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Utilization of the PCM latent heat for energy savings in buildings
Jan Fořt, Anton Trník, and Zbyšek Pavlík
Citation: AIP Conference Proceedings 1863, 150002 (2017);
View online: https://doi.org/10.1063/1.4992324
View Table of Contents: http://aip.scitation.org/toc/apc/1863/1
Published by the American Institute of Physics
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Utilization of the PCM Latent Heat for Energy Savings in
Buildings
Jan FoĜt1, a), Anton Trník1, b) and Zbyšek Pavlík1, c)
1Department
of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Technical University
in Prague, Thákurova 7, 166 29 Prague, Czech Republic
a)
Corresponding author: jan.fort.1@fsv.cvut.cz
b)
anton.trnik@fsv.cvut.cz
c)
pavlikz@fsv.cvut.cz
Abstract. Increase of the energy consumption for buildings operation creates a great challenge for sustainable
development issues. Thermal energy storage systems present promising way to achieve this goal. The latent heat storage
systems with high density of thermal storage via utilization of phase change materials (PCMs) enable to improve thermal
comfort of buildings and reduce daily temperature fluctuations of interior climate. The presented study is focused on the
evaluation of the effect of PCM admixture on thermal performance of a cement-lime plaster. On the basis of the
experimentally accessed properties of newly developed plasters, computational modeling is carried out in order to rate the
acquired thermal improvement. The calculated results show that incorporation of 24 mass% of paraffinic wax based PCM
decreased the energy demand of approx. 14.6%.
INTRODUCTION
Increasing energy consumption is significantly responsible for the depletion of the natural energy resources.
With the development of architecture, population growth, increased demand on the indoor thermal comfort,
enhanced building services etc., share of the energy consumed for buildings operation increases. According to the
International Energy Agency [1], buildings operation is responsible for 32% of the total commercial energy
consumption produced from fossil fuels. A significant amount of the consumed energy is used for air conditioning
and heating. In addition, the expected rise of exterior temperatures as a consequence of global warming will increase
demand for space cooling in the near future. Therefore, reduction of the consumed energy for buildings HVAC
(Heat, Ventilation and Air Conditioning) systems became an important issue. The European Directive 2010/31
instructs that all new buildings must consume nearly zero energy, which should ensure a drop in greenhouse gas
emissions [2]. The proposed strategy emphasizes increased requirements on the improvement of thermal insulation
systems and efficient cooling devices. Here, thermal energy storage systems can potentially provide reduction of the
energy used for cooling and heating. They are also able to store thermal energy and solve the problem of the
mismatch between demand and charge periods in case of utilization of renewable energy sources, such as solar
irradiation. Application of Phase Change Materials (PCMs) represents smart solution to accumulate heat energy
possessing latent heat storage with high storage density which is much more effective in comparison with sensible
heat storage systems.
Since the PCMs properties were described in detail and their incorporation into the various building elements
was researched in many studies [3-4], the direct contribution of PCM to the energy savings should be verified both
experimentally and numerically based on computational analysis. For example Soares et al. [5] reported on the use
of PCM with the melting temperature of about 10 °C for minimizing the energy usage. Authors concluded that the
obtained energy savings of about 13.5% can be even increased by the optimization of the charging process. A
performed numerical simulation revealed the contribution of PCM embedded in the floor panels for regulation of the
internal temperature. The PCM activity indicator was accessed for optimal amount of used PCM. Based on these
findings, Sajjadian et al. [6] performed simulations of a high performance detached house model with a near passive
house standard in London, where the impact of climate change effect is predicted to be significant. It was shown that
appropriate levels of PCM with a suitable incorporation mechanism in to the building construction has significant
advantages for residential buildings in terms of reducing total discomfort hours and cooling energy loads. Recently,
Stamatiadou et al. [7] presented computational assessment of a full-scale Mediterranean building incorporating
wallboards with phase change materials. In this study, a lightweight residential building in Greece was investigated,
International Conference of Numerical Analysis and Applied Mathematics (ICNAAM 2016)
AIP Conf. Proc. 1863, 150002-1–150002-4; doi: 10.1063/1.4992324
Published by AIP Publishing. 978-0-7354-1538-6/$30.00
150002-1
focusing on the summer comfort when wallboards with PCMs were installed in the external and internal walls. The
cooling needs were lowered by an average of 25.7%, compared to the respective no-PCM scenario.
In this study, the experimental material characterization is connected with the computational modeling in order
to evaluate the contribution of applied PCM admixture for moderation of interior climate using interior plaster.
EXPERIMENTAL
The plaster mix composition was based on incorporation of the powdered polymer microencapsulated paraffinic
wax Micronal 5040 produced by BASF (Germany) into the commercial dry plaster mix Baumit Manu 1 (Baumit).
The applied PCM was chosen because of its finesses, good thermal stability and already proven suitability for
cement-based matrix. The dry cement-lime plaster mix composed of lime, cement, sand and additives was used as a
reference material. The fine spherical particles of Micronal with the diameter about 50 Pm had negative influence on
the workability of the fresh plaster mixture. In order to achieve the same consistency, the amount of batch water was
increased, whereas flow test was employed to control the mix consistency. The composition of the examined mixes
is given in Table 1.
Material
TABLE 1. Composition of the plaster mixes
Dry plaster mixture [kg] Water [kg]
PCM [kg]
Reference plaster
6.3
1.50
-
Mic 8%
6.3
1.95
0.5
Mic 16%
6.3
2.15
1.0
Mic 24%
6.3
2.35
1.5
The casted, matured and dried samples were subjected to experimental tests. Bulk density was determined from
the sample mass and volume. Matrix density was assessed by helium pycnometry using Pycnomatic ATC device
(Thermo Scientific). On the basis of bulk density and matrix density measurements, total open porosity was
calculated [8]. The relative expanded uncertainty of applied testing method was 5%. The hand-held device ISOMET
2114 (Applied Precision) working on a dynamic measurement principle was used for determination of thermal
conductivity. The accuracy of thermal conductivity measurement was 5% of reading +0.001 W/mK. Phase change
temperature and specific heat capacity were obtained by DSC apparatus DSC 822e (Mettler Toledo) [9]. The
following temperature regime was applied: 5 minutes of the isothermal regime (40 °C), cooling of 10 °C/min from
the temperature 40 °C to the temperature – 20 °C, 5 minutes of the isothermal regime (-20 °C), heating of 10 °C/min
from the temperature -20 °C to the temperature 40 °C, 5 minutes of isothermal regime (40 °C).
COMPUTATIONAL
The experimentally measured thermal properties were used as input data for computational analysis of thermal
performance of studied plaster. Here, the climatic loading was simulated in order to evaluate plasters behavior.
Within the computer simulations, the particular studied plasters were applied in a thickness of 20 mm on the interior
surface of a structural wall built from autoclaved aerated concrete P4 – 500. Since material parameters of
autoclaved aerated concrete were not measured within the presented work, they were taken from [10].
The computational analysis was done using computer code SHeM-comp developed at Department of Materials
Engineering and Chemistry, FCE CTU in Prague. The code is a specialized computer simulation tool for the servicelife- and hygrothermal material behaviuor assessment of building envelopes. It is designed as a desktop solution
with connectable material and climatic databases. The solution of partial differential equations created by the
implementation of the formulated heat, moisture, and salt mass balance equations is accomplished within the batch
solver SIFEL [11] using the finite element method. In performed simulations, only heat transport and storage was
studied and the influence of water vapor transport was neglected. During the computational analysis, the described
wall structure was loaded from the exterior side by the reference year climatic data obtained for Šerák, located in the
Czech Republic [12]. From the interior side, the target temperatures of 18 °C (night - 8 hours) and 26 °C during the
day (12 hours) were set. Two hours of linear heating from the 18 °C to 26 °C and linear cooling from 26 °C to 18 °C
were applied.
150002-2
RESULTS AND DISCUSSION
Basic physical properties are together with the thermal conductivity values shown in Table 2. The low powder
density of pure Micronal admixture significantly decreased both the bulk and matrix densities of the developed
plasters. Contrary to that, the total open porosity increased with the higher PCM content. Because of the low thermal
conductivity of Micronal (0.079 W/mK), the thermal conductivities of PCM modified plasters were systematically
lower compared to that of reference plaster.
Material
TABLE 2. Basic physical properties of the studied plasters
Bulk density Matrix density Total open porosity Thermal conductivity
[kg/m3]
[kg/m3]
[%]
[W/mK]
Reference plaster
1 572
2 416
34.9
0.54
Mic 8%
1 346
2 169
37.9
0.39
Mic 16%
1 159
1 882
38.4
0.24
Mic 24%
1 041
1 679
38.1
0.19
The phase change temperature intervals and corresponding specific enthalpies are given in Table 3. Here, no
significant influence of the amount of the incorporated PCM on the phase change temperatures was observed. On
the other hand, the specific enthalpy decreased proportionally to the amount of PCM used.
Material
Micronal
5040
Mic 8%
Mic 16%
Mic 24%
TABLE 3. Phase change properties of studied plasters
Onset phase change temperature [°C]
Specific enthalpy [J/kg]
Heating
Cooling
Heating
Cooling
19.4
22.7
0.0968
0.0998
20.0
22.2
23.3
23.2
0.0045
0.0073
0.0046
0.0078
21.1
24.2
0.0131
0.0134
The accessed curves of the specific heat capacities were applied for the computational modeling in order to
examine the relation between the amount of PCM used and potential energy savings within a year simulation. The
thermal performance of the tested wall is apparent from Figure 1. Here, day 0 corresponds to 1st February.
FIGURE 1. Heat fluxes during daily temperature fluctuations
150002-3
The simulated heat flux data clearly shows the positive effect of PCM on the moderation of temperature
fluctuations during the day and night. The clear relation between the amount of PCM used and heat flux fluctuation
is evident. The highest temperature variations exhibited reference plaster. On the other hand, for plaster with
incorporated 24 mass% of PCM admixture we obtained decrease in simulated heat fluxes of about 40%. The
calculated annual energy savings based on the performed computational simulation are presented in Table 4. The
potential energy savings are expressed per square meter of the wall area provided with particular studied plaster. A
significant benefit of PCM use on thermal performance of the studied wall was observed. The energy savings
reached up ~14.6% what can be considered as highly promising finding for PCM modified plaster application in
practice.
TABLE 4. Annual energy savings
Material
Annual energy consumption [MJ/m2]
Potential energy savings [%]
Reference plaster
Mic 8%
Mic 16%
6.0
5.8
5.3
2.7
10.1
Mic 24%
5.1
14.6
CONCLUSIONS
The performed study revealed a positive effect of researched PCM admixture on thermal performance of newly
developed cement-lime plasters. The obtained results clearly proved influence of the incorporated PCM on the heat
exchange through the modeled wall characterized by computed heat fluxes. With increasing content of PCM in
plaster composition, the heat flux fluctuations decrease what documents improvement of studied wall thermal
performance. The estimated annual energy savings obtained from computational simulation pointed to the
significant reduction of energy consumption necessary for compensation of interior temperature changes in respect
to climatic loading of the modeled wall. A further research based on computational modeling of the whole room or
simple house represent the next step in evaluation of PCM impact on thermal stability of buildings interior climate.
ACKNOWLEDGMENT
This research has been supported by the Czech Science Foundation, under project No 14-22909S, and by the
Ministry of Education, Youth and Sport of the Czech Republic, under project No SGS14/174/OHK1/3T/11.
REFERENCES
1. Petroleum B, Statistical Review of World Energy, 2010.
2. Directive 2010/31/EU of the European parliament and of the council of 19 May 2010 on the energy performance of
buildings.
3. M. Kheradmand, M. Azenha, J.L.B. de Aquiar, K.L. Krakowiak, Energy Buildings 84, 526-536 (2014).
4. Z. Pavlík, A. Trník, M. Keppert, M. Pavlíková, J. Žumár, R. ýerný, Int. J. Thermophys. 35, 767-782 (2014).
5. N. Soares, J. J Costa, A.R. Gaspar, P. Santos, Energy Buildings 59, 82-103 (2013).
6. S.M. Sajjadian, J. Lewis, S. Sharles, Energy Buildings 93, 83-89 (2015).
7. M. E. Stamatiadou, D. I. Katsourinis, M. A. Founti, Indoor Built. Environ., 1-15, doi: 10.1177/1420326X16645384 (2016).
8. Z. Pavlík, M. Keppert, M. Pavlíková, J. Žumár, J. FoĜt, R. ýerný, Cement Wapno Beton 19, 67-80 (2014).
9. Z. Pavlík, A. Trník, J. Ondruška, M. Keppert, M. Pavlíková, P. Volfová, V. Kaulich, R. ýerný, Int. J. Thermophys. 34, 851864 (2013).
10. M. Jerman, M. Keppert, J. Výborný and R. ýerný, Constr. Build. Mater. 41(1), 352-359 (2013).
11. K. Ćurana, L. Fiala, J. MadČra and R. ýerný, “A material database for computational models of heat, moisture, salt and
momentum transport: Construction of the code as an input module and example of application”, AIP Conf. Proc. 1558, 976979 (2013).
12. J. Koþí, J. MadČra, R. ýerný, Energy 83, 749-755 (2015).
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