Materials used as PCM in thermal energy storage in buildings: A review

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Abstract

In recent years the use of thermal energy storage with phase change materials has become a topic with a lot of interest within the research community, but also within architects and engineers. Many publications have appeared, and several books, but the information is disseminated and not very much organised. This paper shows a review of the latest publications on the use of phase change materials (PCM) in buildings. The paper compiles information about the requirements of the use of this technology, classification of materials, materials available and problems and possible solutions on the application of such materials in buildings.

Introduction

The use of storage in a building can smooth temperature fluctuation. Thermal energy storage in buildings can be implemented by sensible heat (increasing and decreasing the temperature of the building envelopes, for example), or by latent heat (with the inclusion of phase change materials – PCM – to increase thermal inertia). The main advantage of latent heat storage is the high storage density in small temperature intervals.

Latent storage can be used for heating and for cooling of buildings, and it can be incorporated as a passive system or also in active systems.

In recent years several reviews have appeared on this topic. Four books on the topic have appeared recently, one authored by Dinçer and Rosen in 2002 [1], a compilation edited by Hadorn in 2005 [2], another by Paksoy in 2007 [3], and another book authored by Mehling and Cabeza in 2008 [4].

The book written by Dinçer and Rosen [1] deals with thermal energy storage (TES) in general, being phase change materials (PCM) just a part of it, and not focused on the application in buildings. In the two compilations by Hadorn [2] and Paksoy [3], different TES technologies are studied, and PCM in buildings have a part on them [5], [6], [7]. Finally, the book by Mehling and Cabeza [4] gives a deep study of the PCM technology.

Several reviews have been published from 2003 to 2009 [8], [9], [10], [11], [12], [13], [14], [15]. The first review was published on 2003 by Zalba et al. [8]. In this work, a review has been carried out of the history of thermal energy storage with solid–liquid phase change focusing in three aspects: materials, heat transfer, and applications. Materials used by researchers as potential PCM were described, together with their thermophysical properties. Commercial PCM were also listed. Different methods of thermal properties characterization can be found. Problems in long term stability of the materials and their encapsulation are discussed. Heat transfer is considered mainly from a theoretical point of view, by using different simulation techniques. Many applications of PCM can be found, divided in ice storage, building applications, conservation and transportation of temperature sensitive materials, water tanks vs. PCM tanks, and others.

In 2004, the research group leaded by M. Farid published two reviews about PCM, one of them focusing on building applications. The first paper [9] reviews previous work on latent heat storage and provides an insight to recent efforts to develop new classes of phase change materials for use in energy storage. Three aspects have been the focus of this review: PCM, encapsulation and applications. There are large numbers of phase change materials that melt and solidify at a wide range of temperatures, making them attractive in several applications. The main advantages of PCM encapsulation are providing large heat transfer area, reduction of the PCM reactivity towards the outside environment and controlling the changes in volume of the storage materials as phase change occurs. Different applications in which the phase change method of heat storage can be applied are also reviewed in this paper.

The other paper [10] summarizes the investigation and analysis of thermal energy storage systems incorporating PCM for use in building applications. Researches on thermal storage in which the PCM is encapsulated in concrete, gypsum wallboard, ceiling and floor have been ongoing for some time and are discussed. The problems associated with the application of PCM with regard to the selection of materials and the methods used to contain them are also discussed.

In 2007 Tyagi and Buddhi [11] published a comprehensive review of various possible methods for heating and cooling in buildings. The thermal performance of various types of systems like PCM trombe wall, PCM wallboards, PCM shutters, PCM building blocks, air-based heating systems, floor heating, ceiling boards, etc., is presented in this paper. It claims that all systems have good potential for heating and cooling in building through phase change materials and also very beneficial to reduce the energy demand of the buildings.

Also in 2007 a new review appeared, authored by Kenisarin and Mahkamov [12]. This paper looks at the current state of research in this particular field, with the main focus being on the assessment of the thermal properties of various PCM, methods of heat transfer enhancement and design configurations of heat storage facilities to be used as a part of solar passive and active space heating systems, greenhouses and solar cooking.

Finally, in 2009 three new reviews have appeared, where materials for PCM application in buildings are discussed. The first one is from Sharma et al. [13], and it summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCM for use in different applications. This paper presents the current research in this particular field, being the main focus the assessment of thermal properties of various PCM. The heat storage applications presented are as a part of solar water-heating systems, solar air heating systems, solar cooking, solar green house, space heating and cooling application for buildings, off-peak electricity storage systems, and waste heat recovery systems. The paper also presents the melt fraction studies of the few identified PCM used in various applications for storage systems with different heat exchanger container materials.

Zhu et al. [14] did an overview of the previous research work on dynamic characteristics and energy performance of buildings due to the integration of PCM. Both active and passive systems are reviewed. Since the particular interest in using PCM for free cooling and peak load shifting, the specific research efforts on both subjects are reviewed separately. A few useful conclusive remarks and recommendations for future work are presented.

Wang et al. [15] present the concept of ideal energy-saving building envelope, which is used to guide the building envelope material selection and thermal performance design. This paper reviews some available researches on phase change building material and phase change energy storage building envelope. At last, this paper presents some current problems that need further research.

Here only the materials used, proposed and studied as potential phase change materials will be looked at. Also, only the applications for buildings should be considered in this paper, therefore the phase change temperature should be restricted to around 15–70 °C.

Section snippets

Classification

In 1983 Abhat [16] gave a useful classification of the substances used for thermal energy storage (Fig. 1). Another classification was given by Mehling and Cabeza in 1997 [6] (Fig. 2).

Several authors [4], [8], [15] have presented a comparison of the advantages and disadvantages of organic and inorganic materials, as shown in Table 1, Table 2.

Materials

Many substances have been studied as potential PCM, but only a few of them are commercialized as so. The books and reviews cited above [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15] have presented different tables with substances, eutectics and mixtures (inorganic, organic and fatty acids), that have been studied by different researchers for their potential use as PCM (Table 3, Table 4, Table 5, Table 6).

Materials to be used for phase change thermal energy

Thermophysical properties

From the information compiled [4], [8], the main characteristics required of phase change materials are those indicated in Table 10.

According to [1], [4], [6], [11], [13], the PCM to be used in the design of thermal storage system should have desirable thermophysical, kinetic and chemical properties:

  • Thermophysical properties

    • Melting temperature in the desired operating temperature range: to assure storage and extraction of heat in an application with a fixed temperature range.

    • High latent heat of

Long term stability

The most important criteria that have limited the use of latent heat stores are the useful life of PCM–container systems and the number of cycles they can withstand without any degradation in their properties. The long term stability of the storage materials is due to two factors: poor stability of the materials properties and/or corrosion between the PCM and the container [1], [4], [7], [8], [9].

Macro and microencapsulated PCM

In almost all cases a PCM has to be encapsulated for technical use, as otherwise the liquid phase would be able to flow away from the location where it is applied. There are two principal means of encapsulation [10]. The first is microencapsulation, whereby small, spherical or rod-shaped particles are enclosed in a thin, high molecular weight polymeric film. The coated particles can then be incorporated in any matrix that is compatible with the encapsulating film. It follows that the film must

Fire retardation of PCM-treated construction materials

In recent years, stringent safety codes and flammability requirements have been imposed on building materials to protect these buildings from fire hazards. The following are some approaches that have been investigated and applied successfully in laboratory tests to fire retard PCM imbibed plasterboard [10]:

  • Adding alternate non-flammable surface to the plasterboard (e.g., aluminum foil and rigid polyvinyl chloride film).

  • Sequential treatment of plasterboard, first in PCM and then in an insoluble

Heat transfer enhancement

Heat transfer enhancement is of most importance in some application such as water tanks, but much less important when the PCM is integrated in building component for the envelope (gypsum boards, insulation materials, concrete, etc.).

There are several methods to enhance the heat transfer in a latent heat thermal store [4], [6], [8], [9], [12]. The use of finned tubes with different configurations has been proposed by various researchers (Fig. 22).

Several other heat transfer enhancement

Conclusions

The use of phase change materials (PCM) for thermal energy storage in buildings has been studied by many researchers, therefore, many products are available in the literature and some in the market. Technical problems found in the past in the use of such materials have been studied and different solutions have been presented, giving the user the opportunity to be sure that the systems designed would be successful. Nevertheless, research is still needed to find new more efficient and cheap

Acknowledgements

The work was partially funded by the European Union (COST Action COST TU0802) and the Spanish Government (project ENE2008-06687-C02-01/CON). The authors would like to thank the Catalan Government for the quality accreditation given to their research groups (2009 SGR 534 and 2009 SGR 645).

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