The use of the photovoltaic system in combination with a thermal energy storage for heating and thermoelectric cooling

A icle The Use o he Pho o ol aic Sys em in Combina ion Wi h a The mal Ene gy S o age o Hea ing and The moelec ic Cooling Jan Sko ajsa * and Ma in Zalesak Facul y o Applied In o ma ics, Tomas Ba a Uni e si y in Zlin, Names i T.G.Masa yka 5555, 760 01 Zlin, Czech Republic; [email p o ec ed] *Co espondence: [email p o ec ed] Recei ed: 11 July 2018; Accep ed: 25 Sep embe 2018; Published: 28 Sep embe 2018   Abs ac : The a icle is ocused on he esea ch o he usage o mode n accumula ion echnology. The p oposed sys em is able o imp o e he he mal com o o building in e io s. Tha ex depic s he echnology, which uses a pho o ol aics and o he enewable ene gy sou ces o ac i e hea ing and cooling. The bases o he p esen ed echnology a e he phase change ma e ial and he mal ene gy s o ages. So, i passi ely imp o es he he mal capaci y o he cons uc ions o he buildings. Mo eo e , he e is a possibili y o use i o ac i e hea ing and cooling. The echnology con ains he moelec ic assemblies, so, he e is a e y in e es ing possibili y o s o e he mal ene gy wi h use o enewable ene gy sou ces (such as pho o ol aic sys em) and he moelec ic coole s side by side. In he manusc ip , he e a e shown measu emen s and esul s o he ac i e ope a ing modes o p oposed echnology. I was ound he echnology is able o wo k in ac i e hea ing and cooling modes. I wo ks qui e well in ac i e hea ing mode. On he o he hand, he moelec ic cooling mode had a p oblem wi h o e hea ing. In he end, he p oblem was sol ed and he cooling mode wo ks. The measu emen s and esul s a e desc ibed in he ex . Keywo ds: PCM; he moelec ic cooling; enewable ene gy sou ces; pho o ol aic; he mal ene gy s o age 1. In oduc ion The consump ion o ene gy by he building sys ems such as hea ing, en ila ion and cooling sys ems (HVAC) a e s ill ising wi h he ongoing inc ease in demand o he mal com o [ 1 ]. Nowadays, he emissions and ene gy demand a e being dec eased by he use o he enewable ene gy sou ces. O hose sou ces, sola , wind, o geo he mal ene gy and hea pumps, a e sui able o buildings. These echnologies, howe e , a e no capable o dealing wi h an insu icien he mal s o age capaci y o he s uc u es. A p esen , he p e e ence is o a pa ame e o su icien he mal insula ion, bu ha does no add ess he accumula ion o he he mal ene gy. The buildings, which a e mos p oblema ic, a e hose cons uc ed om ligh weigh ma e ials, such as wood o ligh weigh conc e es. In hese, ou side hea load a ia ions du ing he day may cause inapp op ia e luc ua ions o he ai empe a u e inside he buildings. The p oblem wi h ligh weigh s uc u es is ha hey a e unable o s o e a su icien amoun o he mal ene gy ha limi s hei abili y o main ain s able condi ions o he indoo en i onmen . As a consequence, he he mal com o is a ec ed. The mal ene gy s o age add esses his p oblem. An op imal way o dec easing he consump ion o ossil ene gy wi h inc easing he mal com o a he same ime is he use o elemen s o he mal ene gy s o ages in combina ion wi h enewable ene gy sou ces, e.g. pho o ol aic sys em in combina ion wi h he moelec ic coole s. Appl. Sci. 2018,8, 1750; doi:10.3390/app8101750 www.mdpi.com/jou nal/applsci Appl. Sci. 2018,8, 1750 2 o 15 1.1. The mal Ene gy S o age The mal ene gy s o age (TES) is a empo a y cap u e o he mal ene gy in he o m o ho o cold subs ances o la e u ilisa ion [ 2 ]. The s o ed he mal ene gy may be used o hea ing o cooling applica ions. So, TES is use ul o add essing he misma ch be ween he supply and demand o ene gy [ 3 ]. The p inciple o TES is based on a empe a u e di e ence (sensible TES) o change o phase (la en TES). The ini ial s a e is a solid s a e when he hea is added, he solid subs ance is hea ing up (sensible hea ), a e ha , a solid- o-liquid phase change ollows (la en hea ). When he hea is s ill added, a liquid is hea ing up (sensible hea ) and hen, a liquid- o- apou phase change occu s (la en hea ) and a e ha , sensible hea ing o he apou occu s (sensible hea ) [ 4 ]. As can be seen, wo o ms o hea a e ecognized: sensible hea and la en hea . The p inciple o sensible hea s o age is based on he ma e ial’s change o hea capaci y and empe a u e du ing he p ocess o cha ging and discha ging [ 5 ]. In case o he sensible hea , he speci ic hea capaci y is he p ima y pa ame e . I de e mines he amoun o ene gy needed o change he empe a u e o 1 kg o he subs ance by 1 K. The amoun o sensible hea ene gy can be calcula ed by Equa ion (1). Q=m·ZT Ti cpdT, (1) whe e mmass (kg), Tiini ial empe a u e (K), T inal empe a u e (K), cpspeci ic hea capaci y (J kg−1K−1). La en hea s o age is elian on he s o age ma e ial abso bing o eleasing hea as i unde goes a solid o solid, solid o liquid o liquid o gas phase change o ice e sa [ 5 ]. Du ing he phase change, he subs ance empe a u e is cons an . E en so, i sabili y o s o ing and eleasing a la ge amoun o he mal ene gy. So, his is he eason why la en hea s o age is a mos e icien me hod o s o ing he mal ene gy [ 6 ]. The quan i y o la en hea is de i ed om he di e ence in en halpy o he wo ele an s a es. The mal ene gy s o age ealised by phase change ma e ials (PCMs) exploi s especially la en hea [ 7 ]. PCM can be packaged in specialised con aine s (panels, ubes, and plas ic bags), o i can be con ained in o dina y building elemen s (ceiling and wallboa ds), o encapsula ed as sel -con ained elemen s [8]. The amoun o ene gy is gi en by he en halpy di e ence du ing he phase change, acco ding o he ollowing Equa ion (2). ∆Q=m·∆h, (2) whe e ∆hen halpy di e ence (J·kg−1). Figu e 1shows he p inciple o he mal ene gy s o age in he o m o la en and sensible hea in he PCMs. 1.2. Phase Change Ma e ial Ma e ials o be used o phase-change TES should ha e phase-change empe a u e in he p ac ical ange o applica ion and hey mus ha e a high la en hea o usion and a high he mal conduc i i y. PCMs should also ha e desi able en i onmen al p ope ies o dec ease he en i onmen al impac o he sys ems du ing hei li ecycle [ 9 ]. Di e en ma e ials conside ed as po en ial PCMs include hyd a ed sal s, pa a in waxes, a y acids, he eu ec ics o o ganic and non-o ganic compounds, e c. PCMs can be di ided in o h ee main g oups—based on he empe a u e anges o e which he TES phase-change occu s: low empe a u e (phase-change empe a u es below 15 ◦ C), mid empe a u e Appl. Sci. 2018,8, 1750 3 o 15 ( he mos popula — om 15 o 90 ◦ C) and high empe a u e PCMs (abo e 90 ◦ C) [ 10 , 11 ]. In ou case, PCMs a e classi ied as o ganic, ino ganic and eu ec ic. Figu e 1. La en and sensible hea , empe a u e ange o he phase change [7]. O ganic PCMs include a wide selec ion o o ganic ma e ials such as a y acids, es e s, alcohols and glycols. The p incipal ad an ages a e hei chemical and he mal s abili y, and high la en hea o usion. They a e usually ecyclable, non-co osi e, and ha e li le o no subcooling [ 1 , 12 ]. Un o una ely, hey ha e some disad an ages: lammable, non-compa ible wi h plas ic con aine s, ela i e la ge olume change, mo e expensi e, low he mal conduc i i y, and lowe phase-change en halpy [ 1 , 13 , 14 ]. Ino ganic PCMs a e desc ibed as hyd a es sal s and me als. They co e a wide ange o applica ion. The main ad an ages a e highe en halpy pe olume, highe he mal conduc i i y, non- lammable, and lowe olume change. Howe e , hey ha e he disad an ages o phase seg ega ion, co osion, lack o he mal s abili y and subcooling [9,12]. The eu ec ic PCMs a e a combina ion o chemical compounds o elemen s ha ha e a single chemical composi ion and ha solidi y a a lowe empe a u e han any o he composi ion ob ained om he same componen s [ 15 ]. Due o hei highe densi y and s abili y in hei liquid s a e, hey ha e been used widely as ionic liquids in high empe a u e sensible he mal s o age sys ems ( he monuclea ene gy, concen a ed sola he mal powe ) [16]. Theo e ically, mos ma e ials can be conside ed as PCMs. On he o he hand, only some o hem can be used o e ec i e and p edic able ene gy s o age. Figu e 2shows some o he many ma e ials sui able o TES. Depending on he applica ion, he PCMs should be selec ed based on hei phase-change empe a u e, should ha e a la ge la en hea , should mel cong uen ly wi h minimum subcooling, and should be chemically s able, inexpensi e, non oxic, and nonco osi e [15]. The mos commonly used PCMs in buildings a e pa a in and sal hyd a es [17,18]. Figu e 2. Classes o he phase change ma e ials and hei common pa ame e s [19]. As p e iously men ioned PCMs can be inco po a ed in o building s uc u es. I con ibu e o lowe ene gy demand by s o ing he mal ene gy in he o m o hea o cold [ 20 ]. Se e al con igu a ions Appl. Sci. 2018,8, 1750 4 o 15 ha e been p oposed in he las wo decades in o de o inco po a e PCM in o cons uc ion ma e ials. T adi ionally, as one o he bes op ion is aken applica ion o he PCM in he en elope o he oom because o i s la ge a ea [ 21 ]. Some o he ecen esea ch show some imp o emen s and speci ic use o he PCM in he buildings and also hei ad an ages and disad an ages [ 22 , 23 ]. The e iciency is no dependen only on he loca ion o he PCM, bu also on hei speci ic pa ame e s, such as mel ing empe a u e ange. Fo example, one o he esea ch shows ha he highes alue o ene gy exi ing om he indoo en i onmen is ensu ed by PCM wi h a mel ing empe a u e equal o 20 ◦C [24]. In eg a ion o he PCMs in o he building’s ene gy sys em can inc ease e iciency o he sys ems. These ac i e sys ems use o he ai low as o ced con ec ion o inc ease amoun o ene gy ob ained om s o age ma e ials [ 25 ]. In common applica ions, PCMs se e as a ese oi o excess he mal ene gy o u u e u ilisa ion. One o he expe imen al ene gy sys ems wi h in eg a ed PCMs and combina ion wi h enewable ene gy sou ces is p esen ed in his a icle. 1.3. The moelec ic Cooling Sys em The moelec ic coole s (TEC) a e solid-s a e hea pumps based on he Pel ie e ec . I enables con e ing elec ical ene gy in o a empe a u e g adien . In comme cial ypes, TECs a e composed o many o n- ype and p- ype semiconduc o junc ions. When a di ec cu en powe sou ce is connec ed, he elec ical cu en lows om he n- ype elemen o he p- ype elemen , and he moelec ic cooling e ec occu s. When he elec ons pass om a lowe ene gy le el elemen (p- ype) o a high ene gy le el elemen (n- ype) he empe a u e o he cold junc ion dec eases. A he same ime, he elec ons ca y he abso bed hea o he ho junc ion. This hea is ans e ed o he hea sink, while he elec ons e u n o a lowe ene gy le el in he p- ype semiconduc o ( he Pel ie e ec ) [26]. The e is also a possibili y o use he mocouples e e se. Tha means, i possible o gene a e elec ical ene gy by he empe a u e di e ence. I he he mal g adien exis s be ween he cold and ho junc ion, a ol age (Seebeck ol age) di ec ly p opo ional o he empe a u e di e ence is gene a ed. TEC sys ems ha e no mechanical mo ing pa s and luids, which ans e hea om he cold side o he ho side o he modules [ 27 ]. TECs ha e many ad an ages such as high eliabili y, low weigh , and lexibili y in in eg a ion. TEC sys ems ha e been applied o he moelec ic e ige a o s [ 27 , 28 ], ca sea s [ 29 , 30 ], elec onic cooling de ices [ 31 , 32 ]. I has been also used in mili a y, ae ospace, ins umen , and indus ial p oduc s [ 33 – 36 ]. One o he a eas o new esea ch o he moelec ic echnology is applying he moelec ic modules (TEM) o domes ic space cooling. TEC sys ems can be also powe ed by a pho o ol aic (PV) wi hou he in e e . Some o he ecen esea ches ocused on he moelec ic coole s and gene a o s (TEC and TEG) a e de ined by he combina ion o sola ene gy and PCMs. TEG is an al e na i e choice o con e ing o sola he mal ene gy in o elec ici y. The echnology desc ibed in his a icle can use ene gy om PV o TEC in combina ion wi h he PCM-based TES. 2. Me hods The p oposed accumula ion echnology is based on he PCM DuPon Ene gain. This PCM is g ouped in o one ac i e elemen [ 37 ]. The PCM uses molecula encapsula ion ha o ms a highly du able PCM and i has a useable empe a u e ange be ween 0 ◦ C and 40 ◦ C. The mass o he PCM is composed o a mix u e o polye hylene and pa a in wax. When he empe a u e o he PCM is abo e 18 ◦ C, he mass begins o mel and abso bs up o 515 kJ · m −2 o hea in he empe a u e ange om 18 ◦ C o 24 ◦ C. This empe a u e ange co esponds o common empe a u e condi ions inside buildings. In he pa ag aphs below a e desc ibed he basics o he p oposesd echnology, i s possible ope a ion modes, used he mocouples and also pho o ol aics. O he speci ic in o ma ion abou his echnology is desc ibed in ou p e ious a icles [38–40]. Appl. Sci. 2018,8, 1750 5 o 15 2.1. Accumula ion De ice The accumula ion de ice (see Figu e 3) was designed and made a he Facul y o Applied In o ma ics o TBU in Zlin (CZE—Czechia). The e we e also made all measu emen s and imp o emen s. The moni o ed oom in which he echnology is loca ed has he dimensions 7 m × 5 m × 2.8 m. The oom has wo ex e io su aces: wall wi h windows and ceiling ( oo ). The o he walls and loo s a e adjacen o o he hea ed oom. The o al design hea loss due o ansmission h ough walls and windows, en ila ion and in il a ion is abou 41 WK −1 . In he summe i is impo an o know he hea gains. In ou case, he maximum hea gains du ing he day (peak gains) om he ou side a e in he ange o 280 o 480 W om May o Sep embe . Sola window gains a e educed by ou doo blinds. This sys em is composed o wo PCM-based accumula ion panels wi h dimensions 1.25 m × 0.083 m × 2.1 m. Technology is equipped wi h a liquid hea exchange and elec ic hea ing oils inside he panels. The p oposed echnology is design as “g een echnology”. So, i can be supplied wi h powe by any common ene gy sou ces, including enewable ene gy sou ces and use hem o hea ing and cooling. Mo eo e , he echnology is able o use pho o ol aic sys ems in combina ion wi h he moelec ic cooling. This abili y is no common in he PCM de ices. So, i can be one o he bigges di e ence and ad an age o he p oposed echnology agains commonly a ailable echnologies. Figu e 3. Accumula ion de ice and he moelec ic assembly on he igh . The echnology can be ope a ed in many di e en modes. Mode choice is dependen on he equi emen s o pa icula expe imen s. I can wo k as a passi e o ac i e sys em. In he s anda d passi e mode, he echnology uses he common accumula ion o he hea o cold by PCM. This mode can dampen peaks in indoo empe a u e and keep i s able du ing he day and nigh . The echnology in ac i e mode is capable o in luencing he indoo empe a u e by eleasing accumula ed hea o o lowe i by using ex e nal cooling. Indi idual ac i e modes o ope a ing a e: disposing o he accumula ed hea o hea ing up he cooled down panels; hea ing by elec ic hea ing oils o by ho wa e ; cooling by he cold wa e o by he moelec ic coole s. 2.2. The moelec ic Coole s As p e iously men ioned, he echnology is equipped wi h six he moelec ic assemblies o he ype L.L.-210-24-00-00, see Figu e 4. These he moelec ic coole s o e liquid- o-liquid hea ans e . TEC assemblies can be powe ed by he pho o ol aics o om he powe g id AC 230 V [41]. Appl. Sci. 2018,8, 1750 6 o 15 Figu e 4. TEC assembly ype L.L.-210-24-00-00. Basic speci ica ions o he TEC modules: - Inpu powe : 194 W, - Cooling powe : 208 W, - Inpu ol age/cu en : 24 V/8.1 A DC. Fo de e mining he numbe o TEC i was necessa y o speci y he cooling capaci y o he echnology. The a e age speci ic hea capaci y o he he mal panel is abou 11 kJ · kg −1 K −1 (16 o 27 ◦C) and i s weigh is abou 129 kg. The cooling o he accumula ion panels akes es . 8 h. Du ing his ime, he accumula ion de ice abso bed abou 15.6 MJ o he cold, mo e p ecisely, his amoun o hea is emo ed om he PCM. So, he o e all pe o mance o he he mocouples mus each abou 0.55 kW. I he he mocouples ha e 50% e iciency he equi ed (inpu ) powe o he he mocouples is abou 1.1 kW. This means i is necessa y o use six he moelec ic assemblies o ype L.L.-210-24-00-00. 2.3. Pho o ol aic Sys em The PV sys em is ins alled o supply he echnology and he mocouples wi h elec ic powe . The ac i e a ea o he PV panels is 11.25 m 2 . Du ing he summe , sola adia ion ecie ed by he pho o ol aic panels a e ages a in ensi y o 750 W m −2 . Real ene gy e iciency o he PV was se a 10.5%. This alue was esul o measu emen in one o ou p e ious esea ches ocused on e i ica ion o he pho o ol aic panels e ec i eness o hei economic e u n [ 42 , 43 ]. The eal a e age powe ou pu is a li le bi lowe han calcula ed and measu ed consump ion o he whole echnology. Howe e , he pho o ol aics can p oduce mo e elec ic powe du ing a sunny day han he he moelec ic assemblies a e capable o consuming. 3. Resul s and Discussion Measu emen s o hea ing o PCMs ha e al eady come unde examina ion many imes. Ou measu emen s and esul s o hea ing he p oposed echnology a e shown in ou p e ious a icles [38–40] . The e o e, he c ucial objec i e o his a icle was o de e mine he beha iou o PCM in empe a u e ange speci ic o cooling. Fo his pu pose, speci ic hea capaci y is pa ame e o g ea impo ance. The alue o PCM used is a ound 6.8 kJ · kg −1 K −1 o empe a u es anging om 10 ◦C o 21 ◦C. The cooling powe is abou 400 W a empe a u e di e ence 12 ◦C. The isk o condensa ion o wa e apou is he mos impo an ac o limi ing he use o cooling de ices. To p e en his om happening, ensu ing ha he empe a u e o hei su ace is a leas 1 K abo e he dew poin o he ambien ai is c ucial. Fo his pu pose, he echnology is able o moni o he alue o he ambien empe a u e, humidi y and dew poin empe a u e. Technology is se o keep he empe a u e o he he mal panels as low as possible bu s ill abo e he dew poin . Simul aneously, echnology is able o compa ed ene gy gained om he PV and consumed by TEC modules (o HP)—in case o low ene gy gains a e u ning o some TEC. O cou se, his au oma ic con ol mode can be by-passed and he echnology can be ope a ed manually wi hou all es ic ion. Appl. Sci. 2018,8, 1750 7 o 15 The hea ing and cooling pe o mance o he accumula ion de ice is also impo an . Fo his pu pose, i is impo an o know he speci ic powe , which is gi en by he alue o he hea ans e coe icien and he ac i e a ea. The a e age hea ans e coe icien is abou 6.4 Wm −2 K −1 and he ac i e a ea is 5.2 m 2 . So, he speci ic hea ing/cooling powe is a ound 33.2 WK −1 . I is, he e o e, clea ha he cooling powe is dependen on he empe a u e di e ence be ween he su ace o he panel and he ambien empe a u e. The highe empe a u e di e ence means highe he powe . As p e iously men ioned, he used PCM has a empe a u e ange o phase change be ween 18 ◦ C and 22 ◦ C. When ac i e cooling is on, he sensible hea is emo ing as i s (abo e 22 ◦ C), hen he phase change occu s (be ween 22 ◦C and 18 ◦C) and hen he sensible hea is emo ing again (unde 18 ◦C). The su ace o he panels can be cooled o he dew poin , bu he mos amoun o ene gy is able o accumula e du ing he phase change. I he panel empe a u e is a ound 18 ◦ C and he ambien ai empe a u e is 25 ◦ C, he cooling powe is app oxima ely 230 W. Fo example, a a empe a u e di e ence o 15 ◦C, he cooling powe is abou 500 W. As p e iously men ioned, he p oposed echnology is designed o be able o use he powe p oduced by he PV. Ene gy p oduc ion co e s he consump ion o TEC modules wi h an a e age cooling ou pu o abou 550 W. This powe is highe han he a e age cooling powe o he accumula ion panel. Howe e , TEC modules lowe he la en hea o he PCM panel, i.e., he su ace empe a u e does no change much, bu accumula ion panel is able o accumula e much mo e ene gy o la e u ilisa ion. I he phase change limi alue is eached, he su ace empe a u e o he panel s a s o dec ease apidly. The lowe empe a u e inc eases cooling ou pu , bu when he echnology is u ned o , he empe a u e e u ns qui e as back o he phase change ange. Du ing designing and ini ial measu emen s was disco e ed a echnical p oblem wi h o e hea ing in cooling mode. This is desc ibed in he ollowing subsec ion. A e his, he e a e p esen ed esul s o measu emen s wi h sol ed he p oblem ou . 3.1. Technical P oblem As we al eady know, hea ing can be p o ided by he elec ic hea ing oils inside he panels o by hea ing he panels by ho wa e om he ho wa e ank—hea ing by he hea pump o an elec ic boile . The echnology has been es ed and measu ed in all hea ing modes. These measu emen s we e success ul and he echnology was e ec i e wi hou ob ious p oblems. A e ha , es measu emen s we e pe o med in cooling mode. As men ioned ea lie , cooling can be done by he hea pump o by he moelec ic modules. The cooling mode wi h he hea pump was made and measu ed wi hou any p oblems. The e we e some di icul ies in measu ing o he he moelec ic cooling. Abo e all, cooling is ine ec i e. Ins ead o dec easing he indoo empe a u e, i was inc easing. Measu emen o he o iginal design o he echnology and he he moelec ic cooling mode is shown in Figu e 5below. As can be seen, e en when he oom was cooling by he echnology, he empe a u e was g owing. The empe a u e go o s a g owing up e y as when he cooling by TEC was u ned on. The indoo empe a u e was abou 27.2 ◦ C a he beginning o he measu emen . A e ac i e cooling by TEC, i eached up o 30.8 ◦ C. The esul was: he echnology ans e ed mo e hea o he oom han i emo ed. A e some ime, i has been ound ou why his p oblem occu s. A clea indica o was he he mog aphic diagnos ics o he accumula ion de ice and all pa s o he he moelec ic modules wi h coole s. In he he mog aphic images below, see Figu e 6, i can be seen all six he moelec ic assemblies and hei empe a u es. The image cap u es he s a e o he de ice wi h ac i e he moelec ic cooling. The lowes empe a u e on he su ace o he ho side is abou 20 ◦ C and he highes empe a u e is abou 45 ◦ C. This g owing up he empe a u e is caused by connec ion o he liquid coole s in se ies. In his place, i can be said, i is also a li le mis ake o design. Maybe, i could be be e o use he pa allel connec ion. On he o he hand, i is possible o ge lowe ou ake empe a u e o chilled wa e . Appl. Sci. 2018,8, 1750 8 o 15 Figu e 5. Technical issue wi h o e hea ing. Figu e 6. Technical issue— he mog aphic diagnos ic. In igu es below, see Figu e 7, i is possible o see de ails and empe a u es o bo h sides o he coldes ( i s in he ow) and ho es assembly (las in he ow). Figu e 7. Technical issue— he mog aphic diagnos ic—de ails. The p oblem wi h he o e hea ing came om he was e hea o he TEC modules. The he moelec ic modules a e i ed wi h he liquid hea exchange s on bo h sides. These a e o he ex ac ion o cold and was e hea . The su ace o he hea exchange (coole ) on he wa m side is e y high. The e o e, he was e hea is adia ed o he su oundings om he su ace o he coole . The p oblem can be sol ed by addi ional insula ion o TEC modules and ho -wa e pipelines. The p oblem has been sol ed by sepa a ing he space wi h he mocouples om he moni o ed space. A ound he he moelec ic sys em, i was enough o build addi ional insula ion o keep he hea in he enclosed space. Howe e , he e is s ill a ees anding cold wa e ank o abso bing he was e hea om he he moelec ic modules. On he o he hand, he wa e ank is addi ionally cooled by he hea pump a a minimum empe a u e o 10 ◦ C. The e o e, i was no necessa y o sepa a e he Appl. Sci. 2018,8, 1750 9 o 15 cold wa e ank om he moni o ed space. So, he inal imp o emen was addi ional ho wa e pipes insula ion. All o he ollowing measu emen s in his a icle we e pe o med wi h his adjus men . 3.2. Measu emen In he ollowing pa ag aphs, he e a e p esen ed measu emen s and esul s o he echnology in di e en cooling modes. The i s measu emen is ocused on common passi e mode— he mos common use o he PCM. In his mode, he PCM-based panels educed he empe a u e luc ua ion and also s abilised he indoo empe a u e du ing passage o a ew days o wa m wea he . An example o he sys em’s beha iou can be seen in Figu e 8. This passi e mode managed o s abilise he indoo empe a u e be ween 23.2 ◦C and 24.0 ◦C when he ou doo empe a u e oscilla ed be ween 5.3 ◦C and 22.7 ◦C. Figu e 8. Passi e mode. Ano he expe imen s ocus is he ac i e cooling mode. The cooling cycle o he hea pump was used in his measu emen . Resul s a e shown in Figu e 9. Figu e 9. Ac i e cooling—hea pump. E e y measu emen is made o wo cooling cycles. One cycle las ed wo days. Ac i e cooling was u ned on du ing he i s day. Du ing he nex day, he panels we e le o jus accumula e hea om he oom. The cycle was hen epea ed. Du ing he i s cooling cycle, he ime i ook o cool down o he su ace empe a u es om 21.4 ◦ C o 17.9 ◦ C o he unmodi ied su ace and om 22.6 ◦ C o 20.0 ◦ C o he modi ied su ace