Jou nal o Building Enginee ing 39 (2021) 102255
A ailable online 8 Feb ua y 2021
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Ven ila ion o buildings wi h hea eco e y sys ems: Tho ough ene gy and
exe gy analysis o indoo he mal wellness
A. Picallo-Pe ez
*
, J.M. Sala-Liza aga, M. Od iozola-Ma i o ena, J.M. Hidalgo-Be anzos,
I. Gomez-A ia an
Resea ch G oup ENEDI, Depa men o The mal Enginee ing, Uni e si y o he Basque Coun y (UPV/EHU), Alameda U quijo, S/N, 48013, Bilbao, Vizcaya, Spain
ARTICLE INFO
Keywo ds:
Hea eco e y en ila ion sys em
Ene gy and exe gy sa ings
Th esholds empe a u e
Indoo ai quali y
ABSTRACT
This wo k analyses deeply and c i ically he beha io o a hea eco e y de ice o he en ila ion sys em, in a
dwelling o he Basque Coun y, unde he ene gy and he exe gy poin o iew. The aim is o show he di e en
esul s ha come om bo h pe spec i es. Hea ing pe iod was moni o ed and da a o he eloci ies and em-
pe a u es o he ex ac ed and eno a ion ai lows ha e been egis e ed. Wi h he da a eco ded, he e ec i e-
ness, ene gy e iciency and exe gy e iciency o he eco e y sys em ha e been calcula ed. La e , ene gy sa ings,
p ima y ene gy sa ings and economic sa ings ha e been e alua ed. Besides, he minimum di e ence be ween
he ou doo and he indoo empe a u es, om which he ope a ion o he eco e y sys em achie es a p ima y
ene gy sa ing, an economic sa ing o an exe gy sa ing we e calcula ed. In addi ion o he exhaus i e moni o ing,
he concen a ion o ca bon dioxide in each oom o he dwelling has been measu ed. The esul s ob ained show
he con enience o using en ila ion sys ems wi h hea eco e y om an ene gy poin o iew (wi h an ene gy
e iciency o 89%), bu no so i an exe gy analysis is pe o med (wi h an exe gy e iciency o 4%). A e all,
Second Law pe spec i e penalizes a lo he elec ici y consump ion o hea ing pu poses, equi ing a empe a u e
di e ences (be ween he indoo and ou doo empe a u es) highe han 32 ◦C in o de o ob ain exe gy sa ings
(no so unde he ene gy pe spec i e, whe e a di e ence o 1.6 ◦C is enough o ha ing sa ings). The indoo ai
quali y analysis con i ms he adequacy in e ms o CO
2
concen a ion. This wo k is pionee in e ms o deep
exe gy applica ion o en ila ion sys ems.
1. In oduc ion
Indoo empe a u e and he mal en i onmen con ol a e essen ial
ac o s o main ain com o able condi ions in ou homes; e en mo e so i
we emain all day inside he dwelling, as is he case o some elde ly
people o he gene al public igh now in he cu en ci cums ances o
Co id-19, whe e he go e nmen has es ablished such equi emen s o
a oid sp eading he i us.
1.1. Ven ila ion in buildings
Ven ila ion is he mechanism h ough which clean ai , in a con olled
manne , is p o ided inside he buildings, Re . [1]. Ven ila ion is needed
o elimina e he con amina ion emi ed by indoo sou ces and o
main ain minimum condi ions o heal hiness. As a esul , he e is an
inc ease in ene gy demand, as indoo ai ( he mally condi ioned bu
pollu ed) is eplaced by clean ou doo , uncondi ioned ai . Howe e ,
based on he e iew o Re . [2], al hough he e ha e been conside able
ad ances in en ila ion in he las wo decades, he e is no a clea
answe as o wha ex en oday’s con ol s a egies o en ila ion can be
imp o ed.
To e alua e he ene gy consump ion o mechanical en ila ion sys-
ems, in addi ion o he one ha he mally condi ions he ai , we need o
add he consump ion o he ope a ional ans ha need o be ins alled. In
Re . [3], o example, simula ions e alua e he impac o agg ega ing
en ila ion sys ems in cold clima es. The expe imen s show how much
powe can be educed wi hou comp omising indoo condi ions.
Ven ila ion demands in mode a e clima es a e, o he wise, s udied in
Re . [4] whe e he minimum ai low a es in o ices and schools a e
analyzed o p ope inside ai quali y. A li e a u e e iew o en ila ion
s a egies in wa m clima es, whe e he cooling demand is mo e
ema kable and ou doo ai a nigh can be use ul, appea s in Re . [5].
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (A. Picallo-Pe ez).
Con en s lis s a ailable a ScienceDi ec
Jou nal o Building Enginee ing
jou nal homepage: h p://www.else ie .com/loca e/jobe
h ps://doi.o g/10.1016/j.jobe.2021.102255
Recei ed 3 Sep embe 2020; Recei ed in e ised o m 22 Janua y 2021; Accep ed 28 Janua y 2021
Jou nal o Building Enginee ing 39 (2021) 102255
2
I is clea ha ene gy consump ion inc eases wi h he inc ease in he
demand o en ila ion and depends mainly on he se e i y o he
clima e in which he building is loca ed and he ype o he ins alled
sys em. In Re . [6] he usage o di e en en ila ion ypes ac oss i e
di e en clima e zones is in es iga ed o check he use ends and e-
qui emen s. Acco ding o he ou comes, as he clima e became wa me ,
he ope a ing ime o he na u al en ila ion inc eased, while he ope -
a ing ime o he mechanical en ila ion dec eased. Summe was he
season wi h he longes na u al en ila ion un ime and sho es me-
chanical en ila ion un ime, while he win e end was e e sed. In
cold clima e egions, p obably due o he esul ing he mal discom o ,
he use o supply mechanical en ila ion sys ems was much lowe han
ha o ene gy eco e y en ila ion sys ems.
An analysis o ai quali y and ene gy cos in each housing block
should be pe o med o selec he sys em ha , ul illing ai quali y e-
qui emen s, ope a es a he lowes possible cos . Achie ing ai quali y
goals and limi ing consump ion depends on he co ec ope a ion o he
en ila ion sys em, and his co ec ope a ion depends on he sui able
design and ins alla ion and he good insula ion o he dwelling, Re . [7].
I was p o ed ha , wi hou a p ope ly designed en ila ion sys em, CO
2
concen a ion can inc ease conside ably in closed spaces, e en o un-
desi able alues highe han 1000 ppm, so con olled mechanical
en ila ion has o be ins alled o a oid heal h ela ed diseases, Re . [8].
Ne e heless, i he co ec na u al en ila ion design is made, con ol-
ling he na u al en ila ion ai supply, he pollu an s can be educed and
hea ing and cooling loads can also be educed [9]. Acco ding o Re . [2]
i does no make sense o educe he ene gy equi emen i i a ec s
nega i ely people’s com o and heal h. As an example, supe -insula ed
homes wi h na u al and decen alized en ila ion sys ems a e examined
in Re . [10].
The need o gua an ee a minimal low o en ila ion makes i
necessa y o ins all mechanical sys ems, since na u al en ila ion sys-
ems canno gua an ee he minimum equi ed h oughou he yea by
he legisla ion o he di e en coun ies, o example, in Spain he e is
he Building Technical Code (CTE), Re . [11]. To e ine such egula ion,
a p oposal o de e mine he design en ila ion a e in oducing an in-
doo ai quali y c i e ia in CTE was p oposed in Re . [12].
The e a e di e en ypes o mechanical en ila ion sys ems and a
b ie o e iew is gi en in Re . [13]. Acco ding o his e e ence, he
en ila ion sys ems a e classi ied as: mixing en ila ion, displacemen
and pe sonalized and hyb id ai dis ibu ion. Ano he mo e gene al
classi ica ion can be ound in Re . [14] whe e he sys ems a e di ided in
he ollowing g oups: na u al in ake and mechanical ex ac ion sys ems,
mechanical supply and na u al ex ac ion, mechanical balanced, and
on-demand-con olled en ila ion sys ems. Besides, as ema ked in
Re . [15], hyb id echnologies o hea eco e y a e cu en ly a he
cen e o in e es .
1.2. Reco e y sys ems in en ila ion
Hea eco e y sys ems (HRS) a e pieces o equipmen ha allow a
pa o he condi ioned indoo ai ene gy p o ided o be eco e ed wi h
a sys em o mechanical en ila ion. They ha e a hea exchange ha
pu s he indoo ai ha is ex ac ed in o he mal con ac wi h he ou -
doo ai o enewal. In win e , hey p ehea he cold ou doo ai and, in
summe , hey cool i down. These sys ems ha e some il e s o imp o e
he quali y o he ou doo ai . In his way, i is possible o eco e a high
pe cen age o he ene gy used o hea o cool he indoo ai , which
would be comple ely los wi hou he HRS. Acco ding o Re . [16], hea
eco e y echnology can eco e up o 90% o he en ila ion hea los-
ses, depending on ai igh ness and he insula ion o he building.
Re . [17] gi es a summa y o hea eco e y echnologies o esiden ial
building applica ions, including he in eg a ion o hea eco e y wi h
some ene gy-sa ing sys ems.
Acco ding o one classi ica ion, he e a e h ee ypes o hea eco e y
sys ems: c oss low, in which ho and cold ai ci cula e in o hogonal
di ec ions so ha hey c oss each o he , pa allel low when he lows a e
pa allel and o a y low, which has a o o wi h high he mal ine ia
whose o a ion is d i en by an engine.
1.3. A esea ch gap o exe gy analysis in eco e y sys ems
A g ea amoun o pape s deal wi h ene gy pe o mances in hea
eco e y sys ems in buildings, bu ew o hem go beyond and make an
exe gy analysis. The exe gy analysis, in con as o ene gy analysis,
enables he compa ison o he pe o mances o he a ious componen s
in he sys em. A e all, i is based no only in ene gy quan i y bu also in
i s quali y, so ha all componen s a e analyzed unde he same baseline.
As said, pape s dealing wi h exe gy analysis o HRS in buildings a e
sca ce, e en i in he las yea s some wo k has a isen. On he one hand,
Re . [18] analyses hea eco e y en ila ion sys ems unde di e en
ou doo condi ions, using exe gy analysis and non-equilib ium he -
modynamics. Resul s show ha commonly used ene gy e ec i eness
pa ame e s make i di icul o compa e he di e en sys ems and ela e
hem o each o he and ha exe gy pa ame e s should be used ins ead.
Re . [19] combines dimensionless indices o achie e uni e sal da a o
exe gy analysis o hea eco e y exchange s o echnological design o
managemen . One o he ou comes o his wo k is ha exe gy e iciency
alues o hea ans e p ocesses a e a hei lowes . The idea o
Re . [20], on he o he hand, is o be e u ilize he ene gy in an
ai -handling uni h ough he exe gy analysis. To do ha , he use ulness
o ins alling HRS is in es iga ed unde he Second Law poin o iew.
Mechanically con olled en ila ion sys ems a e analyzed in Re . [21]
and, apa om he exe gy analysis, he ene gy and inance iabili y o
hose sys ems a e in es iga ed in esiden ial p emises o di e en cli-
ma es in I aly. As a esul , he mechanically en ila ed sys ems allow
sa ing p ima y ene gy, and he inancial payback ime is ai ly low,
pa icula ly in cold clima es. The book o Re . [22] in oduces he pas-
si e and ac i e sys ems o condi ioning he indoo clima e o deepen he
p inciple o bio-clima ic design. Ai handling uni s we e also exe ge i-
cally analyzed in Re . [23], bu , in his case, a s ep o wa d was done and
a he moeconomic analysis was also ca ied ou . As a whole, Re . [24]
p o ides an o e iew o he p esen s a e-o - he-a o exe gy esea ch
o e he las 3 decades.
Al hough some wo k has eme ged, exe gy esea ch in hea eco e y
sys ems o buildings a e s ill equi ed, since he in o ma ion ob ained
om he Second Law analysis gi es essen ial in o ma ion on he p ope
use o ene gy, which canno be acqui ed wi h a common ene gy analysis.
1.4. Aim o he esea ch
This wo k was ca ied ou o make a s ep o wa d, beyond he clas-
sical ene gy analysis, in o de o deeply and c i ically analyze o he
pe o mance o en ila ion sys ems wi h hea eco e y. Because o his,
om he da a ob ained du ing he comple ely hea ing pe iod o a
dwelling ( unning om Oc obe o Ma ch), his wo k analyses a me-
chanical en ila ion sys em wi h hea eco e y. To begin wi h, he en-
e gy e iciency o he HRS and he p ima y ene gy sa ings a e
calcula ed. La e comes he calcula ion o exe gy e iciency and he
p ima y exe gy sa ings. The esul s show he di e en conclusions ob-
ained when he analysis is pe o med om he poin o iew o he Fi s
Law wi h espec o an analysis wi h he Second Law pe spec i e.
A e his In oduc ion, Sec ion 2 deduces he exp essions o calcu-
la e he seasonal a e age e ec i eness o a HRS, and he seasonal ene gy
and exe gy e iciencies, as well as ene gy and exe gy sa ings and p i-
ma y ene gy and exe gy sa ings o he en ila ion sys em. The nex s ep
is o de ine he h eshold alues o he ou doo empe a u es om which
he e is no ene gy, o exe gy, o economic sa ings. Sec ion 3 desc ibes
sho ly he en ila ion and moni o ing sys em analyzed. Sec ion 4 con-
ains he eal da a ob ained by he moni o ing sys em and p esen s he
co esponding g aphs and ables. Wi h he exp essions om Sec ion 2
and he da a om Sec ion 3, he esul s ob ained appea in Sec ion 4.
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
3
Sec ion 5 con ains he discussion and, inally, Sec ion 6 ge s he con-
clusions o his wo k.
2. Me odology o deeply analize he ope a ion o a en ila ion
sys em
This sec ion deals wi h he me hodology ollowed along he wo k in
o de o ca y ou a deep ene gy and exe gy analysis o en ila ion wi h
eco e y sys ems. The exp essions o be used along he calcula ions o
cha ac e ize he pe o mance o a en ila ion sys em a e he e de eloped.
2.1. E ec i eness, ene gy and exe gy e iciency o a en ila ion sys em
wi h hea eco e y
Le us conside a hea eco e y sys em in which he subsc ip s 0 and
1 co espond o he s a es o he ou doo ai a he inle and ou le o he
eco e y sys em, espec i ely. Likewise, 2 and 3 co espond o he
ex ac ed indoo ai a he inle and ou le o he eco e y sys em, see
Fig. 1.
Using ˙
V o he ai low a e in oduced in o he building, and
assuming ha i is he same as he ex ac ed one ( he en ila ion sys em
is balanced); using
ρ
0,
ρ
2 o he densi ies o he ou doo and indoo ai
espec i ely; and supposing, o example, some win e condi ions, om
he ene gy balance, we can w i e he equa ion, Re . [25]:
˙
V
ρ
2(h2−h3) + ˙
W =˙
V
ρ
0(h1−h0) +
˙
Ql(1)
whe e ˙
W is he powe o he wo ans o o e come he load losses and ˙
Ql
is he a e o hea losses, which is app oxima ely negligible.
E ec i eness cha ac e izes he ope a ion o he HRS, Re . [26],
which, as we know, is he hea exchanged wi h espec o he maximum
hea ha ideally been exchanged. Supposing ha he a io o he he mal
capaci y o he wo ai lows is he same, he e ec i eness o he hea
eco e y exchange is
ε
=T1−T0
T2−T0
(2)
The e ec i eness a ies om 1 h o ano he , because he ou doo
empe a u e changes, so i is be e o de ine an a e age e ec i eness
ε
=∑H
i=1
ε
ihi
H(3)
whe e hi is he numbe o hou s in which he e ec i eness is
ε
i and H is
he o al numbe o hou s in he pe iod, o example, o hea ing.
Re e ing o he ene gy e iciency o he HRS, i can be de ined as i s
ou pu ( he en halpy inc ease o he en ila ion supply ai ) di ided by
he en halpy dec ease o he exhaus ai plus he an ene gy inpu , and
hen
η
1=
˙
V
ρ
0(h1−h0)
˙
V
ρ
2(h2−h3) + ˙
W
=1−
˙
Ql
˙
V
ρ
2(h2−h3) + ˙
W
(4)
I he HRS we e adiaba ic ( he a e o hea losses is negligible and
hen, app oxima ely, he dec ease o en halpy o he ex ac ion ai co-
incides wi h he inc ease o en halpy o he eno a ion ai ), he e o e i s
ene gy e iciency is nea uni y. Ne e heless, we can also de ine he
e iciency supposing he indoo ai en halpy as he only one a ailable,
since he en halpy in s a e 3 is pa o he losses; ha is
η
2=
˙
V
ρ
0(h1−h0)
˙
V
ρ
2h2+˙
W
=1−
˙
V
ρ
2h3+˙
Ql
˙
V
ρ
2h2+˙
W
(5)
In he same way as o e ec i eness, he a e age e iciency is a mo e
in e es ing pa ame e .
We can also de ine he ene gy pe o mance o he HRS as he
en halpy inc ease o he en ila ion supply ai di ided by he an ene gy
inpu . The hea inpu om he exhaus ai is dis ega ded in his indica o
in a simila way as i is done when e alua ing he COP o a hea pump;
we hen ha e
η
3=
˙
V
ρ
0(h1−h0)
˙
W
(6)
On he o he hand, wi h an exe gy balance in he eco e y sys em we
ha e
˙
V
ρ
2(b2−b3) + ˙
W =˙
V
ρ
0(b1−b0) + ˙
I ec (7)
whe e he e m ˙
I ec encompasses he exe gy associa ed wi h he hea los
and he in e nal exe gy des uc ion, due o he he mal and mechanical
i e e sibili ies and bi is exe gy o he i- h low. Indeed, since he exe gy
o ai in s a e 3 is inally des oyed, i mus be included in he e m o
i e e sibili ies (˙
IT, ec) and since s a e 0 is ambien ai , he exe gy bal-
ance gi es
˙
V
ρ
2b2+˙
W =˙
V
ρ
0b1+˙
IT, ec (8)
being he exe gy e iciency
1
ϕ2=
˙
V
ρ
0b1
˙
V
ρ
2b2+˙
W
=1−
˙
IT, ec
˙
V
ρ
2b2+˙
W
(9)
Simila ly o wha has been said o he ene gy, we can de ine an
exe gy pe o mance indica o dis ega ding he exe gy inpu om he
exhaus ai and hen we ha e
ϕ3=
˙
V
ρ
0b1
˙
W
(10)
As o he e ec i eness and ene gy e iciency, we will ob ain he
a e age seasonal exe gy e iciency o he equipmen in a simila way.
The ene gy and exe gy e iciencies o he HRS depend mainly on he
ou doo empe a u e, since he amoun and quali y o he hea ans-
e ed o he en ila ion ai supply depends on ha empe a u e.
2.2. Ene gy and exe gy sa ings o a en ila ion sys em wi h hea eco e y
Now le us u n o a mechanical en ila ion sys em wi h hea e-
co e y o a dwelling. The objec i e is o e alua e he p ima y ene gy
sa ings, compa ing a en ila ion sys em wi h hea eco e y e sus a
mechanical sys em wi hou eco e y. A e he ene gy analysis, in a
second phase, we e alua e he exe gy sa ings in o de o highligh he
in e es o his ype o analysis and o ob ain addi ional in o ma ion.
Fig. 2 a) ep esen s schema ically he simple exhaus en ila ion
Fig. 1. Schema ic o a hea eco e y exchange .
1
subsc ip 2 and 3 we e delibe a ely used in o de o ollow he analogy wi h
he p e ious ene gy e iciency de ini ions.
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
4
sys em (wi hou HRS and only one ex ac ion an), compa ed o he
sys em wi h HRS in Fig. 2 b). In il a ion ai lows, which may di e
acco ding o he en ila ion sys em, a e no aken in o accoun in his
analysis.
In win e condi ions, he hea con ibu ing o wa m up ha ai low
om he ex e nal condi ions o he indoo empe a u e T2 o he
apa men is
˙
Q=
ρ
0
˙
V(cp,a+
ω
0cp, )(T2−T0)(11)
being cp,a and cp, he speci ic hea o d y ai and apo espec i ely,
and
ω
0 he absolu e humidi y o ou doo ai . Assuming ha he low is
he same o he ex ac ed ai as o he eno a ion ai (as wha occu s in
a well-balanced sys em), he empe a u e a he ou le o he HRS is
T1=T0+
ε
(T2−T0)(12)
The e o e, he a e o he mal ene gy sa ings ( ˙
ES) due o his hea
eco e y is
˙
ES =
ρ
0
˙
V(cp,a+
ω
0cp, )
ε
(T2−T0)(13)
Now, he elec ici y consump ion o he an in he supply ai duc
(˙
W ,s) needs o be sub ac ed om hese sa ings (since i is no needed in
he sys em wi hou hea eco e y) in addi ion o he elec ici y con-
sump ion o he an in he ex ac ion duc needed o o e come he
p essu e losses in he HRS.
Being Δp hese p essu e losses, we ha e
Δp =C
˙
V2(14)
whe e C is a coe icien , supplied by he equipmen manu ac u e . Then
he elec ici y consump ion due o he p essu e losses in he ecupe a o
is
˙
W ,eΔp =1
η
el,m
˙
VΔp (15)
whe e
η
el,m is he elec ical e iciency o he d i e mo o . Then he su -
plus o elec ici y consump ion due o he HRS is
˙
Wsu
=˙
W ,s+˙
W ,eΔp (16)
Hence, he a e o ne ene gy sa ings is
˙
ESn=
ρ
0
˙
V(cp,a+
ω
0cp, )
ε
(T2−T0) − ˙
Wsu
(17)
Acco ding o his exp ession, he e will be an en i onmen al
empe a u e h eshold abo e which ˙
ESn<0 will ake place. Then, om
he pe spec i e o he Fi s Law, he eco e y ceases o be iable when
he e a e no ne ene gy sa ings; ha is, when
˙
ESn=
ρ
0
˙
V(cp,a+
ω
0cp, )
ε
(T2−T0) − ˙
Wsu
=0(18)
Supposing ha he e ec i eness o he eco e y hea exchange e-
mains cons an , he h eshold alue o he ou side empe a u e om
which he e a e no ene gy sa ings is
T0=T2+
˙
Wsu
ε
˙ma(cp,a+
ω
0cp, )(19)
Mo e in e es ing han he ˙
ESn, is he P ima y Ene gy Sa ing. Fo his, i
is necessa y o ansla e he consump ion o elec ici y o P ima y En-
e gy (PE), depending on he ene gy mix o he coun y. Rega ding he
he mal ene gy, o ansla e i o PE, we will ha e o ake in o accoun
he e iciency o he gene a ion and dis ibu ion o he hea ing sys em in
he building, since i ha he mal ene gy we e no eco e ed, i would
ha e o be supplied by he hea ing sys em. The e o e, i
η
el is he ene gy
e iciency o he elec ical sys em a a na ional le el and
η
g is he gen-
e a ion and dis ibu ion ene gy e iciency o hea ing, he ne sa ings o
p ima y ene gy is
˙
PESn=
ρ
0
˙
V(cp,a+
ω
0cp, )
ε
(T2−T0)
η
g
−
˙
Wsu
η
el
(20)
Now, conside ing he g ea di e ence in quali y be ween he ene gy
sa ed in he eco e y sys em (low empe a u e he mal ene gy) and he
ene gy consump ion (elec ici y), i is ob ious ha i is e y con enien
o analyze he ue bene i o he eco e y sys em h ough an exe gy
analysis. In ac , due o he high he modynamic quali y o elec ici y,
we ind ha al hough hea eco e y can sa e ene gy, i may ha e highe
consump ion in exe gy, so i migh be no ecommended o eco e hea
om he pe spec i e o Second Law. I is wo h no ing ha by using
exe gy o he analysis, he h eshold empe a u e om which no sa -
ings a e achie ed is much lowe han he h eshold empe a u e ob-
ained wi h ene gy analysis.
Using exe gy analysis, he a e o exe gy sa ings o he HRS is
˙
ExS =
ρ
0
˙
V(cp,a+
ω
0cp, )[T1−T0−T0ln T1
T0](21)
whe e T1 is calcula ed in Eq. (12), so ha he a e o Ne Exe gy Sa ing
gi es
Fig. 2. Mechanical en ila ion a) wi hou eco e y b) wi h hea eco e y (as in he case s udy).
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
5
˙
ExSn=
ρ
0
˙
V(cp,a+
ω
0cp, )[
ε
(T2−T0) − T0ln(1+
ε
(T2−T0)
T0)]−˙
Wsu
(22)
Then, om he Second Law pe spec i e, he eco e y is no longe
easible when he e a e no exe gy sa ings, his is ˙
ExSn=0. I we
conside ha he hea exchange e ec i eness emains cons an , he
empe a u e h eshold om which he eco e y ceases o be in e es ing
appea s by sol ing his ollowing equa ion
T0[
ε
+ln(1+
ε
(T2
T0
−1))]=
ε
T2−
˙
Wsu
ρ
0
˙
V(cp,a+
ω
0cp, )(23)
Using his exp ession, we can calcula e he h eshold alue o T0
abo e which ˙
ExSn is nega i e. On he o he hand, in he same way as he
ene gy analysis has been done e alua ing he P ima y Ene gy Sa ings,
exe gy analysis can be e e ed o P ima y Exe gy (PEx). In his case, he
exe gy e iciency o elec ici y gene a ion a he na ional le el ϕg, as well
as he exe gy e iciency o hea ing p oduc ion and dis ibu ion ϕg in he
building, a e conside ed. The e o e, he sa ings o p ima y exe gy is
˙
PExSn=
ρ
0
˙
V(cp,a+
ω
0cp, )[T1−T0−T0ln T1
T0]
ϕg
−
˙
Wsu
ϕel
(24)
Le us now make some economic conside a ions. I cE and cF a e he
uni cos o elec ici y and uel espec i ely (bo h in
€
/kWh uni s), om
an economic poin o iew, he eco e y ceases being iable when
˙
EcoSn=
ρ
0
˙
V(cp,a+
ω
0cp, )
ε
(T2−T0)
η
g
cF−˙
Wsu
cE=0(25)
And hen, i he eco e y sys em e ec i eness is conside ed o
emain cons an , he h eshold alue o he ou doo empe a u e om
which he e a e no cos sa ings is
T0=T2+
˙
Wsu
η
g
ερ
0
˙
V(cp,a+
ω
0cp, )cE
cF
(26)
These ene gy, exe gy and economic analyses e e o win e condi-
ions, in which he eco e y sys em p ehea s he ou doo ai . Summe
condi ions equi e simila analyses, bu , con e sely, he eco e y sys em
p e-cools he ou doo ai ha en e s he oom.
3. Desc ip ion o he en ila ion and he moni o ing sys em
A measu emen campaign was done in wo en ila ion sys ems wi h
HRS. They co espond o wo dwellings o a block o dwellings loca ed in
Vi o ia (Basque Coun y) bu we only p esen he esul s o one o hem.
The da a used o ep esen he g aphics co espond o he pe iod be-
ween 20 h o Feb ua y and Ma ch 21, 2017, e en i he campaign was
ca ied ou du ing he six-mon h hea ing pe iod. Fig. 3 a) shows he
ypical con igu a ion o all he building’s po als and Fig. 3 b) a loo
plan wi h he schema ic o he balanced en ila ion sys em wi h hea
eco e y. The dwelling co esponds o he sou h- acing con igu a ion,
wi h he eco e y sys em jus in on o he access doo . The o he
dwelling has a no h con igu a ion, wi h he eco e y sys em away om
i s doo , a he opposi e end o he co ido .
Table 1 shows he su ace and olume o each oom o he dwelling; a
young couple wi h wo young child en occupy his dwelling.
The en ila ion sys em has a maximum ai low o 150 m
3
/h.
Depending on hei needs, he ai low a e can be modi ied manually o
by p og amming a schedule. Besides, he en ila ion sys em is always in
ope a ion, so ha an au oma ic bypass sys em a oids o e hea ing o
supe -cooling. Fig. 4 shows he placemen o he senso s. The ollowing
measu emen s we e made:
•Ai empe a u e in he supply duc a he inle (T
0
), and a he ou le
o he eco e y sys em (T
1
) and ai empe a u e in he ex ac ion
duc a he inle (T
2
) and ou le (T
3
) o he HRS.
Fo ha ou -wi e P 100, class 1/10 DIN (±0.03 ◦C o 0 ◦C, ±0.08 ◦C)
a 100 ◦C ha e been used.
•Ai eloci y was measu ed in he s aigh sec ion o he duc s, be-
ween he ou side and he HRS; a he inle o he eco e y sys em o
he supply ai (V
0
) and a he ou le o he eco e y sys em o he
ex ac ion ai (V
2
).
A P odual he moanemome e , model IVL20 (Range 0–50 m/s ±7%
a 25 ◦C, 0–50 ◦C ±0.5 ◦C a 25 ◦C) has been used.
•An AR-485 single-phase ne wo k analyze has measu ed he ac i e
powe o he ans.
•In addi ion, o assessing he indoo ai quali y o ooms, he CO
2
concen a ion in he li ing ooms and in he bed ooms has been
measu ed wi h a P oduce HDH CO
2
Con olle (±40 ppm, ±3% o
he ac ual alue).
3.1. Da a ob ained
Fig. 5 a) shows he supply ai empe a u e a he inle and ou le o
he eco e y sys em, wi hou conside ing he bypass pe iods; a
ema kable p ehea ing o 7.0 ◦C is obse ed (wi h a ange o a ia ion
o ±3.5 ◦C). Besides, he minimum in ake ai empe a u e is 16 ◦C. To
comple e he o e all beha io o he sys em, Fig. 5 b) shows he em-
pe a u es including he pe iods in which he eco e y sys em ope a es in
bypass mode.
The ai eloci y in he ex ac and supply duc s appea in Fig. 6 a),
whe e wo di e en speeds o he en ila ion sys em a e dis inguished
and, in addi ion, he ope a ing schedule is also included in Fig. 6 b). This
scheduled ime able co e s he pe iods o maximum occupancy and
ac i i y o he highes speed egime, while he lowes speed is se o he
pe iod o absence o occupan s and low me abolic and domes ic ac i i y.
F om an ene gy poin o iew, his is a s a egy o inc ease ene gy e i-
ciency and ha has no nega i e consequences on indoo ai quali y. The
ela ionship be ween he eloci y o he supply and he ex ac ion ai is
app oxima ely uni y, since he low a es a e i ually equal. Howe e ,
he mass low a e o ex ac ion ai is sligh ly lowe han ha o supply,
so he dwelling has a small ex il a ion.
Fig. 7 shows he ac i e powe consumed by he ans. Acco dingly, he
consumed powe anges be ween wo le els, co esponding o he wo
speeds o he en ila o s; o he lowe le el he powe is 35.6 W and
a ound 56.6 W o he highe one.
Du ing he measu emen pe iod, he condi ion o he il e s was
examined o check he accumula ed di , see Fig. 8. Hence, in o de o
make he en ila ion sys em wo k in op imal condi ions, i is necessa y
o clean o eplace pe iodically he il e s, since di causes addi ional
p essu e losses and in luences he indoo ai quali y.
Du ing he selec ed pe iod, he o al elec ici y consump ion was
29.3 kWh, so he a e age alue o he speci ic ene gy consump ion o he
ans in he pe iod conside ed was 0.23 kWh/m
3
.
3.2. Indoo ai quali y
In addi ion o he exhaus i e moni o ing o he HRS, he indoo ai
quali y (IAQ) was analyzed in e ms o CO
2
concen a ion, using he
equi emen s de ined by he Basic Documen o Heal hiness o he
Buildings Technical Code (HS3 DB o he CTE) [27] and he classi ica-
ion based on IDAs de ined by EN ISO 15665 as e e ences, see Table 2.
As al eady men ioned, wo adul s sha e oom 1, and wo mino s (4
yea s old and a newbo n) a e in NW and SE acing bed ooms. The da a
p esen ed in Fig. 9 co espond o he d y zones (bed ooms and li ing
oom).
Fig. 9 a) p esen s he e olu ion o he CO
2
concen a ion du ing a
wo king day in each o he ooms, while Fig. 9 b) shows he case o he
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
6
amily on a weekend. Bo h p o iles a e e y simila , bu his is because
bo h adul s wo k du ing he weekend. The inc eases and dec eases in he
CO
2
concen a ion e lec he occupa ion and non-occupa ion pe iods
espec i ely.
Fig. 10 p esen s he pe cen age o ime in which he CO
2
concen-
a ion co esponds o a ce ain ca ego y. When analyzing he esul s, i
is impo an o conside he pe iods when he ooms a e occupied and
no occupied.
Acco ding o Fig. 10, he indoo ai quali y is good, since as we can
see, he pe cen age o ime in which he indoo ai quali y pe ains o he
IDA IV ca ego y (CO
2
concen a ion g ea e han 1000 ppm) is e y low
in all ooms. To comple e he indoo ai quali y analysis, he alues
co esponding o he CO
2
a e age and maximum concen a ions du ing
he pe iod conside ed a e also p esen ed.
4. Calcula ions
This sec ion deals wi h he case s udy’s nume ical esul s: he i s
pa analyses he ene gy and economic sa ings a he cu en si ua ion.
Then, a he modynamic s udy o he HRS was done in ene gy and exe gy
e ms and, in he las sec ions, he h eshold empe a u es o ob aining
ad an ageous ope a ing condi ions a e calcula ed.
4.1. Ene gy sa ing analysis
Du ing he measu emen pe iod, i a simple exhaus en ila ion
sys em we e used ins ead, he hea ing demand associa ed wi h such ai
enewal would ha e been ˙
m(cp,a+
ω
0cp, )(T2−T0)⋅Δ =170 kWh.
Howe e , he en ila ion is pe o med wi h a hea eco e y sys em, so
he demand calcula ed om he eco ded da a is ˙
m(cp,a+
ω
icp, )(T2−
T1)⋅Δ =63 kWh. The e o e, he educ ion in hea ing demand due o ai
enewal is a ound 63%. Keep in mind ha he s udy-pe iod co esponds
o he end o win e and beginning o sp ing, so ha empe a u es begin
o inc ease; he e o e, he ull po en ial o HRS is no a ained, so ha
mo e ene gy would be eco e ed in he coldes mon hs.
The ene gy consump ion o he addi ional supply an plus he con-
sump ion in he ex ac ion an due o p essu e losses in he HRS ( ˙
Wsu
,
om Eq. (16)) is es ima ed as hal o he o al elec ici y consump ion
(which includes he supply an and he ex ac an), so ha i co e-
sponds o 14.6 kWh o he pe iod conside ed. Besides, he hea ing
sys em o he dwelling consis s o a na u al gas boile wi h an ene gy
e iciency equal o 92%. Then, he ene gy sa ings in hea ing uel con-
sump ion, Eq. (18), is 117 kWh du ing he de ined pe iod.
The hea ing season in Vi o ia-Gas eiz uns om he las Sa u day o
Fig. 3. a) Pho og aph o he building b) Floo plan wi h he schema ic o he en ila ion sys em.
Table 1
Su ace and olume o he dwelling’s ooms.
2 PORTAL. N◦2. 1◦L
Room Su ace [m
2
] Volume [m
3
]
NO bed oom 6.70 17.15
SE bed oom 9.99 25.67
SO bed oom 8.24 21.34
Li ing oom 18.27 43.75
Ki chen 4.78 12.24
Bad oom 2.62 6.34
Fig. 4. Measu ing poin .
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
7
Oc obe o he las Sunday o Ma ch. Table 3 con ains he hea ing de-
mands a io o he o he hea ing mon hs in ela ion o he measu emen
pe iod, based on he deg ee-days me hodology [28] and he egis e ed
da a in he yea 2017.
2
This is a simple and app oxima e me hodology
based on he idea ha hea ing demand is p opo ional o he numbe o
deg ees in which he a e age daily ou doo empe a u e alls below an
indoo empe a u e h eshold (so-called deg ee-days), du ing he hea -
ing pe iod (o abo e i , du ing he cooling pe iod).
In acco dance wi h his p opo ionali y, he uel ene gy sa ings in
hea ing o als a alue o 561 kWh. In such pe iod, he elec ici y con-
sump ion due o he addi ional supply an and he consump ion in he
ex ac ion an due o he p essu e losses in he HRS is 70 kWh so ha he
eco e ed uel consump ion is 8 imes highe han he elec ici y con-
sump ion in he hea ing pe iod.
As he indoo ecommended empe a u e in dwellings o he sum-
me mon hs is in he ange o 23–26 ◦C, we ha e chosen a alue o 25 ◦C.
Acco ding o he egis e ed me eo ological da a in Vi o ia-Gas eiz, 31%
o he ime, he ou doo empe a u e is abo e 25 ◦C and he e o e, in
such hou s, he HRS p ecools he ou doo ai . Du ing he emainde
ime, he HRS wo ks in bypass mode so ans con inue wo king
h oughou he yea . Consequen ly, ou side he hea ing season he
elec ici y ex a consump ion is 108 kWh.
Le us suppose ha a cooling sys em, wi h a chille o COP =3,
main ains he dwelling a 25 ◦C in he wa mes mon hs.
3
Acco ding o
he ou doo empe a u e dis ibu ion, we ha e ound ha he eco e ed
ene gy ob ained by p ecooling he ou doo ai in he HRS is equal o 6
kWh, so ha he sa ings in elec ici y consump ion in he chille would
be equal o 2 kWh. As expec ed, in he no-hea ing pe iod, he elec ici y
consump ion sa ings (2 kWh) a e much lowe han he elec ici y con-
sump ion in he ans (108 kWh). Summe is mild in Vi o ia-Gas eiz and,
as said, he e a e e y ew hou s whe e he empe a u es a e high.
Acco dingly, i is necessa y o check, e e ing o p ima y ene gy (PE,
Eq. (20)), i he ene gy sa ings on p ehea ing (561 kWh o uel) and
p ecooling (2 kWh o elec ici y) compensa es o his addi ional elec-
ici y consump ion du ing he whole yea (178 kWh). The e o e, since
he elec ici y con e sion ac o is 2.403 [29], he su plus in elec ical
ene gy consump ion in he ans du ing he whole yea , e e ed o p i-
ma y ene gy, is 428 kWh
PE
. Con e sely, he con e sion ac o o na u al
gas is 1.195 [29] so he p ima y ene gy sa ings in hea ing due o he
eco e ed hea a e equal o 670 kWh
PE
and he p ima y ene gy sa ings
in no-hea ing pe iod a e 4 kWh
PE
, making a o al o 674 kWh
PE
.
The e o e, when e e ing o p ima y ene gy, he addi ional yea ly
elec ici y consump ion in he ans o he en ila ion sys em is ully
o se by simply eco e ing hea in win e .
All he abo e esul s a e summa ized in Fig. 11. Fig. 11 a) shows he
yea ly dis ibu ion o hea ing and no-hea ing pe iod (which includes
bo h, mid and cool season) wi h he co esponding ene gy sa ings and
he ex a elec ici y consump ion in he ans. Fig. 11 b) compa es he
sa ings and he su plus in elec ici y consump ion o e he yea in en-
e gy and p ima y ene gy e ms; ne sa ings a e also ema ked. The e-
sul s ob ained jus i y he lack o cooling sys ems in Vi o ia-Gas eiz.
4.2. Economic sa ings analysis
In addi ion o ene gy sa ings, economic analysis mus be done o
measu e he ad an age o en ila ion sys ems wi h hea eco e y in
ela ion o a sys em wi hou eco e y.
To make his analysis, i is aken in o accoun ha he uni cos o
elec ici y is 12.4 c
€
/kWh, and ha o na u al gas is 5.09 c
€
/kWh.
The e o e, o he whole yea , he addi ional consump ion o elec ical
Fig. 5. Supply ai empe a u e, ou doo (T
0
) and in ake (T
1
) a) wi hou bypass pe iods b) including bypass pe iods.
Fig. 6. a) Ai eloci y a he supply duc (V
0
) and a he ex ac ion duc (V
2
) b)
Ope a ion schedule.
Fig. 7. Elec ic powe consumed by he en ila ion sys em.
2
HDD o Vi o ia- Gas eiz acco ding o Eu os a a e equal o 2273.
3
In he cold clima e o Vi o ia-Gas eiz, he Spanish ene gy legisla ion does
no equi e a speci ic cooling sys em.
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
8
ene gy implies an addi ional cos o 22.1
€
, and he sa ings in na u al gas
cos s a e equal o 28.5
€
, so ha 6.4
€
a e sa ed yea ly.
Acco ding o he economic da a supplied by he ins alle , a double
low en ila ion sys em wi h eco e y o a 3-bed oom dwelling cos s
2300
€
and wi hou eco e y 1250
€
, so he cos inc emen is 1050
€
.
The e o e, he payback ime o he HRS is 164 yea s, which sugges s
ha his sys em is no economically iable o he clima ic condi ions
and economic en i onmen o he case.
4.3. E ec i eness o he hea eco e y sys em
The e ec i eness o he HRS was calcula ed e e y 10 min using Eq.
(2) and he esul s o he en i e conside ed pe iod a e ep esen ed in
Fig. 12 a). The in e als o when he sys em ope a es in bypass mode
can be seen, as well as he ine ia o he sys em, when i goes om bypass
mode o exchange mode.
Fig. 12 b) shows he e ec i eness o he HRS only in he pe iods in
which he sys em ope a es in exchange mode. To ob ain his ope a ion
mode, he e ec i eness alues abo e 50% a e il e ed. The alues in
exchange mode ep esen a ound 70% o he o al pe iod conside ed
and, as al eady men ioned, he en ila ion sys em has been p og ammed
o ope a e a wo speeds.
The a e age e ec i eness o he HRS, when he sys em wo ks a low
speed, is 87.3%, while i is equal o 86.1% when wo king a high speed.
4.4. Ene gy e iciency
I we calcula e he
η
1
ene gy e iciency in he common way, ha is, as
he a io be ween he en halpy inc emen in ou doo ai low
(˙
V
ρ
0(h1−h0)) and he sum o en halpy inc emen o he ex ac ed ai
low and an consump ion (
˙
V
ρ
i(h2−h3) +
˙
W ), he a e age alue o he
HRS e iciency is
η
1
=89%, Eq. (4); he e o e, i is close o an adiaba ic
sys em.
Howe e , i we calcula e he ene gy e iciency by using Eq. (5),
whe e he indoo ai en halpy is conside ed as he only a ailable and he
en halpy in s a e 3 is aken as pa o he losses, he e iciency is he a io
be ween he eco e ed en halpy (
˙
V
ρ
0(h1−h0)) and he sum o exhaus
ai en halpy and elec ici y consump ion (˙
V
ρ
ih2+˙
W ). In such case, he
a e age e iciency is equal o
η
2
=31%, Eq. (5).
I he en halpy om he exhaus ai is dis ega ded, simila ly o wha
is done when e alua ing he COP o a hea pump, hen Eq. (6) is used o
calcula e he ene gy e iciency.
Fig. 13 shows he alues o hese h ee e iciencies o he HRS only in
he pe iods in which he sys em ope a es in exchange mode. As can be
seen in Fig. 13, he ene gy inpu o he ans is e y small in compa ison
o he ene gy ou pu and, hus, he alues o he ene gy e iciency
η
3 is
e y high, wi h an a e age alue o 3.17 and a maximum alue o 8.85.
4.5. Exe gy e iciency
By using Eq. (9), he a e age exe gy e iciency o he pe iod has
been calcula ed, esul ing ϕ2=4.0%. The dynamic alues o he ex-
change mode calcula ed e e y 10 min a e in Fig. 14. Simila ly, by using
Eq. (10), we ound ha by dis ega ding he exe gy o he exhaus ai , he
Fig. 8. Pho os o he supply and ex ac ion il e s a e he ope a ing pe iod.
Table 2
Classi ica ion o indoo ai quali y.
Ca ego y CO
2
concen a ion [ppm]
IDA I ≥400
IDA II 400–600
IDA III 600 - 1000
IDA IV 1000 ≤
Fig. 9. E olu ion o CO
2
concen a ion in a) a wo king day b) weekend.
A. Picallo-Pe ez e al.
Jou nal o Building Enginee ing 39 (2021) 102255
9
a e age exe gy e iciency is ϕ3=4.4% and he alues in 10-min in-
e als a e also ep esen ed in Fig. 14. As we can obse e, in exe gy
e ms, he e iciency o he HRS is much lowe due o he low-quali y o
he ene gy eco e ed e sus he high-quali y o he elec ici y inpu in o
he ans.
The ene gy
η
3 and exe gy ϕ3 e iciencies o he HRS as a unc ion o
he ou doo T
0
empe a u e a e ep esen ed in Fig. 15. No e he di e en
scales o he ene gy e iciency (le y-axis) and exe gy e iciency ( igh
y-axis).
4.6. Th eshold empe a u es o ene gy sa ings in he hea ing pe iod
Gi en a ixed indoo se empe a u e, he hea eco e ed depends on
he ou doo empe a u e, so, he lowe i is, he mo e hea is eco e ed.
This is he same as saying ha he eco e y sys em is mo e e ec i e
when he di e ence be ween he indoo and ou doo empe a u es a e
g ea e . The elec ic powe consump ion o he an, howe e , does no
depend on he en i onmen al condi ions, because in ope a ion, he
consump ion is ixed. The ollowing calcula ions a e ela ed o he
hea ing pe iod when he eco e y sys em is unc ioning.
As p e iously s a ed and ep esen ed in Fig. 7, when wo king a
speed 1, he a e age an powe consump ion is equal o 35.6 W, and
when wo king a speed 2, i is 56.6 W. The indoo com o empe a u e
is conside ed o be a 20 ◦C, he a e age ai mass lows in each egime
a e 0.0244 kg/s and 0.041 kg/s, and he a e age e ec i eness a e equal
o 86.7% and 86.5% espec i ely. The e o e, using Eq. (19) and EES
sol e Re . [31], he h eshold empe a u es, i.e. he limi alues o
ou doo empe a u e abo e which he e a e no ene gy sa ings ( ˙
ESn=
0), a e 18.4 ◦C and 18.5 ◦C in espec o each speed.
To calcula e h eshold empe a u es in ela ion o he consump ion
o p ima y ene gy, one mus use Eq. (20) and equal i o ze o ( ˙
PESn=0),
which now inco po a es he con e sion ac o s o inal o p ima y en-
e gy o elec ici y and he mal ene gy. In his case, he h eshold
empe a u es a e 16.8 ◦C and 17.0 ◦C o speed 1 and speed 2,
espec i ely.
Table 4 ga he s all he abo e esul s. The e o e, i he ou doo em-
pe a u e is lowe han hose indica ed in Table 4, he use o he HRS o
en ila ion is ad an ageous (du ing he hea ing pe iod) compa ed o a
simple exhaus en ila ion sys em.
Fig. 16 a) shows he cumula i e equency o he ou doo ai em-
pe a u e in Vi o ia-Gas eiz o he hea ing pe iod. Acco dingly, o he
ypical me eo ological yea , he empe a u e o he ou doo ai is below
18 ◦C du ing mos o he win e , mo e speci ically du ing 99.8% o he
hea ing pe iod.
The accumula ed equency cu es a e also gi en o he o he wo
capi als o he Basque Coun y, Bilbao and San Sebas ian, see Fig. 16 b).
Du ing he hea ing pe iod, in he case o Bilbao, he ou doo ai em-
pe a u e is lowe han he calcula ed h eshold empe a u e 97% o he
ime. In he case o San Sebas ian, he pe cen age is close o 93%.
Fig. 10. a) Pe cen age o ime o each indoo ai ca ego y and b) a e age and
maximum CO
2
concen a ion (ppm).
Table 3
Ra io o hea ing demands.
PERIOD HEAT RATIO
21/10–20/11 0.64
21/11–20/12 1.00
21/12–20/01 1.07
21/01–20/02 1.09
21/02–20/03 1.00
Fig. 11. a) Hea ing and no-hea ing pe iods along he yea and b) ene gy sa ing, ex a elec ici y consump ion and p ima y ene gy sa ing.
A. Picallo-Pe ez e al.
