Search

This paper presents a multistep methodology combining unsupervised and supervised learning techniques for the identification of the daily heating energy consumption patterns in buildings. The relevant number of typical profiles is obtained through unsupervised clustering processes. Then Classification and Regression Trees are used to predict the profile type corresponding to external variables, including calendar and climatic variables, from any given day. The methodology is tested with a variety of datasets for three different buildings with different uses connected to the district heating network in Tartu (Estonia). The three buildings under analysis present different energy behaviors (residential, kindergarten and commercial buildings). The paper shows that unsupervised clustering is effective for pattern recognition since the results from the classification and regression trees match the results from the unsupervised clustering. Three main patterns have been identified in each building, seasonality and daily mean temperature being the variables that have the greatest effect. The results concluded that the best classification accuracy is obtained with a small number of clusters with a classification accuracy from 0.7 to 0.85, approximately. The authors would like to thank GREN Eesti [44] for providing data from the substations for academic purposes. The authors would like to acknowledge the Spanish Ministry of Science and Innovation (MICINN) for funding through the Sweet-TES research project (RTI2018-099557-B-C22). This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 768567.

Xylitol shares the good thermophysical properties of other sugar alcohols that are candidates for thermal storage purposes, with one singularity: it shows noticeable supercooling coupled with a low crystallization rate. This makes it a suitable material for long-term heat storage applications based on supercooled PCMs, but its thermal endurance for TES purposes remains unknown. Accordingly, a stability test was performed, which consisted of placing several tubes with fresh xylitol inside a heating cabinet, where they remained under isothermal condi-tions for periods of up to 150 days. Both open and closed (tight) tubes were employed under various test tem-peratures. Samples were afterwards analyzed by differential scanning calorimetry, X-ray diffraction and high performance liquid chromatography. The thermal properties and structure of the material remained stable during the 150 days of the test at 10 degrees C above its melting point, while at higher temperatures degradation was observed in the material over shorter periods. The behavior is noticeably better than the thermal endurance of other sugar alcohols reported in the literature, such as mannitol, dulcitol, erythritol and inositol. This work was supported by the Spanish Ministry of Science and Innovation (MICINN) through the Sweet-TES research project (RTI2018-099557-B-C22). The authors also greatly appreciate the technical and human support provided by SGiker of UPV/EHU; especially Aitor Larrañaga and Mamen Sampedro for their valued help.

[EN] An accurate characterization and prediction of heat loads in buildings connected to a District Heating (DH) network is crucial for the effective operation of these systems. The high variability of the heat production process of DH networks with low supply temperatures and derived from the incorporation of different heat sources increases the need for heat demand prediction models. This paper presents a novel data-driven model for the characterization and prediction of heating demand in buildings connected to a DH network. This model is built on the so-called Q-algorithm and fed with real data from 42 smart energy meters located in 42 buildings connected to the DH in Tartu (Estonia). These meters deliver heat consumption data with a 1-h frequency. Heat load profiles are analysed, and a model based on supervised clustering methods in combination with multiple variable regression is proposed. The model makes use of four climatic variables, including outdoor ambient temperature, global solar radiation and wind speed and direction, combined with time factors and data from smart meters. The model is designed for deployment over large sets of the building stock, and thus aims to forecast heat load regardless of the construction characteristics or final use of the building. The low computational cost required by this algorithm enables its integration into machines with no special requirements due to the equations governing the model. The data-driven model is evaluated both statistically and from an engineering or energetic point of view. R-2 values from 0.70 to 0.99 are obtained for daily data resolution and R-2 values up to 0.95 for hourly data resolution. Hourly results are very promising for more than 90% of the buildings under study. ( This study has been carried out in the context of RELaTED project. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 768567. This publication reflects only the authors' views and neither the Agency nor the Commission are responsible for any use that may be made of the information contained therein.

The influence of a microencapsulated phase change material (PCM), a lightweight aggregate (LWA) and cellulose fibers on the behavior of cement-lime mortar was investigated. Lightweight aggregates and cellulose fibers were added in order to reduce thermal conductivity. PCM in two different amounts, 10% and 20%, was included to increase thermal inertia of mortars, taking advantage of its heat storage capacity. An experimental program was carried out to assess the effect on physical, mechanical and thermal properties of the different additions and combinations. Thermal conductivity of mortars with PCM at solid and liquid states were measured and Differential Scanning Calorimetry (DSC) was used to evaluate mortars’ enthalpy. Twelve cement-lime mortars designed for rendering applications, were studied and the experimental results were compared. It was observed that the type and amount of component affected physical, mechanical and thermal mortar properties. Lightweight aggregates increased porosity while reduced strength and thermal conductivity. Cellulose fibers did not modify significantly mortar properties. PCM increased mortar enthalpy while acted as a filler, reducing porosity and strength. However, enthalpy was not linearly related only to the amount of PCM and also depended on mortar composition. LWA increased the enthalpy of PCM cement-lime mortars.

The eutectic mixture formed by urea and sodium nitrate can be an interesting candidate for use as a phase change material for thermal energy storage in space heating and domestic hot water applications. It shows a melting point of 85 °C, a melting enthalpy of 172 J/g and a price around 0.9 €/kg. However, the thermal stability of the mixture is a great concern for this application. A preliminary evaluation of the thermal stability was performed and previously reported by the authors. It consisted of an accelerated thermal cycling test with 210 thermal cycles and the material showed a stable behavior. Nevertheless, the long-term stability of urea in the liquid state at temperatures below 100 °C is uncertain and requires a specific study. The main objective of the present work is to evaluate the long-term thermal stability of the mixture when it is exposed to long periods of use under conditions representative of actual applications, by means of analyzing the thermal and compositional behavior of samples remaining at 100 °C for several periods up to one year. A methodology is proposed, which intends to isolate the thermal degradation phenomenon from others, such as phase segregation, supercooling, and polymorphism, that can be introduced by thermal-cycling. It also aims to be more representative of the actual application than the accelerated thermal cycling approach. The authors would like to acknowledge the Ramon Areces Foundation for funding and the Spanish Ministry of Science, Innovation and Universities (MICINN) through the Sweet-TES research project (RTI2018-099557-B-C22). The author Laura Quant wants to thank the financial support of the University of the Basque Country UPV/EHU, through the Personnel Research Training Program to carry out PhD thesis in cotutelle between the University of the Basque country and the Universit ' e de Pau et des Pays de l'Adour (2016 call). Research efforts in this field are also coordinated through the IEA ES Annex 33/SHC Task 58. Finally, the authors greatly thank the technical and human support provided by SGiker of UPV/EHU; especially to Aitor Larranaga, Mamen Sampedro and Alfredo Sarmiento for their valued help.

This paper presents a novel framework for the identification of different consumption patterns of heating loads of buildings. The approach to analyzing the consumption data is carried out by a combination of unsupervised clustering models. Density based clustering is used for outlier detection in the original dataset and K-means for pattern recognition. The proposed framework is then applied to a real building connected to the district heating in Tartu (Estonia). Three main day-types are identified for the building as an outcome of the clustering process, with different patterns throughout these days. More than 60% of the analyzed Cluster Validation Indexes studied in this paper show that classifying the daily demand profiles in three clusters is the optimal classification.

Deliverable 2 of Subtask 3P is a collection of questionnaires regarding experimental devices that are used by the experts of Task 58 / Annex 33 to investigate the degradation of Phase Change Materials (PCM). Three types of experiments are considered: Tests on degradation of PCM over thermal cycling (type I), tests on degradation of PCM with stable supercooling (type II), and tests on degradation of phase change slurries (type III).

As the material development is done at different institution the objective of the work was to collect the materials which are under research and development to get an overview on the most relevant properties of these materials and application which are addressed.

Deliverable 1 of Subtask 3P is an inventory of properties of Phase Change Materials (PCM) that change comparing experiments in the lab environment with tests under application conditions. Examples where no change is observed are also included.

There is little understanding of the relative importance of natural convection when designing latent heat thermal energy storage (LHTES) systems based on geometric parameters and/or phase change material (PCM) properties. For high temperature shell-and-tube LHTES systems, this study aims: (i) to determine the error of ignoring natural convection, and (ii) to quantify this error for different geometric parameters and PCM properties. In particular, the study defines the circumstances under which natural convection is important and the error of choosing a ‘conduction-only modelling approach’. To do so, the performance of LHTES systems with nine geometric aspect ratios and three commercial PCMs (of different melting points) were analyzed by means of a validated CFD model. The results showed that the error is a function of the process under analysis (melting or solidification) and the ratio of stored/delivered energy divided by the maximum capacity of PCM (i.e. its effectiveness). Geometry also plays a critical role in the relative importance of natural convection. The study demonstrates that a specific system geometry (i.e. a dimensionless number defined based on the inner and outer radius as well as the length of shell-and-tube geometry: S = R 2 - r o 2 2 r o L ) can be used to determine the relevance of natural convection. It was found that regardless of PCM type, the error is of neglecting natural congestion is small if S 0.005 . For S > 0.005 , the error depends on the following non-dimensional groups: r o L , R a , S t e , a n d B i . As might be expected, the Rayleigh number was found to be the most influential group. Notably, a critical Rayleigh number value (8 × 105) was found, below which the error of neglecting natural convection is

One of the key factors that currently limit the commercial deployment of latent heat thermal energy storage (LHTES) systems is their complex design procedure. The optimization of such kind of systems requires a compromise between the storage capacity and the charging/discharging power, and therefore, there is a need of modeling tools that allow their fast and accurate simulation. In light of this, a novel correlation that allows the straightforward determination of the discharging time of plate-based LHTES systems is developed in the present article. To approach this objective, an experimentally validated CFD model was used. Simulations with 3 commercial phase change materials (PCMs) were first employed to gain knowledge of the melting and solidification behavior of the system. Then, a theoretical formulation of the heat transfer problem involved was performed so as to identify those dimensionless numbers concerned in the process. Afterwards, 15 virtual PCMs were defined and CFD simulations were performed. The obtained discharging time results were adjusted by regression to get the exponents and coefficients of the dimensionless numbers involved in the correlation. Finally, to validate the correlation, simulations with five additional PCMs were carried out and their results were compared with those obtained from the correlation. By means of the obtained expression, the maximum plate thickness capable to provide a desired discharging power can be determined as a function of the properties of the PCM and the operation constraints of the application without the need of simulations. The technique eases the design process of this kind of systems and decreases the amount of time needed to size them from days/hours to minutes.

The use of georeferenced information system and Light Detection and Ranging (LiDAR) data in combination with traditional data analytics tools is very promising in urban scale engineering and especially in energy urban planning. This paper explores the use of new DH networks for industrial waste heat exploitation and for that purpose, a case-study in Vitoria-Gasteiz (Spain) is proposed. The methodology explained in this paper explores the incorporation of data from industrial emplacements, buildings and road network in order to identify optimal areas in the city for the construction of a new district-heating network. An area of influence of a buffer of radius 1.5km from the industry location is defined and the proposed algorithm divides this area into grids of different sizes. The path for the network is calculated by optimizing the economic performance of the network. The results show that the district-heating may be built in the south-west direction from the industry and among the 40 configurations studied, payback periods from 6 to 8.5 years are obtained.

Industrial waste heat recovery shows significant potential for increasing energy efficiency in industry. However, to design strategies that exploit this potential, it is necessary to have data about the quantity and characteristics of industrial waste heat flows. This information is not always readily available and many companies do not even have a systematic record of these energy flows. Hence, bottom-up methodologies to estimate that recovery potential by means of key transfer figures are useful tools within this field. In the present article, four different methods are applied to determine the industrial waste heat recovery potential in the Autonomous Community of the Basque Country (northern Spain), an energy-intensive industrial region with large energy dependency from the outside. Besides, the analysis of the economic viability of the industrial waste heat recovery is essential, because it determines the final adoption of energy efficiency measures. For that aim, the authors develop an easy-to-apply bottom-up methodology to carry out an assessment for the economic potential of the estimated industrial waste heat at different temperature levels. This method is applied to 129 companies, whose potentials are characterized and discussed. The obtained results show that, for waste heat streams above 400 ?C, more than 90% of the studied companies present payback periods below five years. For those industries with waste heat temperatures below 200 ?C, the ratio decreases to around 40%, still a noticeable value. The estimations show a significant opportunity to implement solutions to recover this wasted energy, especially in the iron and steel sector and the petrochemical industry. The development of public policies that encourage these measurements would be also beneficial. The authors would like to acknowledge the Spanish Ministry of Science and Innovation (MICINN) for funding through the SweetTES research project (RTI 2018099557BC22) .

This research studies a binary mixture composed of sodium nitrate and urea for use as a phase change material in latent thermal energy storage systems between 75 and 90 °C. This temperature is suitable for heating and domestic hot water applications, such as solar thermal systems and cogeneration devices. This work is divided into two parts. In Part I, the phase diagram of the system was experimentally determined via DSC, the synthetic visual method and X-ray diffraction. A eutectic composition was found at 71.25% (w/w) urea and 21.75% (w/w) sodium nitrate. The main thermal properties and density of this composition were studied in detail to evaluate its potential as a PCM. The results showed a melting temperature of 85 °C and a melting enthalpy of 172 J/g. These properties are suitable for the intended purpose. Currently, the mixture presents an approximated market price below 1€/kg, which is highly competitive. In this Part II, the water uptake of the material was evaluated to gain knowledge of its hygroscopic behavior. XRD measurements were also performed to study the formation of new phases or compounds caused by the presence of water. In addition, because urea undergoes thermal degradation upon heating, a preliminary accelerated thermal cycling study was performed to determine the thermal reliability of the mixture. After 210 accelerated thermal cycles, the latent melting enthalpy of the sample was reduced by 1.2%. These results were complemented by chromatographic analysis used to detect any presence of degradation byproducts. According to the results, the mixture formed by sodium nitrate and urea shows potential for use as a PCM in the applicable temperature range. Further research focused on thermal degradation over longer periods of use is encouraged to establish whether the material has a proper lifespan for actual thermal energy storage applications.

This research studies a binary mixture composed of sodium nitrate and urea for use as a phase change material in latent thermal energy storage systems between 75 and 90 °C. This range of temperatures is suitable for heating and domestic hot water applications, such as solar thermal systems and cogeneration devices. The work is divided into two parts. In this Part I, the phase diagram of the system was experimentally determined via DSC, the synthetic visual method and X–ray diffraction. A eutectic composition was found at 71.25% (w/w) urea and 28.75% (w/w) sodium nitrate. The main thermal properties and density of this composition were studied in detail to evaluate its potential as a PCM. The results showed a melting temperature of 85 °C and a melting enthalpy of 172 J/g. These properties are suitable for the intended purpose. Currently, the mixture presents a market price below 1 €/kg, which is highly competitive. In Part II, the water uptake of the material was evaluated to gain knowledge of its hygroscopic behavior. In addition, because urea undergoes thermal degradation upon heating, a preliminary accelerated thermal cycling test was performed to study the thermal reliability of the mixture. According to the results, the eutectic mixture formed by sodium nitrate and urea has potential for use as a PCM in the intended temperature range. Further research focused on thermal degradation over longer periods of use is encouraged to establish whether the material has a proper lifespan for actual thermal energy storage applications.

The present article studies the binary mixture comprised by erythritol and urea for its application as a phase change material (PCM) in latent hat thermal energy storage systems for heating and domestic hot water applications. A sequential methodology was employed to evaluate the suitability of the mixture as a PCM. First, a preliminary evaluation was performed by means of the modeling of the phase diagram and by hot–stage microscopy. Afterwards, the results were refined with more precise techniques, such as Differential scanning calorimetry, the synthetic visual method and X-ray diffraction. The results showed a eutectic composition formed by 54.9% (w/w) erythritol and 45.1% (w/w) urea, with a melting temperature of 81.13 °C and a latent melting enthalpy of 248 J/g. The specific weight of the eutectic composition was measured at different temperatures. The density of the liquid PCM at 95 °C presented a value of 1.282 g/cm 3 and thus, the proposed eutectic mixture shows a volumetric storage capacity of 318 MJ/m 3 . These properties are suitable for the applications aimed. The current market price of the mixture is nearby 2.5€/kg, which can be regarded as reasonable. Since urea undergoes thermal degradation upon heating, a preliminary accelerated thermal cycling test was performed. After 85 thermal cycles, the enthalpy of the eutectic mixture was reduced by 3.6%. In contrast, pure urea showed a decrease of 75% of its initial storage ability. According to the results, the eutectic mixture formed by erythritol and urea can be a good candidate for use as a PCM in medium temperature range applications. Further research is required to evaluate the stability of the mixture on longer periods of use. The methodology employed has proven to be adequate for the development of new eutectic PCMs.

A simple shell and tube heat exchanger provides a straightforward design for near-term integration of latent heat thermal energy storage (LHTES) systems in concentrated solar thermal-tower (CST-tower) plants, but currently there is no literature available for this configuration in the 286–565 °C temperature range. Therefore, the primary objective of this work is to evaluate the potential of this configuration for CST-tower plants. In addition, a proper design method of this storage configuration should simultaneously account for the effects of geometric parameters and the number of modules. The present work optimizes these parameters for market ready phase change materials (PCM) that are suitable in the aforementioned temperature range. This optimization consisted of fixing the PCM volume while varying the other geometric parameters (namely, L, L/d, R/ro) simultaneously over a wide range. The goal was to achieve the highest amount of total stored/delivered energy with a minimum heat transfer surface area. This analysis revealed that there was an optimum area between 36 and 63 m2 GJ−1 (or 0.12–0.22 m2 kWhth−1), depending on the PCM employed. This optimum surface area can be obtained with several combinations of geometric parameters, but only certain combinations were found to achieve the highest total stored/delivered energy. The charging and discharging efficiency for the selected PCMs was found to be ∼99% and 75–85%, respectively. Using the optimized designs, the cost of this shell and tube LHTES system was found to vary between 27 and 170 US$ kWhth−1, which indicates that with further development it may be competitive with conventional sensible storage systems (e.g. two-tank molten salts).

The feasibility of individual natural gas fired boiler-based heating systems in the retrofitting of buildings constructed in the 50–60 s in Bilbao (northern Spain) is evaluated in this paper. A holistic approach through dynamic simulations using TRNSYS is employed for the purpose. An existing dwelling previously monitored and used to validate the model applied is selected as a case study. 54 different scenarios are evaluated, which arise from the combination of 3 different envelope options, 2 types of heat production units, 3 heat production temperatures and 3 comfort temperature set-points. The cases are evaluated in terms of energy results, economic aspects, and the influence of user behaviour. Regarding the latter, the influence of the potential rebound effect is also evaluated. The results show energy savings nearby 10% when condensing boilers are compared with high efficiency boilers. In relation to hot water production temperature, energy savings between 5 and 10% are found when the temperature is lowered from 60 to 50 °C. The greatest impact on energy consumption is related to the occupants’ behaviour: reductions up to 89% are achieved if the indoor temperature set-point is lowered 2 °C. This is reinforced with the results related to the rebound effect, which show significant differences on energy consumption values. These evidences demonstrate that the user behaviour is an essential feature to be considered in studies regarding buildings energy performance. As a consequence, the holistic approach herein employed emerges as a key tool to be applied in further works related with the topic.

Thermal energy storage is a key technology to overcome the structural mismatch between energy supply and demand in thermal energy systems. Its use is essential for a proper integration of renewable or efficient technologies in day-to-day applications, such as heating and domestic hot water. Latent heat thermal energy storage, which is based on the use of phase change materials, has been studied in depth in the literature due to its advantages over conventional storage methods. It can provide a higher compactness and lower thermal losses than traditional sensible heat storage systems. However, to optimize the operation of latent thermal energy storage systems into heating and domestic hot water applications, it is still required to obtain additional information on the effects of the system parameters that can be easily altered and/or controlled. These parameters mainly are: operating temperature range, mass-flow rate and prototype length. This paper aims at evaluating these parameters for an innovative plate-based latent thermal energy storage system previously developed by the authors. The used phase change material is a commercial paraffin wax (RT60) with an approximated phase change temperature of 58 °C. A full-scale experimental setup was developed and forty-two experimental tests were conducted. The tests combined six temperature ranges from 45 to 70 °C, three mass-flow rates from 1.8 to 3 l/min and two module arrangements: a single prototype and two prototypes connected in series. The results showed that, for a specified temperature difference between the charging and discharging inlet temperature, the stored energy depended strongly on the selected temperature range. The thermal power during charging and discharging was strongly affected by the difference between the inlet temperature and the phase change temperature of the PCM. Higher mass-flow rates linearly reduced the required time for completion of charging or discharging. Finally, the addition of a second LHTES prototype in series enhanced the storage capacity of the system, but also increased the required time to complete the process. The obtained results can aid the proper design and operation of the system under specific constraints imposed by a specific application. They are also valuable as a starting point for the design of new plate-based LHTES systems, considering both different geometries and phase change materials.

This article studies new binary eutectic mixtures of sugar alcohols for their use as phase change materials (PCMs) in the 50–90 1C temperature range. This range is suitable for domestic solar thermal systems and cogeneration devices. The mixtures studied were composed of erythritol and xylitol, erythritol and sorbitol, and xylitol and sorbitol. Their phase diagrams were experimentally established by differential scanning calorimetry and X-ray powder diffraction. Polarized thermomicroscopy was employed to determine the crystallization rate of the pure materials and eutectic compositions. Additionally, the polymorphic behavior of the pure materials was assessed and compared with data from the literature. The results showed that, with respect to thermal properties and economic aspects, the eutectic compositions found are suitable for the intended purpose. Unfortunately, their crystallization rates are noticeably low, which limits their use as PCMs. A modeling approach based on thermodynamics was used to predict solid–liquid equilibria of the studied mixtures and their melting enthalpies. The simulated results were in good agreement with experimental results. The modeled and experimental results were finally used to highlight a few practical aspects relevant for the development of new eutectic mixture-based PCMs.

This article describes the development of a CFD 2D model of a new type of ventilated active facade which includes a PCM (Phase Change Material) in its outer layer. The model was carried out using the software Fluent. The numerical results were compared against experimental data obtained by means of a real-scale PASLINK test facility. Two different approaches were tested to model the PCM. To model the radiation, S2S and DO sub-models were tested. RNG k–e , Standard k–ω and SST k–ω turbulence models were compared to model the air flow inside the ventilated layer. The results showed that for the geometry under consideration it was suitable to consider the PCM to be a solid material with variable C p . The DO model accurately reproduced the radiation phenomena. For an air flow rate that resulted in a turbulent regime inside the air chamber, the RNG k–e model showed good agreement between the experimental data and the simulated results. The developed model can be considered suitable for the simulation and optimization of the facade under turbulent flow conditions. Further research should be conducted to improve the accuracy of the model for low-Reynolds-number turbulence conditions.

This paper presents an innovative finned-plate latent heat thermal energy storage system for its integration in cogeneration systems. For optimization purposes it is very important to maximize the efficiency of the computational calculations. Therefore, three approaches are presented for the simulation of the same storage system: a numerical model, a simplified analytical one and a simplified numerical model. These three models are applied to the simulation of a prototype which has been tested experimentally by means of a test benchmark for storage systems. The simplified analytical and simplified numerical models are implemented by the definition of an effective heat transfer coefficient. From the comparison of the results it was concluded that the three approaches gives rise to a good agreement with the test results. However, the simplified analytical model fails to predict long configurations. On the other hand, the simplified numerical model presents very good results for every configuration, reducing the computational cost of the numerical model from several hours to minutes.

This article describes an evaluation of the thermal performance of a new type of ventilated active facade that includes a phase change material (PCM) in its outer layer. The research was carried out experimentally by means of a real-scale PASLINK test cell facility, located in the city of Vitoria-Gasteiz in Spain. The results of an experiment performed in March 2010 are presented and evaluated. The behavior of the facade was compared with different traditional constructive systems, using the results of computational simulations performed with the Design Builder software. The experimental results showed that the melting–solidification processes that take place in the PCM led to an increase in the heat absorption during the phase-change temperature intervals, which reduced overheating of the facade. The air circulating through the ventilated chamber was overheated up to 12 °C during the daytime. Because of the PCM solidification, 2.5 h after the solar radiation faded out, the air circulating through the chamber was still warmed by 2 °C. The energy efficiency of the facade during the testing period is attributable to the 10–12% incident radiation gains. This efficiency was found to be a function of the circulating air flow rate. The simulations results showed that the thermal inertia of the ventilated facade with a PCM is higher than that of the four traditional solutions evaluated in the study. Further research is required to study the influence of the air flow rate through the ventilated chamber.

The present article evaluates the influence of the experimental conditions in the determination of the subcooling of sodium sulfate decahydrate (Glauber's salt) nucleated with anhydrous and hydrated sodium tetraborate (borax). Experiments have been carried out by means of Differential Scanning Calorimetry (DSC) and by two other custom experimental procedures designed by the authors, in order to ensure that, the small samples tested in the DSC and the large samples tested using those experimental techniques, undergo the same or equivalent thermal processes. Two types of samples have been evaluated, the first one composed of sodium sulfate decahydrate nucleated with 5% sodium tetraborate decahydrate, and the second one being 32.3% anhydrous sodium sulfate, 1.4% anhydrous sodium tetraborate, and the balance water. The influence in the determination of the subcooling of experimental conditions such as the cooling rate, the maximum heating temperature, and the holding time at the maximum temperature has been researched. The results indicate that the mass/temperature/time variables have a complex interaction in the subcooling attained. As a result, the DSC technique underestimates the reduction of subcooling that can be attained in large masses of Glauber's salt by nucleation with borax.

In order to evaluate the accuracy and performance of two different heat transfer models for PCM containing systems, a thermal testing has been performed in a conductivimeter. A mixture of PCM and gypsum was submitted to a cyclic surface temperature change inside the conductivimeter, measuring heat fluxes and temperatures. The results of this test were used to validate two different heat transfer models, based on finite differences and on neural networks. Both heat transfer models were compared with the test results, showing good agreement with experimental data in both cases (mean error less than 5%) and a better performance (accuracy and calculation time) for the neural network.

4th International Conference on Solar Heating and Cooling for Buildings and Industry (SHC) -- DEC 02-04, 2015 -- Istanbul, TURKEY, WOS: 000387506400026, An overview on the recent results on the engineering and characterization of sorption materials, PCMs and TCMs investigated in the working group WG A1 "Engineering and processing of TES materials" of IEA SHC Task 42 / ECES Annex 29 (Task 4229) entitled "Compact Thermal Energy Storage" is presented. (C) 2016 The Authors. Published by Elsevier Ltd.

The IEA joint Task 42 / Annex 29 is aimed at developing compact thermal energy storage materials and systems. In Working Group B, experts are working on the development of compact thermal energy storage applications, in the areas cooling, domestic heating and hot water and industry. The majority of application projects were in the field of room heating and domestic hot water. In this article, an overview is given of a large number of applications. The storage technologies used in the applications are latent heat storage, open and closed solid sorption, liquid sorption and salt hydrates and composites thereof. On a broad front, a lot of progress was made in the development of components and systems, providing knowledge and experience regarding the design, numerical modeling, building, testing and economical assessing of components and storage systems. Most important findings are that the interaction of storage materials with the materials of components can be deciding for the technical feasibility, that a number of components, like reactor, heat exchangers and evaporators are less understood than initially thought and need more development, that the inclusion of storage materials in systems generate new challenges like the occurrence of non-condensable gases and thermo-mechanical effects and that standardized and simplified system approaches are needed.

In order to reduce the required volume for thermal energy storage, a finned plate latent heat thermal energy storage system for domestic applications is presented in this paper. This innovative design allows the exchanging of energy between water and the RT60, used as the phase change material. The simulation of that system is covered by a validated mathematical model. The model, based on a simplified numerical approach, is used for the optimal design of the final prototype, which is compared with a conventional 500 l hot water tank usually integrated in domestic heating and domestic hot water applications. It is obtained that the resulting design is in the order of one half of the water tank volume, resulting in a more compact configuration which can be easily integrated in the space. This solution will bring a great opportunity for thermal storage especially in those applications where there is a lack of available space, as it is the case of residential flats.

For the correct design of thermal storage systems using phase change materials (PCMs) in any application, as well as for their simulation, it is essential to characterise the materials from thermophysical and rheological standpoints (phase change enthalpy, thermal conductivity in solid and liquid phases, viscosity and density in function of temperature). Taking advantage of the different research groups facilities available in two international networks: within the IEA (International Energy Agency), the ECES Implementing Agreement (Energy Conservation through Energy Storage IA) and SHC Programme (Solar Heating and Cooling) Task 42/Annex 24 ‘‘Compact Thermal Energy Storage – Material Development for System Integration’’, and the COST Action TU0802 ‘‘Next generation cost effective phase change materials for increased energy efficiency in renewable energy systems in buildings (NeCoE-PCM)’’ a set of Round Robin Tests (RRTs) was proposed. The objective was to come to comparable results for PCMs using Differential Scanning Calorimetry (DSC) to determine their melting enthalpy as well as their melting and solidification behaviour. The first RRT was without defining the procedure, the second one with a predefined procedure for the measurements, but not for calibration and the third one with a predefined procedure for calibration, for the measurements and also for the data evaluation. This paper presents the conclusions after the three RRT. The main conclusion of the paper is that enthalpy in function of temperature determined using a dynamic method for DSC can be influenced by certain reasons and finally a methodology to avoid these influences have been proposed.

An important prerequisite to select a reliable phase change material (PCM) for thermal energy storage applications is to test it under application conditions. In the case of solid&ndash, liquid PCM, a large amount of thermal energy can be stored and released in a small temperature range around the solid&ndash, liquid phase transition. Therefore, to test the long-term stability of solid&ndash, liquid PCM, they are subjected to melting and solidification processes taking into account the conditions of the intended application. In this work, 18 experimental devices to investigate the long-term stability of PCM are presented. The experiments can be divided into thermal cycling stability tests, tests on PCM with stable supercooling, and tests on the stability of phase change slurries (PCS). In addition to these experiments, appropriate methods to investigate a possible degradation of the PCM are introduced. Considering the diversity of the investigated devices and the wide range of experimental parameters, further work toward a standardization of PCM stability testing is recommended.