Search

Cooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. The right use of PCM in the envelope can minimize peak cooling loads, allow the use of smaller HVAC technical equipment for cooling, and has the capability to keep the indoor temperature within the comfort range due to smaller indoor temperature fluctuations. This article presents an overview of different PCM applications in buildings for reducing cooling loads under different climate conditions, and the factors affecting the successful and the effective use of the PCM. Many drawbacks have been found in PCM applications, mainly the intense impact of summer weather conditions over the PCM performance, which prohibits its complete solidification during night, and thus, limiting its effectiveness during the day. Proposed solutions are reviewed in this article. Finally, a topology diagram is presented to summarize the steps leading to an effective use of PCM in building applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Proposition of a hybrid water heating system. [•] Numerical dynamic modeling of the proposed hybrid system. [•] Simulations for typical winter and summer days in the Lebanese climate. [•] Development of an energetic, economic optimal management problem for the proposed hybrid system. [Copyright &y& Elsevier]

Integrating heat exchanger pipes with structural foundations in one system has created a new renewable solution for buildings' thermal loads. However, the interaction between thermal and geotechnical loads makes their design more complex and challenging. This review-study represents the current state of knowledge about the thermal and thermo-mechanical behaviors of energy piles. It also investigates the key parameters that affect their design concerning the piles' dimensions, the arrangement of pipes, concrete admixture, and fluid characteristics. It is found that the thermal efficiency improves significantly by increasing the number of pipes inside the piles and by adding thermally conductive materials to the concrete within acceptable limits. Besides, this paper reviews most of the studies conducted on optimizing vertical ground heat exchangers coupled with heat pumps. Objective functions, decision variables, design constraints, and optimization methods are specified and listed. It is concluded that a multi-objective optimization is highly recommended to enhance the dual performance of an energy pile system coupled with a heat pump using the 4E evaluation criteria (energy, exergy, economy, and environment) while ensuring the safety of the foundation under thermal cyclic loads. [ABSTRACT FROM AUTHOR]

This paper investigates the thermal performance of a translucent solar wall providing, concurrently, storage and restitution of heat, super thermal-acoustic insulation and daylighting to the interior environment. The wall is composed of glazing, silica aerogel used as a transparent insulation material (TIM) and glass bricks filled with fatty acid, an eutectic phase change material (PCM). To assess the TIM–PCM wall thermal behavior, experimentations were conducted in-situ in a full-sized test cell located in Sophia Antipolis, southern France. Experimental data shows that the tested wall is more effective in winter and might cause overheating during the summer mainly due to solar gains and un-cycling behavior of PCM which remains in liquid state. To enhance the energy performance of the wall in summertime, a numerical model describing the heat transfer mechanisms occurring in the PCM layer in combination with the other transparent wall layers is developed. Then, the model of the wall is linked to TRNSYS software to assess the thermal performance of the whole building. The numerical model is validated experimentally and a good agreement is shown comparing the simulated values with the measured data for seven consecutive days in summer and winter. The importance of considering the natural convection effect in the liquid PCM is also demonstrated. Moreover, it was shown that shading devices can effectively reduce overheating while natural night ventilation decreases the indoor temperature without affecting the PCM performance since the outdoor temperature is always higher than the phase change temperature. The use of a glass with selective solar reflection properties depending on the season instead of the ordinary glazing is shown also to be very effective way to overcome the overheating problem. Finally, the TIM-PCM wall is tested under different climate conditions and passive solutions are given to ensure thermal comfort in summer season. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a review of the progress made in analytical modeling of 2D and 3D textile composites is presented. The review covers the most known analytical models developed in the last 30years to evaluate the elastic properties of textile composites. A discussion of these models is presented, where the corresponding advantages and disadvantages are revealed. In addition, a comparative study of some selected analytical models is presented. Results obtained from previous analytical, numerical and experimental studies are presented in order to show the potential of investigated analytical models. It is shown that recently developed analytical models, applied on different kinds of textile composites, could yield good results, while maintaining more flexibility, easy to apply and the less time consuming in comparing with numerical FE (Finite Element) models. [Copyright &y& Elsevier]

Abstract: An improved analytical modeling, three stages homogenization method “3SHM”, of a 2.5D interlock woven composite is proposed. The development of the analytical model based on mixed iso-strain and iso-stress assembling models (the stiffness and the compliance averaging models) is presented. A finite element (FE) modeling is carried out in order to use its results in the development of the analytical model. It is proved that a model based only on an iso-strain condition could not give accurate results, while a mixed iso-strain and iso-stress model yields more accurate estimations. the developed homogenization method as well as the geometrical modeling, that takes into account the real geometry of undulated yarns, proposed by the analytical model leads to very good agreement in comparing with results obtained from FE models and available experimental data from the literature. [Copyright &y& Elsevier]

This study experimentally investigates the supercooling and natural convection behavior in three PCM, namely pure octadecane (organic), a eutectic PCM, and sodium acetate trihydrate (inorganic). The aim is to explore the effect of different factors on the degree of supercooling and on the natural convection, and to provide data for numerical simulation models. Results show that the type of PCM, the temperature of the cooling fluid, and mechanical shocks have a direct effect on the degree of supercooling. The supercooled PCM shows a high sensitivity to any changes in the applied conditions. The thermal insulation of the unheated PCM boundaries has a major effect on the solidification and melting dynamics and topology, particularly regarding the solid-liquid interface. The cross-sectional temperature profiles, the inclination of the solid-liquid interface, and the melting rate show that regardless of the PCM, natural convection plays a significant role during heating but not during cooling. [ABSTRACT FROM AUTHOR]