Ene gy implica ions o mee ing indoo ai quali y and he mal com o
s anda ds in Medi e anean schools using na u al and mechanical
en ila ion s a egies
M. Maiques
*
, J. Ta agona , M. Gangolells , M. Casals
Uni e si a Poli `
ecnica de Ca alunya, G oup o Cons uc ion Resea ch and Inno a ion (GRIC), C/ Colom, 11, Ed. TR5, 08222 Te assa (Ba celona), Spain
ARTICLE INFO
Keywo ds:
Indoo ai quali y
The mal com o
Na u al en ila ion
Mechanical en ila ion
Educa ional buildings
Ene gy e iciency
HVAC
ABSTRACT
Educa ional buildings o en ace signi ican challenges wi h indoo ai quali y and he mal com o , mainly due
o a lack o mechanical en ila ion and ai condi ioning sys ems. Resea ch has demons a ed ha hese issues
nega i ely a ec s uden s’lea ning. The main objec i e o his pape was o assess compliance wi h indoo ai
quali y and he mal com o s anda ds in educa ional buildings, by quan i ying HVAC ene gy implica ions unde
na u al and mechanical en ila ion s a egies. Fo his pu pose, an educa ional building model ha has 4
class ooms occupied by s uden s om di e en age g oups was simula ed in 11 Medi e anean clima e zones, o
4 en ila ion s a egies, and wi h 2 building o ien a ions. The esul s e eal ha na u al en ila ion is e ec i e
only in mild Medi e anean clima es, wi h ai quali y non-compliance anging om 0 % o 2 % and he mal
com o non-compliance be ween 2 % and 5 %. As expec ed, mechanical en ila ion always ensu es accep able
indoo ai quali y and he mal com o . I achie es a e age HVAC ene gy sa ings o 80 % compa ed o na u al
en ila ion. When conside ing ha s uden s’CO
2
gene a ion a es a y depending on he age, sys ems wi h CO
2
senso s u he educe HVAC demand (8 %), while main aining com o le els. Building o ien a ion was ound o
ha e a signi ican impac o na u ally en ila ed buildings. Sou h- acing o ien a ions can educe HVAC ene gy
demand by up o 42 % (1,989 kWh/m
2
⋅yea ), whe eas mechanically en ila ed buildings show minimal sensi-
i i y o o ien a ion (up o 36 kWh/m
2
⋅yea ). This esea ch will help public au ho i ies o he educa ional
communi y and a chi ec u e and enginee ing sec o s when hey a e planning, designing and e o i ing
educa ional buildings. Educa ional building manage s will also bene i om his esea ch by being able o
op imise building en ila ion h ough he e ec i e managemen o exis ing esou ces.
1. In oduc ion
As ecen ly highligh ed by he new Ene gy Pe o mance o Buildings
Di ec i e 2024/1275 [1], imp o ed li ing s anda ds and inc eased
conce ns o human heal h and well-being ha e unde sco ed he
impo ance o ensu ing indoo com o in buildings, wi h a pa icula
emphasis on indoo ai quali y and he mal com o . The COVID-19
pandemic u he highligh ed he impo ance o main aining adequa e
indoo ai quali y, gi en ha he main mode o i us ansmission occu s
ia ai bo ne in ec ious pa icles [2,3,4], wi h ansmission isks
heigh ened in densely occupied indoo spaces wi h p olonged exposu e
[5]. Simul aneously, clima e change has unde sco ed he need o ensu e
p ope he mal com o , as i has led o subs an ial modi ica ions in
global wea he pa e ns, including an inc eased equency o p olonged
hea wa es and ex eme empe a u e e en s in he Medi e anean a ea
[6]. In schools, poo indoo ai quali y and he mal discom o ha e
been demons a ed o ad e sely impac s uden pe o mance, con ib-
u ing o educed concen a ion, nega i e heal h e ec s, and highe a es
o illness among s uden s [7,8,9].
Indoo ai quali y is achie ed h ough he en ila ion o indoo
spaces, which aims o dilu e ai bo ne pollu an concen a ion o
accep able le els. Indoo ai quali y is commonly quan i ied by
Abb e ia ions: BMR, Basal me abolic a e; CO
2
, Ca bon dioxide; DMV, Di ec mechanical en ila ion; HVAC, Hea ing, en ila ion and ai condi ioning; IAQ, Indoo
ai quali y; IMV, Indi ec mechanical en ila ion; NV100, Full opening o windows and doo s na u al en ila ion s a egy; NV50, Hal opening o windows and doo s
na u al en ila ion s a egy; PVGIS, Pho o ol aic geog aphical in o ma ion sys em; RITE, Spanish Regula ion o The mal Ins alla ions in Buildings; TBC, Technical
Building Code; TC, The mal com o .
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (M. Maiques).
Con en s lis s a ailable a ScienceDi ec
Ene gy &Buildings
jou nal homepage: www.else ie .com/loca e/enb
h ps://doi.o g/10.1016/j.enbuild.2024.115076
Recei ed 26 Sep embe 2024; Recei ed in e ised o m 31 Oc obe 2024; Accep ed 17 No embe 2024
Ene gy & Buildings 328 (2025) 115076
A ailable online 19 No embe 2024
0378-7788/© 2024 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (
h p://c ea i ecommons.o g/licenses/by-
nc-nd/4.0/ ).
measu ing he concen a ion le el o ca bon dioxide (CO
2
), which is
p ima ily inc eased by he espi a o y ac i i y o occupan s. CO
2
is used
as a ace gas and se es as a su oga e indica o o indoo ai quali y, as
i is ypically well dispe sed in occupied a eas and is easy and eliable o
measu e [10,11,12]. Ai enewal can be achie ed h ough ei he na u al
o mechanical en ila ion sys ems. Na u al en ila ion elies on passi e
design s a egies ha allow ai o low h ough building openings using
na u al o ces such as wind and he mal buoyancy. Al hough na u al
en ila ion has no ope a ional cos s, i s e iciency is highly dependen on
ex e nal condi ions such as clima e, building o ien a ion and wind. Due
o i s di ec connec ion wi h he ou side en i onmen , occupan he mal
com o migh be signi ican ly comp omised [13]. In con as , me-
chanical en ila ion egula es ai enewal o ensu e indoo ai quali y
h ough ac i e ene gy equipmen , using a duc sys em wi h ans. Due o
he high in es men and ope a ional cos s associa ed wi h mechanical
en ila ion sys ems, hei adop ion in educa ional buildings has been
limi ed. As a esul , mos educa ional buildings in Eu ope lack me-
chanical en ila ion sys ems [14,15]. The e o e, na u al en ila ion is
he only a ailable en ila ion me hod. The e ec i eness o his me hod
elies on he occupan s’subjec i e assessmen o com o . Ven ila ion
esul s in ene gy losses due o he exchange o indoo and ou doo ai ,
leading o comp omised he mal com o . The mal com o is ensu ed
by using hea ing sys ems and ai condi ioning equipmen o main ain
com o able indoo empe a u es. The e o e, balancing indoo ai
quali y and he mal com o is essen ial [16].
P e ious esea ch in ol ing on-si e measu emen s in na u ally
en ila ed educa ional buildings ac oss Eu ope has demons a ed ha
elying exclusi ely on na u al en ila ion is insu icien o main ain
accep able indoo ai quali y du ing all occupied pe iods wi hou
a ec ing he mal com o . S udies conduc ed in London [17], Spain
[18,19], I aly [20,21], Po ugal [22], Cyp us [23] and Tu key [24]
consis en ly de e mined ha CO
2
concen a ion limi s a e o en excee-
ded. This highligh s he need o imp o ed en ila ion s a egies o
ensu e ha indoo ai quali y and he mal com o a e e ec i ely ach-
ie ed. Along his line, Miao e al. [15] assessed indoo ai quali y and
he mal com o in 32 na u ally en ila ed schools in he Medi e anean
clima e based on an ex ensi e moni o ing campaign. Thei esul s
indica ed ha he minimum equi emen s o bo h aspec s we e only
me 46 % o he ime. Poo indoo ai quali y was mainly due o closing
windows and doo s in win e , whe eas he mal discom o mainly
occu ed in summe due o high indoo empe a u e.
O he s udies based on on-si e measu emen s in schools equipped
wi h mechanical en ila ion sys ems ha e concluded ha bo h CO
2
-
based and cons an ai low en ila ion sys ems a e e ec i e in main-
aining op imal CO
2
concen a ion le els [25]. In he con ex o he
COVID-19 pandemic, esea ch has demons a ed ha mechanical
en ila ion has a posi i e impac on con olling in ec ion [26,27,28,29].
Addi ionally, demand-con olled en ila ion sys ems ha e been shown
o main ain accep able indoo ai quali y and o e mo e ene gy-e icien
solu ions [30].
Few s udies ha e quan i ied he impac o na u al and mechanical
en ila ion s a egies on indoo ai quali y, he mal com o and ene gy
consump ion in schools unde a simula ion-based app oach. Be na do
e al. [31] conduc ed a yea -long simula ion o a school building in he
ci y o Coimb a, Po ugal, using mechanical en ila ion s a egies o e a
yea . Thei esul s showed ha ex ending he ope a ing hou s o me-
chanical en ila ion sys ems could imp o e ai exchange a es wi hou
inc easing ene gy consump ion. Howe e , he s udy did no quan i y he
impac o hese changes on indoo ai quali y and he mal com o .
Pollozhani e al. [32] e alua ed he unc ionali y o na u al and me-
chanical en ila ion s a egies wi hin he COVID-19 pandemic con ex in
a class oom o an Aus ian uni e si y. Thei esea ch combined on-si e
measu emen s o na u al en ila ion s a egies wi h simula ions o
a ious mechanical en ila ion app oaches using building pe o mance
simula ion so wa e. They concluded ha a ade-o be ween accep -
able indoo ai quali y, he mal com o and ene gy e iciency can only
be achie ed h ough mechanical o hyb id en ila ion me hods. In a
ecen s udy, Rizzo e al. [33] explo ed he po en ial o enhancing in-
doo ai quali y and he mal com o in a Mal ese school h ough he
simula ion o an educa ional building wi h a demand-con olled en i-
la ion sys em o a one-yea pe iod. The indings indica ed ha wi h his
sys em, CO
2
le els a e main ained below he ecommended h eshold
o a leas 76 % o he yea , depending on class oom o ien a ion.
Finally, Zemi is e al. [34] simula ed a class oom in La ia wi h na u al
en ila ion s a egies. They concluded ha hey a e no able o p o ide
p ope he mal com o le els wi h hese s a egies.
To he au ho s’knowledge, he abo emen ioned simula ion-based
esea ch ini ia i es ypically assumed a cons an CO
2
gene a ion a e,
along he lines o mos cu en s anda ds (i.e. he Spanish Technical
Building Code [35]. Howe e , ASTM D6245-18 “S anda d Guide o
Using Indoo Ca bon Dioxide Concen a ions o E alua e Indoo Ai
Quali y and Ven ila ion”[36] and ecen expe imen al indings by
Tugo es e al. [37] indica e ha he CO
2
gene a ion a e o indi iduals is
in luenced by ac o s such as age, gende , weigh and le el o physical
ac i i y. Mo eo e , exis ing esea ch in he ield ypically simula es
educa ional buildings in a speci ic loca ion unde pa icula clima e
condi ions. In addi ion, s udies ha e no explo ed he impac o building
o ien a ion in ela ion o each en ila ion s a egy.
The e o e, o o e come he a o emen ioned gap, his pape quan-
i ies, o he i s ime, he ene gy equi ed o ensu e indoo ai quali y
and he mal com o in schools unde na u al and mechanical en ila-
ion s a egies. I p o ides a comp ehensi e analysis ha conside s he
in luence o ailo ed CO
2
gene a ion a es and he e ec o building
o ien a ion in all Medi e anean clima e ypes. The esul s o his
esea ch will p o ide aluable insigh s o he design and upg ading o
educa ional buildings, wi h he ul ima e pu pose o op imising he
alloca ion o o en sca ce economic esou ces, and hus p o iding ools
o assis in decision-making o he ins alla ion o mechanical en ila ion
sys ems.
This pape is s uc u ed in i e sec ions. Sec ion 2 ou lines he
me hodological s eps employed in his esea ch. Sec ion 3 in oduces he
speci ic case s udy implemen ed. Sec ion 4 p esen s and discusses he
esul s. Finally, Sec ion 5 summa ises he conclusions de i ed om his
esea ch.
2. Me hodology
Fig. 1 summa ises he me hodological s eps aken o assess he en-
e gy implica ions o ensu ing indoo ai quali y and he mal com o in a
building. This p ocess in ol es he c ea ion o a building model h ough
he use o dynamic ene gy simula ion so wa e. The simula ion o he
model equi es inpu da a de ining he building condi ions, including
space occupancy, bounda y condi ions such as wea he da a, ou doo
CO
2
le els and building o ien a ion, as well as con ol pa ame e s o
indoo ai quali y and he mal com o based on ele an s anda ds.
Addi ionally, he en ila ion s a egies o be e alua ed mus be de ined.
Finally, he simula ion o his da a gene a es key pe o mance indica o s
o indoo ai quali y, he mal com o and ene gy consump ion o
HVAC sys ems. Each s ep is explained in mo e de ail in he ollowing
sec ions.
2.1. De elopmen o he building model and da a inpu
Fi s , dynamic ene gy simula ion so wa e mus be used o de elop
he building model. As shown in Fig. 1, he simula ion o he building
model equi es inpu da a (occupancy in e nal gains, bounda y condi-
ions and con ol pa ame e s).
Rega ding occupancy in e nal gains, occupan s a e conside ed o be
in e nal sou ces o CO
2
and hea gains. The in luence o occupancy is
assessed acco ding o he guidelines speci ied in ASTM [36], which
de ine he CO
2
gene a ion a e o indi iduals. Addi ionally, ASTM [36]
de e mines he basal me abolic a e (BMR), which ep esen s
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
2
indi iduals’hea gene a ion. The CO
2
gene a ion a e (VCO2) exp essed
in L/s⋅pe son depends on an indi idual’s body size and le el o physical
ac i i y. This a e is de e mined by ASTM [36] using Equa ion (1).
VCO2=RQ ⋅BMR⋅M⋅(T/P)⋅0.000211 (1)
Whe e RQ indica es he espi a o y quo ien , a dimensionless pa ame e
ha ep esen s he a io o he olume ic a e o CO
2
p oduc ion o he
a e o oxygen consump ion by an indi idual. This alue depends on
die , wi h es ablished li e a u e on human nu i ion sugges ing an
app oxima e alue o 0.85 [38].BMR ep esen s he basal me abolic a e
o indi iduals exp essed in MJ/day (Table 1). M ep esen s he me a-
bolic a e pe uni o su ace a ea, exp essed in dimensionless uni s o
me abolic equi alen (me ). This pa ame e se es o quan i y he a e o
human ene gy use associa ed wi h speci ic physical ac i i ies. T e e s o
he zone empe a u e (K) and P o he zone p essu e (kPa).
The occupancy in e nal hea gains a e also de e mined by he basal
me abolic a e (Table 1).
The bounda y condi ions o he building, such as he wea he pa -
e ns, ou doo CO
2
concen a ion and building o ien a ion, mus be
de ined acco ding o he speci ic loca ion. A ypical me eo ological
yea ’s wea he ile, which p o ides a comp ehensi e se o hou ly
wea he da a o an en i e yea based on his o ical wea he da a, is
equi ed o he simula ion so wa e.
Rega ding he con ol pa ame e s o indoo ai quali y and he mal
com o , maximum indoo CO
2
concen a ion and empe a u e se poin s
mus be de ined acco ding o he co esponding s anda ds.
2.2. Iden i ica ion and cha ac e isa ion o en ila ion s a egies
This pape explo es wo en ila ion s a egies: (i) na u al en ila ion,
achie ed h ough he opening o windows and doo s, which is a com-
mon s a egy employed in many educa ional buildings ha lack al e -
na i e en ila ion sys ems, and (ii) mechanical en ila ion,
implemen ed in newe school acili ies.
2.2.1. Na u al en ila ion
Na u al en ila ion is commonly achie ed h ough la ge openings
such as windows o doo s. In cases wi h inle and ou le openings o
simila size and minimal in e nal esis ance, he olume ai low (q ),
exp essed in m
3
/s, can be de e mined by conside ing bo h wind and
buoyancy e ec s. Acco ding o Schulze &Eicke [39], olume ai low
can be calcula ed along he lines o Equa ion (2).
q =Cd⋅Ae ⋅
Cp,1⋅u2
w,1−Cp,2⋅u2
w,2
2±(Tin −Tou )g⋅hs
Tin
√(2)
Whe e Cd ep esen s he discha ge coe icien , which is assumed o be
0.60. Ae (m
2
) deno a es he e ec i e opening su ace. Cp,1and Cp,2a e
he wind p essu e coe icien s o he inle and he ou le espec i ely,
uw,1and uw,2(m/s) a e he e e ence wind speeds a he cen oid o he
inle and he ou le openings espec i ely. Tin and Tou (K) a e he em-
pe a u e o he indoo building and he ou doo ambien ai espec i ely
and gis he g a i y accele a ion (9.81 m/s
2
). Finally, hs(m) ep esen s
he s ack heigh , which is he di e ence be ween he midpoin s o he
inpu and ou pu openings.
2.2.2. Mechanical en ila ion
Con en ional mechanical en ila ion sys ems ope a e h ough an ai
loop ins alled in each he mal zone o he building. The sys em equip-
men ypically includes a mixing box ha combines he eci cula ed ai
om he zone wi h esh ou doo ai , a an ha eci cula es he mixed ai
back in o he zone, and a ne wo k o duc s a anged in a loop (Fig. 2).
This a angemen allows egula ion o bo h he eci cula ed ai low a e
and he p opo ion o ou doo ai .
2.2.3. In il a ions
Rega dless o he en ila ion s a egy, buildings na u ally ha e
c acks in hei en elopes, which cause ai enewal. The ai low (Q)
Fig. 1. Me hodology.
Table 1
Equa ions o calcula ing he basal me abolic a e.
Age (yea s) Basal me abolic a e (MJ/day)
Males Females
<30.249⋅m−0.127 0.244⋅m−0.130
3 o 10 0.095⋅m+2.110 0.085⋅m+2.033
10 o 18 0.074⋅m+2.754 0.056⋅m+2.898
18 o 30 0.063⋅m+2.896 0.062⋅m+2.036
30 o 60 0.048⋅m+3.653 0.034⋅m+3.538
≥60 0.049⋅m+2.459 0.038⋅m+2.755
Sou ce: adap ed om [36]
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
3
exp essed in (kg/s) h ough an in il a ion depends on he p essu e
di e ence ac oss he c ack and he measu emen condi ions, as
desc ibed by Equa ion (3).
Q=CF⋅CT⋅CQ⋅(ΔP)n(3)
Whe e CFis he c ack ac o and co esponds o he pe cen age o c ack
ape u e in ela ion o c ack size, i is assumed o be 1. CQis he ai mass
low coe icien (kg/s⋅Pa
n
a 1 Pa), ΔP is he p essu e di e ence ac oss
he c ack (Pa), and n ep esen s he ai low exponen . CTis he e e ence
condi ion empe a u e co ec ion ac o , es ima ed as indica ed in
Equa ion (4).
CT=[
ρ
o
ρ
]n−1
⋅[
υ
o
υ
]2n−1(4)
Whe e
ρ
(kg/m
3
) and
υ
(m
2
/s) deno a e he ai densi y and he ai ki-
ne ic iscosi y, espec i ely, in he speci ic ai empe a u e and hu-
midi y a io condi ions.
ρ
o
(kg/m
3
) and
υ
o
(m
2
/s) ep esen he ai
densi y and he kine ic iscosi y, espec i ely, in he e e ence ai
condi ions.
2.3. Key pe o mance indica o analysis
Key pe o mance indica o s a e analysed wi hin indoo ai quali y,
he mal com o , and hea ing, en ila ion, and ai condi ioning (HVAC)
ene gy pe o mance domains.
2.3.1. Indoo ai quali y
Indoo ai quali y is assessed by examining he indoo CO
2
concen-
a ion. In his case, he sugges ed indica o is hou s o unme indoo ai
quali y (UHCO2). This indica o measu es he numbe o hou s in a pe iod
ha su pass he CO
2
limi concen a ion se by he applicable s anda d
(Equa ions (5) and (6)).
UHCO2=∑
N
i=1
(CO2i−CO2limi )(5)
(x) = {1i x >0
0i x <0
UHCO2(%) = unme CO2hou s
∑N
i=1i⋅100 (6)
Whe e Nis he o al numbe o hou ly alues,CO2i(ppm) ep esen s he
CO
2
concen a ion a hou iand CO2limi (ppm) he CO
2
limi concen-
a ion ecommended by he applicable s anda d.
2.3.2. The mal com o
The mal com o is e alua ed h ough indoo empe a u e alues. In
his case, he sugges ed indica o is unme he mal com o hou s (UHT).
This indica o measu es he o e all hou s in a pe iod in which he indoo
empe a u e is ou o an accep able empe a u e ange se by he
applicable s anda d (Equa ions (7) and (8)).
UHT=∑
N
j=1
g(Tj<Tmin o Tj>Tmax)(7)
g(x) = {1i x =T ue
0i x =False
UHT(%) = unme T hou s
∑N
j=1j⋅100 (8)
Whe e Nis he o al numbe o hou ly alues, Tj(◦C) he empe a u e a
hou j,Tmin (◦C) he minimum empe a u e ecommended by he
applicable s anda d, and Tmax (◦C) ep esen s he maximum empe a u e
allowed by he applicable s anda d.
2.3.3. HVAC ene gy pe o mance
Fo he e alua ion o building ene gy pe o mance, he mon hly
HVAC ene gy demand (Em) and he annual HVAC ene gy demand (Ey),
exp essed in kWh/m
2
, a e calcula ed (Equa ions (9) and (10)).
Em=∑Nm
i=1Em,i
A(9)
Ey=∑
12
i=1
Em(10)
Whe e Em,i ep esen s he HVAC ene gy demand o hou iin mon h m
(kWh) and Ais he o al a ea (m
2
).
3. Desc ip ion o he case s udy
A building model wi h a ious zones eplica ing he beha iou o
school class ooms was c ea ed and simula ed using Ene gyPlus [40]
V23.1.0 so wa e. The model includes na u al en ila ion h ough
ope able ex e nal windows and in e nal doo s, and an HVAC sys em o
hea ing, ai condi ioning and mechanical en ila ion. This model was
simula ed in di e en Medi e anean egions o e alua e he impac o
clima e on indoo ai quali y, he mal com o and HVAC ene gy de-
mand. Addi ionally, he in luence o he occupan s’age and he impac
o class oom o ien a ion was assessed.
3.1. Desc ip ion o he building model and da a inpu
This sec ion desc ibes he building model c ea ed o he simula ions
and he da a inpu .
3.1.1. Building model
The building has a wo-le el ec angula layou wi h a o al loo
a ea o 297.2 m
2
and a la oo (Fig. 3). The g ound loo is di ided in o
h ee zones, as shown in Fig. 4: (i) he Hall 0 zone, (ii) Class oom A0
o ien ed o he sou hwes (iii) and Class oom B0 o ien a ed o he
sou heas . Hall 0 has a single no h- acing window (3.0 m x 1.3 m), while
he wo class ooms a e each equipped wi h a single sou h- acing window
(4.0 m x 1.5 m). Addi ionally, wo doo s (1.0 m x 2.0 m), p o ide access
be ween he hall a ea and he espec i e class ooms. The layou o he
i s loo mi o s ha o he g ound loo , which has an iden ical
con igu a ion. On he i s loo , ooms a e designa ed as Hall 1, Class-
oom A1 and Class oom B1. Addi ionally, he e is a ho izon al ape u e
communica ing Hall 0 o he g ound loo and Hall 1 o he i s loo . In
he base case, class ooms a e o ien ed o he sou h (Fig. 4).
Table 2 desc ibes he p ope ies o he building en elope cons uc-
ion ma e ials om he ou e mos laye o he inne mos laye .
Rega ding he HVAC sys em, he building is equipped wi h a iable
ai olume equipmen . This ype o sys em con ols he d y bulb
Fig. 2. Diag am o a mechanical en ila ion sys em ope a ion.
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
4
empe a u e by a ying he olume o supply ai . The hea ing, ai -
condi ioning and en ila ion sha e he same duc sys em (Fig. 5). Fo
he mal com o , he ci cula ing ai is hea ed o cooled by he hea ing
coil o cooling coil depending on he clima e equi emen s. Fo en i-
la ion, he p opo ion o ou side ai and eci cula ed ai in he mixing
box is a ied o mee he ai quali y equi emen s. Each condi ioned
zone has one o hese loops ha is comple ely independen om he
o he s, p o iding ully independen esul s o each zone. As he ou
class ooms sha e he same cha ac e is ics, he speci ica ions o all he
componen s a e he same in each sys em.
3.1.2. Da a inpu
This sec ion de ines he occupancy in e nal gains o he building, he
bounda y condi ions and he con ol pa ame e s o he case s udy.
3.1.2.1. Occupancy in e nal gains. Occupancy in e nal loads con ibu e
o CO
2
gains and he mal gains. To accu a ely simula e he beha iou o
a school en i onmen , each o he ou class ooms a e assumed o hos
he same numbe o occupan s (Fig. 6), dis inguishing be ween week-
days and weekends.
Gi en ha each class oom con ains s uden s o he same age g oup,
bu all class ooms hos di e en g ade s uden s (Table 3), basal me a-
bolic a e and CO
2
gene a ion a e we e compu ed using Equa ion (1)
wi h a Mon e Ca lo app oach. The applica ion o he p esc ibed equa ion
equi es he de e mina ion o occupan s’body mass, he gende o he
occupan s and he ac i i y pe o med in each zone.
Fig. 3. Ene gyPlus building model de eloped.
Fig. 4. Building layou o he g ound loo (le igu e) and he i s loo ( igh igu e).
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
5
Fo he pu pose o his esea ch, body mass da a we e andomly
selec ed om he dis ibu ion o child body mass da a [41]. Mean alues
and s anda d de ia ions o each age and gende a e de ailed in Table 4.
A gende dis ibu ion o 52 % males and 48 % emales was conside ed,
based on he a e age bi h a e in Ca alonia om 2000 o 2022 [42].
Rega ding he me abolic a e, andom alues anging om 1.2 o 1.6
MET we e conside ed, co esponding o ac i i ies such as si ing quie ly,
eading, w i ing, yping and s anding, in acco dance wi h he ASTM
[36] s anda d. Fu he mo e, an indoo empe a u e o 23 ◦C was
assumed, acco ding o he Spanish Regula ion o The mal Ins alla ions
in Buildings (RITE) [43], along wi h an a mosphe ic p essu e o 101 kPa.
Table 5 summa ises he esul s used as inpu s o in e nal CO
2
gains
in he building simula ions.
3.1.2.2. Bounda y condi ions. In acco dance wi h he Spanish Technical
Table 2
The mal p ope ies o cons uc ion ma e ials.
Elemen Ma e ial Thickness (cm) Conduc i i y (W/m⋅K) Densi y (kg/m
3
) Speci ic hea (J/kg⋅K)
Ex e nal walls S ucco 2.54 0.69 1858.14 836.80
B icks 10.15 0.73 1922.22 836.80
Gypsum plas e boa d 1.90 0.73 1601.85 836.60
In e nal walls Gypsum plas e boa d 1.90 0.73 1601.85 836.60
Insula ion 20.33 0.57 1121.29 836.80
Gypsum plas e boa d 1.90 0.73 1601.85 836.60
G ound loo slab Conc e e 20.33 1.73 2242.59 836.80
Fi s loo slab Conc e e 17.30 1.73 2242.59 836.80
Ceiling S one 1.23 1.44 881.02 1673.60
Fel and memb ane 0.95 0.19 1121.29 1673.60
Dense insula ion 2.54 0.04 91.31 836.80
Conc e e 5.09 1.73 2242.59 836.80
Fig. 5. HVAC sys em diag am.
Fig. 6. Occupancy p o ile o he class ooms.
Table 3
S uden s’age.
Class oom Age (yea s)
A0 4
B0 10
A1 13
B1 16
Table 4
Body mass dis ibu ion depending on s uden s’age.
Age (yea s) Body mass (kg)
Male Female
Mean S anda d de ia ion Mean S anda d de ia ion
4 18.04 2.57 14.91 1.44
10 36.05 7.32 36.11 6.26
13 49.21 8.45 64.98 1.82
16 64.98 11.82 57.84 8.96
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
6
Building Code [35], he ou doo ai CO
2
concen a ion was assumed o
be 400 ppm o all loca ions. The Spanish Technical Building Code (TBC)
desc ibes di e en win e and summe clima e zones depending on he
loca ion. The win e clima e is ep esen ed wi h a le e (
α
, A, B, C, D and
E), whe e
α
is he wa mes win e and E he coldes one. The summe
clima e is ep esen ed wi h a numbe om 1 o 4, whe e 1 ep esen s he
coldes summe and 4 he wa mes . Fo he analysis o he Medi e a-
nean zone, he building model was simula ed in all he win e -summe
clima e combina ions ound in he Spanish Medi e anean egions. Fo
each clima e zone, a ep esen a i e loca ion was selec ed (Table 6 and
Fig. 7). As shown in Table 6, all hese clima es we e ela ed o he
K¨
oppen-Geige clima e classi ica ion sys ems, which is e ec i e in ca -
ego ising long- e m pa e ns based on a e age empe a u e and p e-
cipi a ion and se es as a global e e ence o unde s anding clima e
ypes [44].
In his pape , he ypical me eo ological yea iles equi ed o he
dynamic ene gy simula ion so wa e o each loca ion we e ob ained
om he Pho o ol aic Geog aphical In o ma ion Sys em (PVGIS) web-
page [45].
3.1.2.3. Con ol pa ame e s. Ven ila ion me hods and ela ed con-
s ain s we e iden i ied in acco dance wi h he Spanish Regula ion o
The mal Ins alla ions in Buildings (RITE) s anda d [43]. In his s an-
da d, he indoo ai quali y equi emen s a e s a ed depending on he
space’s end use (Table 7). In his case, conside ing ha he building
se es as a school, he maximum accep able indoo CO
2
concen a ion is
900 ppm (IDA 2).
Acco ding o he Spanish Regula ion o The mal Ins alla ions in
Buildings [43], he empe a u e se poin alue o he hea ing pe iod
( om 1 Janua y o 30 Ap il and om 1 Oc obe o 31 Decembe ) mus be
21 ◦C. Fo he cooling pe iod ( om 1 May o 30 Sep embe ), i mus be
25 ◦C.
3.2. De ini ion o en ila ion s a egies
To compa e en ila ion me hods in e ms o indoo ai quali y,
he mal com o and HVAC ene gy demand, he model was simula ed o
he en ila ion s a egies de ailed in Sec ion 2.
Fo he applica ion o he en ila ion s a egies, wo na u al
en ila ion s a egies using he building’s openings and wo mechanical
en ila ion s a egies speci ied by he Spanish Regula ion o The mal
Ins alla ions in Buildings [43] we e analysed. In app oaches whe e
na u al en ila ion is used, he e is no con ol mechanism o ensu e ha
ai quali y s anda ds a e me .
3.2.1. Na u al en ila ion s a egies
P e ious s udies [23,15,37] based on on-si e measu emen s in he
Medi e anean egion ha e ound c oss- en ila ion h ough windows
and doo s o be he mos e ec i e na u al en ila ion s a egy. Addi-
ionally, Miao e al. [15] pe o med a la ge moni o ing campaign in 32
na u ally en ila ed schools in he Medi e anean egion, iden i ying an
a e age window and doo opening a ea o 6.6 m
2
. Fu he mo e, He -
acleous &Michael [23] esea ch demons a ed ha op imal na u al
c oss- en ila ion in educa ional buildings is achie ed when applied o
20 min e e y 2 h. Based on hese indings, and consis en wi h ypical
school ope a ions cha ac e ised by 1-hou lessons, he selec ed na u al
en ila ion s a egy is o open windows and in e nal doo s o 10 min pe
hou . Two deg ees o window opening we e conside ed o his
app oach:
- Full opening o windows and doo s (NV100), co esponding o a o al
opening a ea o 8 m
2
.
- Hal opening o windows and doo s (NV50), co esponding o a o al
opening a ea o 5 m
2
.
In all cases, he e is no mechanical en ila ion. The e o e, all ai low
wi hin he HVAC ai loop is eci cula ed om he espec i e zone.
3.2.2. Mechanical en ila ion s a egies
Acco ding o he Spanish The mal Building Regula ion [43], wo
mechanical en ila ion con ol s a egies a e de ined:
- Indi ec mechanical en ila ion (IMV): minimum ai low a es a e
es ablished acco ding o he IDA le el (Table 7). In his case, an
ai low a e o 12.5 L/s⋅pe son is equi ed (Table 8).
- Di ec mechanical en ila ion (DMV): minimum ai low a es a e
de e mined by he maximum admissible indoo CO
2
concen a ion,
acco ding o he IDA le el (Table 7). In his case, he maximum
allowable CO
2
concen a ion is 900 ppm (Table 8).
3.3. Key pe o mance indica o s analysis
Indoo ai quali y, he mal com o and HVAC ene gy pe o mance
key pe o mance indica o s a e calcula ed acco ding o he me hodology
desc ibed in Sec ion 2.3. The alues o occupancy in e nal gains,
bounda y condi ions and con ol pa ame e s o he case s udy a e
applied. The esul s ob ained om hese analyses a e subsequen ly
discussed in Sec ion 4.
4. Resul s and discussion
Sec ion 4.1 analyses he impac o clima e zones on he e ec i eness
o na u al and mechanical en ila ion s a egies, h ough an assessmen
o indoo ai quali y, he mal com o and HVAC ene gy demand in
educa ional spaces. Sec ion 4.2 discusses he e ec o building o ien a-
ion depending on he clima e zone and he en ila ion s a egy. Sec ion
4.3 e alua es he in luence o occupan s’age on indoo ai quali y and
HVAC ene gy demand. Finally, Sec ion 4.4 p o ides a global assessmen
o indoo ai quali y, he mal com o and HVAC ene gy demand o all
he en ila ion s a egies and building o ien a ions.
4.1. Analysis o he impac o he clima e zone on en ila ion s a egies
In his sec ion, he balance be ween indoo ai quali y and he mal
com o , along wi h HVAC ene gy demand, is analysed o assess he
Table 5
CO
2
gene a ion a e and he mal gains o occupan s depending on hei age.
Age (yea s) CO
2
gains The mal gains
CO
2
gene a ion (L/h) BMR (W)
Mean S anda d de ia ion Mean S anda d de ia ion
4 41.34 3.83 9.51 1.21
10 63.02 6.70 13.66 1.66
13 73.04 8.43 16.19 2.36
16 88.02 9.87 18.11 3.11
Table 6
Rep esen a i e Medi e anean clima e zones.
Clima e
zone (TBC)
Geog aphical
coo dina es
Region Al i ude
(m)
K¨
oppen-
Geige
clima e
E1 42.448, 1.880 Gi ona 1367 C b
D1 42.101, 1.845 Ba celona 692 C b
D2 40.380, −0.141 Cas ell´
o 832 Csb
D3 41.310, 0.988 Ta agona 947 Csb
C2 42.073, 2.836 Gi ona 75 Csa
C3 38.231, −1.700 Mu cia 355 Bsk
C4 36.799, −3.639 G anada 366 Csa
B3 39.472, −0.386 Valencia 24 Bsh
B4 38.354, −0.490 Alican e 68 Bsh
A3 36.720, −4.433 M´
alaga 20 Csa
A4 36.763, −2.612 Alme ía 11 Bsh
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
7
impac o he clima e zone o each en ila ion s a egy.
4.1.1. Indoo ai quali y and he mal com o
Fig. 8 summa ises he indoo ai quali y and he mal com o pe -
o mance o he class ooms when he building is loca ed in he consid-
e ed clima e zones unde bo h na u al and mechanical en ila ion
s a egies in e ms o pe cen age o unme hou s in a yea (Equa ions (6)
and (8)).
As expec ed, bo h di ec and indi ec mechanical en ila ion s a e-
gies always mee indoo ai quali y and he mal com o equi emen s.
The ully opening windows and doo s na u al en ila ion s a egy
(NV100) la gely ensu es good indoo ai quali y (less han 1 % o unme
CO
2
hou s) bu comp omises he mal com o , pa icula ly in cold cli-
ma es (10 % o unme empe a u e hou s in clima e zones D1 and 14 %
in clima e zone E1). When na u al en ila ion is employed wi h hal he
windows and doo s open (NV50), indoo ai quali y de e io a es, espe-
cially in egions wi h wa me summe s (app oxima ely 3–5 % o unme
CO
2
hou s o A4 and C4 clima e zones). The pe cen age o empe a u e
unme hou s sligh ly dec eases compa ed o he NV100 s a egy bu
emains high in cold clima e zones (a ound 8–10 % in D1 and E1 clima e
zones, espec i ely). The in luence o he clima e zone demons a es ha
employing na u al en ila ion s a egies in mo e ex eme ho and cold
clima es esul s in highe de e io a ion o indoo ai quali y and he mal
com o .
4.1.2. HVAC ene gy demand
Ven ila ion s a egies we e compa ed in e ms o HVAC ene gy de-
mand in all Medi e anean clima e zones (Fig. 9). Colou coding was
employed o acili a e able in e p e a ion. The da kes ed cells indica e
he highes HVAC demand, while he da kes g een cells indica e he
lowes demand.
Fo na u al en ila ion, using hal -open windows (NV50) esul s in
an a e age ene gy sa ing o 50 % o hea ing and 43 % o cooling
compa ed o ully open windows (NV100). Fo mechanical en ila ion, a
di ec mechanical en ila ion s a egy (DMV) ep esen s an a e age
ene gy sa ing o 8 % in hea ing and 7 % in cooling. O e all, mechanical
en ila ion, compa ed o na u al en ila ion, esul s in an a e age HVAC
ene gy demand educ ion o all clima e zones o 90 % in he hea ing
pe iod and 71 % in he cooling pe iod.
Fu he mo e, al hough he pe cen age o sa ings was ound o be
simila ac oss all clima e zones, he o al sa ings in absolu e e ms we e
much mo e signi ican in colde zones du ing he hea ing pe iod and in
wa me zones du ing he cooling pe iod. Fo example, when he di ec
mechanical en ila ion (DMV) s a egy was compa ed wi h he ull
opening na u al en ila ion (NV100) s a egy du ing he hea ing pe iod,
he sa ings we e ound o amoun o 1196 kWh/m
2
⋅yea in he A clima e
zone, whe eas in he E clima e zone, he sa ings we e iplica ed (3459
kWh/m
2
⋅yea ). Simila ly, du ing he cooling pe iod, he DMV s a egy
compa ed o he NV100 s a egy esul ed in sa ings o 457 kWh/m
2
⋅yea
in he 1 clima e zone, while in he 4 clima e zone, he sa ings ose
sligh ly o 662 kWh/m
2
⋅yea .
4.2. Analysis o he impac o building o ien a ion
Fig. 10 summa ises he esul s ob ained when he in luence o
building o ien a ion was e alua ed in all Medi e anean clima e zones
using he de ined en ila ion s a egies. Bubble size is p opo ional o
Fig. 7. Rep esen a i e Medi e anean loca ions.
Table 7
Indoo ai quali y ca ego ies acco ding o he use o buildings.
Ca ego y Ai quali y
le el
End uses Maximum indoo CO
2
concen a ion (ppm)
IDA 1 Op imum Hospi als, clinics,
labo a o ies, nu se y
schools
750
IDA 2 Good O ices, esidences,
eading ooms, museums,
class ooms
900
IDA 3 Medium Comme cial buildings,
ho el ooms, es au an s,
e c.
1200
IDA 4 Low −1600
Sou ce: adap ed om [43]
Table 8
Mechanical en ila ion cons ain s om he RITE egula ion.
Ca ego y Indi ec mechanical
en ila ion (IMV)
Di ec mechanical en ila ion
(DMV)
Ai low a e (L/s⋅pe son) Maximum indoo CO
2
concen a ion (ppm)
IDA 1 20.0 750
IDA 2 12.5 900
IDA 3 8.0 1200
IDA 4 5.0 1600
Sou ce: adap ed om [43]
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
8
Fig. 8. Indoo ai quali y and he mal com o pe o mance in he conside ed clima e zones unde bo h na u al and mechanical en ila ion s a egies.
Clima e
zones
Hea ing and cooling demand (kWh/m
2
·yea )
Na u al en ila ion s a egies
Mechanical en ila ion s a egies
NV100
NV50
IMV
DMV
Hea ing demand (win e clima e zone)
A
1279.12
603.21
91.50
82.40
B
1579.62
770.28
116.76
107.67
C
2199.97 1079.43 139.95 131.18
D
2801.29 1346.81 177.86 164.35
E3670.14 1769.8 232.32 211.17
Cooling demand (summe clima e zone)
1565.54 297.5 110.94 107.95
2
533.15 301.78 144.03 133.74
3
669.96 391.72 154.51 143.17
4
837.14
519.92
200.72
175.01
Fig. 9. Hea ing and cooling demand (kWh/m
2
⋅yea ) o Medi e anean clima e zones.
M. Maiques e al. Ene gy & Buildings 328 (2025) 115076
9
