Concrete is among the oldest construction materials. With the rapid expansion of cities and industries in the modern era, energy demand has increased manifold. Governments all over the world are resorting to alternative and safe energy production and storage solutions.
Image Credit: wrangler/Shutterstock.com
A Brief Overview
Thermal Energy Storage (TES) materials are capable of storing and releasing thermal energy. In the battle against global warming, TES materials are a key component, and concrete, the most commonly utilized construction material, is a popular choice.
Concrete generally is made up of cement, water, sand, and gravel. However, if any other substances are added to the mixture, it leads to a variation in thermal energy storage properties.
Ordinary Portland Cement (OPC) is frequently utilized in concrete, but its restricted specific heat capacity is a major limitation in its applications as a thermal energy storage material. Fly ash, a byproduct of coal combustion can enhance the thermal storage attributes of concrete. Studies have indicated that fly ash concrete exhibits superior thermal conductivity and heat storage capacity compared to conventional OPC concrete.
High-performance concrete (HPC) is an optimized type with advanced strength and durability. HPC has also demonstrated enhanced thermal properties in addition to mechanical characteristics, making it a potential choice for recent advancements in thermal energy storage applications.
Thermal Energy Storage in Lightweight Concrete with Phase Change Material (PCM)
In certain engineering applications, like curing rooms for precast concrete components or concrete blocks, structures may need to retain substantial heat at elevated temperatures for extended durations. These structures are typically made up of thick, massive walls.
To improve the insulation of walls without changing their thickness, materials with high energy storage, such as phase change materials (PCM), can be employed. Phase Change Materials (PCMs) are substances with the ability to absorb and release heat during their phase transition.
Researchers have published a study in Heliyon to investigate the thermal energy storage attributes of lightweight concrete containing two different PCMs with two different fusion points. The two-phase change materials used by the research team were Polyethylene glycol (PEG) and Paraffin (PRF) with fusion points of 42–46 °C and 56–59 °C, respectively.
PCM aggregates were created by infusing liquid PCM into porous concrete through a high-temperature process. Concrete samples were prepared by varying the quantities of the two types of PCM aggregates (ranging from 0:100 to 100:0).
The thermal conductivity coefficient (k) of concrete was assessed at two different temperatures, 25°C and 65°C. The k25 (representing the thermal conductivity of PCM in the solid state) improved as the PCM aggregate content was increased. It was due to the reduction in void spaces which were filled by solid PCM.
In contrast, k65 (representing the thermal conductivity of PCM in the liquid state) decreased with PCM aggregate content due to the impact of latent heat during the phase-changing process. The measured k25 and k65 fell within the range of 0.829–0.842 and 0.447–0.465 W / m °C respectively.
The latent heat of concrete containing hybrid PCM (combination of solid and liquid PCM) aggregates was observed to be higher than that of concrete with single-type PCM aggregates. This suggests that concrete incorporating PCM in hybrid form may be more effective in storing heat at elevated temperatures compared to concrete with singular PCM aggregates.
Nano-Engineered Concrete: Leading to Better Energy Storage
For extremely harsh environments such as in areas where temperatures are less than -5°C, researchers have devised solutions to the problem of extreme cold classified as active and passive solutions.
Passive technologies involve the use of deicing salts, mechanical snow removal, or a combination of both. However, these technologies can be harmful to the infrastructure. Active technologies include various types of heated pavement (HP) and nano-engineered concrete incorporating phase change material (PCM) within cementitious composites.
Researchers published a study in Applied Energy in which they developed a nano-engineered concrete incorporating microencapsulated phase change material (m-PCM) along with a combination of multi-walled carbon nanotubes (MWCNTs) and silica fume (SF) for thermal energy-saving applications. MWCNTs were introduced to enhance both the mechanical and thermal properties of the cementitious composite.
Different proportions of m-PCM (5%, 10%, and 15% by binder weight) were integrated into the cement mortar, while the amounts of MWCNTs and SF remained constant at 0.05% and 10% by binder weight, respectively. A uniaxial compression test was conducted to assess the impact of m-PCM on the mortar's mechanical properties, revealing a notable decrease in mechanical strength.
To examine the thermal response of nanoengineered m-PCM mortars under varying ambient temperatures, a thermal-cycling test was carried out using an electrically controlled heated wire system. The results indicated a reduction of approximately 60% in the energy requirement for thermal regulation in m-PCM mortars with MWCNTs compared to the control specimen.
The results confirmed the efficiency of the nano-engineered concrete thermal energy storage system to be utilized as an active solution for thermal regulation in extremely cold environments.
Case Study: A Comparison of Thermal Energy Storage of Different Concrete Walls
Conducting a thorough analysis of building envelopes is crucial for identifying inadequate thermal performance and, consequently, enhancing design and construction choices to promote sustainability. Buildings within the European Union contribute to approximately 40% of the overall power consumption. In Canada and the USA, this figure rises to 63% and 42%, respectively. Therefore, the study of the thermal characteristics of building components becomes instrumental in realizing substantial cost savings.
A research team has recently published an article in the Journal of Energy Storage, focusing on the thermal behavior of different masonry walls, both with and without plaster, in cold climates, focusing on their energy storage and loss.
The study utilizes a Computational Fluid Dynamics (CFD) model implemented through ANSYS Fluent. The objective is to examine heat transfer from a reference room condition (20 °C) to a cold ambient condition (-20 °C) over 6, 12, and 24 hours, allowing for a comparative analysis of various walls. The model's accuracy is verified through comparison with reported experimental tests employing a hot plate setup.
The research results reveal that the concrete mixture incorporating wood shives (WS1) exhibits the highest stored energy (92% over 24 hours) and the least energy loss (8%) in the overall heat transfer from the reference room to the ambient environment. In contrast, hempcrete (HC11) concrete walls display the lowest energy storage (40%) and the highest loss (60%). Another major observation was that the presence of plaster did not affect the ability of concrete to store thermal energy.
In short, thermal properties, such as conductivity and specific heat capacity, are collectively responsible for controlling the thermal behavior of each concrete type. The type of concrete to be used for thermal energy storage systems depends on the type of environment and the specific requirements.
More from AZoBuild: How Can Concrete be Nano-Engineered?
References and Further Reading
School of Engineering, University of Warwick, (2023). Thermal energy storage. Available at: https://estoolbox.org/index.php/en/12-samples-3/40-tes-introduction
Sukontasukkul, P. et. al. (2020). Thermal storage properties of lightweight concrete incorporating phase change materials with different fusion points in hybrid form for high-temperature applications. Heliyon, 6(9). Available at: https://doi.org/10.1016/j.heliyon.2020.e04863
Haider, Z et. al. (2023). Development of nanomodified-cementitious composite using phase change material for energy saving applications. Applied Energy, 340, 121067. Available at: https://doi.org/10.1016/j.apenergy.2023.121067
Qasem, N. et. al. (2023). Thermal energy storage and losses in various types of masonry concrete walls. Journal of Energy Storage, 67, 107555. Available at: https://doi.org/10.1016/j.est.2023.107555