Resea ch A icle
De e minan s o Ca bon Dioxide Exposu e o Residen s and
S a o Nu sing Homes: A Field Moni o ing S udy in Spain
Alba Fue es ,
1
Ro y V. Jones ,
1
Ma ía Te esa Baque o ,
2
Roge Ve gés ,
2
and Nu ia Fo cada
2
1
School o he Buil En i onmen , Uni e si y o Reading, Reading, UK
2
G oup o Cons uc ion Resea ch and Inno a ion (GRIC), Uni e si a Poli ècnica de Ca alunya (UPC), Te assa, Spain
Co espondence should be add essed o Alba Fue es; [email p o ec ed]
Recei ed 23 Sep embe 2024; Accep ed 24 Ma ch 2025
Academic Edi o : Faming Wang
Copy igh © 2025 Alba Fue es e al. Indoo Ai published by John Wiley & Sons L d. This is an open access a icle unde he
e ms o he C ea i e Commons A ibu ion License, which pe mi s use, dis ibu ion and ep oduc ion in any medium,
p o ided he o iginal wo k is p ope ly ci ed.
P o iding high ai quali y is c ucial o he heal h and well-being o olde people li ing in nu sing homes. A measu emen
s udy was unde aken in 22 communal ooms o fi e nu sing homes in Spain o in es iga e he effec s o hea ing,
en ila ion, and ai -condi ioning (HVAC) sys ems, oom cha ac e is ics, and occupan ac i i ies on he indoo ai quali y. The
s udy included 196 pe iods o da a collec ion (equi alen o 5282 measu emen s). To he au ho s’knowledge, his is he fi s
s udy o indoo ai quali y in Spanish nu sing homes. The s udy ound ha mean CO
2
concen a ions we e consis en ly below
es ablished s anda ds, al hough no able peaks we e e iden due o specific ac i i ies. Na u al and c oss en ila ion had a clea
ole in main aining CO
2
concen a ions below ecommended le els. The findings indica e ha lowe occupancy densi y may be
equi ed in ooms whe e high-CO
2
-gene a ing ac i i ies ake place, such as gym–physio he apy ooms. The esul s showed ha
he olde esiden s and s affwe e bo h mo e he mally com o able a highe CO
2
concen a ions. This sugges s ha s iking a
balance be ween ai quali y and he mal com o is necessa y. The s udy p o ides use ul insigh s o he design o en ila ion
sys ems and spa ial layou s o nu sing homes, which can achie e highe le els o indoo ai quali y and occupan well-being.
Keywo ds: ca bon dioxide; hea ing; indoo ai quali y; nu sing homes; olde people; en ila ion and ai -condi ioning
1. In oduc ion
Buil spaces, bo h indoo s and ou doo s, mus be adap ed o
he needs o he olde popula ion. Resea ch in his field is
ising as he numbe o people o e 65 yea s wo ldwide is
p ojec ed o iple by 2037, and in Spain specifically, hey
will cons i u e 27% o he popula ion [1]. Consequen ly,
demand o assis ed li ing and nu sing home acili ies will
g ow apidly, and unde s anding how such spaces should
be designed and ope a ed o he benefi o hei p ima y
use s is c ucial.
Olde people spend almos 90% o hei ime indoo s
[2–4], and he e o e, indoo en i onmen al condi ions ha e
g ea e effec s on hei heal h and well-being [5–8]. As hma,
espi a o y in ec ions, ca dio ascula sickness, ch onic
obs uc i e pulmona y disease, cance , nausea, uppe espi-
a o y difficul ies, and cogni i e impai men a e jus some
o he heal h condi ions ha ha e been linked o poo indoo
ai quali y (IAQ) [9–11]. Low en ila ion a es and c owded
indoo en i onmen s ha e also been shown o inc ease le els
o bac e ia, gases, pa icula e ma e , and i uses which can
lead o nega i e heal h ou comes o he olde people [12].
Fu he mo e, indoo en i onmen al ac o s, including ca -
bon dioxide (CO
2
) le els, ha e been associa ed wi h beha -
iou al issues like wande ing, agg ession, and agi a ion in
olde people wi h demen ia which nega i ely impac s hei
quali y o li e [13, 14].
P e ious esea ch, such as by Reddy e al. [3], a gued
ha in addi ion o in oducing en o ceable IAQ s anda ds,
nu sing homes should be egula ly moni o ed o p oac i ely
iden i y and add ess weaknesses and ha esou ces should
be made a ailable o emedial measu es o imp o e IAQ,
Wiley
Indoo Ai
Volume 2025, A icle ID 4153784, 17 pages
h ps://doi.o g/10.1155/ina/4153784
such as sou ce con ol, imp o ed en ila ion and fil a ion,
and he use o ai cleane s. The au ho s p opose ha his
would esul in imp o ed heal h, well-being, and quali y o
li e o he olde people and as a esul educe medical cos s.
Many p e ious s udies ha e unde aken measu emen s
o CO
2
concen a ion and assessed i s effec s on humans
[15–18]; howe e , field s udies specifically add essing nu s-
ing homes a e lacking in he li e a u e compa ed o o he
building ypes. Rela ed o he cu en pape , Gue a San in
e al. [19] s udied a ange o spaces in a Passi haus ca e
home o people wi h demen ia in England and ound ha
he pe cen age o ime ha CO
2
concen a ions exceeded
900 ppm was highes in win e , and he esea che s also
aised conce ns abou he posi ioning o he mechanical en-
ila ion (MV) in bed ooms o main ain good IAQ. Baude
e al. [20] epo ed a mean CO
2
concen a ion o 572 1±
106 0 ppm measu ed o e 4.5 days in ou elde ly ca e acil-
i ies in F ance, al hough peaks in excess o 1000 ppm we e
also obse ed. Mendes e al. [7] s udied six u ban ca e cen-
es o olde people in Po ugal and ound ha CO
2
concen-
a ions exceeded an in e na ional ecommended le el o
1080 mg/m
3
(600 ppm CO
2
) in win e bu ell below his
le el in summe . The au ho s concluded ha low en ila ion
a es and c owded indoo condi ions we e associa ed wi h
he highe concen a ions obse ed. Gup a e al. [21] mea-
su ed CO
2
le els in wo lounges in wo diffe en London-
based ca e homes and ound mean concen a ions o
1027 ppm in one and below 500ppm in he o he . The a i-
a ion was a ibu ed o a la ge floo a ea, lowe occupancy
densi y, and g ea e en ila ion.
Al hough no specifically s udies o nu sing homes, Chen
e al. [11] in es iga ed he indoo en i onmen o u al olde
people’s houses in se e al clima ic zones o China and disco -
e ed high CO
2
le els a nigh , which we e associa ed wi h
dec eased en ila ion a es due o he closu e o doo s (Ds)
and windows (Ws). Also, Se ano-Jiménez e al. [22] in es i-
ga ed na u ally en ila ed social housing occupied by olde
adul s du ing diffe en seasons in Spain. High le els o CO
2
we e
pa icula ly e iden in win e , and his was a ibu ed o lowe
en ila ion a es (i.e., esh ai infil a ion and occupan en ila-
ion beha iou , such as opening Ws) du ing he win e season.
These p e ious s udies ha e shown ha CO
2
concen a-
ions in buildings occupied by olde people some imes
exceed in e na ionally ecommended le els, and his may
esul in nega i e heal h and well-being consequences o
his popula ion. The cu en s udy adds o his limi ed bu
g owing body o li e a u e by epo ing on, o he au ho s’
bes knowledge, he fi s s udy o CO
2
concen a ions in
nu sing homes unde aken in Spain.
The aims o he cu en pape we e (i) o measu e he
concen a ions o CO
2
in a ange o diffe en space ypes
(li ing, dining, occupa ional he apy, and gym–physio he -
apy ooms) in fi e Spanish nu sing homes and compa e
hese wi h ecommended alues om na ional and in e na-
ional s anda ds; (ii) o assess he effec s o hea ing,
en ila ion, and ai -condi ioning (HVAC) egimes, oom
cha ac e is ics, and occupan ac i i ies on he le els o CO
2
obse ed; and (iii) o discuss he implica ions o he findings
o imp o ing ai quali y in nu sing homes.
2. Me hodology
The s udy was ca ied ou in fi e nu sing homes loca ed in
Mad id, Spain, be ween Ap il and Augus 2021 (wa m
mon hs) and be ween Oc obe 2021 and Feb ua y 2022
(cold mon hs).
The CO
2
measu emen s we e aken in 22 communal
ooms used in he fi e nu sing homes by he building esi-
den s (olde people) and he suppo s aff(ca egi e s and
he apis s) du ing he day while doing hei ypical ac i i ies.
These include he li ing oom, whe e he nu sing home es-
iden s spend ime wa ching TV and doing o he quie ac i -
i ies such as playing ca ds o eading; dining oom, whe e
esiden s ha e hei meals; gym–physio he apy oom, whe e
esiden s pe o med di ec ed physical exe cises, such as ligh
mo emen s wi h he help o he physio he apis , in g oups
while sea ed; and occupa ional he apy oom, whe e esi-
den s ypically pa icipa e in g oup ac i i ies, such as wo d
games and singing.
The nu sing home esiden s we e all olde han 65 yea s
old wi h a ange o diffe en cogni i e and physical abili ies.
The suppo s affwe e non esiden s and we e gene ally
younge adul s (25–35 yea s old). In ela ion o he s udy,
hey we e hose wi h he capaci y o open o close Ws and
Ds o en ila e he ooms.
The esea ch was app o ed by he e hics commi ee o
he Uni e si a Poli ècnica de Ca alunya (UPC, Spain), and
in o med consen was ob ained om pa icipan s be o e
da a collec ion commenced. The e e ence numbe o he
e hics applica ion is 2020.01.
2.1. Room Cha ac e is ics. The communal ooms in es i-
ga ed we e mos ly loca ed on he g ound floo (L0) o he
nu sing homes. The dimensions o he ooms a ied
be ween nu sing homes and he ac i i y hey we e designed
o , wi h he li ing ooms and dining ooms being he la g-
es . Apa om one oom (occupa ional he apy oom in
NH4), he es all had a leas one W and one D, which could
be open o closed du ing he measu emen s o p o ide na -
u al and c oss en ila ion. All ooms we e also en ila ed by
MV sys ems, which we e solely con olled by a p ep o-
g ammed schedule o ope a ion.
The MV sys ems in he nu sing homes we e cen alised
and ope a ed acco ding o specific p ep og ammed sched-
ules. In NH1, he HVAC sys em includes wo boile s, one
chille , and wo-pipe an coil uni s. Ven ila ion is p o ided
by ou supply and exhaus ans s a egically posi ioned a
diffe en ends o he building, each se ing specificfloo s
wi hin hei espec i e zones. These ans do no include hea
eco e y sys ems. Ven ila ion ope a es wice daily, ollowing
peak occupancy pe iods, bu i is no linked o any moni o -
ing sys em o op imise ai flow o adjus based on eal- ime
needs. In NH2, he HVAC sys em is a VRV wi h 16 ou doo
uni s: h ee pe floo dedica ed o he ooms and one se ing
he common a eas. The en ila ion sys em ea u es hea
eco e y uni s, wi h wo uni s pe floo loca ed in he alse
ceilings o he common a eas. NH3 and NH4 bo h employ
an HVAC sys em wi h wo boile s, wo chille s, and wo-
pipe an coils o hea ing and cooling. In NH3, o ced
2 Indoo Ai
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en ila ion is deli e ed ia fi e zoned ans ha ope a e o
2 h a ound midday. In con as , NH4 elies en i ely on
na u al en ila ion, achie ed by opening Ws ea ly in he
mo ning and a e lunch o p omo e ai flow. In NH5, he
HVAC sys em consis s o a wo-pipe se up wi h one chille
and one boile connec ed o an coil uni s and ai handling
uni s ha se e he common a eas.
The ai flow a es in hese sys ems we e no manually
adjus able by s affand we e se o unc ion acco ding o
he a o emen ioned schedules, hough specific ai flow a es
we e no measu ed in his s udy. Main enance o he MV
sys ems was ca ied ou pe iodically o ensu e hei p ope
unc ioning, hough he equency and ex en o hese p oce-
du es a ied ac oss he nu sing homes.
Fan coils we e used o cool o hea he spaces. Table 1
p esen s he main cha ac e is ics o he in es iga ed ooms
in each nu sing home. All ooms had a simila floo o ceil-
ing heigh o 2.8–3.1 m. Figu e 1 p o ides some addi ional
in o ma ion o he in es iga ed ooms.
All fi e nu sing homes we e in a eas no classified as
highly pollu ed. Each acili y was loca ed wi hin 2 km o a
S a e Me eo ological Agency (Agencia Es a al de Me eo olo-
gía, AEMET) wea he s a ion, ensu ing eliable en i onmen-
al moni o ing. Ou doo CO₂le els emained be ween 400
and 420 ppm, consis en wi h ypical backg ound concen a-
ions and indica ing no significan ele a ion due o pollu-
ion. No e ha he exac loca ions o he nu sing homes
a e no disclosed o main ain anonymi y in acco dance wi h
he s udy’s e hical p ocedu es.
2.2. Da a Acquisi ion. The da a collec ion was unde aken
be ween Ap il and Augus 2021 and Oc obe 2021 and
Feb ua y 2022 in fi e diffe en nu sing homes. Du ing hose
mon hs, each nu sing home was isi ed 7–11 imes by he
esea che s. In each isi , CO
2
concen a ions we e mea-
su ed in he ou ypes o ooms discussed in he pape .
The measu emen s ook place be ween 10:00 am and
6:00 pm, in in e als up o 60 min (excluding he s abilisa-
ion pe iod) pe oom, depending on he oom and he ac i -
i y being ca ied ou by he esiden s.
A o al o 22 communal ooms we e moni o ed du ing
he s udy, esul ing in 196 pe iods o da a collec ion (equi -
alen o 5282 measu emen s). This sample is compa able o
ha o o he s udies such as [23], which ocused on ou
academic buildings and 15 ooms, and [24], which analysed
six buildings.
The numbe o occupan s p esen in each oom du ing
each measu emen pe iod was coun ed and eco ded di ec ly
by he esea che . Du ing he measu emen pe iod, he oom
occupancy and he en ila ion condi ions (by means o he
MV o he opening o Ds/Ws) did no change.
2.2.1. CO
2
Measu emen s. A po able ai quali y da alogge
(Del a OHM HD 21ABE17, accu acy: ±50 ppm + 3%o he
eading, ange o 0–5000 ppm) was used o eco d CO
2
mea-
su emen s e e y minu e. Be o e da a collec ion commenced,
he senso was calib a ed acco ding o he manu ac u e ’s
ins uc ions. The equipmen was allowed a 10-min s abiliza-
ion pe iod be o e measu emen s began. Regula checks
we e pe o med du ing he s udy o ensu e he senso
emained wi hin i s specified accu acy ange.
The senso was placed a a heigh be ween 1.2 and 1.5 m
om floo le el (acco ding o he ANSI/ASHRAE S anda d
62.1 [25], he heigh o he b ea hing zone is desc ibed as
0.75–1.8 m abo e he floo ) and mo e han 1 m away om
walls, Ws, and en ila ion ou le s.
2.2.2. The mal Com o Su ey. Du ing he CO
2
measu e-
men pe iods, he nu sing home esiden s and suppo s aff
we e also su eyed o de e mine hei he mal sensa ion o e
(TSV). A cus omised igh -he e- igh -now su ey was used
o collec subjec i e com o e alua ions. The ques ionnai e
consis ed in one simple ques ion abou he TSV, which
was assessed using he ASHRAE 7-poin he mal sensa ion
scale (−3cold,−2cool,−1sligh ly cool,0neu al,+1sligh ly
wa m,+2wa m,+3ho ) [26]. The TSV was assessed by ask-
ing pa icipan s: “How do you eel a his p ecise momen ?”
Afigu e-based su ey was gi en o esiden s o acili a e
hei unde s anding o he he mal scales.
On a e age, 80% o he occupan s o he oom being
measu ed comple ed he TSV su ey (see occupancy num-
be s in Table 1). Th oughou he s udy and i s mul iple mea-
su emen pe iods, a o al o 3359 su eys we e comple ed:
2873 we e filled by esiden s (2189 women, 684 men), and
486 we e comple ed by suppo s aff(435 women, 51 men).
2.3. Da a Analysis
2.3.1. IAQ S anda ds. The Spanish echnical s anda d o he
design o HVAC sys ems [27] es ablishes diffe en IAQ
le els depending on building ype. Fo nu sing homes, i ec-
ommends “Good ai quali y”(IDA2), as a maximum CO
2
concen a ion le el o 500 ppm abo e he ou doo ai CO
2
concen a ion (conside ed o be 300–400 ppm by his
Spanish s anda d) [28]. The e o e, he Spanish s anda d
ecommends maximum CO
2
le els o 800–900 ppm in nu s-
ing homes.
Simila ly, he Eu opean s anda d EN 13779 [29], which
se s up he pe o mance equi emen s o en ila ion and
oom-condi ioning sys ems o non esiden ial buildings,
ecommends a “Medium IAQ”(IDA2) o 400–600 ppm
CO
2
concen a ion le els abo e he le el o ou doo ai
(conside ed o be 400 ppm by his EU s anda d).
The CO
2
concen a ions measu ed du ing he expe i-
men a ion we e classified acco ding o he IAQ ca ego ies
defined by EN 13779 (Table 2), and an 800–900 ppm CO
2
concen a ion ange was used as a ecommended IAQ o
nu sing homes in line wi h he Spanish echnical s anda d.
2.3.2. Me hods o Analysis. Desc ip i e s a is ical analysis
(minimum, maximum, mean, median, and s anda d de ia-
ion) was used fi s o desc ibe CO
2
le els and da a ends
in ela ion o (i) oom ype, (ii) en ila ion egime (MV
ON/OFF and Ws and Ds open/closed), (iii) hea ing o
cooling egime (hea ing/cooling ON/OFF), and TSV (unidi-
mensional). Fo each o hese scena ios, he cumula i e e-
quency o CO
2
le els alling in each o he IAQ ca ego ies
was analysed.
3Indoo Ai
ina, 2025, 1, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1155/ina/4153784 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [16/04/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
P edic i e s a is ical analysis ( eg ession) was used o
unde s and how CO
2
le els (dependen a iable) can be p e-
dic ed gi en diffe en independen a iables. In his s udy,
eg essions we e used o show how mean CO
2
le els a e
ela ed o a e age occupancy densi y (g oups o 1 m
2
/p)
and (i) oom ype, (ii) en ila ion egime, and (iii) hea ing/
cooling egime. In e alua ing eg ession fi s, conside a ion
was gi en o he expec ed CO
2
le els in a i ually infini e
space (a ound 400 ppm, as a ep esen a ion o an open
space), indica ing a nonlinea dec ease wi h occupancy
densi y. An assessmen o mul iple eg ession lines (linea ,
loga i hmic, powe , and exponen ial) indica ed ha a powe
TABLE 1: Main cha ac e is ics o he in es iga ed communal spaces.
Nu sing home Space Floo a ea (m
2
) Floo le el Window a ea (m
2
) A e age occupancy (min–max)
NH1
Occupa ional he apy oom 35.0 L0 1.6 9 (7–16)
Li ing oom 123.3 L0 14.4 17 (10–34)
Gym–physio he apy oom 47.0 L0 12.6 14 (10–16)
Dining oom 54.3 L0 3.4 19 (11–27)
NH2
Occupa ional he apy oom 101.9 L1 29.9 16 (8–20)
Li ing oom a 56.7 L2 11.4 19 (11–27)
Li ing oom b 145.3 L1 29.9 17
Li ing oom c 156.4 L0 11.4 14 (9–19)
Gym–physio he apy oom 172.5 L1 14.7 19 (14–25)
Dining oom 167.6 L0 26.8 37 (28–49)
NH3
Occupa ional he apy oom 65.4 L0 17.3 23 (17–30)
Li ing oom 126.4 L0 17.3 36
Gym–physio he apy oom 61.0 L0 10.3 10 (8–12)
Dining oom 81.1 L1 8.1 23 (17–31)
NH4
Occupa ional he apy oom 89.2 L0 —14 (12–17)
Li ing oom 125.5 L0 21.7 25 (18–35)
Gym–physio he apy oom 89.2 L0 3.0 18 (12–19)
Dining oom 81.5 L0 29.1 41 (28–48)
NH5
Occupa ional he apy oom 97.5 L0 15.5 20 (7–32)
Li ing oom 103.7 L0 28.9 28 (15–36)
Gym–physio he apy oom 47.1 L0 14.5 11 (7–15)
Dining oom 81.5 L1 17.5 37 (31–43)
(a) (b) (c) (d)
Figu e 1: Examples o he in es iga ed ooms in he nu sing homes: (a) occupa ional he apy oom, (b) li ing oom, (c) dining oom, and
(d) gym–physio he apy oom.
4 Indoo Ai
ina, 2025, 1, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1155/ina/4153784 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [16/04/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
eg ession line p o ided he bes coefficien s o de e mina-
ion. A powe eg ession line is ep esen ed as y=ax
b,
R2=n, whe e yis dependen and xis he independen
a iable. The R2was used o measu e he p opo ion o
he a ia ion in he dependen a iable which is explained
by he model [30].
Da a we e analysed using Mic oso Excel and S a is ical
Package o he Social Sciences (SPSS).
3. Resul s
3.1. O e iew o CO
2
Concen a ion Measu emen s. Du ing
he s udy, 5282 CO
2
concen a ion measu emen s we e col-
lec ed in he dining ooms (1817), li ing ooms (1192),
gym–physio he apy ooms (908), and occupa ional he apy
ooms (1365) o fi e nu sing homes.
Measu ed CO
2
le els anged om 287 o 1558 ppm, wi h
he highes equency o measu emen s alling wi hin he
500–800-ppm ange. Table 3 con ains he desc ip i e s a is-
ical analyses (minimum, maximum, mean, median, and
s anda d de ia ion) o he CO
2
le els eco ded du ing he
s udy. I can be obse ed ha all mean alues a e below
he 800-ppm h eshold, indica ing ha all ooms achie ed
a leas an IAQ ca ego y o IDA3, as shown in Table 2.
The nume ical da a on he numbe and pe cen age o
CO
2
concen a ion measu emen s alling in he ou IAQ
ca ego ies a e p esen ed in Table 4. In his s udy, CO
2
le els
exceeded 800 ppm in 15.8% o he cases, while 4.2% o he
measu emen s we e abo e 1000 ppm, and 0.3% exceeded
1400 ppm.
3.2. CO
2
Concen a ion by Room Type. This sec ion p o-
ides an o e iew o he CO
2
concen a ions in each
oom ype s udied in he fi e nu sing homes: occupa-
ional he apy oom, gym–physio he apy oom, li ing
oom, and dining oom.
TABLE 3: Desc ip i e s a is ical analysis o he CO
2
concen a ion measu emen s.
No. o measu emen s Min (ppm) Max (ppm) Mean (ppm) Median (ppm) SD
CO
2
le els by oom ype (5282 measu emen s)
Dining oom 1817 373 1334 645 619 158
Li ing oom 1192 379 1090 541 521 119
Gym–physio he apy oom 908 384 898 596 574 118
Occupa ional he apy oom 1365 287 1558 713 669 119
CO
2
le els by en ila ion egime (5173 measu emen s) (MV = mechanical en ila ion)
MV OFF 1103 379 1558 638 596 179
MV ON 4070 287 1558 632 592 175
MV OFF: W+D closed 333 395 1558 660 596 235
MV OFF: W+D opened 193 386 1090 613 582 144
MV OFF: Ei he W o D opened 577 379 1202 633 602 147
MV ON: W+D closed 526 395 1558 739 703 250
MV ON: W+D opened 830 384 997 555 547 117
MV ON: Ei he W o D opened 2714 287 1334 635 603 160
CO
2
le els by hea ing/cooling egime (5282 measu emen s)
Hea ing 1817 387 1557 665 628 170
Cooling 1564 287 1314 561 540 124
No cooling/hea ing 1901 386 1558 655 594 197
CO
2
le els by he mal sensa ion o e (TSV) ( esiden s and suppo s aff) (3359 measu emen s)
TSV <0 447 336 1058 619 615 123
TSV = 0 2528 336 1058 625 599 136
TSV >0 384 336 1058 622 599 140
TABLE 2: Recommended CO
2
alues acco ding o EN 13779 [29] s anda d.
IAQ ca ego y Desc ip ion CO
2
le el abo e le el o ou doo
ai (ppm) ( ypical ange)
To al CO
2
le el (ppm), based on
ou doo CO
2
le el o 400 ppm
IDA1 High IAQ ≤400 ≤800
IDA2 Medium IAQ 400–600 800–1000
IDA3 Mode a e IAQ 600–1000 1000–1400
IDA4 Low IAQ >1000 >1400
5Indoo Ai
ina, 2025, 1, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1155/ina/4153784 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [16/04/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
The min, max, and mean (wi h SD) o CO
2
concen a-
ions measu ed in each oom ype a e p esen ed in
Table 3. In his s udy, mean CO
2
le els we e below he
800–900-ppm ecommended le els o nu sing homes [27]
in all oom ypes, wi h he highes mean CO
2
concen a ion
o 713 ppm measu ed in he occupa ional he apy oom.
Howe e , he maximum alues sugges ha all oom ypes,
apa om he gym–physio he apy oom (wi h a CO
2
con-
cen a ion o 898 ppm), eached CO
2
le els abo e he ec-
ommended alues. Again, he occupa ional he apy oom
eco ded he highes CO
2
concen a ion alue o 1558 ppm.
Figu e 2 shows he cumula i e equency (%) o CO
2
measu emen s alling in he ou IAQ ca ego ies o each
oom ype. Fo example, 72% o he CO
2
measu emen s
aken in he occupa ional he apy ooms we e wi hin ca e-
go y IDA1 (CO2< 800 ppm), while 28% o he measu e-
men s exceeded his ecommended le el. F om hose,
17.7% ell in ca ego y IDA2 (800 < CO2< 1000 ppm), 9.1%
in ca ego y IDA3 (1000 < CO2< 1400 ppm), and 1.2% in
ca ego y IDA5 (CO2> 1400 ppm). O e all, he oom ype
wi h he highes equency o measu emen s in ca ego y
IDA1 and he e o e wi h he highes IAQ du ing he s udy
was he li ing ooms (95.6%). Ca ego ies IDA3 (mode a e
IAQ) and IDA4 (low IAQ) had he highes equencies in
he occupa ional he apy ooms (combined equency alue
o 10.3%) and dining ooms (combined equency alue
o 3.6%).
3.3. CO
2
Concen a ion by Ven ila ion Regime. CO
2
concen-
a ions we e analysed o diffe en oom en ila ion scena -
ios, including whe he he MV was ac i e o no (ON/OFF)
and whe he he Ws o Ds we e opened o closed a he ime
o he measu emen s. Ws and Ds we e conside ed o be
opened o closed based on isual inspec ion by he
esea che s.
The min, max, and mean (wi h SD) o CO
2
concen a-
ions measu ed in he diffe en en ila ion scena ios a e p e-
sen ed in Table 3. When s udying he CO
2
le els based on
only he MV being ON/OFF, no pa icula diffe ences we e
obse ed in he a e age concen a ion o he ange o mea-
su emen s (min and max alues). While he ecommended
alue o 800–900 ppm was exceeded in bo h scena ios, he
mean le els [638 ppm (MV OFF), 632 ppm (MV ON)]
s ayed below hese. The effec o he Ws and Ds being
opened o closed was also in es iga ed. Mean CO
2
le els
we e below he 800–900-ppm ecommended le els in all sce-
na ios, wi h he highes mean CO
2
concen a ion o 739 ppm
occu ing when he MV was ON and bo h Ws and Ds we e
closed. In con as , he lowes mean CO
2
le el (555 ppm)
was associa ed wi h he scena io when he MV was ON
and bo h Ws and Ds we e opened. Maximum alues sugges
ha all en ila ion scena ios eached CO
2
le els abo e he
ecommended alues. The scena ios whe e he Ws and Ds
we e closed ( ega dless o he MV being ON o OFF)
eco ded he highes concen a ion alue o 1558 ppm.
TABLE 4:CO
2
concen a ion measu emen s and equency (%) by IAQ ca ego y.
All da a
No. o
measu emen s
IDA1
(<800 ppm)
IDA2
(800–1000 ppm)
IDA3
(1000–1400 ppm)
IDA4
(>1400 ppm)
5282 4447 84.2% 612 11.6% 207 3.9% 16 0.3%
CO
2
le els by oom ype (5282 measu emen s)
Dining oom 1817 1506 82.9% 246 13.5% 65 3.6% 0.0 0.0%
Li ing oom 1192 1139 95.6% 36 3.0% 17.0 1.4% 0.0 0.0%
Gym–physio he apy oom 908 819 90.2% 89 9.8% 0.0 0.0% 0.0 0.0%
Occupa ional he apy oom 1365 983 72.0% 241 17.7% 125 9.1% 16 1.2%
CO
2
le els by en ila ion egime (5173 measu emen s)
MV OFF 1103 951 86.2% 100 9.1% 44 4.0% 8 0.7%
MV ON 4070 3387 83.2% 512 12.6% 163 4.0% 8 0.2%
MV OFF: W+D closed 333 287 86.2% 14 4.2% 24 7.2% 8 2.4%
MV OFF: W+D opened 193 176 91.2% 12 6.2% 5 2.6% 0 0.0%
MV OFF: Ei he W o D opened 577 488 84.6% 74 12.8% 15 2.6% 0 0.0%
MV ON: W+D closed 526 346 65.8% 100 19.0% 72 13.7% 8 1.5%
MV ON: W+D opened 830 799 96.3% 31 3.7% 0 0.0% 0 0.0%
MV ON: Ei he W o D opened 2714 2242 82.6% 381 14.0% 91 3.4% 0 0.0%
CO
2
le els by hea ing/cooling egime (5282 measu emen s)
Hea ing 1817 1444 79.5% 312 17.2% 53 2.9% 8 0.4%
Cooling 1564 1489 95.2% 65 4.2% 10 0.6% 0 0.0%
No hea ing/cooling 1901 1514 79.6% 235 12.4% 144 7.6% 8 0.4%
CO
2
le els by he mal sensa ion o e (TSV) ( esiden s and suppo s aff) (3359 measu emen s)
TSV <0 447 416 93% 24 5% 7 2% 0 0%
TSV = 0 2528 2224 88% 250 10% 54 2% 0 0%
TSV >0 384 333 87% 45 12% 6 2% 0 0%
6 Indoo Ai
ina, 2025, 1, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1155/ina/4153784 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [16/04/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
Figu e 3 shows he cumula i e equency (%) o CO
2
measu emen s alling in he ou IAQ ca ego ies o each
en ila ion scena io. O e all, he en ila ion scena io wi h
he highes equency o measu emen s in ca ego y IDA1
(<800 ppm) and he e o e wi h he highes IAQ du ing he
s udy in ol ed he MV being ON and he Ws and Ds opened
(96.3%). Ca ego ies IDA3 (mode a e IAQ) and IDA4 (low
IAQ) had he highes equency in he scena ios when he
Ws and Ds we e closed, ega dless o whe he he MV was
ON o OFF.
Figu e 3 also p o ides an indica ion o he effec ha he
s a e (opened/closed) o Ws and Ds had on he CO
2
concen-
a ions. Fo example, wi h he MV ON, he pe cen age o
CO
2
measu emen s unde 800 ppm was educed om
96.3% (wi h Ws and Ds opened) o 65.8% (wi h Ws and
Ds closed). This effec was less significan when he MV
was OFF, whe e he diffe ence be ween ha ing he Ws and
Ds opened (91.2%) o closed (86.2%) was only 5% o
measu emen s unde 800 ppm.
3.4. CO
2
Concen a ion by Hea ing/Cooling Regime. CO
2
concen a ions we e also analysed o diffe en oom hea ing
and cooling egimes, including whe he he oom was being
cooled o hea ed o no hea ing/cooling ( ee- unning) was
aking place a he ime o he measu emen s.
The min, max, and mean (wi h SD) o CO
2
concen a-
ions measu ed in he diffe en hea ing/cooling egimes a e
p esen ed in Table 3. Mean CO
2
le els we e below he
800–900-ppm ecommended le els in all scena ios, wi h
he highes mean CO
2
concen a ion o 665 ppm occu ing
when he hea ing sys em was on. In con as , he lowes
mean CO
2
le el (561 ppm) was associa ed wi h he scena io
when he cooling sys em was on. Maximum alues sugges
ha all hea ing/cooling scena ios eached CO
2
le els abo e
he ecommended alues.
The cumula i e equency (%) o CO
2
measu emen s
alling in he ou IAQ ca ego ies o each hea ing/cooling
scena ios is shown in Figu e 4. The highes IAQ (ca ego y
IDA1, <800 ppm) was measu ed in si ua ions when he
cooling sys em was on (93.0% o he measu emen s). In con-
as , ca ego ies IDA3 and IDA4 had he highes equency
when he e was no hea ing o cooling in ope a ion (cumula-
i e equency o 8.2% o measu emen s o e 1000 ppm).
3.5. CO
2
Concen a ion by Occupancy Densi y. Occupancy
densi y was calcula ed as he amoun o floo a ea o he
oom pe occupan (m
2
/p). In his s udy, he occupancy den-
si y anged om 1.0 o 17.0 m
2
/p.
The effec o occupancy densi y on he CO
2
concen a-
ion le els was s udied o he diffe en oom ypes, en ila-
ion egimes, and hea ing/cooling egimes. The mean CO
2
le el o each pe iod o da a collec ion was plo ed agains
he co esponding a e aged occupancy densi y (in g oups
o 1 m
2
/p).
0 100 200 300 400 500 600 700 800 900 1000 1200 1300 1400 1500 1600 1700
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Pe cen (%)
CO2 concen a ion le el (ppm)
IDA1 IDA2 IDA3 IDA4
1100
Occupa ional he apy oom
Gym-physio he apy oom
Li ing oom
Dining oom
To al
Figu e 2: Cumula i e equency (%) o CO
2
measu emen s by oom ype.
7Indoo Ai
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3.5.1. CO
2
Concen a ion by Occupancy Densi y and Room
Type. The mean occupancy densi y a ied om oom o
oom: dining oom, wi h a mean o 3.3 m
2
/p ( anging om
1.0–11.0 m
2
/p); li ing oom, wi h a mean o 5.6 m
2
/p ( ang-
ing om 2.0–17.0 m
2
/p); gym–physio he apy oom, wi h a
mean o 5.8 m
2
/p ( anging om 2.0–12.0 m
2
/p); and occupa-
ional he apy oom, wi h a mean o 4.8 m
2
/p ( anging om
2.0–13.0 m
2
/p).
Figu e 5 shows he mean occupancy densi y plo ed
agains he co esponding mean CO
2
concen a ion le els
o each moni o ing pe iod and by oom ype. The esul s
show ha he mean CO
2
le els dec eased as he floo a ea
pe pe son (m
2
/p) inc eased o all oom ypes. Howe e ,
diffe en co ela ion le els we e ound o each oom ype.
Fo ins ance, he gym–physio he apy oom powe line showed
an R2o 0.89, whe eas he occupa ional he apy oom p o-
ided an R2o jus 0.26. This would sugges ha he specific
ac i i ies ca ied ou in each oom ype influence diffe en ly
he CO
2
concen a ions ela i e o he mean occupancy den-
si y. Thus, ac i i ies wi h high me abolic demands, such as
hose in a gym–physio he apy se ing, p esen ed a s onge
co ela ion wi h he occupancy densi y compa ed o less phys-
ically demanding ooms, such as a li ing oom.
In addi ion, esul s also showed ha o main ain a mean
CO
2
le el o 800 ppm, occupan densi y should be a leas
3.8 m
2
/p in he dining oom, 3.5 m
2
/p in he gym–physio-
he apy, 1 m
2
/p in he li ing oom, and 3.8 m
2
/p in he occu-
pa ional he apy oom.
3.5.2. CO
2
Concen a ion by Occupancy Densi y and
Ven ila ion Regime. The occupancy densi y in each measu e-
men was plo ed agains he co esponding mean CO
2
con-
cen a ion le els in wo diffe en en ila ion scena ios: wi h
he MV ON o OFF. Figu e 6 shows ha , in bo h en ila ion
scena ios, mean CO
2
le els declined as he mean occupancy
densi y inc eased. Resul s sugges ha mean CO
2
concen a-
ions is s ongly co ela ed (R2=081) wi h he mean occu-
pancy densi y when he MV was ON. Con e sely, when
he MV is inac i e, mean CO
2
concen a ions can no be
confiden ly explained by he mean occupancy densi y
(R2=046). Tha would sugges ha he e a e o he ac o s
beyond jus occupancy densi y, such as oom ype, ha
would influence he CO
2
le els. Fu he esea ch in o he
nu sing homes is equi ed o es ablish hese ela ionships.
3.5.3. CO
2
Concen a ion by Occupancy Densi y and
Hea ing/Cooling Regime. Mean CO
2
le els dec eased as he
floo a ea/pe son a io inc eased in all h ee scena ios o hea ing,
cooling o no hea ing/cooling ( ee- unning) (Figu e 7). Resul s
show co ela ions equal o abo e 0.6 ac oss diffe en hea ing/
cooling scena ios: cooling (R2=073), hea ing (R2=060), and
ee- unning (R2=076). This would sugges ha he hea ing/
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700
CO2 concen a ion le el (ppm)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Pe cen (%)
MV OFF: W + D opened
MV OFF: Ei he W o D opened
MV OFF: W + D closed
MV ON: W + D opened
MV ON: Ei he W o D opened
MV ON: W + D closed
IDA 4IDA 3IDA 1 IDA 2
Figu e 3: Cumula i e equency (%) o CO
2
measu emen s by en ila ion egime.
8 Indoo Ai
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cooling egime is an impo an indica o o conside when
e alua ing he mean CO
2
concen a ions based on occupancy
densi y. While he R-squa ed alues indica e mode a e o
s ong co ela ions, i is essen ial o acknowledge ha o he
ac o s, such as oom ype as a o emen ioned, may con ibu e
significan ly o unde s anding he na u e o his concen a ion
dec ease.
3.6. CO
2
Concen a ion O e Time. Tempo al dynamics o
CO
2
a e plo ed in Figu e 8 based on oom ype and en ila-
ion egime. The esul s indica e ha c oss en ila ion was
he mos effec i e me hod o main aining low CO
2
le els.
Tempo al e olu ion o CO
2
le els appea s o a y by oom
ype, ega dless o he en ila ion egime. Specifically, dining
ooms—and o a lesse ex en , occupa ional he apy oom-
s— end o accumula e CO
2
o e ime. In e es ingly, a longe
o al moni o ed ime was associa ed wi h highe CO₂con-
cen a ions, indica ing a endency o accumula ion, pa icu-
la ly in cases wi h insufficien en ila ion.
3.7. CO
2
Concen a ion and TSV. CO
2
concen a ions we e
also s udied in ela ion o he TSVs epo ed by he nu sing
home esiden s and he suppo ing s affsu eyed du ing he
moni o ing pe iods.
The equency (%) o TSVs epo ed in each scale (−3
cold,−2cool,−1sligh ly cool,0neu al,+1sligh ly wa m,
+2 wa m,+3ho ) [26] alling in he ou IAQ ca ego ies is
shown in Figu e 9. In his s udy, he esul s sugges ha
he pe cen age o he nu sing home esiden s (olde people)
epo ing eeling neu al (TSV = 0) and he e o e he mally
com o able inc eases wi h he CO
2
concen a ion le els.
The highes pe cen age (83.9%) o esiden s eeling neu al
(TSV = 0) was eco ded in si ua ions when he CO
2
le els
we e be ween 1000 and 1400 ppm (IDA3). In con as , he
lowes numbe (78.4%) o esiden s eeling neu al (TSV = 0)
was eco ded when CO
2
concen a ions we e below 800ppm
(IDA1). In hose ci cums ances, 14.9% o esiden s epo ed
eeling om sligh ly cool o cold (TSV < 0), compa ed o
6.8% who epo ed eeling sligh ly wa m o ho (TSV > 0).
Simila ly, he suppo s aff epo ed eeling neu al (TSV = 0)
in g ea e equency (63.9%) a CO
2
le els be ween 1000 and
1400ppm (IDA3) and a lowe equency (48.8%) a CO
2
con-
cen a ions be ween 800 and 1000 ppm (IDA2).
When compa ing he TSV o he nu sing home esiden s
and he suppo s aff, i can be obse ed ha esiden s we e
gene ally eeling colde han he s aff. This was pa icula ly
e iden a CO
2
le els below 800 ppm (IDA1) (14.9% o esi-
den s wi h TSV < 0, compa ed o 9% o s aff, and 6.8% o
esiden s wi h TSV > 0, compa ed o 37.1% o suppo s aff).
The mean he mal sensa ion o e (MTSV) o all o es
eco ded o each moni o ing pe iod was calcula ed and sub-
sequen ly ela ed o he CO
2
measu emen s o he pe iod.
Figu e 10 shows box plo s o MTSV o nu sing home esi-
den s and suppo s aff o he ou IAQ ca ego ies. A e age
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Pe cen (%)
IDA1 IDA2 IDA3 IDA4
CO
2
concen a ion le el (ppm)
Cooling
Hea ing
No cooling/hea ing
Figu e 4: Cumula i e equency (%) o CO
2
measu emen s by hea ing/cooling egime.
9Indoo Ai
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sensa ion gap widening a spaces wi h lowe CO
2
le els. The e o e, achie ing a balance be ween ai qual-
i y and he mal com o is essen ial.
While his s udy ocused specifically on CO₂as an indi-
ca o o en ila ion effec i eness, u he esea ch should
explo e he ull spec um o IAQ ac o s. In pa icula , s ud-
ies in es iga ing he p esence o pa icula e ma e , VOCs,
and o he pollu an s in nu sing homes a e needed. Such
esea ch will con ibu e o a mo e comp ehensi e unde -
s anding o how a ious indoo ai pollu an s influence he
heal h and com o o ulne able popula ions, including
olde esiden s and nu sing home s aff.
Da a A ailabili y S a emen
Da a will be made a ailable upon eques .
Con lic s o In e es
The au ho s decla e no conflic s o in e es .
Au ho Con ibu ions
Alba Fue es: w i ing –o iginal d a , in es iga ion, concep-
ualiza ion, da a cu a ion, o mal analysis. Ro y V. Jones:
w i ing –o iginal d a , concep ualiza ion, in es iga ion.
Ma ía Te esa Baque o: w i ing –o iginal d a , in es iga-
ion, da a cu a ion, me hodology. Roge Ve gés: w i ing –
o iginal d a , in es iga ion, da a cu a ion, isualiza ion.
Nu ia Fo cada: unding acquisi ion, p ojec adminis a ion,
me hodology, in es iga ion, w i ing – e iew and edi ing.
Funding
This esea ch was suppo ed by he Spanish Minis y o
Economy, Indus y and Compe i i eness unde he R&D
p ojec Thecoelen, e e ence no. PID2019-106777RB-C21.
Suppo o his esea ch was also p o ided by he Ca alan
agency AGAUR unde i s esea ch g oup suppo p og am
(2021 SGR 00341).
Acknowledgmen s
The au ho s hank Sani as Mayo es and especially Ma c Val-
le and Albe Ayala o p o iding hei nu sing homes and
helping o collec he da a. The au ho s would like o ex end
ou app ecia ion o all he olde people and suppo and
main enance s affwho pa icipa ed in his p ojec .
Re e ences
[1] Na ional Ins i u e o S a is ics, Spanish Popula ion P ojec ions
2022-2072 (P ess no e, 2022), h ps://www.ine.es/p ensa/pp_
2022_2072.pd .
[2] C. Hughes, S. Na a ajan, C. Liu, W. J. Chung, and M. He e a,
“Win e The mal Com o and Heal h in he Elde ly,”
Ene gy Policy 134 (2019): 110954, h ps://doi.o g/10.1016/
j.enpol.2019.110954.
[3] M. Reddy, M. Heida inejad, B. S ephens, and I. Rubins ein,
“Adequa e Indoo Ai Quali y in Nu sing Homes: An Unme
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