Passive cooling of buildings with phase change materials using whole-building energy simulation tools: A review

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Passive cooling of buildings with phase change materials using

whole-1 

building energy simulation tools: A review

Mohammad Saffari1, Alvaro de Gracia2, Svetlana Ushak3, 4, Luisa F. Cabeza1*

1GREA Innovació Concurrent, Universitat de Lleida, Pere de Cabrera s/n, 25001, Lleida, Spain.

2Departament d’Enginyeria Mecànica, Universitat Rovira i Virgili, Av. Països Catalans 26, 43007, Tarragona, Spain.

3Center for Advanced Study of Lithium and Industrial Minerals (CELiMIN), University of Antofagasta, Av. Universidad de

Antofagasta 02800, Campus Coloso, Antofagasta, Chile. 7 

4Solar Energy Research Center (SERC), Av. Tupper 2007 4th Floor, Santiago, Chile.

* Corresponding author: lcabeza@diei.udl.cat 9 

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Abstract 11 

12 

Buildings contribute to climate change by consuming a considerable amount of energy to 13 

provide thermal comfort for occupants. Cooling energy demands are expected to increase 14 

substantially in the world. On this basis, technologies and techniques providing high energy 15 

efficiency in buildings such as passive cooling are highly appreciated. Passive cooling by means 16 

of phase change materials (PCM) offers high potential to decrease the cooling energy demand 17 

and to improve the indoor comfort condition. However, in order to be appropriately 18 

characterized and implemented into the building envelope, the PCM use should be numerically 19 

analyzed. Whole-building energy simulation tools can enhance the capability of the engineers 20 

and designers to analyze the thermal behavior of PCM-enhanced buildings. In this paper, an 21 

extensive review has been made, with regard to whole-building energy simulation for passive 22 

cooling, addressing the possibilities of applying different PCM-enhanced components into the 23 

building envelope and also the feasibility of PCM passive cooling system under different 24 

climate conditions. The application of PCM has not always been as energy beneficial as 25 

expected, and actually its effectiveness is highly dependent on the climatic condition, on the 26 

PCM melting temperature and on the occupants behavior. Therefore, energy simulation of 27 

passive PCM systems is found to be a single-objective or multi-objective optimization problem 28 

which requires appropriate mathematical models for energy and comfort assessment which 29 

should be further investigated. Moreover, further research is required to analyze the influence of 30 

natural night ventilation on the cooling performance of PCM. 31 

32 

Keywords: Passive cooling; PCM; EnergyPlus; TRNSYS; ESP-r; Natural night ventilation; 33 

Whole-building energy simulation. 34 

35  36  37 

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1 40  41  The b 48  rough 49  green 50  proje 51  one-t 52  slight 53  urban 54  49  50  51  52  A sub 56  is rou 57  an ou 58  (Asso 59  57  58  59  To o 62  soluti 63  acces 64  1. Introduc building sect hly 32% of nhouse gas ction 2016, third of the tly by 2050. n areas which bstantial ups ughly 150% utlook of th ociation of S overcome th ions on the t ssible way to ction tor (both resi

the global f emissions [2 the share of final energy .This sector h causes high Figure 1.F surge for coo worldwide a his sharply outheast Asi Figure 2. his global co able since th o diminish c idential and final energy 2]. For insta f energy con y consumpti also contrib her surface a

Final energy con oling energy and about 30 increasing c ian Nations ( . Perspective of oncern, poli he energy eff carbon emiss non-resident use (Figure ance, accord nsumption in ion in all se butes to the and air tempe

nsumption by s demands is 00%-600% in cooling ener (ASEAN), L f cooling energy icy makers ficiency is fo sions [3]. Fo tial buildings e 1) [1] and ding to the n houses and ectors and it urban heat erature in city sector in EU cou expected by n developing rgy demand atin America y demand up to are endeavo ound to be th or instance, s) is responsi emitting ro EU referenc d buildings a t is expected island (UHI y centers tha untries [4]. y 2050. The e g countries [5 in some de a, India, and 2050 [1].  oring to pu e most econo the Roadma ible of consu oughly 36% nce scenario accounts for d to be incr I) phenomen an in outskirt estimated inc 5]. Figure 2 s eveloping n China) [1]. ut energy-eff omic and ins ap 2050 long uming of all trend about reased non in ts [3]. crease shows nations ficient stantly g-term

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policy [6] is seeking pathways to achieve low-carbon economy with a minimum cost in Europe 62 

[7]. The improvement of the building envelope is an essential step to achieve this goal, as 20% 63 

to 60% of all energy consumed in buildings is affected by the design and construction of the 64 

building envelope [5]. 65 

66 

Today, the energy beneficial of the thermal energy storage (TES) is well known. TES is a 67 

promising technology to achieve a low-carbon future [8]. It is accounted as an initiative to 68 

reduce the energy consumption in buildings [8], to alleviate the UHI effects in cities [3] and to 69 

increase the energy efficiency and comfort by creating a balance between diurnal and nocturnal 70 

energy demand [9] Energy could be stored physically or chemically. In physical processes 71 

energy is accumulated as sensible or/and latent heat, on the other hand thermochemical energy 72 

storage takes place when a chemical reaction with high heat of reaction happens [10]. For 73 

building applications, mostly sensible and latent heat storage are considered, although today 74 

thermochemical energy storage is increasing in interest within researchers [11]. For sensible 75 

heat TES, massive materials (concrete, stone, etc.) are required to store considerable amounts of 76 

heat, however, in latent heat TES higher amounts of energy per volume can be stored. Latent 77 

heat storage takes place by phase transition of the storage material. When heat is transferred to 78 

the storage material, melting takes place at a specific and quasi constant temperature, storing a 79 

large quantity of heat, which is called melting temperature or phase change temperature. After 80 

this stage, further increase of heat results in an addition of sensible heat storage. This heat then 81 

dissipates by solidification of the storage material. Regularly, for building applications solid-82 

liquid phase change is used since it presents high energy density and no volume expansion 83 

problems. Materials with a solid-liquid phase change which are capable to store heat and cold 84 

are generally called phase change materials (PCMs) [9,10,12]. Previous researches [13–16] 85 

were documented and classified different types of PCM for building applications. These 86 

materials can be incorporated in buildings either as passive [17] or active [18] systems. In 87 

passive design approach the PCM is incorporated into the building construction and elements as 88 

an integrated-design. Enhancing the benefits of sunlight to reduce heating requirements or 89 

reducing energy needs for cooling by minimizing heat gains in summer are principal objectives 90 

of integrated designs. 91 

92 

An appropriate passive design by means of PCM can provide long-term energy efficiency, 93 

thermal comfort, stabilization of indoor air temperature and a reduction of the use and size of 94 

the HVAC systems [19,20]. Commonly, in passive design approach for building applications 95 

the PCM is incorporated into the building envelope as an integrated material into building walls, 96 

roofs, floors, slabs, fenestration, insulation, façade, and shading system [21,22]. However, 97 

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numerical simulation tools since application of PCM requires special attention to proper 99 

materials selection, the location, and the quantity of PCM in the envelope [23]. 100 

101 

With the advent of digital computers, mathematical modeling and computer simulation has now 102 

become a crucial economical and quickest way to providing a broad understanding of the 103 

practical processes involving PCM [24]. Reliable whole-building energy simulation tools can 104 

numerically facilitate design, analysis and optimization of the PCM-enhanced building 105 

component with no need to set up expensive and time consuming whole-building field 106 

experiments [25]. Further on, computer-based simulation tools help designers and engineers to 107 

evaluate potential decisions and achieve long-term targets. For example, some researchers 108 

developed thermal load predictive models of commercial buildings using building energy 109 

simulation software [26]. In another study, whole-building simulation was used for the 110 

benchmarking of residential buildings [27]. Additionally, the validated model can always be 111 

employed for parametric or optimization studies and has more general applications than an 112 

experimental work. Therefore, numerical simulation is a widely-used method for economically 113 

and efficiently analyzing complex physical phenomena, such as the modeling of PCM [24]. 114 

115 

Accordingly, a considerable amount of literature was published on the building energy 116 

simulation pointing out the advantages of using the PCM as a passive cooling or free cooling 117 

approach [21]. The current paper presents a holistic review of the numerical simulation of 118 

buildings containing PCM for passive cooling purposes using whole building energy simulation 119 

tools. The present study is an attempt to address the methods that have been used to evaluate 120 

and analyze the effects of passive PCM-based design on the cooling energy performance in 121 

buildings through whole building energy simulation software. In this regard, an extensive study 122 

was done to address the previous, current and future research trends toward the application of 123 

PCM in buildings for passive cooling by means of building energy modeling tools. 124 

125 

2. Whole-building energy simulation for PCM-based passive design 126 

127 

The use of whole-building energy simulation is an essential step to evaluate and analysis the 128 

performance of PCM-enhanced buildings. These tools can numerically analyze the dynamic 129 

thermal behavior of the building passively enhanced with PCMs. Today, there are many 130 

validated whole-building energy simulation programs which are capable of carrying out 131 

dynamic energy simulation for different applications [28] but there are few validated whole 132 

building energy simulation programs that can analyze energy performance and indoor comfort 133 

of PCM-enhanced passive buildings. This section overviews the commonly used and important 134 

simulation tools for building passive cooling design based on the PCM technology. According 135 

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to literature review, EnergyPlus [29], TRNSYS [30], and ESP-r [31] have been extensively used 136 

by researchers to study the behavior of PCM in buildings and several studies have been carried 137 

out to validate these simulation tools [32]. 138 

139 

2.1. EnergyPlus v8.6.0 140 

141 

EnergyPlus is an open-source and multi-platform building energy performance modeling with 142 

the most popular capabilities of BLAST and DOE-2.1E with many highlighted features. 143 

Furthermore, it is possible to develop new modules and/or control strategies and integrate them 144 

into the program as subroutines using energy management system (EMS) as a dedicated 145 

computer that could be programmed to control the whole energy-related systems of the 146 

building, such as heating, cooling, ventilation, hot water, interior lighting, exterior lighting, 147 

on-site power generation, and mechanized systems for shading devices, window, actuators, 148 

and double facade elements [33]. Additionally, functional mock-up unit (FMU) for co-149 

simulation import interface allows EnergyPlus to conduct co-simulation with various simulation 150 

programs that are packaged as FMUs [34]. Other capabilities which give power to this software 151 

are advanced fenestration analysis as well as general envelope calculations (outside and inside 152 

surface convection algorithms), advanced infiltration, ventilation, room air and multi-zone 153 

airflow calculations, environmental emissions and developed economic evaluation including 154 

energy costs, and life cycle costs. In addition, comparing to other simulation tools, EnergyPlus 155 

includes several developed human thermal comfort algorithms for analyzing the occupant’s 156 

thermal well-being and indoor air quality measures. Moreover, there are several graphical 157 

interfaces for EnergyPlus to simplify the use of this software by different types of users such as 158 

students, researchers, architects and engineers [28,35]. 159 

160 

2.2. TRNSYS v17 161 

162 

TRNSYS is a flexible transient systems simulation program with a modular structure. It is a 163 

component-based simulation program, in which the user selects the components that comprise 164 

the energy system and interconnects them using appropriate input/output ports. The TRNSYS 165 

library consists of various components specifically designed for simulation of buildings, HVAC, 166 

lighting, ventilation, solar energy, thermal energy storage, and also component routines to 167 

support input of weather data or other time-dependent forcing functions and output of 168 

simulation results. In addition it facilitates the addition of new mathematical models not 169 

included in the software and couples them with existing components. TRNSYS became globally 170 

a well-known software for researchers and engineers. It can simulate solar thermal and 171 

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photovoltaic systems, low energy buildings and HVAC systems, renewable energy systems, 172 

cogeneration, fuel cells, and active and passive PCM systems [36]. 173 

2.3. ESP-r 174 

175 

ESP-r is a general purpose, multi-domain building thermal, inter-zone air flow, intra-zone air 176 

movement, HVAC systems and electrical power flow, simulation program. ESP-r allows its user 177 

to explore the complex relationships between form, envelope, air flow, plant and control of a 178 

building. ESP-r is based on a finite volume, conservation approach in which a problem is 179 

transformed into a set of conservation equations which are then integrated at consecutive time-180 

steps in response to climate, occupant and control system impacts [28,31]. In ESP-r, the PCM 181 

can be modelled using the concept of special materials facility [37,38]. 182 

183 

2.4. PCM mathematical models used in whole-building energy simulation software 184 

185 

Energy and comfort analysis of buildings enhanced with PCMs for passive cooling purposes 186 

strongly depend on the PCM melting temperature and quantity, its thermal characteristics, the 187 

location of PCM in the building envelope, climatic conditions, outdoor and indoor boundary 188 

conditions, and design of the building. Mathematical modeling of PCM is an essential step 189 

towards optimal design and proper material selection for passive buildings [39]. On this basis, 190 

several numerical modeling methods have been used in whole-building energy simulation tools 191 

to simulate the thermal response of PCM. These methods could be classified based on their 192 

mathematical model, PCM model, and discretization approach. More importantly, various 193 

experimental, analytical, and comparative analyses were performed with the objective of 194 

producing accurate, reliable, and validated models. Table 1 summarizes the current methods and 195 

models used in whole-building energy simulation tools to simulate the thermal performance of 196 

PCM-enhanced buildings. 197 

198 

Table 1. Numerical methods used to simulate PCM in dynamic building simulation software, adopted from [32]. 199  Software Module identification Mathemati cal method

PCM model Discretization Constrains Validation Refer ence EnergyPlus Conduction Finite Difference (CondFD)

FDM: 1D Enthalpy method Fully implicit/ Crank-Nicolson

-Time step < 3 min -Hysteresis in PCM cannot be modeled currently -Phase change at isothermal temperature cannot be modeled Analytical, comparative & experimental [40– 43]

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TRNSYS

“TYPE285” FVM: 1D Enthalpy method Fully implicit

-Hysteresis and sub-cooling

are not considered Experimental, comparative [44]

“TYPE272” FVM: 1D Heat capacity

method Fully implicit

-Internal convective heat transfer of the liquid state PCM is not considered - PCM with multiple peaks is not supported

Experimental [45]

Modified

"TYPE36" FDM: 1D Enthalpy method Explicit -Low time step

Limited validation using experimental results for concrete [46,47 ]

"TYPE58" FDM: 2D Enthalpy method Explicit NA Experimental [48] "TYPE204" FDM: 3D Heat capacity

method

Implicit,

semi-implicit -Computationally inefficient NA [49]

"TYPE101" FDM: 1D Heat capacity

method Crank-Nicolson

-A correction factor to account for cold bridges has to be used for model accuracy Experimental [50] TRNSYS "Active Wall" Equivalent heat transfer coefficient s Variable heat source function mimicking PCM behavior

--- -Real heat transfer physics

in PCM is not modeled Experimental [51]

"TYPE241" FDM: 1D Heat source

method Implicit NA NA [52]

"TYPE260" FDM: 1D Enthalpy method Implicit

-Thermal properties including heat capacity are based on previous time step (i.e, explicit scheme)

Experimental [53]

Modified

"TYPE101" FDM: 1D Enthalpy method Implicit

-Developed for internal

partition wall Experimental [54]

"TYPE1270" Lumped method using heat balance Quasi-heat source method ---

-Very simplified method -Internal layer within an envelope

- Based on lumped heat balance

-Low accuracy for PCM at fixed temperature Experimental data in literature [55,56 ] "TYPE399" available in TRNSYS v.17

FDM: 1D Enthalpy method Crank-Nicolson

-Hysteresis phenomena of PCM are considered in the model

-It could be applied in both active and passive systems

NA [30,57

]

ESP-r

SPMCMP53-SPMCMP56 FDM: 1D

Heat capacity and heat source

method

Experimental [37,58 –61] --- -Low time step

1D:One-Dimenssional, FDM:Finite Difference Method, FVM: Finite Volume Method, NA: Not Available. 200 

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into the interior

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crease the be ate zones is r ng PCM wall ormance. Res tually for the

3.2. Macro-en er Australian potential ener t heat of 21 ding envelope and dependin to 23%. Figure eover, the f aining Rubith arin et al. elocatable lig n. Such sing ings. Then, t classification of microenca indoor air t ture (18 ºC de. In cases w from about plication of P % to 30% ex enefits of PC required. Fu lboard into l spectively, di e best scenari ncapsulated weather con rgy savings 9 kJ/kg (Fig e. Energy sim ng on the cl 5. BioPCMTM feasibility o herm compac [81] studied ghtweight bu gle-zone bui their research n [128]. The apsulated PC emperature. for heating with HVAC 10 to 130 PCM could i xcept in tropi CM, the optim urther on, Oz lightweight r ifferent retro io 14% of co d PCM pane nditions, Ala by integratin gure 5) with mulation resu limatic regio pouches (Left) of enhancing ct storage mo d the feasib uildings to r ildings wide h was extend PCM plaste CM was insta Two approa and 25 ºC f system the P kWh in di increase the ical areas. A mization of zdenefe and residential bu ofitting scena ooling energy els am el al. [83] ng BioPCM different m ults showed on the total a [84], BioPCMT g the energ odules (CSM bility of red reduce HVA ely used in ded to more c erboard with alled on the i aches were for cooling) PCM passive ifferent clim percentage o As it was conc PCM meltin Dewsbury [8 uildings in C arios with PC y savings we carried out p pouches wi melting points

that the ene annual energ TM inclusion in gy performa M) (Figure 6) ducing the s C needs und mining cam climate zone h 25 ºC of p nner surface considered; with HVAC e system coul mate zones. of comfort h cluded by the ng temperatu 82] investiga Cyprus to inc CM inclusion ere obtained. parametric a ith 0.005 m s (from 20 t ergy saving v gy savings c

attic floor (righ ance of bu was investig severe indoo der major Ch mps or reloc es according peak melting e of walls an controlled i C system an ld achieve co Moreover, hours in all s e authors, in ure under dif ated the imp crease their e n were applie analysis to fin thickness an to 23 ºC) in varies from c could change ht) [85]. uilding proto gated by Saf or air hilean atable to the point d roof indoor d free ooling in FF tudies n order fferent pact of energy ed and nd out nd the nto the city to e from otypes ffari et

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own that abo ir studied cli er than the ing on the H added that i d reduces the 6. Rubitherm C a el al. [70] re honeycom partition wa ycomb into th and about 5% with paraffin, b out 10-15% o mate. Howev total heatin HVAC contr installing thi maintenance SM [86]. to evaluate mb PCM wal alls to passi he partition w % to 7% incr efore to stick th of the annua ver, the ener ng and cool rol, 20%-60 s type of PC e cost. the summer lboards (Fig ively regulat walls showed rease of therm he upper alumin al energy cou rgy savings f ling consum 0% of the co CM panel is s r thermal co gures 7 & 8) ate the indo

d about 0.3-0 mal comfort num skin [87]. uld be for the mption. ooling simple omfort ) were or air 0.7 ºC in the

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ase the therm

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has been com ors as a conc psum plaste ed interest du y building fa nefits due to of microencaps e of a comple PCM separa dential build e attic floor s. However, ce of the bui core. Elements Foam [25]. mmonly appl centrated lay er, however due to its abi

fabrics [73]. the applicat sulated PCM [7 ex thermal st ated by fiber ding (Figure which resul it should be ilding compo s: 1. lied to yer, or r, the lity to There ion of 73]. torage r glass 10.b). lted in noted onents

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3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 signif 346  [63]. 347  347  348  349  350  Simil 357  into 358  analy 359  applic 360  %. B 361  inves 362  energ 363  358  359  360  361  Kośn 367  insula 368  PCM 369  weigh 370  point 371  simul 372  368  ficantly; hen

larly, the pot the resident ysis under h cation of PC By the way, stigate the he gy saving in b Figure ny et al. [59 ation into re M were used. ht blend of t. Different s lation tool to nce, a proper Figure 10. (a) P tential benefi tial attics (F hot and mix CM-enhanced as it has b eat transfer i buildings [90 e 11. Instrument 9] studied th esidential att A 30% by w shape stabil scenarios (as o understand combination PCM-enhanced its of incorpo Figure 11) w xed U.S. cl d insulation been discuss in such com 0]. tation of attic co he passive c tics under w weight unifor lized PCM w s shown in F the underlyi n of thermal d fiberglass; (b) orating the P was investig limates [89] can improv sed in the l mposites and ontaining PCM cooling pote weather cond rm blend of with plastic Figure 12) w ing effects of mass and in Single-story ra PCM-enhance gated throug ]. Therefore e the roof-g literature, fu to evaluate M-enhanced fibe ential due to dition of Pho PCM with fi composite, b were investig f using PCM nsulation sho anch house [63] ed blown fib gh experimen , it was co enerated pea urther resear their potenti r glass insulatio o addition o oenix, Arizo iber insulatio both with 26 ated by ESP in the studie ould be consi ].

ber glass insu ent and num oncluded tha ak loads by rch is requir ial contribut on [89]. of PCM-enh ona. Two typ

ons, and a 90 6.5 ºC of m P-r whole-bu ed building. idered ulation merical at the 70-80 red to ion to hanced pes of 0% by melting uilding

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3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 369  Figur 370  371  Sever 378  insula 379  PCM 380  Confi 381  which 382  on, th 383  in the 384  379  380  3 381  382  Until 400  reduc 401  consu 402  inves 403  poten 404  could 405  more 406  roof s 407  These 408  doped 409  they 410  therm 411  into t 412  proto 413  memb 414  condi 415  by th 416  polyu 417  re 12. Different ral results w ation scenari M-enhanced figurations 2 h are better he best strate e middle of th 3.5. PCM in r l now, far to ce the UHI. umption and stigated (Figu ntial to impro d reduce 54% interestingly surface to th e results are d coatings ca have proved mal condition two different otype. A trad brane enhan ition of Peru he integratio urethane-base t scenarios of P were achiev io with conc cellulose ( -A and Con than dispers egies to integ he attic floor roof oo little atten In a recent p d UHI effect ure 13). From ove both ind % of heat flu y, the PCM-e outdoor PCM-en consistent w an reduce th d that the P ns. Further o t types of roo ditional bitum nced with PC ugia. Their si on of PCM-ed membran CM-enhanced c ed by the a entrated PCM (Configuratio nfigurations sed PCM (Co grate concen r insulation, ntion has be paper by Ro t applying c m the simula door and out ux entering t -incorporated nvironment in with the find

e surface tem PCM can im n, Pisello et ofing membr men roofing CM with 26 imulation res -enhanced b ne, respectiv cellulose insula authors; the M achieves l on 1-A). 2-B with 6. onfiguration ntrated PCM Configuratio een paid to oman et al. [ cool roof an ation results tdoor enviro the building d roof showe n peak hours ding of Karle mperature by mprove both al. [93] inve ranes to incr membrane a 6 ºC of melt sults showed bitumen roof vely. Addit

ation & concent

simulation lower coolin Higher coo 8% and 6.6 n 1-A) with 3 were found ons 2-A and 2

the potentia 91] the poss nd PCM-enh it was conc nment therm indoor envi ed 40% lowe s comparing essi et al. [92 y 12%. These h the microc estigated the rease the ene

and an adva ing point w d 10% and 2 fing membra ionally, wh trated PCM into study show ng loads than oling saving % of coolin 3.1% cooling to be PCM o 2-B, respecti l of passive sibility of red hanced roof cluded that th mal condition ronment thro er heat flux

with the coo 2] which has e findings ar climate and influence of rgy performa nced cool po ere studied u 3% of coolin ane and PC en the insu o attic envelope

wed that the n the scenario gs obtained ng energy sa g savings. F on the bottom ively. PCM syste ducing the e technologie he PCM has ns. The PCM

ough the roo emitting fro ol roof techno s shown that re promising the macrocl f integrating mance of a bu olyurethane-under the cl ng energy sa CM-enhanced ulation layer e [59]. e attic o with d for avings urther m and ems to energy s was s great M roof of and om the ology. PCM g since limate PCM uilding -based limate avings d cool r was

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4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 remo 409  confi 410  durab 411  These 412  perfo 413  furthe 414  coolin 415  condi 416  therm 417  410  411  412  413  Furth 429  build 430  weath 431  the ro 432  indoo 433  on, P 434  melti 435  differ 436  PCM 437  coolin 438  menti 439  than 440  autho 441  are he 442  perio 443  respe 444  ved, cooling rmatory evid bility of coo e promising ormance of b er whole-bui ng energy p itions, and w mal comfort o hermore, the ding with PC her condition oof construc or environme PCM with 2 ng point in rent climate M to increase ng load sav ioned that ad heating load ors of the pre eating domin d than cool ectively. g savings in dence that t l roof memb results open buildings and ilding energy performance with different of occupants thermal per CM-enhanced n of Melbour tion before i ent and to im 1 ºC, 23 ºC nfluence on zones. Even the thermal vings were ddition of P ds. However esent paper w nant and the

ing period w ncreased to the use of P brane by red a new horizo d to enhance y simulation e of these i t constructio . Figure 13. PC rformance of d roof constr rne and Sydn interior steel mprove the t C, 25 ºC, and the cooling ntually, it wa comfort is 2 achieved in CM as a roo r, regarding would like t addition of P with 42.5 an 39.4%. Th PCM as a pa ducing its se on over the a the durabili and optimiz innovative p on design to CM-enhanced c f a typical n ruction was ney. The Bio l layer to mo thermal perf d 27 ºC me g performanc s found that 23 ºC. As co n Sydney an of layer was the results to comment PCM with 2 nd 17.9 mJ/ e recent stu assive coolin evere therma application o ity of buildin zation studies passive syste evaluate the cool roof [91]. naturally ven investigated oPCM meltin oderate the te formance of elting points ce in the si in both citie oncluded by nd Melbourn more effect presented in that both cit 3 ºC resulted /m2 per year udy of Pisel ng approach al stress unde of PCM to im ng materials. s are necessa ems under eir contributi ntilated single d by Jayalath ng at 23 ºC w emperature f the residenti were used imulated bu es the optimu the authors, ne, respectiv tive in reduc n above-men ties of Melbo d in higher s r for Melbou llo et al. [9 h can enhanc der solar radi mprove the co . With this r ary to evalua different cli ion to enhan e-story resid h et al. [56] was integrate fluctuations ial building. to investiga uilding unde um temperat , 25% and 39 vely. It was cing cooling ntioned artic ourne and S savings for h urne and Sy 94] is ce the iation. ooling egard, ate the imatic ce the dential under ed into of the Later ate the er two ture of 9% of s also loads cle the ydney eating ydney,

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3.6. Comparison between existing technologies 430 

431 

Different building models such as office buildings, residential buildings, and simple single-story 432 

were numerically analyzed by researchers, using macro-encapsulated or microencapsulated 433 

PCMs. Various strategies have been applied to integrate the PCM into the building envelope 434 

such as adding concentrated or compact PCM layer [72], PCM dispersed into insulation 435 

materials [95], PCM added to the gypsum boards and plaster [77]. In a great number of articles 436 

parametric analysis has been used to find out the best PCM melting point, latent heat capacity 437 

and layer thicknesses considering its addition in different locations of walls, ceiling, roof and 438 

floor. A considerable number of literatures were been published on the application of PCM 439 

gypsum boards or PCM-enhanced wallboards and concentrated PCM layers/panels for their 440 

high contribution in cooling energy saving, feasibility of installation on the inner surface of 441 

walls an being cheap [96]. More recently, special attention was paid to apply PCM in cool roof 442 

to increase the thermal comfort of occupants, to reduce the cooling energy consumption and to 443 

enhance the durability of cool roof membranes [94,97]. Additionally, through whole-building 444 

energy simulation, now it is possible to analyze the effects of PCM in reducing the heat island 445 

effects in urban area [91] and enhancing the thermal inertia of residential buildings to resist 446 

severe thermal shocks of heat waves by peak load and discomfort hours reduction of indoor 447 

temperature [98]. In addition, the feasibility of improving the thermal performance of 448 

lightweight relocatable buildings for mining camps or post-disaster rapid housing was 449 

investigated [81]. A detailed literature review was done regarding numerical analysis of PCM-450 

integrated buildings based on EnergyPlus, TRNSYS, and ESP-r whole-building energy 451 

simulation tools which is presented in Table 2. According to this literature review on the 452 

simulation-based passive cooling for building applications, EnergyPlus software was the most 453 

prominent tool to investigate the passive cooling effects of PCM in buildings; however, this 454 

does not deny the strength of other energy simulation tools at all. 455 

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457 

Table 2. Passive cooling in buildings by means of whole-building energy simulation tools.

458 

Building type Encapsulation Latent heat

[kJ/kg]

Melting [ºC]

Thickness

[m] Installation Results

Simulation tool Reference

1. Office building NA 175 26 to 29 0.005, 0.01

0.02, 0.03

Inner surface of vertical walls

 Greater cooling performance and comfort were achieved with 3 cm PCM in all vertical walls.

 From 3% to 7.2% cooling savings, depending on the climate zone were achieved.

EnergyPlus Ascione et al. [77]

2. Office building Microencapsulated NA 23 to 28 0.02 Inner surface of partition

walls

 The organic honeycomb PCM was more effective in temperate climate rather than in hot Mediterranean climate.

EnergyPlus Evola el al. [70]

3. Single-room house Macroencapsulated 165-200 20 to 25 0.005 Parametric analysis was performed

 From 17% to 23% of energy savings depending on the climate zone were achieved.

 PCM had very little effect in hot and humid climates.

EnergyPlus Alam et al. [83]

4. Passive house duplex home

Macroencapsulated 165-200 23, 25 0.015 Interior surface of the

envelopes

 PCM installed on the interior surface of the walls provided higher comfort.

 About 50% of discomfort hours were decreased using PCM melting at 25 ºC.

EnergyPlus Sage-Lauck et al. [99]

5. Passive house duplex home

Macroencapsulated 165-200 23, 25, 27, 29

0.015 All exterior & interior vertical and horizontal envelopes

 Zone uncomfortable hours were reduced by 93% adding PCM (3.1 kg/m2) melting at 25 ºC.

EnergyPlus Campbell et al. [100]

6. Residential building Microencapsulated 70 18 to 28 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04

Interior surface of the interior envelopes

 From 46% to 62% of cooling savings were achieved under warm climate condition.

 The best savings achieved with 4 cm layer PCM.

EnergyPlus Soares et al. [74]

7. Research center building Macroencapsulated 281 230, 235, 267 20, 21, 24, 29

0.0064 Between insulation & interior gypsum board of all exterior walls

 The cooling savings were insignificant (1%).  Night ventilation coupled with PCM increased the

cooling performance to about 9%.

EnergyPlus Seong et al. [68]

8. Historic building NA 110 27, 32 0.03 Interior and exterior faces

of the envelope

 PCM application was not feasible and it increased the annual energy consumption.

EnergyPlus Ascione et al. [76]

9. Office building Microencapsulated 33.5 21 to 26 0.013 Interior and exterior faces

of the envelope

 Cooling savings were increased in all cases with PCM.  Annual savings between -25% to 33% depending on

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the PCM melting point were achieved.

10. Single-story house Microencapsulated 112 23 0.01117 Between interior framing

and the air gap

 10% reduction in annual wall-generated heating and cooling.

 Proper combination of thermal mass and insulation is required.

EnergyPlus Kosny et al. [63]

11. Single-story house Microencapsulated 170 29 0.1 On the attic floor  70-80% reductions of roof-generated peak hour loads. EnergyPlus Kosny et al. [23]

12. Office building Microencapsulated 41 23 0.02 Inner surface of the

interior partition walls

 PCM storage efficiency increased by 10% to 30 %. EnergyPlus Evola et al. [64] 13. Residential building Microencapsulated 110 23, 25, 27 0.012, 0.024,

0.036, 0.48, 0.06

On the inner surface of the vertical walls

 PCM cooling savings in August 2011 was recorded as 40%.

 The cooling savings are expected to increase further by 2050.

EnergyPlus Sajjadian et al. [65]

14. Residential building Microencapsulated 70 26 0.052 On the inner surface of

the vertical walls and ceiling

 The use of PCM during the cold months of Montreal was not very effective; however, energy savings were achieved in warmer seasons.

 In Mediterranean climate (Palermo) 87% of cooling reduction was shown at peak hours.

EnergyPlus Guarino et al. [69]

15. Simplified cubicle NA 223 22 to 32 0.003-0.020 Parametric analysis for

different locations of PCM

 21-32% reduction of heat gains achieved by using PCM

 Better energy performance achieved when PCM was installed to the exterior surface of the envelope.

EnergyPlus Lei et al. [66]

16. Residential building Microencapsulated 70 21.7 0.005 After exterior layer of

mosaic tile and cement.

 Low annual cooling energy savings achieved (2.9%).  PCM with higher melting points should be studied in

Hong Kong climate.

EnergyPlus Chan [67]

17. ASHRAE-140 case-600

Macroencapsulated 148 23, 25, 27 0.005

0.01

Interior surface of vertical walls & ceiling

 10 to 15 % annual energy savings achieved with 10 mm concentrated PCM melting at 27 ºC.

EnergyPlus Saffari et al. [72]

18. Residential building Macroencapsulated 200 23 0.015 Inner surface of the

exterior walls.

 47-76% cooling savings at peak hour were obtained.  Higher energy savings (28-63%) achieved in the

heating period.

EnergyPlus Nghana et al. [102]

19. Hospital building Macroencapsulated 196 177 188 21-24 18-29 26-28 0.074 0.003 0.0063

Rooftop, innermost layer, middle layer

 The PCM-enhanced roof reduced the heat flux through the roof to the building interior by 54% at peak hour.  The sensible heat flux from roof surface to the

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152 160 21-24 28.5-30.2 0.0033 0.0162

surrounding environment decreased by 40%.

20. Office building Macroencapsulated 219 27, 29 0.01 Before the inner layer of

walls, attic, ceiling, floor

 Annual cooling loads were reduced by 47% using PCM melting at 27 ºC coupled with fan-assisted night ventilation.

EnergyPlus Solgi et al. [103]

21. Cubicle (single-zone building)

Microencapsulated 46 25(peak

melting)

0.0125 Inner surface of vertical walls & roof

 The highest cooling savings recorded from 150 to 171 kWh.

 PCM optimization is needed to improve savings in some climates.

EnergyPlus Marin et al. [81]

22. Cubicle (single-zone building)

Macroencapsulated 170 26 0.01, 0.02 Interior surface of exterior

walls before bricks

 The most influential factors for cooling savings were defined as PCM melting point and thermal conductivity.

EnergyPlus Mazo et al. [104]

23. Residential building Microencapsulated 140 26 0.15 Inner surface of vertical

walls & ceilings

 The cooling energy consumption reduced by 14%. EnergyPlus Ozdenefe & Dewsbury [82]

24.Prototype test-room Microencapsulated 110 26 0.004, 0.01 Exterior surface of the

roof

 PCM in roofing membranes resulted in 9.4% to 39.4% of cooling energy savings.

EnergyPlus Pisello et al. [93]

25.Test-room Microencapsulated 70 18-24 0.005 Interior surface of walls  The annual cooling reduced by 50% in

heating-dominant climate.

 Natural/fan-assisted ventilation can increase the cooling performance in highly glazed buildings.

EnergyPlus Guarino et al. [105]

26.Single-story building Macroencapsulated 182 25, 27, 29 0.03 Interior surface of walls, exterior surface of walls, interior & exterior surface of walls

 PCM finishing layer melting at 25 ºC could save cooling energy from 2% to 13% under Mediterranean climate condition.

EnergyPlus Ascione et al. [106]

27. Multi-story office building

Macroencapsulated 250 27 0.010 Before interior vertical

mortar wall

 PCM saved summer cooling energy needs from 1500 to 2300 kWh in 3 cities of China with cold and hot summer climate condition.

 Optimization of PCM melting temperature has been suggested as a solution to increase energy savings and economic benefits.

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28. Two-story residential building

Macroencapsulated 219 29 0.02

(optimization applied)

Interior Surface of roof before gypsum board

 PCM layer melting at 29 ºC added to roof envelope and no economic savings observed under climate condition of Iran.

EnergyPlus Baniassadi et al. [108]

29.Two-story house Macroencapsulated 134 25 0.02 Into ceiling and

into ceiling and walls interior surfaces

 PCM could reduce discomfort hours from 34% to 52% depending on the behavior of occupants.

EnergyPlus Jamil et al. [109]

30. Two-story house Microencapsulated 86 24 0.22 Inner Surface of all

external walls

 PCM has significant effect in reducing overheating in residential building in the UK.

 A proper combination of insulation and PCM level should be investigated.

 The effectiveness of PCM in lightweight buildings is higher.

EnergyPlus Auzeby et al. [110]

31. Residential building Macroencapsulated 219 27 0.02 Inner Surface of walls and

ceiling

 PCM passive cooling system combined with mechanical night ventilation could reduce the hours of extreme heat stress by 23% to 32% in Melbourne.

EnergyPlus Ramakrishnan et al. [98]

32. Residential building Macroencapsulated 200 (parametric study 50 to 300) 20 to 27 (parametric study)

0.0125 Interior surface of walls, exterior surface of walls, in the middle of wood assembly

 In Phoenix cooling savings were insignificant (0.8% annual cooling savings )

 In Seattle 15.8% of annual cooling savings recorded.

TRNSYS Al-Saadi and Zhai [44]

33. Single-story residential building

Macroencapsulated 210 21, 23, 25, 27

0.0121 Interior Surface of roof before steel finishing

 In Melbourne 39% and in Sydney 25% of cooling energy savings achieved.

TRNSYS Jayalath et al. [56]

34. Single-story residential building Microencapsulated 119 26.50 0.15, 0.255, 0.357, 0.459, 0.083, 0.050 Homogenously blended PCM into cellulose insulation of attic, condensed layer of PCM into different locations of the attic

 PCM-enhanced cellulose achieved 3.1% of cooling savings.

 Concentrated PCM layer achieved from 0.56% to 6.6% of cooling savings.

ESP-r Kośny et al.[59]

NA: Not available 459 

460  461 

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4. Passive PCM-enhanced building with natural ventilation 462 

463 

Natural ventilation is considered as a passive or free cooling method in which the cool nighttime 464 

air flows into the building zone to provide cooling [111]. In natural ventilation cooling system, 465 

the flow process is driven by wind and/or stack effect. An appropriate use of natural ventilation 466 

techniques can enhance the PCM performance by increasing the possibility of full charging and 467 

discharging process [112]. Coupling PCM as an innovative thermal mass with natural night 468 

ventilation could be an ideal solution to increase the cooling performance of buildings, 469 

nevertheless, it is not the only parameter found to be critically important for the appropriate and 470 

efficient operation of PCM in buildings. Many factors such as outdoor air temperature, wind 471 

speed, wind direction etc. affect the performance of this passive system. Therefore, using 472 

numerical simulation tools which are capable of simulating both the PCM and the natural 473 

ventilation effects on the energy performance of the building is essential. Natural night 474 

ventilation creates a heat sink system by help of wind and indoor-outdoor temperature 475 

difference to provide cool air or to remove excessive or unwanted heat stored in the building 476 

envelope resulting better indoor air quality, comfort and cooling loads reduction. 477 

Several publications have mentioned the advantages of passive cooling by means of natural 478 

ventilation using numerical simulation [113–115]. 479 

480 

In the literature, there are numerous studies of coupling thermal mass and natural night 481 

ventilation by means of whole-building energy simulation [116,117], nevertheless, there are 482 

only a few examples in which the effect of coupling PCM with natural night ventilation is 483 

analyzed [68,70,109]. Also, some authors have investigated the effect of fan-assisted night 484 

ventilation with high ratios of air exchange per hour (ach) which was highly effective to 485 

discharge the PCM. Studies have found that the integration of natural night ventilation strategies 486 

[69,82] or fan-assisted night ventilation [103] can effectively increase the cooling performance 487 

of the PCM-enhanced buildings in climates with cool nighttime outdoor temperature. For 488 

example the effectiveness of night ventilation to enhance the performance of PCM passive 489 

system was investigated by Evola et al. [70]. Different air change rates per hour (2-8 ach) were 490 

applied between 21:00 and 06:00 which caused a reduction in the mean daily and peak operative 491 

temperature; nevertheless, introducing more than 4 ach did not add significant benefits. 492 

However, the simulation results showed that coupling the proper night ventilation with PCM 493 

system can improve the thermal comfort by 10% in comparison to the PCM-enhanced model 494 

without night ventilation. With the same objective Seong et al. [68] showed that adding 6 495 

m3/m2-h of ventilation during the night period can enhance the annual cooling performance by 496 

about 9% compared to the PCM model without night ventilation. With the same objective, the 497 

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naturally ventilated 5-star energy rated house located in Melbourne using passive PCM cooling 499 

approach was studied by Jamil et al. [109]. Two different scenarios were considered to apply the 500 

PCM into the building envelope; spreading PCM melting at 25 ºC only in ceiling, and 501 

incorporating the same PCM in ceiling and walls. Additionally, controlled (manual) night 502 

ventilation by opening 20% of windows from 19:00 to 7:00 to boost the solidification of PCM 503 

since the nighttime outdoor temperature was always below 23 ºC (below the melting point of 504 

used PCM). Their results showed that a combination of PCM in ceiling coupled with natural 505 

night ventilation can increase the effectiveness of PCM for passive cooling and reduce the 506 

discomfort hours (according to ASHRAE 55-2013 [118]) up to 34% (with PCM only in 507 

ceilings), and 52% (with PCM in ceilings and walls); nonetheless, this improvement strongly 508 

depends on the behavior of occupants to properly follow the proper night ventilation strategy. In 509 

addition, Solgi et al. [103] applied fan-assisted night ventilation to an office building in order to 510 

improve the annual cooling performance and the thermal comfort condition. The night 511 

ventilation with specific indoor-outdoor temperature control strategy was considered between 512 

24:00-7:00 with different fan ach (5 to 30). The simulation results were shown that the annual 513 

cooling load could be reduced from 30% in the PCM-enhanced case to about 46% in the PCM 514 

model with fan-assisted night ventilation with 15 ach, nevertheless, further increase of air 515 

change per hour showed an increase in the total energy consumption. 516 

517 

5. Technical barriers 518 

519 

When designing a passive system based on the PCM technology, one crucial fact that should be 520 

considered is that the PCM passive system can improve the energy efficiency of buildings, 521 

nonetheless, the discomfort due to the elevated humidity ratio should be considered in hot and 522 

humid climates. Very high humidity ratios might affect the thermal comfort of the occupants 523 

which is consistent with findings of [67,69,83,102]. Although high cooling energy savings 524 

could be achieved by proper PCM passive solutions but the ability of these materials to absorb 525 

the latent heat is very limited. Accordingly, in regions with high ratios of humidity, a proper 526 

HVAC system should be selected to control the dehumidification in order to provide the 527 

occupants with thermal comfort [119]. Also, solar renewable system could be a solution to 528 

provide cooling and dehumidification [120]. 529 

530 

On the other hand, a proper PCM design ties with a balance between energy provisions and 531 

comfort criteria. It should be considered that adding the PCM does not always ensure the 532 

increase of comfort but in order to get the best results, the PCM melting range should be within 533 

the comfort range [101], otherwise limited energy savings could be achieved [121]. Moreover, 534 

the highest comfort level does not certainly lead to high savings in energy, but, the highest 535 

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comfort might be achieved by cost of higher energy consumption which is also discussed by 536 

other authors [72]. 537 

538 

As it has been discussed, night cooling could be an effective way to enhance the performance of 539 

the passive PCM system. For example, in office buildings it offers the opportunity for system 540 

downsizing in climates where the air temperature decreases at night [100]. However, it should 541 

be considered that this outdoor temperature decrease should be lower than the PCM melting 542 

point in order to be able to solidify the PCM; otherwise, night ventilation may have reverse 543 

effect on the cooling performance in climate with high temperature nights [122]. In addition, 544 

more sophisticated night ventilation techniques [113] considering the outdoor boundary 545 

conditions such as wind pressure coefficients and wind velocity along with customized control 546 

strategies coupled with passive PCM approach could be studied and investigated using whole-547 

building energy simulation tools. 548 

549 

Also it is noticeable to mention that in many simulation-based studies the parametric analysis is 550 

unfairly referred as optimization; however, to the best of authors knowledge, no report was 551 

found so far using optimization algorithms to optimize the e.g. PCM melting point temperature, 552 

and very few literature is available on the multi-dimensional analysis [74] and until now little 553 

importance has been given to single- and multi-objective mathematical optimizations [101] and 554 

there few cases of multi-objectives optimization of PCM-enhanced passive buildings, however, 555 

recently more attention has been paid to simulation-based optimization of passive PCM 556 

buildings to increase the thermal comfort and energy performance of building [106], to 557 

optimization the thickness of insulation and PCM layers [121], and to investigate the life cycle 558 

and environmental impact of building with PCM [123–125]. Parametric analysis may help to 559 

find the best solution among the available options but not always the optimum solution and it is 560 

time consuming. In order to find the optimum solution in such systems, optimization tools and 561 

statistical methods are appreciable to reduce the simulation cost and to increase the energy 562 

efficiency [126]. 563 

564 

Simulation-based studies can give valuable information about the energy and comfort benefits 565 

due to the integration of PCM in buildings, however, it should be taken into account that today, 566 

only few commercially available computer models use separate enthalpy–temperature curves for 567 

melting and freezing such as ESP-r [37]. Currently, in EnergyPlus whole-building energy 568 

simulation software identical algorithm for thermal characteristics of melting and freezing 569 

processes is used. On this basis, PCMs without noticeable subcooling should be considered for 570 

simulation [127]. 571 

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5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 6 574  575  Acco 584  terms 585  feasib 586  Köpp 587  are c 588  Addit 589  summ 590  as h: 591  contin 592  585  586  587  588  The f 596  build 597  condi 598  Amer 599  the M 600  for p 601  using 602  existi 603  597  6. Potential ording to the s of energy bility of usin pen Geiger m categorized tionally, the mer dry, w: w hot arid, k: nental, and F feasibility of dings by app itions worldw rica [81], Au Middle-East . passive cooli g the PCM h ing buildings l of passive P e findings of saving in d ng passive P main climates in A: equa e level of pr winter dry, m : cold arid, F: polar frost Figure 14.W f enhancing t plying the P wide such as ustralia [83], A considera ing in buildi

has been stu s [77] includ PCM use in f researchers different clim PCM system s classificatio atorial, B: a recipitation i m: monsoon a: hot summ t. World Map of K the cooling e PCM techno s some regio New Zealan able amount ings under w udied for ne ing historica n different cl s, the applic mates. On t m will be dis on (Figure 1 arid, C: wa is defined as nal. Further d mer, b: warm Köppen–Geiger energy perfo ology has be ons in Europ nd [101], and of literature warm tempe ew construc al buildings [ limates ation of PCM this basis, i scussed and 14). In this cl arm tempera s W: desert, details are pr m summer, c climate classifi ormance and een studied pe [69,70,77] d some specif e was publish rature clima tion building 76]. M yielded d in the follow categorized lassification ate, D: sno S: steppe, rovided rega c: cool summ ication [128]. the indoor th under vario , North Ame fic regions in hed on the ap ates (C). The gs and for r different resu wing section d according

the main cli ow and E: f: fully hum arding tempe mer, d: extr thermal comf ous climatol erica [102], n Asia [66,67 pplication of e practicabil retrofitting o ults in ns the to the imates polar. mid, s: erature emely fort in ogical South 7] and f PCM lity of of the

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6.1. Equatorial (A) 597 

598 

Lei et al. [66] examined the effectiveness of PCM in climate of Singapore (Af) conducting 599 

parametric studies. The PCM with 28 ºC melting point temperature was used which could 600 

significantly decrease the heat gains which was estimated about 21-32% per year, nonetheless, 601 

the energy savings results were not presented. Further on, in the studied climate, better energy 602 

performance was achieved when the PCM was applied to the exterior walls since during night 603 

the stored heat could dissipate to the outdoor environment and not to the air-conditioned zone. 604 

In another study which was performed by Alam et al. [83] the potential of PCM to reduce the 605 

annual energy consumption was negligible in Darwin (Aw) due to hot and humid summers and 606  hot winters. 607  608  6.2. Arid (B) 609  610 

Campbell and Sailor [100] measured the impacts of integrating PCM in high performance 611 

super-insulated homes lacking from insufficient thermal mass to increase the thermal storage 612 

and stabilize the temperature fluctuation in such buildings in cooling season over different 613 

climate zones across the United States. The simulation results were shown only 6.4% of 614 

occupants thermal comfort increase in hot-arid climate of Phoenix (BWh) due to elevated 615 

nighttime temperatures and low storage density of PCM melting at 25 ºC. However, these 616 

results are in consistent with findings of Al-Saadi and Zhai [44], where 0.8% savings of annual 617 

cooling load achieved in Phoenix. Also, it should be highlighted that some researchers achieved 618 

about 46% savings in cooling energy consumption using the PCM with 27 ºC melting 619 

temperature into the external walls, ceiling and roof under climate condition of Yazd (BWk) by 620 

taking advantage of the night cooling and control strategy [103]. From the results mentioned 621 

above, it can be seen that the PCM passive system works better in cold arid climates since at 622 

nighttime the accumulated heat in the PCM can be dissipated by the cool outdoor air 623 

temperature. This effect could be increased in regions with high altitudes. For example some 624 

researchers [83] achieved about 23.5% annual energy savings with PCM melting at 22 ºC under 625 

climate condition of Adelaide (BSk) with about 700 m of altitude. 626 

627 

6.3. Warm Temperate (C) 628 

629 

A great effort has been made to study the energy-related impacts by applying the PCM into the 630 

building envelope in warm temperature climate. For example, the study carried out by Ascione 631 

et al. [106] adds more results regarding the application of passive PCM technology to improve 632 

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condition (Csa). Different wall compositions enhanced with PCM-enhanced gypsum 634 

plasterboard melting at 25 ºC, 27 ºC, and 29 ºC were numerically studied and optimized. 635 

According to their results, the integration of PCM melting at 25 ºC, adding PCM to the inner 636 

surface of vertical walls could improve the annual cooling energy performance by roughly 2%, 637 

4%, 7% and 13% in Madrid, Nice, Athens, and Naples, respectively. Moreover, the simulation 638 

results of Campbell et al. [100] showed significant improvements in occupant comfort in Los 639 

Angeles (Csb), Portland (Csb), and Denver (Cfa). The results were shown up to 44% and 79% 640 

reductions in zone discomfort hours in Los Angeles and Denver, respectively. However, the 641 

highest thermal comfort was achieved in Portland with about 93% reductions in uncomfortable 642 

hours using 3.1 kg/m2 of PCM melting at 25°C. As argued by the authors, these thermal comfort

643 

improvements could be associated with less severe daytime temperature and also cool nighttime 644 

temperature which facilitated the proper charging and discharging of the PCM. Similarly, 645 

Ramakrishnan et al. [98] concluded that enhancing the thermal inertia of non-air-conditioned 646 

buildings in Melbourne (Cfb) by adding PCM with 27 ºC melting point into vertical walls and 647 

ceiling can effectively reduce heat stress risks during extreme heat waves by 23%, however, 648 

when mechanical night ventilation was considered, discomfort hours reduced to 32%. However, 649 

it should be considered that when mechanical ventilation system is considered the building is no 650 

longer non-air-conditioned. 651 

652 

Furthermore, Chan [67] investigated the cooling energy performance of the living room and 653 

bedroom of a typical residential flat with PCM-enhanced facade under the climate condition of 654 

Hong Kong (Cwa). The results showed very low annual cooling energy savings (2.9%) for the 655 

living room and approximately 1% rise in the cooling energy consumption for the bedroom. 656 

Consequently, a very long payback period in years (91 years) was estimated. As it was argued 657 

by the author, the melting point temperature of the selected PCM which was 21.7 ºC could not 658 

adequately absorb the heat; and the interior surface temperature of the PCM wall was mostly 659 

above 28 ºC, even at night and the PCM could barely discharge. So that, the existence of the 660 

low cooling savings implies that PCM with higher melting point should be used under this 661 

climatic region. Likewise, Mi et al. [107] investigated the energy and economic benefit of 662 

adding PCM to vertical walls of a multi-story office building under climate zones of China. 663 

They used PCM with melting temperature of 27 ºC to increase the summer cooling 664 

performance. However, in spite of achieving some cooling savings (e.g. 2100 kWh in case of 665 

Hong Kong), generally low energy and economic benefits were obtained for summer cooling 666 

period. Although, when energy savings for both heating and cooling periods were considered, 667 

the energy and economic benefits increased further. 668 

Figure

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