io (windows and doo
closed) wi h he chosen con igu a ion o na u al en ila ion. As can be seen om he
esul s ob ained, since he backg ound noise le el should no exceed 35 dBA o good
speech in elligibili y, none o he class ooms me his acous ic quali y ecommenda ion.
Wi h ega d o he compa ison be ween he scena io o closed doo s and windows and
he na u al en ila ion con igu a ion selec ed, i was iden i ied ha he na u al en ila ion
con igu a ion causes an inc ease o be ween 6.4 dBA and 12.6 dBA in he backg ound noise
le el o he class ooms analysed. The backg ound noise is an impo an ac o ha a ec s
he acous ic cla i y and quali y o eaching and lea ning p ocess [56].
Backg ound noise is closely ela ed o he signal- o-noise a io (SNR). In his sense, a
high le el o backg ound noise can cause a low o nega i e SNR. The e o e, a poo SNR
causes, on he one hand, di icul ies o s uden s ha ing o unde s and he message. On
he o he hand, i also causes a highe ocal e o among eache s, as he speake ’s speech
le el has o be highe han he backg ound noise le el.
In ac , backg ound noise becomes a p oblem ha has a majo impac on he cu en
si ua ion. Since he class ooms used o he e u n o campus a e la ge , and o ensu e
physical dis ance be ween s uden s he dis ibu ion o s uden s occupies all ows o sea s,
many s uden s a e in posi ions a away om he eache . As a esul , he signal-noise a io
is e y low in he ea posi ions, causing signi ican e ec s on educing wo d iden i ica ion
and in elligibili y.
The loca ion and o ien a ion o he class oom also in luences he impac o he na u al
en ila ion con igu a ion on class oom backg ound noise. This is e iden in he esul s
ob ained o class oom B1-A1, which is o ien ed owa ds a dense a ic a ea and he back-
g ound noise le el was 54.1 dBA. The e o e, mo e ac o s han oom size and en ila ion
s a egy should be aken in o accoun when choosing he class oom. The loca ion and
o ien a ion o he class oom should be conside ed in o de o educe he impac o back-
g ound noise on he eaching-lea ning p ocess. Consequen ly, he p ac ical implica ions o
he indings show ha en ila ion s a egies managemen in educa ional buildings should
conside he ollowing design and ope a ion guidelines:
•
The class oom selec ion mus ake in o accoun bo h he heal h ecommenda ions and
he impac o backg ound noise. P io i y should be gi en o selec ing hose indoo
spaces ha : 1) mee he heal h equi emen s (minimum dis ances, VR, e c.) and 2)
(due o hei loca ion and o ien a ion) ha e a backg ound noise le el ha does no
in e e e wi h he eaching-lea ning ac i i ies.
•
In hose cases whe e i is no possible o mee he c i e ion s a ed in he p e ious poin ,
an adap a ion in e en ion mus be ca ied ou (i.e., ins alla ion o passi e, ac i e,
au oma ion-based o hyb id noise con ol de ices). Noise con ol solu ions o na u al
en ila ion openings mus ensu e he equi ed VR while also ensu ing he backg ound
noise does no in e e e wi h he pe o mance o s uden s and eache s.

Senso s 2021,21, 6122 17 o 21
The limi a ions p esen ed in he s udy s em om he e ec o indoo and ou doo
en i onmen al condi ions ( he local and pa icula condi ions o each indoo spaces as well
as he wind speed and ou doo empe a u es). Addi ionally, his s udy ollows he p o ocols
s a ed by he Spanish Go e nmen and Uni e si y o G anada p e en ion guidelines. One
o his p o ocols is he IAQ managemen o bo h buildings is o en ila e ( o a leas 1
h be o e and a e each class) by opening all windows. This p ocedu e achie es indoo
empe a u e and ela i e humidi y le els simila o hose ou side, so he e ec o hese
ac o s should be aken in o accoun i di e en condi ions would apply.
5. Conclusions
The aim o his s udy was o analyse he na u al en ila ion s a egies h ough he
con igu a ion o window and doo openings, in acco dance wi h he ecommenda ions
es ablished in he COVID Ac ion Plan o he Uni e si y o G anada, which complies wi h
he ecommenda ions while main aining he maximum deg ee o com o o he use . To
his end, he impac o hese measu es on he acous ic en i onmen o he class oom was
analysed, so ha bo h s uden s and eaching s a main ain sa e le els o p o ec ion agains
he ansmission o SARSCOV-2 wi hou a ec ing hei eaching-lea ning ac i i ies.
The esul s ob ained show ha a co ec choice o con igu a ion can sa is y he VR
needs while ensu ing ha he indoo space is sa e o he occupan s. The measu e-
men s we e ca ied ou in ou di e en class ooms wi h an occupancy pe a ea anging
om
2.20 m2
/s uden o 4.77 m
2
/s uden . These spaces we e selec ed acco ding o he
COVID-19
con ingency plan se up a he beginning o he 2020/2021 academic yea in
each uni e si y cen e. The na u al en ila ion con igu a ion ha me he equi ed ACH
was chosen o assess he impac on backg ound noise inside he class oom. The main
esul s ob ained we e:
•
Na u al c oss- en ila ion is an e ec i e s a egy o achie e he ACH le els equi ed o
ensu e ha he indoo spaces mee he guideline ecommenda ions o a sa e e u n
o campus.
•
The e a e di e ences in he speci ic na u al en ila ion s a egy depending on he
con igu a ion o class ooms and building o ien a ion. Thus, o he class ooms in
building B1 he con igu a ion o all windows opened and main doo opened should
be selec ed no ma e he ype o possible en ila ion (na u al en ila ion h ough
windows o c oss- en ila ion h ough co ido s). On he o he hand, in B2 he speci ic
con igu a ion depends on he class oom ype, i.e., all windows opened and main doo
opened in he case o sou h-o ien a ed class oom, o only windows a he end opened
and main doo opened in he case o he case o no h-o ien a ed class oom achie e
be e esul s due o he di e en o ien a ion o he building. This ac highligh s he
needs o pe o ming speci ic s udies o selec he bes s a egy o implemen na u al
c oss- en ila ion.
•
The a e age VR alue p o ided by he selec ed con igu a ion o each class oom was
8.3 ACH, 6.1 ACH, 8.4 ACH and 8.8 ACH o class ooms B1-A1, B1-A2, B2-A1 and
B2-A2, espec i ely. The e o e, he a e age ACH alue is abo e 6 ACH in all he
selec ed na u al en ila ion con igu a ions.
•
The backg ound noise le el is s ongly a ec ed by he selec ed na u al en ila ion
con igu a ion. The backg ound noise le els wi h he selec ed na u al en ila ion
con igu a ion we e be ween 43.2 and 54.1 dBA. As can be seen, all class ooms exceed
he ecommended 35 dBA backg ound noise le el limi o backg ound noise in
eaching spaces. Consequen ly, he eaching ac i i y managemen has o ake in o
accoun no only he ACH, bu also i s impac on he indoo en i onmen al condi ions
such as he acous ic en i onmen . Since a high alue o backg ound noise le el
can in e e e wi h he eaching and lea ning p ocess and e en in e e e wi h he
pe o mance o s uden s and eache s, educa ional building adminis a o s need o
conside his issue. In hose cases whe e in o de o achie e a na u al en ila ion
s a egy ha p o ides he equi ed VR, he backg ound noise le el exceeds 35 dbA,
Senso s 2021,21, 6122 18 o 21
building manage s should make in e ening adap a ions (i.e., ins alla ion o passi e,
ac i e, au oma ion-based o hyb id noise con ol de ices).
Since his esea ch p o es ha he bes s a egies o achie e a VR alue ha complies
wi h he s anda d imply a signi ican impac in o he indoo en i onmen al a iables
such as indoo noise le els, some ac ions o imp o e he indoo acous ic beha iou o
class ooms a e ecommended. Fo example, he need o elec oacous ic suppo o inc ease
speech in elligibili y, imp o ing he acous ic condi ioning o class ooms, inc easing noise
insula ion wi h o he class ooms and o he common a eas, and ein o cing he compliance
o ou doo noise le els achie ing he acous ic quali y c i e ia p esc ibed o sensi i e
acous ic a eas such as he educa ional ones. The e o e, he managemen , o ganiza ion and
planning o indoo spaces o educa ional buildings mus no only ensu e occupan s’ sa e y,
bu also no in luence he pe o mance o eaching ac i i ies. Ac ion plans a e equi ed
ha allow buildings’ adminis a o s o achie e adequa e na u al en ila ion s a egies and
implemen e ec i e noise educ ion measu es in indoo spaces.
Finally, u u e s udies should ocus on he en i onmen al condi ions o na u al en-
ila ion wi h occupancy in he class ooms, in o de o e alua e no only he objec i e
a iables o he IEQ ac o s, bu also he subjec i e a iables associa ed wi h he pe cep ion
and com o o occupan s wi h ega d o he window and doo opening con igu a ions
es ablished.
Au ho Con ibu ions:
M.L.d.l.H.-T. and A.J.A. concep ualiza ion, pe o med he expe imen s,
o mal analysis and ca ied ou he pos -p ocessing; D.P.R. and M.D.M.-A., concep ualiza ion, p ojec
adminis a ion, unding acquisi ion and supe ised he manusc ip . All au ho s ha e ead and
ag eed o he published e sion o he manusc ip .
Funding:
This esea ch was unded by he Consejo Gene al de la A qui ec u a Técnica (CGATE),
and he S a e Resea ch Agency (SRA) o Spain and Eu opean Regional De elopmen Funds (ERDF)
unde p ojec PID2019-108761RB-I00.
Ins i u ional Re iew Boa d S a emen : No applicable.
In o med Consen S a emen : No applicable.
Da a A ailabili y S a emen : Da a a e p o ided upon eques o he co esponding au ho .
Acknowledgmen s:
The i s wo au ho s wish o hank he suppo o he Minis e io de Ciencia,
Inno ación y Uni e sidades o Spain unde an FPU g an .
Con lic s o In e es : The au ho s decla e no con lic o in e es .
Appendix A
This sec ion con ains da a ob ained om he expe imen al es s o decay me hod and
he a e age ACH esul s.
Table A1. Decay cu es in Class oom B1-A1.
Senso Con igu a ion 1 (C-1) Con igu a ion 2 (C-2) Con igu a ion 3 (C-3)
Reg ession R2 ACH Reg ession R2 ACH Reg ession R2 ACH
Senso 1 y = −8.5562x −0.0116 0.99 8.6 y = −5.8032x −0.0643
0.97
5.8 y = −4.8164x −0.013
0.99
4.8
Senso 2 y = −8.1303x + 0.032 0.99 8.1 y = −5.6655x −0.0146
0.99
5.7 y = −4.5337x + 0.0213
0.99
4.5
Senso 3 y = −7.8861x + 0.0128 0.99 7.9 y = −5.6654x −0.0067
0.98
5.7 y = −4.4275x + 0.0039
0.98
4.4
Senso 4 y = −8.4811x + 0.0253 0.99 8.5 y = −5.4554x −0.0361
0.98
5.5 y = −5.0707x −0.0076
0.97
5.1
Senso 5 y = −9.4362x + 0.0788 0.99 9.4 y = −5.1062x −0.0007
0.99
5.1 y = −4.9633x + 0.0372
0.99
5.0
Senso 6 y = −7.8993x + 0.0444 0.99 7.9 y = −5.0867x −0.0127
0.99
5.1 y = −4.2515x + 0.0065
0.98
4.3
Senso 7 y = −7.3562x −0.0178 0.99 7.4 y = −5.2405x + 0.0546
0.99
5.2 y = −4.3029x −0.0154
0.97
4.3
Senso s 2021,21, 6122 19 o 21
Table A2. Decay cu es in Class oom B1-A2.
Senso Con igu a ion 1 (C-1) Con igu a ion 2 (C-2) Con igu a ion 3 (C-3)
Reg ession R2ACH Reg ession R2ACH Reg ession R2ACH
Senso 1 y = −6.337x + 0.1217 0.96 6.3 y = −4.7516x + 0.0131
0.97
4.8 y = −3.2131x + 0.0578
0.96
3.2
Senso 2 y = −5.5545x + 0.1072 0.96 5.6 y = −4.4593x + 0.0234
0.98
4.5 y = −3.6485x + 0.0048
0.96
3.6
Senso 3 y = −4.9443x + 0.1088 0.92 4.9 y = −4.3944x + 0.062
0.95
4.4 y = −3.997x + 0.0927
0.97
4.0
Senso 4 y = −6.314x + 0.1222 0.98 6.3 y = −5.0606x + 0.0484
0.98
5.1 y = −3.2628x + 0.0311
0.99
3.3
Senso 5 y = −5.7117x + 0.0777 0.99 5.7 y = −5.1964x + 0.0938
0.98
5.2 y = −3.8595x + 0.1546
0.96
3.9
Senso 6 y = −6.6585x + 0.1135 0.93 6.7 y = −4.7563x −0.0159
0.95
4.8 y = −4.1027x + 0.1336
0.95
4.1
Senso 7 y = −6.9932x + 0.1164 0.94 7.0 y = −5.0269x + 0.0316
0.97
5.0 y = −4.0927x + 0.1599
0.96
4.1
Table A3. Decay cu es in Class oom B2-A1.
Senso Con igu a ion 1 (C-1) Con igu a ion 2 (C-2) Con igu a ion 3 (C-3)
Reg ession R2ACH Reg ession R2ACH Reg ession R2ACH
Senso 1 y = −37.373x + 0.3503 0.97 37.4 y = −12.071x −0.1136
0.95
12.1 y = −6.9297x −0.0104
0.99
6.9
Senso 2 y = −17.728x + 0.0923 0.99 17.7 y = −10.227x + 0.1121
0.96
10.2 y = −7.4124x + 0.0203
0.99
7.4
Senso 3 y = −39.807x + 0.0103 0.99 39.8 y = −24.743x + 0.1323
0.97
24.7 y = −8.431x + 0.0709
0.99
8.4
Senso 4 y = −15.465x + 0.008 0.98 15.5 y = −10.332x + 0.0293
0.99
10.3 y = −7.6596x + 0.0606
0.99
7.7
Senso 5 y = −17.138x + 0.0901 0.99 17.1 y = −9.9033x −0.0758
0.97
9.9 y = −9.0858x + 0.0245
0.99
9.1
Senso 6 y = −29.454x + 0.1544 0.94 29.5 y = −11.694x −0.1097
0.96
11.7 y = −9.5583x + 0.049
0.99
9.6
Senso 7 y = −17.66x + 0.0902 0.98 17.6 y = −9.9647x −0.0078
0.98
10.0 y = −9.58x + 0.0345
0.99
9.6
Table A4. Decay cu es in Class oom B2-A2.
Senso Con igu a ion 1 (C-1) Con igu a ion 2 (C-2) Con igu a ion 3 (C-3)
Reg ession R2ACH Reg ession R2ACH Reg ession R2ACH
Senso 1 y = −19.547x −0.0038 0.94 19.5 y = −9.2905x + 0.1220
0.97
9.3 y = −5.9718x + 0.0009
0.98
6.0
Senso 2 y = −10.564x −0.015 0.99 10.6 y = −7.6267x + 0.1165
0.97
7.6 y = −5.9458x + 0.0431
0.99
5.9
Senso 3 y = −18.071x −0.0384 0.96 18.1 y = −10.101x + 0.0051
0.97
10.1 y = −5.3937x −0.0211
0.99
5.4
Senso 4 y = −13.097x + 0.0481 0.99 13.1 y = −8.4722x + 0.1049
0.96
8.5 y = −5.5117x −0.0074
0.99
5.5
Senso 5 y = −12.97x + 0.0908 0.98 13.0 y = −7.3876x + 0.1053
0.97
7.4 y = −5.7052x + 0.0387
0.99
5.7
Senso 6 y = −16.88x −0.0424 0.97 16.9 y = −10.316x + 0.0732
0.98
10.3 y = −7.0921x −0.0266
0.99
7.1
Senso 7 y = −17.514x + 0.1204 0.97 17.5 y = −8.3386x + 0.0169
0.98
8.3 y = −7.0636x + 0.0025
0.98
7.1
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