Elsevier

Construction and Building Materials

Volume 122, 30 September 2016, Pages 637-648
Construction and Building Materials

Thermal performance and cost analysis of mortars made with PCM and different binders

https://doi.org/10.1016/j.conbuildmat.2016.06.114Get rights and content

Highlights

  • PCM mortars based in different binders were used to study the thermal behavior.

  • The thermal behavior and cost analyses were evaluated based in Portuguese climate.

  • The PCM mortars reveal higher thermal regulation and lower energy needs.

  • The PCM mortars showed a decrease of the cost related to the energy consumption.

Abstract

The high energetic consumption is one of the biggest concerns of modern society. The incorporation of phase change materials (PCM) in construction materials allows regulates the temperature inside the buildings. The main objective of this study was the characterization of the thermal performance of PCM mortars based in different binders. It was possible to observe that the incorporation of PCM in mortars leads to a decrease of the maximum temperatures, increase of the minimum temperatures, significant lag time delay, reduction of the heating and cooling needs, and consequent decrease of the cost of HVAC systems operation, for all tested seasons.

Introduction

The energy is an essential factor for economic and social development, and for improvement of the life quality in all countries. Energy sources can be non-renewable or renewable. Non-renewable energy sources possess the possibility to deplete over time, such as petroleum, coal and natural gas. Renewable energy sources represent inexhaustible resources such as biomass, hydro, wind, geothermal and solar.

The economic growth of the countries in the last years has caused rapid increase in energy consumption, which affects the population and the environment [1]. The energy efficiency of buildings is now one of the main objectives of regional, national and international energy management [2]. The buildings are one of the leading sectors in energy consumption at developed countries. In the European Union the buildings are responsible for 40% of energy consumption and 40% of carbon dioxide (CO2) emission to the atmosphere. Currently, the European Union has the 2020 energy strategy that proposes the reduction of 20% in primary energy consumption and CO2 emissions and the increase of 20% in energy consumption coming from renewable sources [3].

In a sustainable approach, buildings should be designed to ensure the thermal comfort of the occupants throughout the year, with minimum auxiliary energy for heating and cooling. In non-sustainable approaches, buildings are increasingly dependent on heating and cooling systems to ensure thermal comfort inside, resulting in the increase in energy consumption and greenhouse gases emissions. Consequently, there is also an increase in building utilization costs, caused by the impact of HVAC systems operation [2], [4].

Every year the energy powered by the sun that reaches the entire land surface is about 10,000 times higher than the actual energy consumption per year worldwide [5]. Taking into account that the European building sector is responsible for high energetic consumptions, it is important to find a way to take advantage of the solar energy. Thus, it becomes imperative to obtain a constructive solution that will minimize these consumptions, improving the energetic efficiency of buildings without damaging the environment. In order to reach a solution for this problem, it is also important to define and develop strategies to displace the consumption from peaks or hours of greatest demand, to off-peak periods.

Mortars with Phase Change Materials (PCM) incorporation for interior coating can be seen as a key for solving or at minimizing, the massive energetic consumption related to buildings. These materials have the ability to reduce temperature variations due to its capability to alter its own state depending on the environmental temperature, absorbing and releasing energy into the environment. Thus, mortars doped with PCM bring social, economic and environmental benefits, demonstrating a significant contribution to a more sustainable construction. The social benefits are directly connected with the increase in thermal comfort. The environmental aspect concerns to the reduction of fossil fuels depletion related with the decrease on air conditioning equipment usage. The economic benefits are related with the reduction of energy consumption and lag time for lower demand hours [6].

Materials with incorporation of PCM can be applied in floors, walls or ceilings, as well as being an integrating part of the most complex energetic system [6]. However, the application of PCM in walls is the preferential solution to explore the potential of these materials, due to the large areas in buildings.

The PCM can be incorporated in construction materials by different methods: direct incorporation, immersion, encapsulation, shape-stabilization and form stable composite PCMs [7]. The direct incorporation is the simplest method in which PCM is directly mixed with the construction materials. In the immersion method, the construction products are dipped into the liquid PCM, absorbing the PCM by capillarity. However, the material can interfere with the hydration products and affect the mechanical and durability properties of the doped construction materials [8]. The shape-stabilized PCM can be prepared by integrating the PCM into the supporting material. The shape-stabilized PCM are mainly classified as composite PCM and are usually fabricated by embedding PCM into shape stabilization supports, such as high density polyethylene, styrene, butadiene, polymethacrylic acid, polystyrene resin, etc. [9]. There are two types of encapsulation: macroencapsulation and microencapsulation. The macroencapsulation is based in the introduction of PCM into tubes, panels or other large containers. It is usually done in containers with more than 1 cm diameter and presents better compatibility with the material, improving the handling in the construction [10]. The microencapsulation consists in covering PCM particles with a material, usually a polymer, commonly known as capsule, with dimensions between 1 μm and 60 μm [10], [11]. The main advantages of this technique are related with the capability to prevent PCM leakage during phase transition, increasing its chances of incorporation into various construction materials, providing high heat transfer rate through its larger surface area and more facility to handle [7].

Some studies were published about the use of construction materials with incorporation of PCM microcapsules. Initially, the incorporation of microencapsulated PCM in gypsum plasterboard was the subject of several studies performed due to its low cost and various application possibilities [12], [13], [14]. Darkwa et al. [13] investigated the behavior of two solutions with incorporation of PCM into gypsum plasterboard. On one side, plasterboard with 12 mm thickness, all impregnated with PCM, was used, to compare with another situation in which they applied single plasterboard with 10 mm thickness, covered with 2 mm of PCM laminate. The PCM amount incorporated in both cases was the same. The results showed that the PCM laminate use is more efficient, since it contributed to an increase in the minimum temperature. Other solutions were also developed such as alveolar PVC panels, blocks and bricks [15], [19]. Cabeza et al. monitored the behavior of concrete test cells, with and without addition of 5% of PCM microcapsules. The PCM was incorporated into the concrete used on the roof, and south and west walls. During the summer and without ventilation a decrease in the maximum temperature and a time lag of 2 h were recorded [10].

The mortars with incorporation of PCM has been a target of study and interest for the scientific community. However, the characterization and comparison of the thermal performance of mortars based on different binders is one of the main knowledge gaps. Thus, the main objective of this work was the study of the thermal behavior and cost analysis of mortars with incorporation of phase change materials exposed to current temperatures of Portugal. Mortars made with different binders and PCM contents were developed. Microscope observations, thermal tests and cost analyses were performed in eight different compositions based in aerial lime, hydraulic lime, gypsum and cement. For each binder, mortars without PCM and with incorporation of 40% of PCM microcapsules, were tested.

Section snippets

Materials

The influence of adding PCM in interior coating mortars was studied. The materials selection took into account previous works [16], [17], [18]. Mortars were developed based on the following binders: aerial lime, hydraulic lime, gypsum and cement. The used aerial lime had a purity of 90% and density of 2450 kg/m3. The gypsum corresponds to a traditional one, with high fineness and density of 2740 kg/m3. The hydraulic lime was a natural one (NHL5), with density of 2550 kg/m3. CEM II B-L 32.5N cement

Workability

The workability tests showed that the incorporation of 40% of PCM leads to an increase in water content higher than 8% for all tested binders with the exception of aerial lime mortars (Table 1). The decrease of water content in aerial lime mortar can be explained by the presence of a higher superplasticizer content, related with the presence of higher binder dosage to obtain an adequate mechanical classification (CSII) of all used mortars [22]. On the other hand, the increase in water content

Cost analysis

Currently, there is a huge concern with the high energy consumption, verified in the residential sector associated to heating and cooling needs of buildings. The energy used for heating and cooling buildings represents 30% of the total energy consumption in the different countries of the European Union, or about 75% of the total energy consumption in buildings [26]. On the other hand, it is expected that the PCM use has a beneficial impact on energy costs, since it allows to reduce the

Conclusion

This study allowed the comparison of the thermal performance of mortars prepared using PCM microcapsules and different binders. The workability, flexural strength, compressive strength, microstructure and costs of the developed mortars were also evaluated.

The incorporation of PCM caused an increase in the amount of water added to the mortars in order to achieve a suitable workability. This is related with the fineness of the PCM microcapsules. The evaluation of the mechanical strengths showed a

Acknowledgement

The authors acknowledge the Portuguese Foundation for Science and Technology (FCT) for the financial support of PhD scholarship SFRH/BD/95611/2013.

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