Development and validation of the numerical model of an innovative PCM based thermal storage system

Because of the high costs of experimental tests in the real conditions of buildings, numerical simulation, developed analytical methods and different modelling studies are needed to predict the behaviour and results of phase change materials (PCMs) usage in buildings in order to optimize the thermal energy storage techniques and to make them more efficient and cost-effective. The aim of this study is to develop a numerical model reproducing the behaviour of an innovative water-PCM heat exchanger for cooling purposes particularly created for HIKARI, the first positive energy, mixed use district in France. Once numerically calibrated and experimentally validated, this model was used to optimize the system\u27s technology applying Genetic Algorithms methods. The model presented in this article was developed based on the heat balance approach and solved using the finite difference method. It was validated both numerically, using a Computational Fluid Dynamics model and experimentally using both the results of an innovative experimental prototype designed and constructed in laboratory conditions and HIKARI in situ monitoring results. The Normalized Mean Bias Error and the Coefficient of Variation of the Root Mean Squared Error, used to analyse the validation results, show that the choice of the heat balance approach provided a valid model able to reproduce the PCM-water heat exchange with high accuracy

Experimental test bed design and development for PCM-water exchangers characterization

\ua9 2017 Elsevier Ltd Despite the thorough research on thermal energy storage (TES) techniques of the last years, especially when based on the use of phase change materials (PCMs), the release to market of efficient technologies is quite recent. For this reason it appears necessary, nowadays, to develop accurate and fast numerical tools, useful for the optimization of this technique. In this paper, the design and the development of an experimental prototype reproducing the behaviour of a PCM-Water heat exchanger with TES purposes is presented. The prototype will be used in the future for the experimental validation of a numerical model that will be used for the optimization of an innovative TES technology at low temperatures. The construction of this prototype appeared fundamental for a complete experimental validation. In fact, it allows us to recreate particular conditions that could be impossible to obtain from the in situ monitoring given the complexity of the reference system. In the end, the results obtained thanks to the protocol application have been analysed in order to decree if they could be used for the comparison between the experimental and the numerical results

Study on transient heat transfer through multilayer thermal insulation: Numerical analysis and experimental investigation

This paper reports on a numerical and experimental study of heat transfer phenomena through two different multilayer fibrous insulations for building applications. The investigated samples were composed of different layers of fibrous materials and aluminium foils, placed between one or two air gaps in the vertical dimension. An experimental apparatus (a guarded hot box) has been used to measure heat transfer through the samples, while a finite volume numerical model combined radiation/conduction heat transfer was developed to predict the temperature distribution and heat transfer in such insulation systems comprised of the materials separated by multiple reflective foils. The model takes into account the coupling between the solid conduction of the fibrous system and the gaseous conduction and radiation. The radiation heat transfer through the insulation system has been modelled via the two flux approximation. The numerical results were compared with the experimental data from the guarded hot box for model validation, as well as to assess the effectiveness of the reflective foils in changing the resistance of the insulations. The comparative verification of the model showed that the numerical results were consistent with the experimental data through the environmental conditions under examination. © 2010 Tsinghua University Press and Springer-Verlag Berlin Heidelberg

Numerical estimation of time lags and decrement factors for wall complexes including Multilayer Thermal Insulation, in two different climatic zones

In the current contribution, time lags and decrement factors for a building wall including different Multilayer Thermal Insulation (MTI) configurations have been calculated numerically. For this investigation purpose, a numerical model which can take care of composite walls was developed. The combined conduction, radiation and convection heat transfer equation was solved explicitly via a control volume discretization. In order to investigate the thermal behavior of a wall under certain outdoor climates, meteorological data that served as boundary conditions were applied to the outer surface of this wall. The outdoor air temperatures were averaged over a number of years after been obtained from hourly measurements in both locations under study. Regarding the solar radiation, it was calculated using a clear-sky model during the summer period. The influence of geographic coordinates' location on the insulating performance of MTI applications was investigated while the wall configurations were supposed to be located in two different climatic zones. The selection of a particular wall configuration involved not only the outdoor climate, but also the whole building characteristics, orientation, etc. The results of the present study are useful for further development in order to conceive and design the optimum MTI configuration, adjusted in specific geographic coordinates and orientations. © 2011 Elsevier Ltd

Review of natural ventilation models

Natural ventilation (NV) is an important and efficient passive technique toreduce building cooling energy need and improve indoor air quality. NVdesign requires profound knowledge and accurate prediction of air flowand heat transfer in and around buildings that are highly dependent onvarying external and internal conditions, as well as the building geometryand local site conditions. This paper reviews the important NV models andsimulation tools and the comparisons of their prediction capabilities. A review of the analytical models reveals that these models are generallyonly applicable to specific geometries and driving forces. The complexinteractions between combined driving forces and complex geometriesresults in sets of non-linear equations which must be solved numerically.Prevalent network airflow models are identified and compared, whichgenerally use the same theory, and yield similar, often nearly identicalresults in inter-model comparison studies. Airflow network modelsincorporated into whole building energy simulation tools are alsoassessed.Results have shown that the current airflow model can be usedto model most NV mechanisms, with an exception of wind-driven singlesidedventilation. For the predictable cases, the most accuracy is achievedfor cases with small and simple openings. For larger openings andespecially complicated openings, the model’s predictions are lessaccurate. Furthermore, the model is heavily dependent on severalsomewhat ambiguous coefficients including: wind profile exponent,pressure coefficient, and discharge coefficient

Guidelines to study numerically and experimentally reflective insulation systems as applied to buildings

There is now widespread acceptance that insulation of the building's envelope plays a key role in efficient reduction of their energy consumption. Consequently, in the course of scientific and technological development, reflecting insulation systems are the object of an international discourse regarding their insulating performances. This study summarizes recent experimental and theoretical research on reflecting insulating systems carried out on an international level. Furthermore, as well as reviewing the existing literature, this contribution aims to introduce an experimental and theoretical framework sketched from the last international norms of standardization, while at the same time the major findings of an original research on reflected insulating systems in the framework of a PhD thesis are presented. To this end, a new data-driven transient heat transfer model was created to estimate the insulation capacity of typical reflecting insulating systems. The main guidelines to create an appropriate numerical model that can be easily modified in order to be valid for all the possible geometries of reflecting insulating systems are briefly presented, while the simulation results regarding a typical reflective insulating system are presented and discussed. © 2012 Taylor & Francis

Numerical estimation of air gaps' influence on the insulating performance of multilayer thermal insulation

This study aims to provide insights regarding the benefits of multilayer thermal insulations in building applications placed in combination with two air gaps. For this purpose, a numerical approach was developed to determine the influence of the air gap thickness on the overall thermal resistance of a composite wall. A validated combined radiation/conduction heat transfer numerical model was employed to predict the temperature distribution and heat transfer in typical multilayer insulation complexes comprised of insulating materials separated by multiple reflecting foils. The radiation scheme was based on the two-flux approximation, in order to model both optically thick and optically thin fibrous materials. The heat transfer equation was solved explicitly for a composite wall. A basic methodology for designing simulation scenarios was employed in order to reduce the number of simulated cases. Furthermore, strict entry requirements were provided in order to reduce extraneous variation due to the complexity of physical phenomena that should be investigated in such a case study. Finally, total nine different configurations were selected as initial state, where the theoretical thermal resistances were calculated and compared, leading towards an empirical polynomial equation that calculates the overall thermal resistance of such a composite wall complex departing from the two air gap thickness values. © 2011 Elsevier Ltd

Occupant presence and behavior: A major issue for building energy performance simulation and assessment

International audienc

Air–PCM heat exchanger for peak load management: Experimental and simulation

Peak power consumption is becoming an increasing problem worldwide and particularly in France during the late afternoon winter periods. This paper describes the experimental and numerical studies carried out to investigate the potential of a PCM (phase change material) – Air heat exchanger, conceived for load shifting purposes.The objective is to possess the necessary tools for the development of advanced control strategies taking into account various factors: peak power reduction, thermal comfort and indoor air quality. The experimental approach involved the construction of a heat exchanger coupled to an experimental cell. The heat storage system is composed of a set of PCM (paraffin) plates, embedded in the exchanger and integrated in a ventilation system.In parallel, a numerical model was developed using the apparent heat capacity approach and the finite differences method. Furthermore, a series of characterization tests was conducted and the experimental data were used for model calibration and validation. The model was then coupled with a building simulation program, presenting good agreement between the integrated model prediction and the experimental data. Finally, a preliminary control strategy of the test cell is presented along with results demonstrating the capabilities of such system for peak load management

Uncertainty in building fan pressurization tests: Review and gaps in research

International audienc