Analysis of impact of natural ventilation strategies in ventilation rates and indoor environmental acoustics using sensor measurement data in educational buildings

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 Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a il- ia ions. Copy igh : © 2021 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). 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 Re e ences 1. Sa bu, I.; Seba chie ici, C. Aspec s o indoo en i onmen al quali y assessmen in buildings. Ene gy Build. 2013 ,60, 410–419. [C ossRe ] 2. Lamb, S.; Kwok, K.C. A longi udinal in es iga ion o wo k en i onmen s esso s on he pe o mance and wellbeing o o ice wo ke s. Appl. E gon. 2016,52, 104–111. [C ossRe ] 3. Anda gie, M.S.; Aza , E. An applied amewo k o e alua e he impac o indoo o ice en i onmen al ac o s on occupan s’ com o and wo king condi ions. Sus ain. Ci ies Soc. 2019,46, 101447. [C ossRe ] 4. Al-Ali, D.; Kamoona, G.M.I. E ec i eness o Nanoma e ial in he Roo o he Building o Achie e Ene gy Conse a ion o Indoo En i onmen o he Building. J. Eng. 2021,27, 126–148. [C ossRe ] 5. Liu, J.; Yang, X.; Jiang, Q.; Qiu, J.; Liu, Y. Occupan s’ he mal com o and pe cei ed ai quali y in na u al en ila ed class ooms du ing cold days. Build. En i on. 2019,158, 73–82. [C ossRe ] 6. Almeida, R.M.; Pin o, M.; Pinho, P.G.; de Lemos, L.T. Na u al en ila ion and indoo ai quali y in educa ional buildings: Expe imen al assessmen and imp o emen s a egies. Ene g. E ic. 2017,10, 839–854. [C ossRe ] 7. Annesi-Maesano, I.; Baiz, N.; Bane jee, S.; Rudnai, P.; Ri e, S.; G oup, S. Indoo ai quali y and sou ces in schools and ela ed heal h e ec s. J. Toxicol. En i on. Heal h B 2013,16, 491–550. [C ossRe ] 8. Ye, W.; Zhang, X.; Gao, J.; Cao, G.; Zhou, X.; Su, X. Indoo ai pollu an s, en ila ion a e de e minan s and po en ial con ol s a egies in Chinese dwellings: A li e a u e e iew. Sci. To al En i on. 2017,586, 696–729. [C ossRe ] 9. Simoni, M.; Annesi-Maesano, I.; Sigsgaa d, T.; No back, D.; Wieslande , G.; Nys ad, W.; Canciani, M.; Ses ini, P.; Viegi, G. School ai quali y ela ed o d y cough, hini is and nasal pa ency in child en. Eu . Respi . J. 2010,35, 742–749. [C ossRe ] [PubMed] 10. Men ese, S.; Mi ici, N.A.; Elbi , T.; Palaz, E.; Mumcuo˘glu, D.T.; Co uke , O.; Baka , C.; Oymak, S.; O kun, M.T. A long- e m mul i-pa ame ic moni o ing s udy: Indoo ai quali y (IAQ) and he sou ces o he pollu an s, p e alence o sick building synd ome (SBS) symp oms, and espi a o y heal h indica o s. A mos. Pollu . Res. 2020,11, 2270–2281. [C ossRe ] Senso s 2021,21, 6122 20 o 21 11. B ook, R.D.; Rajagopalan, S.; Pope III, C.A.; B ook, J.R.; Bha naga , A.; Diez-Roux, A.V.; Holguin, F.; Hong, Y.; Luepke , R.V.; Mi leman, M.A. Pa icula e ma e ai pollu ion and ca dio ascula disease: An upda e o he scien i ic s a emen om he Ame ican Hea Associa ion. Ci cula ion 2010,121, 2331–2378. [C ossRe ] 12. Kama uzzaman, S.; Sab ani, N. The e ec o indoo ai quali y (IAQ) owa ds occupan s’ psychological pe o mance in o ice buildings. J. Des. Buil 2011,4, 49–61. 13. Ha e inen-Shaughnessy, U.; Shaughnessy, R.J.; Cole, E.C.; Toyinbo, O.; Moschand eas, D.J. An assessmen o indoo en i onmen- al quali y in schools and i s associa ion wi h heal h and pe o mance. Build. En i on. 2015,93, 35–40. [C ossRe ] 14. Toyinbo, O.; Shaughnessy, R.; Tu unen, M.; Pu us, T.; Me sämuu onen, J.; Ku ni ski, J.; Ha e inen-Shaughnessy, U. Building cha ac e is ics, indoo en i onmen al quali y, and ma hema ics achie emen in Finnish elemen a y schools. Build. En i on. 2016 , 104, 114–121. [C ossRe ] 15. Qabbal, L.; Younsi, Z.; Naji, H. An indoo ai quali y and he mal com o app aisal in a e o i ed uni e si y building ia low-cos sma senso . Indoo Buil En i on. 2021. [C ossRe ] 16. Ba e man, S. Re iew and ex ension o CO2-based me hods o de e mine en ila ion a es wi h applica ion o school class ooms. In . J. En i on. Res. Public Heal h 2017,14, 145. [C ossRe ] [PubMed] 17. Pe sily, A. Challenges in de eloping en ila ion and indoo ai quali y s anda ds: The s o y o ASHRAE S anda d 62. Build. En i on. 2015,91, 61–69. [C ossRe ] 18. Ba e man, S.; Su, F.C.; Wald, A.; Wa kins, F.; Godwin, C.; Thun, G. Ven ila ion a es in ecen ly cons uc ed US school class ooms. Indoo Ai 2017,27, 880–890. [C ossRe ] 19. ASHRAE. ANSI/ASHRAE S anda d 62.1-2016 Ven ila ion o Accep able Indoo Ai Quali y; ASHRAE: A lan a, GA, USA, 2016. 20. ASHRAE. ANSI/ASHRAE S anda d 62.2-2016 Ven ila ion o Accep able Indoo Ai Quali y in Residen ial Buildings; ASHRAE: A lan a, GA, USA, 2016. 21. B elih, N.; Seppänen, O. Ven ila ion a es and IAQ in Eu opean s anda ds and na ional egula ions. In P oceedings o he 32nd AIVC Con e ence and 1s Tigh Ven Con e ence in B ussels, B ussels, Belgium, 12–13 Oc obe 2011; pp. 12–13. 22. B i ish S anda ds Ins i u ion (BSI). BSI/BS EN 15242:2007 Ven ila ion o Buildings: Calcula ion Me hods o he De e mina ion o Ai Flow Ra es in Buildings Including In il a ion; BSI: London, UK, 2008. 23. Mendell, M.J.; Elisee a, E.A.; Da ies, M.M.; Spea s, M.; Lobscheid, A.; Fisk, W.J.; Ap e, M.G. Associa ion o class oom en ila ion wi h educed illness absence: A p ospec i e s udy in C ali o nia elemen a y schools. Indoo Ai 2013,23, 515–528. [C ossRe ] 24. Wo ld Heal h O ganiza ion (WHO). WHO Co ona i us (COVID) Dashboa d. 2020. A ailable online: h ps://co id19.who.in / (accessed on 10 Sep embe 2021). 25. Minis e io de Sanidad Gobie no de España. Sanidad. A ailable online: h ps://www.mscbs.gob.es/p o esionales/saludPublica/ ccayes/ale asAc ual/nCo /ciudadania.h m (accessed on 1 July 2021). 26. Minis e io de Sanidad Gobie no de España. Sanidad. E aluación del Riesgo de la T ansmisión de SARS-CoV-2 Median e Ae osoles Medidas de P e ención y Recomendaciones. A ailable online: h ps://www.mscbs.gob.es/p o esionales/saludPublica/ccayes/ ale asAc ual/nCo /documen os/COVID19_Ae osoles.pd (accessed on 1 July 2021). 27. Nishiu a, H.; Oshi ani, H.; Kobayashi, T.; Sai o, T.; Sunagawa, T.; Ma sui, T.; Waki a, T.; COVID, M.; Team, R.; Suzuki, M. Closed en i onmen s acili a e seconda y ansmission o co ona i us disease 2019 (COVID-19). medRxi 2020. [C ossRe ] 28. Pa k, S.; Choi, Y.; Song, D.; Kim, E.K. Na u al en ila ion s a egy and ela ed issues o p e en co ona i us disease 2019 (COVID-19) ai bo ne ansmission in a school building. Sci. To al En i on. 2021,789, 147764. [C ossRe ] 29. Dai, H.; Zhao, B. Associa ion o he in ec ion p obabili y o COVID-19 wi h en ila ion a es in con ined spaces. Build. Simul. 2020,13, 1321–1327. [C ossRe ] 30. Zi elonghi, A.; Lai, M. The ole o class oom olume, occupancy, oice educ ion and p2 masks in ansmission isk o SARS-CoV2 in schools. medRxi 2021. [C ossRe ] 31. UNESCO. Educa ion: F om Dis up ion o Reco e y. A ailable online: h ps://en.unesco.o g/co id19/educa ion esponse (accessed on 1 July 2021). 32. Field, C.D.; Dige ness, J. Acous ic design c i e ia o na u ally en ila ed buildings. J. Acous . Soc. Am. 2008 ,123, 3814. [C ossRe ] 33. To esin, S.; Alba ici, R.; Ale a, F.; Babich, F.; Obe man, T.; Kang, J. Acous ic design c i e ia in na u ally en ila ed esiden ial buildings: New esea ch pe spec i es by applying he indoo soundscape app oach. Appl. Sci. 2019,9, 5401. [C ossRe ] 34. E çakmak, U.B.; Dökmeci Yö üko˘glu, P.N. Compa ing Tu kish and Eu opean noise managemen and soundscape policies: A p oposal o indoo soundscape in eg a ion o a chi ec u al design and applica ion. In Acous ics; Mul idisciplina y Digi al Publishing Ins i u e: Basel, Swi ze land, 2019; pp. 847–865. 35. To esin, S.; Ale a, F.; Babich, F.; Bou deau, E.; Ha ie-Cla k, J.; Kang, J.; La ia, L.; Radicchi, A.; Alba ici, R. Acous ics o suppo i e and heal hy buildings: Eme ging hemes on indoo soundscape esea ch. Sus ainabili y 2020,12, 6054. [C ossRe ] 36. Al omon e, S.; Allen, J.; Bluyssen, P.M.; B age , G.; Heschong, L.; Lode , A.; Schia on, S.; Vei ch, J.A.; Wang, L.; Wa gocki, P. Ten ques ions conce ning well-being in he buil en i onmen . Build. En i on. 2020,180, 106949. [C ossRe ] 37. Tang, S.-K. A e iew on na u al en ila ion-enabling açade noise con ol de ices o conges ed high- ise ci ies. Appl. Sci. 2017,7, 175. [C ossRe ] 38. Fusa o, G.; Yu, X.; Kang, J.; Cui, F. De elopmen o me acage o noise con ol and na u al en ila ion in a window sys em. Appl. Acous . 2020,170, 107510. [C ossRe ] Senso s 2021,21, 6122 21 o 21 39. Fusa o, G.; Yu, X.; Lu, Z.; Cui, F.; Kang, J. A me awindow wi h op imised acous ic and en ila ion pe o mance. Appl. Sci. 2021 , 11, 3168. [C ossRe ] 40. Shield, B.M.; Dock ell, J.E. The e ec s o noise on child en a school: A e iew. Build. Acous . 2003,10, 97–116. [C ossRe ] 41. Shield, B.M.; Dock ell, J.E. The e ec s o en i onmen al and class oom noise on he academic a ainmen s o p ima y school child en. J. Acous . Soc. Am. 2008,123, 133–144. [C ossRe ] 42. C andell, C.C.; Smaldino, J.J. Class oom acous ics o child en wi h no mal hea ing and wi h hea ing impai men . Lang. Speech. Hea . Se . Sch. 2000,31, 362–370. [C ossRe ] 43. K is iansen, J.; Pe sson, R.; Lund, S.P.; Shibuya, H.; Nielsen, P.M. E ec s o class oom acous ics and sel - epo ed noise exposu e on eache s’ well-being. En i on. Beha . 2013,45, 283–300. [C ossRe ] 44. K üge , E.L.; Zannin, P.H. Acous ic, he mal and luminous com o in class ooms. Build. En i on. 2004 ,39, 1055–1063. [C ossRe ] 45. Kla e, M.; Hellb ück, J.; Seidel, J.; Leis ne , P. E ec s o class oom acous ics on pe o mance and well-being in elemen a y school child en: A ield s udy. En i on. Beha . 2010,42, 659–692. [C ossRe ] 46. Be glund, B.; Lind all, T.; Schwela, D.H.; Wo ld Heal h O ganiza ion. Guidelines o Communi y Noise; Wo ld Heal h O ganiza ion: Gene a, Swi ze land, 1999. 47. Ame ican Na ional S anda ds Ins i u e (ANSI); Acous ical Socie y o Ame ica (ASA). ANSI/ASA S12.60-2010/Pa 1 Ame ican Na ional S anda d Acous ical Pe o mance C i e ia, Design Requi emen s, and Guidelines o Schools, Pa 1: Pe manen Schools; Acous ical Socie y o Ame ica: Mel ille, NY, USA, 2010. 48. DB-HE. Documen o Básico Aho o de Ene gia. 2019. A ailable online: h ps://www.codigo ecnico.o g/Documen osCTE/ Aho oEne gia.h ml (accessed on 1 July 2021). 49. UGR. Plan de Con ingencia. Plan de Ac uación COVID-19. 2020. A ailable online: h ps://co id19.ug .es/in o macion/plan- con ingencia (accessed on 1 July 2021). 50. Huang, Q.; Ma zouk, T.; Ci ligeanu, R.; Malms om, H.; Elia , E.; Ren, Y.-F. Ven ila ion Assessmen by Ca bon Dioxide Le els in Den al T ea men Rooms. J. Den . Res. 2021,100, 810–816. [C ossRe ] [PubMed] 51. Allen, J.; Spengle , J.; Jones, E.; Cedeno-Lau en , J. 5-S ep Guide o Checking Ven ila ion Ra es in Class ooms. Heal hy Buildings. Ha a d Heal hy Buildings P og am. 2020. A ailable online: h ps://schools. o heal h.o g/ en ila ion-guide/ (accessed on 1 July 2021). 52. Ins i u o de Diagnós ico Ambien al y Es udios del Agua, IDAEA-CSIC, Mesu a. Guía Pa a Ven ilación en Aulas. 2020. A ailable online: h ps://digi al.csic.es/bi s eam/10261/221538/14/guia_ en ilacion_aulas_CSIC-Mesu a_ 4.pd (accessed on 1 July 2021). 53. Asociación Española de No malización (UNE-ISO). UNE-ISO 1996-2:2020. Acous ics. Desc ip ion, Measu emen and Assessmen o En i onmen al Noise. Pa 2: De e mina ion o Sound P essu e Le els; Asociación Española de No malización (UNE-ISO): Mad id, Spain, 2020. 54. Puglisi, G.E.; As ol i, A.; Can o Cu i a, L.; Ca ullo, A. Assessmen o indoo ambien noise le el in school class ooms. In P oceedings o he Con e ence on Noise Con ol–Eu oNoise, Maas ich , The Ne he lands, 31 May–3 June 2015. 55. Calosso, G.; Puglisi, G.E.; As ol i, A.; Cas ellana, A.; Ca ullo, A.; Pelle ey, F. A one-school yea longi udinal s udy o seconda y school eache s’ oice pa ame e s and he in luence o class oom acous ics. J. Acous . Soc. Am. 2017 ,142, 1055–1066. [C ossRe ] [PubMed] 56. Wen, X.; Lu, G.; L , K.; Jin, M.; Shi, X.; Lu, F.; Zhao, D. Impac s o a ic noise on oadside seconda y schools in a p o o ype la ge Chinese ci y. Appl. Acous . 2019,151, 153–163. [C ossRe ]