The industrial sector is increasingly obliged to reduce its energy consumption and greenhouse gases emissions to contribute to the world organizations’ targets in energy transition. An energy efficiency solution lies in the development of thermal energy storage systems, which are notably lacking in the low-temperature range (50–85 °C), for applications such as district heating or low-temperature waste heat recovery. This work aims to bring a latent heat storage solution from material selection to prototype evaluation. The first part of this paper is dedicated to the characterization and aging of a phase change material selected from a screening of the literature (fatty acid mixture mainly composed by stearic and palmitic acid). Then, this material is encapsulated and tested in a prototype whose performances are evaluated under various operating conditions. Finally, a numerical model validated by the experimental results is used to explore the influence of a wider range of operating conditions, dimensioning choices, and material conductivity improvements.

This paper presents the first passive solar wall providing simultaneously super insulation, heat storage and daylighting to the inner space. The wall's external layer is composed of a silica aerogels bed for high insulation and solar radiation transmission. The second layer, internal, is composed of glass bricks filled with a eutectic phase change material (PCM) for heat storage and restitution. The whole wall is translucent. The experimentations carried out to characterize thermal and optical properties of the materials used are described. Then results are given for a full scale comparative experimentation on a twin zones building located in the south of France for the solar wall and a standard opaque high thermal capacity wall. Results show the heat losses through the wall are very low while the heat and light gains are high: The U value of the solar wall is 0.59 W m(-1) K-1 and 0.72 W m(-1) K-1 respectively when the PCM is in liquid and solid state. With the test building in free floating condition, the temperature difference between the outdoor and indoor air provided by the wall is about 9 degrees C in winter. The wall can provide up to 500 lux to the inner environment, which is sufficient for conference rooms. The tested wall has proven more effective in winter and shoulder season, particularly for cold sunny climates, but may cause overheating in summer. (C) 2015 Elsevier Ltd. All rights reserved.

In this paper, a dynamic model is proposed for the charging process of a cold energy storage made of a fixed bed of spherical nodules containing a Phase Change Material (PCM). During the charging process, even if the temperature of the cooling liquid that flows through the storage is uniform, the solidification process does not begin at the same temperature among the nodules due to the supercooling phenomenon. A first number distribution can be defined according to the solid mass fraction among the nodules experiencing solidification. At the end of the solidification process, the temperature of the solid phase is not the same among the nodules population having completed the solidification. A second number distribution can be defined according to their mean temperature. In order to calculate the time evolution of these two number distributions, we propose to use the population balance equation approach coupled with nodules energy balance equations. The resulting partial differential equations are spatially discretized by the finite difference method. The supercooling phenomenon is taken into account as a boundary condition of the population balance equation associated with the solid mass fraction by using a nucleation kinetic model. The resulting set of ordinary differential equations is numerically solved. The model is applied for simulating the charge cycle of an ice storage system. Good agreement between simulation results and experimental data is achieved.

Performances of spherical macrocapsules (nodules) currently used in latent heat-based thermal energy storage (TES) industrial units have been enhanced by the addition of graphite particles to the phase change material (PCM). Two different graphite types, namely graphite flakes (GF) and expanded natural graphite (ENG), have been tested at constant PCM content in the nodule. Using water as PCM, both graphite types have been proven to lead to significant reduction in storage/discharge durations (up to 35% and 58% for a graphite load of only 13%wt) without reduction in storage capacity. Therefore, enhancement using ENG greatly enhances efficiency, but it is also more expensive. GF maybe preferred, considering both its ease of use and economical issues. At the highest experimented graphite load (13%wt) the overall thermal behavior of the nodule is advantageously improved, with simultaneously no apparent supercooling,a very stable phase change plateau, and very sharp and straight sensible heat exchange periods. The graphites induce both extensive thermal power enhancement and improvement in thermal behaviors. These experimental results have been simulated using numerical Comsol®-based models with success. The simulated charge/discharge steps have shown that the air gap present in the nodules induces modifications in the phase change front profile only at the beginning of the periods.