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Journal ArticleDOI

Experimental investigation of wallboard containing phase change material: Data for validation of numerical modeling

TL;DR: In this article, an experimental comparative study is described, using cubical test cells with and without PCM composite, concerning the air and wall temperatures, and the results are compared with a numerical modeling and show that hysteresis must be considered to predict correctly the heat transfer.
About: This article is published in Energy and Buildings.The article was published on 2009-05-01 and is currently open access. It has received 215 citations till now. The article focuses on the topics: Thermal energy storage & Heat transfer.

Summary (4 min read)

1 Introduction

  • Nowadays, thermal energy storage systems are essential for reducing dependency on fossil fuels and then contributing to a more efficient environmentally benign energy use [1].
  • As demand in thermal comfort of buildings rises increasingly, the energy consumption is correspondingly increasing.
  • As the temperature increases, the material changes phase from solid to liquid.
  • Even if these conditions are more realistic, all of the weather parameters are not known (or measured).
  • From a numerical point of view, having experiments with and without PCM is useful to verify the basic modeling.

2 Description of the test cells MICROBAT

  • Two identical test cells are used to investigate the effects of the PCM wallboards.
  • The design of the test cells is presented part 2.1.
  • The phase change material tested is described part 2.2.
  • The part 2.3 deals with the measurement systems and the probes, the experimental protocol is given part 2.4.

2.1 Design of the cells

  • Two identical test cells are used in the study.
  • Each test cell is a cubical enclosure with an internal dimension of 0.50m .
  • This face is called the active face because of its low thermal inertia and low thermal resistance.
  • It enhances the heat transfer between the exterior and the interior of MICROBAT.
  • The witness box has five normal faces whereas the PCM box contains three PCM faces which are the back face, the right face and the left face.

2.2 Phase change material tested

  • The product tested, ENERGAINr has been achieved by the Dupont de Nemours Society and is constituted of 60% of microencapsulated paraffin within a copolymer.
  • This rate corresponds to 3◦C/h which is an average heating rate in a light weight building during summer season and when solar gains are maximum.
  • The freezing curve (cooling from 34◦C to 1◦C) and the melting curve (heating from 1◦C to 34◦C), also known as Two curves are presented.
  • This curve is typical of the hysteresis loop.

2.3 Instrumentation and measurements

  • All of the temperatures are measured using Pt100 sensors with a calculated resolution of ±0.25◦C.
  • In each test cell the set of probes is: the internal face temperature, measured at the center of the face, with a probe included in the wall surface, the active face external temperature, measured at the center of the face, the air temperature, measured at the center of the cubical air volume.
  • The time step chosen between two series of measurement is 2mn and the duration of each test is about three days.

2.4 Experimental protocol

  • The two MICROBAT test cells are placed into a climatic chamber.
  • The climatic chamber temperature can vary between −10◦C and 40◦C as a function of time.
  • The active face allows to impose the same external temperature for each test cell.
  • Two types of external temperature evolutions are investigated: a temperature step, heating and cooling, a sinusoidal temperature evolution.
  • Concerning the heating/cooling temperature step, three cases are tested depending on the slope (SL) i.e. the time needed to reach the constant temperature value: 1hour, 2hours or 3hours.

3 Temperature step

  • The first experiment concerns the temperature steps (heating and cooling) and the present part deals with the results of the cases tested.
  • The part 3.1 deals with general considerations concerning the measurements.
  • The air temperatures is analyzed part 3.2 and the internal face temperature part 3.3.

3.1 General considerations

  • The box without PCM is strongly insulated but with a relatively low thermal inertia.
  • The figure 7 shows the measured temperatures for the internal faces and air in the test cell without PCM for the case SL = 1hour.
  • Except for the active face, the other faces temperatures and the air temperature are nearly identical.
  • The temperature gradient in the box does not affect the heat transfer, and particularly the convection heat transfer.
  • This conclusion is valid for all the cases tested and then only air temperature is presented in the following paragraphs of the article.

3.2.1 Heating step

  • The air temperature measured for the three kinds of heating steps and for the two test cells is presented in figure 8.
  • The air temperature for the box without PCM is close to the exterior temperature with a little time lag due to the low thermal inertia of the box.
  • The air temperature evolution of the witness box is nearly exponential.
  • The table 3 summarizes the τ values for the heating step cases.

3.2.2 Cooling step

  • The air temperature measured for the three kinds of cooling steps and for the two test cells is presented in figure 9.
  • This flat part of the curve lasts about 1h.
  • The PCM composite is composed of microencapsulated paraffin spheres included in a copolymer matrix.
  • As the solidification proceeds, the melt volume decreases with a simultaneous decrease in the magnitude of natural convection within the melt and the process is therefore much longer [14].

3.3 Test cell with PCM: temperature evolution

  • The phase change material included in the wallboards stores/releases energy transferred from the air volume mainly by convection.
  • Then, the wall surfaces temperatures are an important feature in the phase change phenomenon.
  • The figures 10 and 11 present the internal faces temperature , for the cell with PCM, and for the heating and cooling steps.
  • For all the cases tested, the three PCM walls have the same surface temperature.
  • For all of the cases tested, the temperature difference between the six faces of the cell never exceeds 5◦C.

3.4 Discussion

  • Of course, the presence of PCM allows to delay the box air temperature increase or decrease (as long as the temperature varies within the phase change range).
  • The analysis of the time lag defined paragraph 3.2.1 shows that the more the thermal excitation is rapid, the more the PCM is efficient.
  • In buildings, rapid thermal excitation can be solar spot or internal load.
  • For the PCM used in wallboards, hysteresis exists and has clearly been exhibited in paragraph 2.2.
  • This phenomenon has been few studied in literature and never been taken into account in numerical modeling as well as in experimental analysis.

4 External sinusoidal temperature evolution

  • The response of the MICROBAT to an external temperature step allows to characterize the time lag due to PCM wallboards.
  • In order to characterize the phase difference and the decrement factor due to PCM, an external sinusoidal temperature evolution is used, case which is closer to the real building configuration.
  • The phase difference ζ is defined as the time difference between outdoor temperature maximum and indoor temperature maximum.
  • The decrement factor f is defined as the ratio between indoor temperature amplitude and outdoor temperature amplitude.
  • For the walls with PCM, the temperature curve has two breaks of slope: one at about 19◦C and one at about 22◦C.

5 Numerical modeling

  • In the previous section, experimental data are described so that in the present section numerical modeling can be held.
  • Then, the numerical results are presented in paragraph 5.2.
  • The paragraph 5.3 is a discussion concerning the numerical modeling.

5.1 Presentation of the numerical modeling

  • In order to solve numerically the problem, a finite-difference method is used: the continuous information contained in the exact solution of the differential equation are replaced by discrete temperature values.
  • Only the longwave radiation exchanges are considered in the present modeling.
  • The internal exchanges occur between the internal surfaces of the walls.
  • The software MATLAB is used for all the simulations.

5.2 Numerical results

  • The experimental data are compared with the numerical results obtained from their modeling.
  • The figure 14 shows the comparisons between experiments and modeling for the heating step.
  • The figure (d) shows that the freezing specific heat curve is not adapted for the heating step modeling.
  • The modelings (a), (b) and (c) use the equivalent specific heat obtained with the data of the figure 4 freezing curve.
  • For the three cases, the numerical data are in quite good agreement with experiment, excepted for the flat part of the curve around 19◦C.

5.3 Discussion concerning the numerical modeling

  • The main problem of the PCM modeling is the way to introduce the phase change.
  • The equivalent specific heat has been tested.
  • Unfortunately, the paraffin used is not an eutectic mixture, so hysteresis occurs during the phase change.
  • When simulating heating step or cooling step separately, the numerical data are in good agreement with experiments only if the corresponding specific heat curve is used, e.g. melting curve and cooling curve.
  • The hysteresis phenomenon must the be taken into account correctly in order to predict the PCM composite thermal behavior.

6 Conclusions and outlook

  • The objective of this article is first, providing reliable experimental data that can be used for the validation of numerical modeling and then, studying some features related to the use of phase change material wallboard.
  • The external temperature is the thermal excitation; a heating/cooling step and a sinusoidal evolution are tested.
  • The effects of PCM wallboard are to cause time lag between indoor and outdoor temperature evolutions and to reduce the external temperature amplitude in the cell.
  • The effect of hysteresis phenomenon has been clearly exhibited with the experimental data: the melting process arises at a temperature higher than for the solidification process.
  • Further investigations are needed to have a better numerical description of this special phase change feature.

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Citations
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Journal ArticleDOI
TL;DR: In this article, the authors summarized previous works on latent thermal energy storage in building applications, covering PCMs, the impregnation methods, current building applications and their thermal performance analyses, as well as numerical simulation of buildings with PCMs.

1,569 citations


Cites background or methods from "Experimental investigation of wallb..."

  • ...[60,61] Copolymer Paraffin wax 60% [44] CSM panel with brick RT27; SP 25 A 8 ---[62] Gypsum board MPCM 28D 23%, 30% 40% [63] Aluminium Paraffin A22; Paraffin A26 ---[64] Honeycomb panel Mixture of Tetradecane and Octadecane ---[65] Concrete (Regular block; Autoclaved block) Butyl stearate (Autoclaved block) Unicere 55 (Autoclaved block) Unicere 55 (Regular block) 5....

    [...]

  • ...Kuznik and Virgone [61] also tested two identical test cells under two kinds of external temperature evolutions, heating and cooling steps with various slopes and sinusoidal temperature evolution with 24h period....

    [...]

Journal ArticleDOI
TL;DR: In this article, a comprehensive review of the integration of phase change materials in building walls is presented. But, even if the integrated phase change material have a good potential for reducing energy demand, further investigations are needed to really assess their use.
Abstract: The present paper is the first comprehensive review of the integration of phase change materials in building walls. Many considerations are discussed in this paper including physical considerations about building envelope and phase change material, phase change material integration and thermophysical property measurements and various experimental and numerical studies concerning the integration. Even if the integrated phase change material have a good potential for reducing energy demand, further investigations are needed to really assess their use.

856 citations

Journal ArticleDOI
TL;DR: In this paper, the authors explore how and where phase change materials (PCMs) are used in passive latent heat thermal energy storage (LHTES) systems, and present an overview of how these construction solutions are related to building's energy performance.

817 citations

Journal ArticleDOI
TL;DR: In this article, an extensive review on the incorporation of PCM into construction materials and elements by direct incorporation, immersion, encapsulation, shape-stabilization and form-stable composite PCMs is presented.
Abstract: The building sector is the dominant energy consumer with a total 30% share of the overall energy consumption and accounts for one-third of the greenhouse gas emissions around the world. Moreover, in recent years the energy demands for buildings have increased very rapidly due to increase in the growth rate of population and improvement in living standards of people. Furthermore, fossil fuels will continue to dominate the world's primary energy by 2030. Thus, the increase in energy demand, shortage of fossil fuels and environmental concerns has provided impetus to the development of sustainable building and renewable energy resources. Thermal energy storage is an efficient method for applying to building envelopes to improve the energy efficiency of buildings. This, in turn, reduces the environmental impact related to energy usage. The combination of construction materials and PCM is an efficient way to increase the thermal energy storage capacity of construction elements. Therefore, an extensive review on the incorporation of PCM into construction materials and elements by direct incorporation, immersion, encapsulation, shape-stabilization and form-stable composite PCMs is presented. For the first time, the differentiation between shape-stabilized and form-stable composite PCM has been made. Moreover, various construction materials such as diatomite, expanded perlite and graphite, etc. which are used as supports for form-stable composite PCM along with their worldwide availability are extensively discussed. One of the main aims of this review paper is to focus on the test methods which are used to determine the chemical compatibility, thermal properties, thermal stability and thermal conductivity of the PCM. Hence, the details related to calibration, sample preparation, test cell and analysis of test results are comprehensively covered. Finally, because of the renewed interest in integration of PCM in wallboards and concrete, an up-to-date review with focus on PCM enhanced wallboard and concrete for building applications is added.

516 citations

Journal ArticleDOI
TL;DR: In this article, a review of phase change material (PCM) technologies tailored for building applications is presented with respect to technological potential to improve indoor environment, increase thermal inertia and decrease energy use for building operation.

367 citations

References
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Journal ArticleDOI
TL;DR: In this paper, composite PCM drywall samples (i.e., randomly-mixed and laminated) have been evaluated in a model passive solar building and the results showed that the laminated PCM sample with a narrow phase change zone was capable of increasing the minimum room temperature by about 17% more than the randomly mixed type.

97 citations

Journal ArticleDOI
TL;DR: In this paper, the Nusselt number in the phase change material (PCM) during melting is one order of magnitude higher than during solidification, which indicates the consumption of a large part of the HTF energy in heating the molten wax rather than melting of the solid wax.
Abstract: This study concerns experimental evaluation of heat transfer during energy storage and release for the phase change of paraffin wax in spherical shells. Measurements are made using air as the heat transfer fluid (HTF), copper spheres with diameters of 2, 3, 4, and 6 cm. A detailed temperature field is obtained within the spheres using 10 thermocouple wires. Values of the air velocity and temperature used in the experiments are 4-10 m/s and 60-90°C, respectively. Measured times for melting and solidification varied over a range of 5-15 and 2-5 minutes, respectively. Calculations show that the Nusselt number in the phase change material (PCM) during melting is one order of magnitude higher than during solidification. Results indicate that the Nusselt number for melting has a strong dependence on the sphere diameter, lower dependence on the air temperature, and a negligible dependence on the air velocity. Variations in the Fourier number for melting and solidification show similar trends. An increase in the Nusselt number for a larger sphere diameter is attributed to increase in natural convection cells in the PCM inside the spheres. The larger volume allows for the free motion for the descent and rise of cooler and hotter molten wax. During the solidification process, the solid wax is evenly formed through the sphere, starting from the outer surface and moving inward. As the solidification proceeds, the melt volume decreases with a simultaneous decrease in the magnitude of natural convection within the melt. The higher values of Fourier number for melting indicate the consumption of a large part of the HTF energy in heating the molten wax rather than melting of the solid wax.

93 citations

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Q1. What have the authors contributed in "Experimental investigation of wallboard containing phase change material: data for validation of numerical modeling" ?

In this paper, an experimental comparative study is described, using cubical test cells with and without PCM composite.