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Thermal energy storage systems utilising phase change materials offer significantly higher energy densities compared to traditional solutions, and are therefore attracting growing interest in both research and application fields. However, the further development of this technology requires effective methods to enhance thermal efficiency. We propose a horizontal periodic shell-and-tube structure as an efficient latent heat thermal energy storage unit. This research aims to analyse heat transfer not only between the tube containing the heat transfer fluid and the phase change material but also between adjacent shell-and-tube units. The results obtained for a single cell within the periodic structure are compared with those of reference single shell-and-tube units with insulated adiabatic and highly conductive shells. The enthalpy–porosity approach, combined with the Boussinesq approximation, is applied to address the heat transfer challenges encountered during melting and solidification. The periodic horizontal shell-and-tube structure proves to be an efficient latent heat thermal energy storage unit with short melting and solidification times. In contrast, the non-periodic case with neglected conduction in the shell increases the melting and solidification times by 213.8% and 21%, respectively. The shortest melting and solidification times were recorded for the case with a periodic horizontal shell-and-tube structure and shell aspect ratios of 0.44 and 1, respectively. [ABSTRACT FROM AUTHOR]

Reducing energy consumption in residential and commercial buildings is an important research topic. Thermally activated building systems are a promising technology for significantly reducing energy consumption. The high thermal inertia, large surfaces, and radiative nature are advantages of these systems, but, on the other hand, this makes the system control and design complex. A transient simulation is also required to address the dynamic behavior of the system. The influence of 19 factors (material, design, and operating parameters) on the air temperature and mean radiant temperature inside the room as well as the required cooling equipment power were analyzed to better understand the system. The screening experiment was conducted using the random balance design method, and measurement data were used to validate the resistance–capacitance model. The analysis was performed using the Plackett–Burman design and a design with randomly selected points from a full factorial experiment. The results show that internal heat gains and the inlet water temperature have a significant influence on the system, and the influence of the screed's properties is insignificant compared to other parameters. It should be borne in mind that the obtained results and conclusions are valid for the assumed range of factors' variability. [ABSTRACT FROM AUTHOR]

An important issue in the design of installations with borehole heat exchangers (BHE) is knowledge of the thermo-physical properties of the grouting material and soil. The objectives of this work is to estimate the thermal conductivity and specific heat of the grouting material and the soil. The estimated values were determined on the basis of two numerical heat transport models in the borehole and using the results of the small sandbox experiment. The design of experiment technique (DOE) and the response surface methodology (RSM) were used to achieve the aim of this work. Numerical calculations were carried out with the use of the new finite element with multiple degrees of freedom (MDF) and a quasi-3D model in ANSYS package. The estimation requires minimization of four output parameters (quality criteria), and therefore it is a multiple-objectives optimization problem. Based on the DOE, RSM and multiple-objective optimization the material properties of BHE and soil was determined. For both models the discrepancies Y1P1 are below 4 %, Y2P1 are below 11.5%, Y1P2 are below 6.5 % and Y2P2 are below 11.5 %. The average discrepancies below 5 % based on the verification measurements with different operating parameters was obtained. It is noteworthy that for the two different models the same values of the estimated parameters were obtained.

Changes in the energy sector, associated with the move away from fossil fuels, pose a challenge for appropriate thermal energy management in residential buildings. The important element to deal with the variability of renewable energy in thermal systems is latent heat thermal energy storage. Due to the low thermal conductivity of phase change materials, a number of techniques are proposed to enhance the heat transfer process. In this research, the global sensitivity of fin geometrical parameters on the melting and solidification times and energy efficiency of these processes was investigated. The computational model of the phase change was developed using the finite volume method with the enthalpy-porosity model and Boussinesq approximation. Numerical simulations were carried out according to the design of experiments technique. The multi-dimensional response surface was developed, and the multi-objective optimisation was done. The research shows that the melting process is most influenced by the position of the top fin (α angle) and the solidification process by the position of the bottom fin (γ angle). The angle of the tree fin (β) has a different effect on both processes, with the energy efficiency decreasing during melting and increasing during solidification. Maximum values for the energy efficiencies of melting ( η m = 0.973 ) and solidification ( η s = 0.988 ) were obtained for α = 18. 2 ° , β = 89. 0 ° , L = 10.7 mm and γ = 21. 0 ° . [ABSTRACT FROM AUTHOR]