- Email: [email protected]
Development of microencapsulated phase change material with poly (methyl methacrylate) shell for thermal energy storage
ScienceDirect ScienceDirect Energy Energy Procedia Procedia 00 00 (2018) (2018) 000–000 000–000
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Energy Procedia 158 Energy Procedia 00(2019) (2017)4483–4488 000–000 www.elsevier.com/locate/procedia
th 10 10th International International Conference Conference on on Applied Applied Energy Energy (ICAE2018), (ICAE2018), 22-25 22-25 August August 2018, 2018, Hong Hong Kong, Kong, China China
Development microencapsulated change Theof 15th International Symposiumphase on District Heatingmaterial and Coolingwith Development of microencapsulated phase change material with poly poly (methyl (methyl methacrylate) methacrylate) shell shell for for thermal thermal energy energy storage storage Assessing the feasibility of using the heat demand-outdoor aa b c a Su ** ,, Tongyu Zhou Li Lv Weiguang Sufor Tongyu Zhoub,, Yilin Yilin Lic,, Yuexia Yuexia Lva temperatureWeiguang function a long-term district heat demand forecast a aSchool
of Mechanical Mechanical & & Automotive Automotive Engineering, Engineering, Qilu Qilu University University of of Technology Technology (Shandong (Shandong Academy Academy of of Sciences), Sciences), 250353, 250353, Jinan, Jinan, Shandong, Shandong, School of a,b,c a a China b c c China b bDepartment of Architecture and Built Environment, University of Nottingham Ningbo China, 315100, Ningbo,Zhejiang, China Department of Architecture and Built Environment, University of Nottingham Ningbo China, 315100, Ningbo,Zhejiang, China c a of and Shanghai for and 516 Jungong Road, 200093,Shanghai, China c School IN+ Center for Innovation, TechnologyUniversity and Policyof Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal School of Environment Environment and Architecture, Architecture, University ofResearch Shanghai- Instituto for Science Science and Technology, Technology, 516 Jungong Road, 200093,Shanghai, China
I. Andrić c
Abstract Abstract
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
This This research research focused focused on on the the development development of of MEPCMs MEPCMs for for thermal thermal energy energy storage storage in in low low carbon carbon buildings buildings with with poly (methyl methacrylate) (PMMA) shell. The experimental results showed that the best MEPCM Abstract poly (methyl methacrylate) (PMMA) shell. The experimental results showed that the best MEPCM sample sample was was prepared prepared with with 1 1 wt% wt% of of the the thermal thermal initiator initiator and and the the surfactant surfactant of of S-1DS. S-1DS. The The differential differential scanning scanning calorimetric calorimetric (DSC) the has aa latent heat aa melting 22.68 Districtanalysis heating showed networksthat are commonly addressed the literature onekJ/kg of theand most effective temperature solutions for of decreasing the (DSC) analysis showed that the best best sample sample has in latent heat of ofas170 170 kJ/kg and melting temperature of 22.68 ℃. ℃. Meanwhile, the core contents encapsulation efficiencies calculated according to measured greenhouse gas from the buildingand sector. These systems require highwere investments which are returned through the heat Meanwhile, theemissions core material material contents and encapsulation efficiencies were calculated according to the the measured results of Those two for sample of PMMA-5 were higher than theoretical sales. Due the changed conditions building renovationand policies, heat demand in the future could decrease, results of the theto DSC. DSC. Those climate two values values for the theand sample of PMMA-3 PMMA-3 and PMMA-5 were even even higher than theoretical values due to the evaporation of shell monomer during encapsulation processes. Finally, the thermogravimetric prolonging the investment return period. values due to the evaporation of shell monomer during encapsulation processes. Finally, the thermogravimetric (TG) (TG) analysis the showed good thermal stability behaviors above ℃ and therefore The mainof of this paperMEPCM is to assesssamples the feasibility of using heat demand – outdoor temperature function demand analysis ofscope the fabricated fabricated MEPCM samples showed goodthe thermal stability behaviors above 161 161 ℃ for andheat therefore satisfy the environmental requirements for applications. forecast. district of Alvalade, located Lisbon (Portugal), was used as a case study. The district is consisted of 665 satisfy theThe environmental requirements forinmost most applications. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district Copyright © Elsevier All rights ©renovation 2019 The Authors. Published byLtd. Elsevier Ltd. reserved. Copyright © 2018 2018 Elsevier Ltd. All rights reserved. scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were
This is an open access article the CC license (http://creativecommons.org/licenses/by-nc-nd/4.0/) thby the authors. compared with results from aunder dynamic heatBY-NC-ND demand model, previously developed andofvalidated Selection and peer-review responsibility of scientific International Conference on Selectionunder and responsibility peer-review under under responsibility of the the scientific committee committee of the the 10 10th Conference International Conference on Peer-review of the scientific committee of ICAE2018 – The 10th International onsome Applied Energy. The results showed that when only weather change is considered, the margin of error could be acceptable for applications Applied Energy (ICAE2018). Applied Energy (ICAE2018). (the error in annual demandParaffin, was lower thanenergy 20% for all Poly weather scenarios considered). However, after introducing renovation Keywords: Keywords: Microencapsulation, Paraffin, Thermal Thermal energy storage, storage, Poly (methyl (methyl methacrylate) methacrylate) scenarios,Microencapsulation, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and 1. Introduction 1.renovation Introduction scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and Previous studies proved that microencapsulated Previous studies have have microencapsulated phase phase change change material material (MEPCM) (MEPCM) was was one one of of the the key key improve the accuracy of heatproved demandthat estimations.
potential potential materials materials for for saving saving energy energy consumption consumption in in buildings buildings because because it it can can balance balance the the mismatch mismatch between between heating heating © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
** Corresponding Corresponding author. author. Tel.: Tel.: +86 +86 18265416996. 18265416996. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier th Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 10 th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10 International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.764
Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
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and cooling demands automatically [1, 2]. The researches pointed that the latent heat thermal energy storage materials suitable for various applications in buildings, such as melting temperatures up to 21℃ are more suitable for cooling applications [3], 22-28℃ for thermal comfort applications, 29-60 ℃ for hot water supply and over 120℃ for waste heat recovery applications [4]. For instance, an experimental study carried out on a novel translucent full scale passive solar MEPCM wall by Berthou et al. [5] revealed that it could be used to provide significant improvement of indoor temperatures in both cold and sunny climates. Darkwa et al. developed a non-deform MEPCM [6] for thermal energy storage application. Su et al.[7] developed MEPCM for hot water supply in low carbon buildings and proved the energy storage density would increase from 84,000 kJ/m3 to 128,735 kJ/m3 by added 50 wt% MEPCM. Previous researches also showed that polymers based methyl methacrylate (MMA) are the commonest shell materials for MEPCMs preparation with in-situ suspension-like polymerization method [8] since the MMA can be self-polymerized [9] and crosslinked with the other monomers [10]. Meanwhile, good quality MEPCMs can be produced by combining appropriate proportions of surfactants. For example, Su et al. [10] also combined two surfactants (Brij-30 and Brij-58) to develop MEPCM samples. Wang et al. [11] stabilized oil/water emulsion with organically modified SiO2/TiC nanoparticles as surfactants and developed organic-inorganic hybrid shell MEPCMs. Su et al. [12] also successfully fabricated MEPCM samples with the surfactant of nanosilicon dioxide hydrosol. To this end, different types of surfactants (i.e. nano-silicon dioxide hydrosol and Sodium 1-dodecanesulfonate (S-1DS)) were used to prepare MEPCM samples with paraffin wax and poly (methyl methacrylate) (PMMA) in this research. Meanwhile, the effects of weight percentage of initiator and types of surfactants were also studied. 2. Materials and methods 2.1. Materials As summarized in Tab.1, the paraffin of n-octadecane was introduced as a core material because of its relatively high latent heat capacity and appropriate phase change temperature. While the MMA (purity of 98 %, Sinopharm Chemical Reagent Co.,Ltd.) was used as shell monomer. Nano-SiO2 hydrosol (ZS-30, 30 wt%, Zhejiang Yuda Chemical Industry Co., Ltd) and sodium 1-dodecanesulfonate (S-1DS) (Sinopharm Chemical Reagent Co.,Ltd) were used as a surfactants. Usually, based on the weight of shell monomer, thermal initiators in the range of 0.5 wt% to 3wt% are used for crosslinking PMMA [13]. To this end, the AIBN (purity of 98 %, Aladdin) with the weight percentages of 0.5 %, 1.0 %, 2.0 % and 3.0 % was used as oil-soluble thermal initiator. Table 1: Raw materials of MEPCM preparation with PMMA shell Sample
MMA (g)
PCM (g)
PMMA-1
3
PMMA-2
3
PMMA-3
3
7
PMMA-4
3
7
PMMA-5
3
7
PMMA-6
3
7
Surfactant material
Surfactant (g)
AIBN (g)
Initiator weight (wt%)
7
0.5
0.090
3.0%
7
0.5
0.060
2.0%
0.5
0.030
1.0%
0.5
0.015
0.5%
0.5
0.030
1.0%
0.5
0.015
0.5%
Nano-SiO2 hydrosol
S-1DS
2.2. Fabrication process The typical procedure for using oil-soluble initiators to fabricate MEPCMs with PMMA shell is as following: The oil phase was prepared by mixing the shell monomer (MMA) and the melted n-ocatadecane at 40 °C with a predetermined amount of thermal initiator (AIBN). The oil phase was then homogenized into water phase with 90 ml of deionized water and a certain amount of surfactant (nano-SiO2 hydrosol or S-1DS) at a speed of 7000 rpm for 5 minutes to form a stable O/W emulsion. The next stage was to transfer the homogeneous emulsion into a threeneck round bottom flask before it was deoxygenated with nitrogen gas for one hour at a stirring speed of 250 rpm.
Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
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The microencapsulation reaction was then carried out in the flask immersing in a water bath of 80 °C and was continuously agitated under a speed of 250 rpm for 5 hours. Finally, the microcapsules were collected, washed and then dried in an oven at 60 °C for 20 hours. 3. Results and discussion 3.1. Morphology analysis of MEPCM samples The fabricated MEPCM samples were depicted by a scanning electron microscope (SEM) manufactured by Sigma VP (Carl Zeiss Co. Ltd.), as demonstrated in Fig. 1. The SEM images showed that the particle sizes of PMMA capsules are in the range of 5-20 μm and that is the same as the initial diameters of MEPCM particles in slurry. However, most of the capsules manufactured with the surfactant of nano-SiO2 hydrosol in Fig. 1 (a) to (d) were deformed after drying due to some weakness of the PMMA shell. On the other hand, the capsules fabricated with the surfactant of S-1DS showed much better morphology and integrity, and the PMMA-5 demonstrated the best particle morphology and integrity, while the PMMA-6 showed a lot of wrinkles on the surfaces of the capsules. That means the morphologies of microcapsules were particularly influenced by the type of surfactant and the dosage of the thermal initiator. In this research, the optimization of the capsules morphology was achieved with the surfactant of S-1DS and 1 wt% thermal initiator.
Figure 1: SEM images of fabricated MEPCM samples
Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
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3.2. Energy storage capacity According to differential scanning calorimetric (DSC) (DSC6220, SII Nanotechnology) measurement results, the melting points of MEPCMs were reduced by 0.2-1.87 ℃ compared with the n-octadecane (PCM core material), as shown in Fig. 2. Meanwhile, the thermal energy storage capacities of fabricated MEPCM samples were achieved as much as 149 kJ/kg, 143 kJ/kg, 166 kJ/kg, 142 kJ/kg, 170 kJ/kg and 150 kJ/kg for the PMMA-1, PMMA-2, PMMA3, PMMA-4, PMMA-5 and PMMA-6, respectively. The DSC analysis results also showed that the dosage of thermal initiator did effect on the thermal energy storage capacities and the core material contents of MEPCM samples, and the highest core material contents for the surfactant of nano-SiO2 and S-1DS were achieved by using 1 wt% of thermal initiator. The research outcomes by Romio et al. [14] showed that the polymerization rate of MMA was increased by a higher initiator dosage. To this end, the dosage of AIBN need to be optimized and the best concentration of initiator is 1 % in this study. According to the initial core/shell ratio in Tab.1, the theoretical core material content should be 70 % with the latent heat of 151.2 kJ/kg. However, the experimental results in Tab.2 showed the energy storage capacity of PMMA-3 and PMMA-5 were higher than 70 % and that means the encapsulation efficiencies [15] were more than 100 %. However, the high encapsulation efficiency did not mean good encapsulation quality since deform of MEPCM capsules existed in Fig. 1. On the contrary, the high encapsulation efficiency was mainly due to the reducing of weight percentage of shell that caused by the evaporation of shell monomer. The evaporation resulted by the low flash point of MMA which is only 9 ℃ and relatively high reaction temperature of 80 ℃ for the selfcrosslinking of MMA [16].
Figure 2: DSC curves of MEPCM samples Table 2: Properties of paraffin and MEPCM samples Paraffin
23.12
Latent (kJ/kg) 216
--
Encapsulation efficiency (%) --
PMMA-1
21.25
149
69.0%
98.5%
PMMA-2
22.80
143
66.2%
94.6%
PMMA-3
22.66
166
76.9%
109.8%
PMMA-4
22.07
142
65.7%
93.9%
PMMA-5
22.68
170
78.7%
112.4%
PMMA-6
22.92
150
69.4%
99.2%
Material
Melting temperature (℃)
heat
Core material (wt%)
Author name / Energy Procedia 00 (2018) 000–000 Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488
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3.3. Thermal stability As shown in Fig. 3, the thermogravimetric (TG) (EXSTAR6000 TG/DTA6300, SII NanoTechnology Inc.) analysis results showed that the weight loss starting temperatures for n-octadecane, PMMA-1, PMMA-2, PMMA-3, PMMA-4, PMMA-5 and PMMA-6 were at 129.0 ℃, 178.6 ℃, 167.6 ℃, 161 ℃, 165.8 ℃, 204.4 ℃ and 192.9 ℃, respectively. That means the thermal stability of the MEPCMs was enhanced more than 32 ℃by the PMMA shell compared with the paraffin core of n-octadecane after encapsulation. However, due to the deformed state of the capsules fabricated with the surfactant of nano-SiO2, the thermal stability of those samples (PMMA-1 to PMMA-4) was demonstrated much lower than the capsules fabricated with the surfactant of S-1DS (PMMA-5 and PMMA-6). For instance, compared with the original core material the weight loss starting temperature at 129.0 ℃, the weight loss starting temperatures for PMMA-5 and PMMA-6 were increased more than 63.9 ℃ while the maximum value for the capsules manufactured with the surfactant of nano-SiO2 was only 49.6 ℃. Especially for the PMMA-5 the thermal stability was increased by 75.4 ℃ due to the integrated nature of the shell. The TG analysis also proved the best MEPCM sample of PMMA-5 has the highest thermal stability.
Figure 3: TG curves of MEPCM samples
4. Conclusions In general this study has developed several MEPCM samples for thermal energy storage in low carbon building. The experimental results proved that the qualities of capsules were mainly affected by the type of surfactants and the dosage of initiator. Meanwhile, capsule morphologies, thermal storage capacities, core material contents, encapsulation efficiencies and thermal stabilities were analysed and evaluated by SEM, DSC and TG, respectively. The key findings are summarized as follows: 1)
The core material contents and encapsulation efficiencies of the PMMA-3 and PMMA-5 were higher than theoretical values due to the evaporation of MMA (shell monomer) during encapsulation processes.
2)
The experimental results show that the thermal stabilities of PMMA samples were between 161 ℃ and 204.4 ℃ and enhanced by more than 32 ℃.
3)
The best MEPCM sample with PMMA shell was manufactured with the surfactant of S-1DS and thermal initiator of 1 wt%. The latent heat and thermal stability of the best PMMA samples were obtained as 170 kJ/kg and 204.4 ℃ respectively.
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Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
Acknowledgements The authors are thankful for the Doctoral Scientific Research Foundation of Qilu University of Technology (No. 0412048475) and Natural Science Foundation of Shandong Province (No. ZR2017LEE017). References [1] Konuklu Y, Ostry M, Paksoy HO, Charvat P. Review on using microencapsulated phase change materials (PCM) in building applications. Energy and Buildings. 2015;106:134-55. [2] Souayfane F, Fardoun F, Biwole P-H. Phase change materials (PCM) for cooling applications in buildings: A review. Energy and Buildings. 2016;129:396-431. [3] Oró E, de Gracia A, Castell A, Farid MM, Cabeza LF. Review on phase change materials (PCMs) for cold thermal energy storage applications. Applied Energy. 2012;99:513-33. [4] Agyenim F, Hewitt N, Eames P, Smyth M. A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS). Renewable and Sustainable Energy Reviews. 2010;14:615-28. [5] Berthou Y, Biwole PH, Achard P, Sallée H, Tantot-Neirac M, Jay F. Full scale experimentation on a new translucent passive solar wall combining silica aerogels and phase change materials. Solar Energy. 2015;115:733-42. [6] Darkwa J, Su O, Zhou T. Development of non-deform micro-encapsulated phase change energy storage tablets. Applied Energy. 2012;98:441-7. [7] Su W, Darkwa J, Kokogiannakis G. Development of microencapsulated phase change material for solar thermal energy storage. Applied Thermal Engineering. 2017;112:1205-12. [8] Su W, Darkwa J, Kokogiannakis G. Review of solid–liquid phase change materials and their encapsulation technologies. Renewable and Sustainable Energy Reviews. 2015;48:373-91. [9] Yang Y, Ye X, Luo J, Song G, Liu Y, Tang G. Polymethyl methacrylate based phase change microencapsulation for solar energy storage with silicon nitride. Solar Energy. 2015;115:289-96. [10] Su W, Darkwa J, Kokogiannakis G, Zhou T, Li Y. Preparation of microencapsulated phase change materials (MEPCM) for thermal energy storage. Improving Residential Energy Efficiency International Conference. Wollongong, Australia2017. [11] Wang H, Zhao L, Song G, Tang G, Shi X. Organic-inorganic hybrid shell microencapsulated phase change materials prepared from SiO2/TiC-stabilized pickering emulsion polymerization. Solar Energy Materials and Solar Cells. 2018;175:102-10. [12] Su W, Darkwa J, Kokogiannakis G. Nanosilicon dioxide hydrosol as surfactant for preparation of microencapsulated phase change materials for thermal energy storage in buildings. International Journal of Low-Carbon Technologies. 2018:cty032-cty. [13] Weston RC, Dungworth HR. Particulate compositions and their manufacture. Google Patents; 2004. [14] Romio AP, Sayer C, De Araujo PHH, Alhaydari M, Wu L, Rocha SRPD. Nanocapsules by Miniemulsion Polymerization with Biodegradable Surfactant and Hydrophobe. Macromolecular Chemistry and Physics. 2009;210:747-51. [15] Zhang H, Wang X. Synthesis and properties of microencapsulated n-octadecane with polyurea shells containing different soft segments for heat energy storage and thermal regulation. Solar Energy Materials and Solar Cells. 2009;93:1366-76. [16] Qiu X, Li W, Song G, Chu X, Tang G. Fabrication and characterization of microencapsulated n-octadecane with different crosslinked methylmethacrylate-based polymer shells. Solar Energy Materials and Solar Cells. 2012;98:283-93.
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available
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www.elsevier.com/locate/proc www.elsevier.com/locate/proc edia edia
Energy Procedia 158 Energy Procedia 00(2019) (2017)4483–4488 000–000 www.elsevier.com/locate/procedia
th 10 10th International International Conference Conference on on Applied Applied Energy Energy (ICAE2018), (ICAE2018), 22-25 22-25 August August 2018, 2018, Hong Hong Kong, Kong, China China
Development microencapsulated change Theof 15th International Symposiumphase on District Heatingmaterial and Coolingwith Development of microencapsulated phase change material with poly poly (methyl (methyl methacrylate) methacrylate) shell shell for for thermal thermal energy energy storage storage Assessing the feasibility of using the heat demand-outdoor aa b c a Su ** ,, Tongyu Zhou Li Lv Weiguang Sufor Tongyu Zhoub,, Yilin Yilin Lic,, Yuexia Yuexia Lva temperatureWeiguang function a long-term district heat demand forecast a aSchool
of Mechanical Mechanical & & Automotive Automotive Engineering, Engineering, Qilu Qilu University University of of Technology Technology (Shandong (Shandong Academy Academy of of Sciences), Sciences), 250353, 250353, Jinan, Jinan, Shandong, Shandong, School of a,b,c a a China b c c China b bDepartment of Architecture and Built Environment, University of Nottingham Ningbo China, 315100, Ningbo,Zhejiang, China Department of Architecture and Built Environment, University of Nottingham Ningbo China, 315100, Ningbo,Zhejiang, China c a of and Shanghai for and 516 Jungong Road, 200093,Shanghai, China c School IN+ Center for Innovation, TechnologyUniversity and Policyof Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal School of Environment Environment and Architecture, Architecture, University ofResearch Shanghai- Instituto for Science Science and Technology, Technology, 516 Jungong Road, 200093,Shanghai, China
I. Andrić c
Abstract Abstract
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
This This research research focused focused on on the the development development of of MEPCMs MEPCMs for for thermal thermal energy energy storage storage in in low low carbon carbon buildings buildings with with poly (methyl methacrylate) (PMMA) shell. The experimental results showed that the best MEPCM Abstract poly (methyl methacrylate) (PMMA) shell. The experimental results showed that the best MEPCM sample sample was was prepared prepared with with 1 1 wt% wt% of of the the thermal thermal initiator initiator and and the the surfactant surfactant of of S-1DS. S-1DS. The The differential differential scanning scanning calorimetric calorimetric (DSC) the has aa latent heat aa melting 22.68 Districtanalysis heating showed networksthat are commonly addressed the literature onekJ/kg of theand most effective temperature solutions for of decreasing the (DSC) analysis showed that the best best sample sample has in latent heat of ofas170 170 kJ/kg and melting temperature of 22.68 ℃. ℃. Meanwhile, the core contents encapsulation efficiencies calculated according to measured greenhouse gas from the buildingand sector. These systems require highwere investments which are returned through the heat Meanwhile, theemissions core material material contents and encapsulation efficiencies were calculated according to the the measured results of Those two for sample of PMMA-5 were higher than theoretical sales. Due the changed conditions building renovationand policies, heat demand in the future could decrease, results of the theto DSC. DSC. Those climate two values values for the theand sample of PMMA-3 PMMA-3 and PMMA-5 were even even higher than theoretical values due to the evaporation of shell monomer during encapsulation processes. Finally, the thermogravimetric prolonging the investment return period. values due to the evaporation of shell monomer during encapsulation processes. Finally, the thermogravimetric (TG) (TG) analysis the showed good thermal stability behaviors above ℃ and therefore The mainof of this paperMEPCM is to assesssamples the feasibility of using heat demand – outdoor temperature function demand analysis ofscope the fabricated fabricated MEPCM samples showed goodthe thermal stability behaviors above 161 161 ℃ for andheat therefore satisfy the environmental requirements for applications. forecast. district of Alvalade, located Lisbon (Portugal), was used as a case study. The district is consisted of 665 satisfy theThe environmental requirements forinmost most applications. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district Copyright © Elsevier All rights ©renovation 2019 The Authors. Published byLtd. Elsevier Ltd. reserved. Copyright © 2018 2018 Elsevier Ltd. All rights reserved. scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were
This is an open access article the CC license (http://creativecommons.org/licenses/by-nc-nd/4.0/) thby the authors. compared with results from aunder dynamic heatBY-NC-ND demand model, previously developed andofvalidated Selection and peer-review responsibility of scientific International Conference on Selectionunder and responsibility peer-review under under responsibility of the the scientific committee committee of the the 10 10th Conference International Conference on Peer-review of the scientific committee of ICAE2018 – The 10th International onsome Applied Energy. The results showed that when only weather change is considered, the margin of error could be acceptable for applications Applied Energy (ICAE2018). Applied Energy (ICAE2018). (the error in annual demandParaffin, was lower thanenergy 20% for all Poly weather scenarios considered). However, after introducing renovation Keywords: Keywords: Microencapsulation, Paraffin, Thermal Thermal energy storage, storage, Poly (methyl (methyl methacrylate) methacrylate) scenarios,Microencapsulation, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and 1. Introduction 1.renovation Introduction scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and Previous studies proved that microencapsulated Previous studies have have microencapsulated phase phase change change material material (MEPCM) (MEPCM) was was one one of of the the key key improve the accuracy of heatproved demandthat estimations.
potential potential materials materials for for saving saving energy energy consumption consumption in in buildings buildings because because it it can can balance balance the the mismatch mismatch between between heating heating © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
** Corresponding Corresponding author. author. Tel.: Tel.: +86 +86 18265416996. 18265416996. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected] 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier th Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 10 th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10 International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.764
Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
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and cooling demands automatically [1, 2]. The researches pointed that the latent heat thermal energy storage materials suitable for various applications in buildings, such as melting temperatures up to 21℃ are more suitable for cooling applications [3], 22-28℃ for thermal comfort applications, 29-60 ℃ for hot water supply and over 120℃ for waste heat recovery applications [4]. For instance, an experimental study carried out on a novel translucent full scale passive solar MEPCM wall by Berthou et al. [5] revealed that it could be used to provide significant improvement of indoor temperatures in both cold and sunny climates. Darkwa et al. developed a non-deform MEPCM [6] for thermal energy storage application. Su et al.[7] developed MEPCM for hot water supply in low carbon buildings and proved the energy storage density would increase from 84,000 kJ/m3 to 128,735 kJ/m3 by added 50 wt% MEPCM. Previous researches also showed that polymers based methyl methacrylate (MMA) are the commonest shell materials for MEPCMs preparation with in-situ suspension-like polymerization method [8] since the MMA can be self-polymerized [9] and crosslinked with the other monomers [10]. Meanwhile, good quality MEPCMs can be produced by combining appropriate proportions of surfactants. For example, Su et al. [10] also combined two surfactants (Brij-30 and Brij-58) to develop MEPCM samples. Wang et al. [11] stabilized oil/water emulsion with organically modified SiO2/TiC nanoparticles as surfactants and developed organic-inorganic hybrid shell MEPCMs. Su et al. [12] also successfully fabricated MEPCM samples with the surfactant of nanosilicon dioxide hydrosol. To this end, different types of surfactants (i.e. nano-silicon dioxide hydrosol and Sodium 1-dodecanesulfonate (S-1DS)) were used to prepare MEPCM samples with paraffin wax and poly (methyl methacrylate) (PMMA) in this research. Meanwhile, the effects of weight percentage of initiator and types of surfactants were also studied. 2. Materials and methods 2.1. Materials As summarized in Tab.1, the paraffin of n-octadecane was introduced as a core material because of its relatively high latent heat capacity and appropriate phase change temperature. While the MMA (purity of 98 %, Sinopharm Chemical Reagent Co.,Ltd.) was used as shell monomer. Nano-SiO2 hydrosol (ZS-30, 30 wt%, Zhejiang Yuda Chemical Industry Co., Ltd) and sodium 1-dodecanesulfonate (S-1DS) (Sinopharm Chemical Reagent Co.,Ltd) were used as a surfactants. Usually, based on the weight of shell monomer, thermal initiators in the range of 0.5 wt% to 3wt% are used for crosslinking PMMA [13]. To this end, the AIBN (purity of 98 %, Aladdin) with the weight percentages of 0.5 %, 1.0 %, 2.0 % and 3.0 % was used as oil-soluble thermal initiator. Table 1: Raw materials of MEPCM preparation with PMMA shell Sample
MMA (g)
PCM (g)
PMMA-1
3
PMMA-2
3
PMMA-3
3
7
PMMA-4
3
7
PMMA-5
3
7
PMMA-6
3
7
Surfactant material
Surfactant (g)
AIBN (g)
Initiator weight (wt%)
7
0.5
0.090
3.0%
7
0.5
0.060
2.0%
0.5
0.030
1.0%
0.5
0.015
0.5%
0.5
0.030
1.0%
0.5
0.015
0.5%
Nano-SiO2 hydrosol
S-1DS
2.2. Fabrication process The typical procedure for using oil-soluble initiators to fabricate MEPCMs with PMMA shell is as following: The oil phase was prepared by mixing the shell monomer (MMA) and the melted n-ocatadecane at 40 °C with a predetermined amount of thermal initiator (AIBN). The oil phase was then homogenized into water phase with 90 ml of deionized water and a certain amount of surfactant (nano-SiO2 hydrosol or S-1DS) at a speed of 7000 rpm for 5 minutes to form a stable O/W emulsion. The next stage was to transfer the homogeneous emulsion into a threeneck round bottom flask before it was deoxygenated with nitrogen gas for one hour at a stirring speed of 250 rpm.
Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
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The microencapsulation reaction was then carried out in the flask immersing in a water bath of 80 °C and was continuously agitated under a speed of 250 rpm for 5 hours. Finally, the microcapsules were collected, washed and then dried in an oven at 60 °C for 20 hours. 3. Results and discussion 3.1. Morphology analysis of MEPCM samples The fabricated MEPCM samples were depicted by a scanning electron microscope (SEM) manufactured by Sigma VP (Carl Zeiss Co. Ltd.), as demonstrated in Fig. 1. The SEM images showed that the particle sizes of PMMA capsules are in the range of 5-20 μm and that is the same as the initial diameters of MEPCM particles in slurry. However, most of the capsules manufactured with the surfactant of nano-SiO2 hydrosol in Fig. 1 (a) to (d) were deformed after drying due to some weakness of the PMMA shell. On the other hand, the capsules fabricated with the surfactant of S-1DS showed much better morphology and integrity, and the PMMA-5 demonstrated the best particle morphology and integrity, while the PMMA-6 showed a lot of wrinkles on the surfaces of the capsules. That means the morphologies of microcapsules were particularly influenced by the type of surfactant and the dosage of the thermal initiator. In this research, the optimization of the capsules morphology was achieved with the surfactant of S-1DS and 1 wt% thermal initiator.
Figure 1: SEM images of fabricated MEPCM samples
Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
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3.2. Energy storage capacity According to differential scanning calorimetric (DSC) (DSC6220, SII Nanotechnology) measurement results, the melting points of MEPCMs were reduced by 0.2-1.87 ℃ compared with the n-octadecane (PCM core material), as shown in Fig. 2. Meanwhile, the thermal energy storage capacities of fabricated MEPCM samples were achieved as much as 149 kJ/kg, 143 kJ/kg, 166 kJ/kg, 142 kJ/kg, 170 kJ/kg and 150 kJ/kg for the PMMA-1, PMMA-2, PMMA3, PMMA-4, PMMA-5 and PMMA-6, respectively. The DSC analysis results also showed that the dosage of thermal initiator did effect on the thermal energy storage capacities and the core material contents of MEPCM samples, and the highest core material contents for the surfactant of nano-SiO2 and S-1DS were achieved by using 1 wt% of thermal initiator. The research outcomes by Romio et al. [14] showed that the polymerization rate of MMA was increased by a higher initiator dosage. To this end, the dosage of AIBN need to be optimized and the best concentration of initiator is 1 % in this study. According to the initial core/shell ratio in Tab.1, the theoretical core material content should be 70 % with the latent heat of 151.2 kJ/kg. However, the experimental results in Tab.2 showed the energy storage capacity of PMMA-3 and PMMA-5 were higher than 70 % and that means the encapsulation efficiencies [15] were more than 100 %. However, the high encapsulation efficiency did not mean good encapsulation quality since deform of MEPCM capsules existed in Fig. 1. On the contrary, the high encapsulation efficiency was mainly due to the reducing of weight percentage of shell that caused by the evaporation of shell monomer. The evaporation resulted by the low flash point of MMA which is only 9 ℃ and relatively high reaction temperature of 80 ℃ for the selfcrosslinking of MMA [16].
Figure 2: DSC curves of MEPCM samples Table 2: Properties of paraffin and MEPCM samples Paraffin
23.12
Latent (kJ/kg) 216
--
Encapsulation efficiency (%) --
PMMA-1
21.25
149
69.0%
98.5%
PMMA-2
22.80
143
66.2%
94.6%
PMMA-3
22.66
166
76.9%
109.8%
PMMA-4
22.07
142
65.7%
93.9%
PMMA-5
22.68
170
78.7%
112.4%
PMMA-6
22.92
150
69.4%
99.2%
Material
Melting temperature (℃)
heat
Core material (wt%)
Author name / Energy Procedia 00 (2018) 000–000 Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488
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3.3. Thermal stability As shown in Fig. 3, the thermogravimetric (TG) (EXSTAR6000 TG/DTA6300, SII NanoTechnology Inc.) analysis results showed that the weight loss starting temperatures for n-octadecane, PMMA-1, PMMA-2, PMMA-3, PMMA-4, PMMA-5 and PMMA-6 were at 129.0 ℃, 178.6 ℃, 167.6 ℃, 161 ℃, 165.8 ℃, 204.4 ℃ and 192.9 ℃, respectively. That means the thermal stability of the MEPCMs was enhanced more than 32 ℃by the PMMA shell compared with the paraffin core of n-octadecane after encapsulation. However, due to the deformed state of the capsules fabricated with the surfactant of nano-SiO2, the thermal stability of those samples (PMMA-1 to PMMA-4) was demonstrated much lower than the capsules fabricated with the surfactant of S-1DS (PMMA-5 and PMMA-6). For instance, compared with the original core material the weight loss starting temperature at 129.0 ℃, the weight loss starting temperatures for PMMA-5 and PMMA-6 were increased more than 63.9 ℃ while the maximum value for the capsules manufactured with the surfactant of nano-SiO2 was only 49.6 ℃. Especially for the PMMA-5 the thermal stability was increased by 75.4 ℃ due to the integrated nature of the shell. The TG analysis also proved the best MEPCM sample of PMMA-5 has the highest thermal stability.
Figure 3: TG curves of MEPCM samples
4. Conclusions In general this study has developed several MEPCM samples for thermal energy storage in low carbon building. The experimental results proved that the qualities of capsules were mainly affected by the type of surfactants and the dosage of initiator. Meanwhile, capsule morphologies, thermal storage capacities, core material contents, encapsulation efficiencies and thermal stabilities were analysed and evaluated by SEM, DSC and TG, respectively. The key findings are summarized as follows: 1)
The core material contents and encapsulation efficiencies of the PMMA-3 and PMMA-5 were higher than theoretical values due to the evaporation of MMA (shell monomer) during encapsulation processes.
2)
The experimental results show that the thermal stabilities of PMMA samples were between 161 ℃ and 204.4 ℃ and enhanced by more than 32 ℃.
3)
The best MEPCM sample with PMMA shell was manufactured with the surfactant of S-1DS and thermal initiator of 1 wt%. The latent heat and thermal stability of the best PMMA samples were obtained as 170 kJ/kg and 204.4 ℃ respectively.
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Weiguang Su et al. / Energy Procedia 158 (2019) 4483–4488 Author name / Energy Procedia 00 (2018) 000–000
Acknowledgements The authors are thankful for the Doctoral Scientific Research Foundation of Qilu University of Technology (No. 0412048475) and Natural Science Foundation of Shandong Province (No. ZR2017LEE017). References [1] Konuklu Y, Ostry M, Paksoy HO, Charvat P. Review on using microencapsulated phase change materials (PCM) in building applications. Energy and Buildings. 2015;106:134-55. [2] Souayfane F, Fardoun F, Biwole P-H. Phase change materials (PCM) for cooling applications in buildings: A review. Energy and Buildings. 2016;129:396-431. [3] Oró E, de Gracia A, Castell A, Farid MM, Cabeza LF. Review on phase change materials (PCMs) for cold thermal energy storage applications. Applied Energy. 2012;99:513-33. [4] Agyenim F, Hewitt N, Eames P, Smyth M. A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS). Renewable and Sustainable Energy Reviews. 2010;14:615-28. [5] Berthou Y, Biwole PH, Achard P, Sallée H, Tantot-Neirac M, Jay F. Full scale experimentation on a new translucent passive solar wall combining silica aerogels and phase change materials. Solar Energy. 2015;115:733-42. [6] Darkwa J, Su O, Zhou T. Development of non-deform micro-encapsulated phase change energy storage tablets. Applied Energy. 2012;98:441-7. [7] Su W, Darkwa J, Kokogiannakis G. Development of microencapsulated phase change material for solar thermal energy storage. Applied Thermal Engineering. 2017;112:1205-12. [8] Su W, Darkwa J, Kokogiannakis G. Review of solid–liquid phase change materials and their encapsulation technologies. Renewable and Sustainable Energy Reviews. 2015;48:373-91. [9] Yang Y, Ye X, Luo J, Song G, Liu Y, Tang G. Polymethyl methacrylate based phase change microencapsulation for solar energy storage with silicon nitride. Solar Energy. 2015;115:289-96. [10] Su W, Darkwa J, Kokogiannakis G, Zhou T, Li Y. Preparation of microencapsulated phase change materials (MEPCM) for thermal energy storage. Improving Residential Energy Efficiency International Conference. Wollongong, Australia2017. [11] Wang H, Zhao L, Song G, Tang G, Shi X. Organic-inorganic hybrid shell microencapsulated phase change materials prepared from SiO2/TiC-stabilized pickering emulsion polymerization. Solar Energy Materials and Solar Cells. 2018;175:102-10. [12] Su W, Darkwa J, Kokogiannakis G. Nanosilicon dioxide hydrosol as surfactant for preparation of microencapsulated phase change materials for thermal energy storage in buildings. International Journal of Low-Carbon Technologies. 2018:cty032-cty. [13] Weston RC, Dungworth HR. Particulate compositions and their manufacture. Google Patents; 2004. [14] Romio AP, Sayer C, De Araujo PHH, Alhaydari M, Wu L, Rocha SRPD. Nanocapsules by Miniemulsion Polymerization with Biodegradable Surfactant and Hydrophobe. Macromolecular Chemistry and Physics. 2009;210:747-51. [15] Zhang H, Wang X. Synthesis and properties of microencapsulated n-octadecane with polyurea shells containing different soft segments for heat energy storage and thermal regulation. Solar Energy Materials and Solar Cells. 2009;93:1366-76. [16] Qiu X, Li W, Song G, Chu X, Tang G. Fabrication and characterization of microencapsulated n-octadecane with different crosslinked methylmethacrylate-based polymer shells. Solar Energy Materials and Solar Cells. 2012;98:283-93.