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Energy and Buildings 44 (2012) 88–93

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

j our na l ho me p age: www.elsev ier .com/ locate /enbui ld

se of microencapsulated PCM in buildings and the effect of adding awnings

ablo Arce, Cecilia Castellón, Albert Castell, Luisa F. Cabeza ∗

REA Innovació Concurrent, Universitat de Lleida, Edifici CREA, Pere de Cabrera s/n, 25001 Lleida, Spain

r t i c l e i n f o

rticle history:eceived 22 August 2011ccepted 10 October 2011

eywords:hermal energy storage (TES)hase change materials (PCMs)hermal inertia

a b s t r a c t

In 2004 the University of Lleida began working on the inclusion and effects of PCM into concrete andperformed experiments employing microencapsulated PCM integrated into concrete walls under differ-ent configurations (free-cooling, open windows, etc.). One of the main drawbacks found was the severeinfluence of high outdoor temperature peaks and solar radiation over the PCM during the summer, whichprevented its solidification during night and thus diminished its achievable potential benefits. The mainobjective of this work is to overcome such a problem and increase the operation time of the PCM andthe thermal comfort achieved. For such a purpose, in 2008–2009 similar experiments have been per-

wnings formed with awnings added to the set-up, providing them with solar protection. This paper discusses theobserved effects over the PCM activation, comfort conditions inside the building, and compares them tothose obtained without employing awnings. Results showed that peak temperatures were reduced about6%. Moreover, PCM remained active for at least 4% more hours, and the comfort time was increased atleast 10% in cubicles with awnings. However, the effect of high outdoor temperatures and solar radiationwas not overcome completely as PCM did not complete full phase change cycles everyday as desired.

. Background

Energy is becoming one of the most important issues in ourociety. Shortage of primary energy, cost of fossil fuels, and environ-ental concerns are the main factors that have prompted research

nto new and more efficient energy systems. Among these systems,hermal energy storage (TES) has become a key technology becauset provides several alternatives. The use of phase change materialPCM) for thermal energy storage has gained importance in recentears [1–8] since it can absorb or release large amounts of latenteat working in narrow margins of temperature. A high energy den-ity and isothermal behaviour during charging and discharging arehe main reasons for PCM to be preferred.

PCMs have been considered for thermal storage in buildingsince before 1980. There are two different ways to use PCM foreating and cooling in buildings: in building walls or componentspassive), and in heat or cold storage units (active).

In the literature, development and testing were conducted forrototypes of PCM wallboard and PCM in concrete systems tonhance the thermal energy storage capacity of standard gypsumallboard and concrete blocks, with particular interest in peak load

hifting and solar energy utilization [2,9,10].Several researchers have investigated methods for impregnat-

ng gypsum wallboard and other architectural materials with phase

∗ Corresponding author. Tel.: +34 973 00 3576; fax: +34 973 00 3575.E-mail address: lcabeza@diei.udl.cat (L.F. Cabeza).

378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.enbuild.2011.10.028

© 2011 Elsevier B.V. All rights reserved.

change materials, as well as the thermal properties of the resultingmixtures.

Fang et al. [11] and Lee et al. [12] developed a composite PCMfor inclusion in construction materials such as gypsum powders andolefin film with good experimental results. Silva et al. [13] studiedthe composition development and mechanical properties of threedifferent gypsum mortars with PCM incorporated for inner plas-tering of buildings. Sari et al. [14] prepared a form-stable phasechange wallboard for low-temperature latent heat TES by incorpo-rating a eutectic mixture of capric acid and stearic acid, and gypsumwallboard.

Authors such as Shilei et al. [15,16], Lai et al. [17], and Ahmadet al. [18] studied experimentally gypsum boards combined withPCM and evaluated their thermal behaviour and derived advan-tages, all with good results. Banu et al. [19] tested ordinary gypsumwallboard impregnated with organic PCM for flammability, findingthat it could be reduced by adding a flame retardant.

Hawes et al. [20] examined the means of PCM incorporation intoconcrete, and the effects of PCM temperature, concrete tempera-ture, immersion time and PCM dilution on PCM absorption duringthe impregnation process. Cabeza et al. [21] performed tests onconcrete mixed with PCM addressing the effects over indoor tem-peratures and thermal inertia; results were compared with thoseemploying only concrete.

Likewise, some experimental work has been performed to inves-tigate the application of PCM in different constructive systems suchas in lightweight construction [22,23], or brick construction [24,25].The use of PCM under passive modes in concrete [26] or in sandwich

P. Arce et al. / Energy and Buil

Nomenclature

T temperature (◦C)h heat transfer coefficient (W/m2 K)

Subscriptso comfort related valuer radioactive valuec convective valuerm mean radiant valuea ambient air related valuef floor surface related valuep1, . . ., p4 wall surface related valuess ceiling surface related valuew with

pait

eewialttetn

tneawsph

atattcp

2

2

(tbSobb

awnings was the following:

wo without

anels [27–29] has also been studied. Other studied applicationsre floor and ceiling free-cooling [30] systems, where passive colds stored during the night in these structural parts of the buildingo be used later on during the day.

In previous works developed by Cabeza et al. [21] and Castellónt al. [26] the inclusion of PCM into a concrete cubicle was analyzedxperimentally, comparing a cubicle with no PCM with another oneith microencapsulated PCM. The effect of ventilation was stud-

ed by opening and closing windows at certain times of the day,nd the first results were very promising. Temperature daily oscil-ations were reduced up to 4 ◦C between both cubicles and peakemperatures in the PCM cubicle were shifted to later hours. Fromhose experiments it was concluded that PCM could only exert a fullffect on a building if a complete phase change cycle takes place,hat is, if the PCM solidifies and melts completely every day, andight ventilation can help this occur.

Nonetheless, two major issues were detected. The first one washat during winter, the low outdoor temperatures caused PCMot to reach its melting temperature, therefore not activating andxerting no effect over the set-up. In order to work this out, theddition of a Trombe wall to the set-up to favour PCM activationas studied [26,31], with good results as the issue was solved. The

econd detected issue was that during summer, the high outdooreak temperatures (around 40 ◦C), the high solar radiation, and theot nights resulted into preventing the solidification of the PCM.

The main aim of this work is to tackle this last problem by usingwnings. Fur such purpose, during 2008–2009 awnings were addedo the cubicles during summer to reduce the high wall temperaturesnd allow the PCM to solidify at night. The effect of the awnings overhe phase change cycle, the potential improvements derived, andhe influence of the combination of PCM–awnings over comfortonditions inside the cubicle are analyzed and discussed in thisaper.

. Experimental procedure

.1. Experimental set-up

In 2004 the research group GREA from the University of LleidaCatalonia, Spain) began the construction of a unique set-up wherehe storage of thermal energy at low temperature in buildings coulde evaluated. The set-up is located in Puigverd de Lleida (Lleida,pain), which represents a typical continental weather (such as the

ne in Madrid) [32], and consists of several cubicles that simulateuildings in which different TES technologies (mainly PCM) haveeen included.

dings 44 (2012) 88–93 89

The part of the set-up where concrete and PCM were testedconsists of two identically shaped cubicles, built with the union ofsix panels (Fig. 1). One cubicle is built with conventional concreteand the other one with concrete containing about 5% in weight ofmicroencapsulated PCM (Micronal® PCM, from BASF; with a the-oretical melting point of 26 ◦C, and a phase change enthalpy of110 kJ/kg [31,33], mixed with the concrete in three of the panels(South, West and roof walls). Wall insulation was not included sothe effects of PCM alone could be studied. The external dimen-sions of the cubicles are 2.64 m × 2.64 m × 2.52 m and the panelsare 0.12 m thick. The distribution of the windows is the following:one window of 1.7 m × 0.6 m at the East and West wall, four win-dows of 0.75 m × 0.4 m at the South wall and the door in the Northwall. For night ventilation during summer days South wall windowscan be opened.

Temperature sensors are installed on the internal surface of eachwall, the roof, the floor, and at the middle of the room at heightsof 1.2 m and 2.0 m, protected to avoid the radiation from the walls.A heat flux sensor is installed on the internal surface of the Southwall. A meteorological station is installed nearby so the outdoortemperature can be measured. The solar radiation is registered bya pyranometer on top of each cubicle. All instrumentation is con-nected to a data logger, which at the same time is connected to acomputer. Data is registered every 5 min.

2.2. Overview of the previous experimental work

Some previous results obtained at this set-up are: an experi-mental study of the PCM inclusion in building envelopes [26], astudy on the use of microencapsulated PCM in concrete walls forenergy savings [21], and a PhD thesis by Castellón [33] on the maintechnical aspects of incorporating and employing PCM in concretemade buildings.

Results from those previous experiments will be the base casefor the comparison of this paper. Last weeks of July 2006 and July2007 are used as the reference case since the experiments wereperformed without awnings. These results are compared to the newones obtained during 2008–2009.

2.3. Methodology

One way to reduce wall temperatures and fully activate the PCMduring summer time is to decrease the number of hours of directsolar radiation on the walls of the cubicle. With this purpose a newexperimental set-up was designed to provide shadows to the South,West, and East walls and also the roof of both cubicles during June,July and August.

Shadows were provided with an awning at the top of the cubi-cles. To evaluate the dimensions of the awning the Sun trajectory inJune, July, and August was assessed using the solar altitude and thesolar azimuth. Results indicated that a 4.4 m × 4 m awning installed12 cm above the roof of the cubicles (3 m × 3 m) would be appro-priate. Fig. 2 shows the experimental set-up.

With this awning the East wall was partially covered duringthe morning (half covered at 10 am), the East and West walls weretotally covered from 1 pm to 3 pm, the West wall was partially cov-ered in the afternoon (half covered at 5 pm), half of the South wallwas shadowed at 10 am, being totally covered at noon, and par-tially covered again in the afternoon. The roof was protected all daylong.

The experimental sequence conducted with the cubicles with

• Free cooling, windows remained opened at night and closed dur-ing the day.

90 P. Arce et al. / Energy and Buildings 44 (2012) 88–93

Fig. 1. View of the concrete cubicles (2006).

(left)

•

smt

(

F

pwitiieb

tatb

Trm = f p1 p2 p3 p4 s

2(2)

The ambient temperature (Ta) was calculated as the average ofthe temperatures measured at 1.2 m and 2.0 m.

Fig. 2. Outer view of the concrete cubicles with awnings

Open windows, the windows were always open (only the win-dows in the South wall could be opened).

As data sets were grouped in weeks, weeks with approximatelyimilar climatic conditions were to be found in order to compareeasurements with and without awnings. The employed criterion

o consider whether one week was similar to the other was:

(a) Outdoor temperature upper and lower limits should not differfrom each other in more than ±3 ◦C (an estimate variation of7%).

b) Solar radiation limits should not differ from each other in morethan ±60–100 W/m2 (approximately 15–18%).

ound matches are shown in Table 1.In order to analyze the PCM phase change cycles, information

rovided by Castellón [33] on the used PCM (Micronal from BASF)as employed. This allowed determining the correspondent melt-

ng range, which is approximately of 25–29 ◦C (Fig. 3). Since PCMemperature in the cubicle cannot be measured directly, and as PCMs part of the wall, the South wall inner temperature was analyzednstead. By knowing all this and as experimental data was takenvery 5 min, the amount of time during which PCM was active coulde quantified.

Finally, in order to analyze the comfort inside the cubicles,

he “operative comfort temperature” method was chosen (Eqs. (1)nd (2)) [34]. It is considered that there are comfortable condi-ions inside the cubicles if the operative comfort temperature liesetween the recommended values at the standard ISO 7730 and

and a bird’s eye view of the roof with an awning (right).

EN-27730 (23–26 ◦C for summer months). The operative comforttemperature (To) is defined by the following expression:

To = hr · Trm + hc · Ta

hr + hc(1)

The value of hr is typically a constant for usual values of innertemperatures and takes a value of about 4.7 W/m2 K. Regarding thevalue of hc, it may be estimated as 4 W/m2 K for a person standingup in air with a speed among 0 and 0.15 m/s.

The mean radiant temperature (Trm) for a person in the cen-ter of a cubic volume can be calculated according to the followingexpression:

T + 0.15 · (T + T + T + T ) + 0.4 · T

Fig. 3. Determination of the meeting range for Micronal PCM from BASF.Based on [33].

P. Arce et al. / Energy and Buildings 44 (2012) 88–93 91

Table 1Comparable weeks according to experiment and cubicle type.

Experiment With awnings Without awnings

Year Month Week Year Month Week

1 2006 July 41 2007 July 4

3

tftcfiys

3

tilaa

e

wwicntretaPi

tbpt(

Open windows 2008 August

Free-cooling 2008 September

. Results and discussion

In this section, results of the experiments and the comparison ofhe behaviour with and without awnings are presented. One weekor each kind of experiment is presented, since same weather condi-ions for both experiments (w/wo awnings) are necessary for a goodomparison. Extensive experiments have been done for both con-gurations (2 years of measurement without awnings and 2 moreears with awnings). However, a representative week is presentedince results are similar.

.1. Free-cooling experiments

The effects of PCM over buildings come from the heat storage byhe PCM in the wall (lowering temperature peaks), and the thermalnertia increase (delaying temperature peak value appearance toater hours along the day). In order to appreciate the influence ofwnings over these effects, registered temperatures with PCM withnd without awnings are compared.

Fig. 4 shows the wall inner temperature values and observedffects along the considered weeks.

In cubicles with PCM and awnings, temperature peak valuesere lowered in 3–4 ◦C (6%) with respect to those with PCM andithout awnings, and peak values appeared 50 min later (a 36%

ncrease in the time delay). Fig. 4 also shows that phase changeycles were completed successfully in cubicles with awnings, butot in those without awnings. This is noticed by seeing how theemperature peaks and valleys are completely out of the meltingange zone, that is, the PCM was able to fully melt and solidify. Theffect of awnings over PCM activation is better seen in Fig. 8, wherehe time that PCM remained active is shown for both free-coolingnd open window experiments. In the first case it is observed thatCM activation in cubicles with awnings was 4% higher than thatn cubicles without awnings.

Fig. 5 shows the operative comfort temperature (To) duringhe considered period. Values represented here have a similar

ehaviour to that of the wall temperature as both are directlyroportional to each other (see Eqs. (1) and (2)). Fig. 5 allows quan-ifying for how long the cubicle stayed within the comfort zone23–26 ◦C).

Fig. 4. Wall inner temperatures during free-cooling experiments.

Fig. 5. Operative comfort temperature during free-cooling experiments.

The effect of awnings is observed better in Fig. 6, where the timein comfort for all the cubicles may be seen. While in cubicles withPCM and awnings the time in comfort increased 7% with respect tothose without PCM and with awnings, in cubicles without awningsthere was a 7% decrease respectively, attributed to the fact that PCMdid not complete full phase change cycles (no energy recharging),therefore, it could not exert a “full” effect over the cubicle. Thereare then 21% more hours in comfort inside cubicles with PCM andawnings, than in those with PCM and without awnings.

The presence of awnings in the cubicles favoured all consideredaspects, not only by emphasizing the formerly studied effects ofPCM over the cubicles, but also by allowing the PCM to completelymelt and solidify, which lately led to achieve more hours in comfortat the inside. The comfort issue detected at the previous work hasbeen solved by using awnings during free-cooling experiments.

3.2. Open window experiments

A similar analysis to that performed for free-cooling experi-ments is presented here. Fig. 7 shows the wall inner temperatureduring the correspondent weeks.

While temperature peaks in cubicles with PCM and awningswere lowered in about 3 ◦C (7%) with respect to those with PCMand without awnings, peak values were attained 15 min before incubicles with awnings, that is, the time delay due to the thermal

Fig. 6. Hours in comfort in the cubicles during free-cooling experiments.

92 P. Arce et al. / Energy and Buildings 44 (2012) 88–93

Table 2Influence of awnings (%) over main PCM effects in buildings by experiment type.

Experiment Wall temperaturepeak reduction

Temperature peakdelay increase

PCM activationtime increase

Comfort timeincrease

Free-cooling 6% 36% 4% 21%Open windows 7% −14% 10% 10%

it

nrtit

aiz

stTaTsi

3

e

F

Fig. 9. Operative comfort temperature during open window experiments.

Fig. 7. Wall inner temperatures during open window experiments.

nertia increase was 14% lower in this case, which leads to thinkhat the influence of climatic conditions was stronger.

Indeed, it is observed that thanks to this influence, PCM didot get to completely solidify in cubicles with awnings during theespective week, and the “incomplete” effect of PCM in this caseranslated into the non-ability to fully increase the cubicle thermalnertia. Nonetheless, the time of PCM being active increased 10%hanks to the use of awnings (Fig. 8).

The operative comfort temperature is seen in Fig. 9. It is appreci-ted that in both cubicles the time in comfort conditions has slightlyncreased as lowest values of To tend to remain within the comfortone.

The amount of time in comfort conditions for both cubicles ishown in Fig. 10. While in cubicles without awnings PCM increasedhis amount to 1%, in cubicles with awnings there was a 4% increase.he hours in comfort increased 10% in cubicles with PCM andwnings with respect to those with PCM and without awnings.hese differences confirm that the use of awnings was beneficial,ince it again accentuated the effects of PCM and increased the timen comfort inside the cubicles.

.3. Summary of results

Table 2 summarizes the advantages of adding awnings over theffects of PCM on the cubicles for the two performed experiments.

ig. 8. PCM activation hours during free-cooling and open window experiments.

Fig. 10. Hours in comfort in the cubicles during open window experiments.

In both experiments, awnings helped PCM exert its effects over thecubicles. However, despite the fact that solar radiation on the wallswas diminished, it was observed that the PCM was not always ableto complete full phase change cycles.

4. Conclusions

Experimental tests have been performed at a set-up which con-sists of several cubicles where different construction materials maybe tested for thermal energy storage purposes in a Mediterraneanclimate. The addition of microencapsulated PCM into two concretemade cubicles (with no insulation) had been previously tested withgood results. However, as the climatic conditions did not allowPCM to complete full phase change cycles during the summer,awnings were added to the cubicles. Free-cooling and open win-dows tests were carried out. PCM effects were favoured by theawnings, as peak temperature reductions were increased about6%, their appearance delay was increased 36% (free-cooling), butdecreased 14% (open windows), and the time in comfort condi-tions increased between 10% and 21%. The active hours of PCMwere increased 4–10%. However, despite the PCM remained active

for a longer period of time, the effect of high outdoor temperatureswas not overcome completely as PCM did not complete full phasechange cycles everyday as desired.

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P. Arce et al. / Energy an

cknowledgements

The work was partially funded by the Spanish governmentproject ENE2008-06687-C02-01/CON) and the European UnionCOST Action COST TU0802), in collaboration with the Cityhall ofuigverd de Lleida. The authors would like to thank the Catalanovernment for the quality accreditation given to their researchroup (2009 SGR 534).

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