Indoor climate assessment of a classroom with mechanical ventilation and operable windows

Ventilation air may be provided in buildings by means of natural or mechanical strategies. When a HVAC system is installed, thermal comfort and indoor air quality (IAQ) may be controlled with higher precision. However, especially between the 70s and the 90s, mechanical ventilation systems have been installed on formerly naturally ventilated buildings without providing any control for natural ventilation. The two ventilation systems are therefore overlapping, without any energy or comfort oriented control strategy, and the occupants are operating windows without any consistent understanding of IAQ and comfort conditions, neither of energy consumption. It may both lead to a substantial energy waste and to low indoor climate conditions. A typical university classroom with exhaust mechanical ventilation and operable windows without switching control has been assessed, in order to understand how occupant behaviour and different ventilation scenarios may influence indoor climate conditions

Analysis and modeling of magnetocaloric effect near magnetic phase transition temperature

International audienceMagnetocaloric behavior of gadolinium near room temperature can be correctly described by the Weiss molecular field theory especially in the paramagnetic state. In this paper, this approach is generalized for binary rare earth alloys which present as Gd a second order phase transition. The magnetic entropy variation can be calculated as a function of the temperature and the applied field. This model was tested on a laboratory synthesized samples of Gd-Tb. The agreement between calculations and experiments shows that this model can be easily used for these alloys in order to optimize their composition and adjust their Curie temperatures. For first order transition materials, the observed magnetocaloric effect enhancement can be explained by magnetoelastic effects which are due to the spontaneous crystal deformation and the structure transformation. A model based on the phenomenological approach of Bean Rodbell is developed to describe such a behavior. It highlights the link between the nature of magnetic transition and the magnetocaloric effect. It can be identified by only two parameters: T 0 the Curie temperature without deformation and η an order parameter which characterizes the transition nature. In this paper we apply this model to describe the giant magnetocaloric effect exhibited by the new Mn 1-x (Ti 0.5 V 0.5) x As materials

ISO 14001 Environmental Management System Approvals In the economic institutions in Algeria

شهدت العقود الأخيرة ظهور وتطور مختلف الممارسات الإدارية المتعلقة بالجودة والبيئة ورغم هذا التطور، فإن تحليل تحليل أسباب لتبني هذه الممارسات الإدارية وآثارها على الشركات لم تحظ بالقدر الكافي من الدراسة والتحلي. وتساهم هذه الدراسة في الأدبيات التجريبية المتعلقة بالجودة البيئية في المؤسسات الإقتصادية في الجزائر، حيث قمنا بتحليل محددات اعتماد معايير ISO 14001 من طرف المؤسسات الإقتصادية في الجزائر بواسطة نموذج الانحدار اللوجستي وذلك باستخدام العديد من المتغيرات التي قد تؤثر على اعتماد ISO 14001  من قبل المؤسسات الاقتصادية في الجزائر. وتبين لنا أن المؤسسات الاقتصادية التي لديها منتجات للتصدير والمؤسسات الكبيرة والمؤسسات الإقتصادية التي تعتبر شركات النفط أحد عملائها هي المؤسسات الأكثر توجها نحو اعتماد معايير ISO 14001Recent decades have seen the emergence and development of various managerial practices that respect quality and the environment. However, analysis of the reasons for adopting these managerial practices by companies and their impact on businesses has been little studied by economists. The aim of this empirical study is to identify the factors that push economic companies in Algeria to adopt ISO 14001 standards. We analyze a logistic regression model that describe the relationship between several determinants and the adoption of ISO 14001 standards, using various variables that may impact the adoption of ISO 14001 standards by economic companies in Algeria. We conclude that the companies oriented to Export and that have a large business as also that transact with oil companies are more oriented to adopt ISO 14001 standards

Energy efficiency and indoor aire quality os seminar rooms in older buildings with and without mechanical ventilation

The present paper reports on an experimental study performed in a seminar room of the University of Luxembourg in a building of the 1970ies without a major renovation. This lecture room is typical for this building period and has a capacity of 60 seats. It is equipped with a mechanical ventilation system that is normally in operation on workdays for 11 hours a day in semester periods (8:00-19:00h), while windows can be opened manually. A Blower-Door-Test revealed that the room is not airtight. During a year, the ventilation system was shut “on” and “off” in periods of some weeks and the consumed final-energy was measured, as well as the indoor climate assessed by physical and psychological measurements. For instance, the measured CO2 concentrations are marginally better with the ventilation system "on", which was not perceived in any way by the occupants during the investigations. It was not possible to properly identify the impact of ventilation on the consumed heat-energy, as the room could not be thermally separated from the rest of the building. But with the system “on” there was a clear increase in consumed primary energy due to the electric consumption of the fans. No relationship between the perceived percentage of dissatisfied and perceived climate could be observed. It is concluded that the typical normal operation modus is questionable for seminar rooms in older buildings with variable occupancy and that a simple shut down or semi-automatic user controlled modus by low-cost retrofit seems advantageous

Ventilation rates and thermal comfort assessment in a naturally ventilated classroom

Ventilation systems are meant (i) to guarantee good indoor air quality (IAQ) by providing and distributing fresh air to the occupied/breathing zone and (ii) to dilute and remove pollutants emitted by indoor sources. On the other hand, inadequate ventilation rates can induce discomfort issues and excessive energy consumption. This study focuses on the performance assessment of natural ventilation strategies in university classrooms, which are characterized by a high occupancy level and the necessity to provide high levels of comfort to perform intellectual work. The high occupancy level creates challenging conditions both in terms of internal gains and CO2 concentration. This paper presents an experimental performance assessment of four natural ventilation strategies applied to a university classroom: single side ventilation, cross ventilation, stack ventilation with and without window supply. Each strategy is evaluated in terms of thermal comfort and air change rate measurements. Thermal comfort assessment were performed during occupancy period (physical parameter measurements and questionnaires) whereas air change rate measurements, based on tracer gas techniques, were performed during unoccupied periods

Passive force balancing of an active magnetic regenerative liquefier

Active magnetic regenerators (AMR) have the potential for high efficiency cryogen liquefaction. One active magnetic regenerative liquefier (AMRL) configuration consists of dual magnetocaloric regenerators that reciprocate in a persistent-mode superconducting solenoid. Issues with this configuration are the spatial and temporal magnetization gradients that induce large magnetic forces and winding currents. To solve the coupled problem, we present a force minimization approach using passive magnetic material to balance a dual-regenerator AMR. A magnetostatic model is developed and simulated force waveforms are compared with experimental measurements. A genetic algorithm identifies force-minimizing passive structures with virtually ideal balancing characteristics. Implementation details are investigated which affirm the potential of the proposed methodology

Evaluation expérimentale des performances des systèmes de ventilation dans le bâtiment : efficacité de ventilation et confort thermique

The performance of a system must be well defined, attainable and above all measurable. This is not the case today for ventilation. On the one hand ventilation performance is usually declined on energy efficiency considerations or simply on a rough estimation of ventilation rates. The performance related to thermal comfort and IAQ are addressed separately through dedicated evaluation tools. On the other hand, the existing evaluation tools today are nowadays limited in their practical applications for in situ measurements, in particular in the case of natural and mixed ventilation. The aim of the present thesis is to examine the existing experimental technics, at full scale building in order to propose improvements on evaluation methods and commissioning protocols. The present thesis deals with ventilation performance taking into account ventilation efficiency as intrinsic performance and thermal comfort as overall performance.The first part is devoted to the in situ assessment of intrinsic ventilation performance (ventilation rates, mean age of air, and air exchange efficiency), based on decay tracer gas techniques. After a theorical analysis of the various performance indexes and their corresponding measurement techniques, an experimental study was carried out in a classroom under different ventilation strategies (mechanical, natural & mixed mode). The analysis proved the importance of the application of the tracer gas decay on ventilation rates accuracy with in particular a strong influence of measurement times and used tracer gas concentration. A methodology has been adapted and tested for the measurement of the air exchange efficiency in natural and mixed mode ventilation, by avoiding measurements in exhaust vents (a technique usually used and advocated by current standards).The second part is devoted to in situ assessment of thermal comfort under different ventilation strategies. Different methods, standards and evaluation techniques were tested and compared with occupants’ perception. The results demonstrated the presence of several inadequacies during the implementation of existing methods and standards. Mainly, it concerns the inadequacy of static methods (PMV PPD) for thermal comfort assessment in the presence of fluctuating thermal conditions, even with mechanical ventilation. Uncertainty analysis related to measurement errors has demonstrated the incoherence of current standards in the classification of comfort categories.La performance d’un système doit être bien définie, atteignable et surtout mesurable. Ce n’est pas le cas aujourd’hui pour la ventilation. D’une part, les performances des systèmes de ventilation sont habituellement exprimées sur des considérations énergétiques ou tout simplement sur une estimation trop approximative des débits de ventilation. Les performances liées au confort thermique et à la qualité de l’air intérieur sont abordées séparément à travers des outils d’évaluation dédiés. D’autre part, les outils d’évaluation existants sont aujourd’hui limités dans leur mise en pratique pour des mesures in situ, notamment lorsqu’il s’agit de ventilation naturelle et mixte. L’objectif de cette thèse est alors d’examiner et d’expérimenter les techniques expérimentales existantes à échelle réelle afin de proposer des améliorations sur les méthodes d’évaluation et de commissionnement. La thèse aborde la performance de la ventilation en prenant en compte l’efficacité de ventilation comme performance intrinsèque et le confort thermique comme performance globale.La première partie est consacrée à l’évaluation in situ des performances intrinsèques de ventilation (taux de ventilation, âges moyens de l’air et efficacité de renouvellement d’air), en se basant sur des techniques de gaz traceurs. Après une analyse théorique des différents indicateurs de performance de ventilation et de leurs techniques de mesure correspondantes, une étude expérimentale a été menée dans une salle de cours sous différentes stratégies de ventilation (mécanique, naturelle et mixte). Les analyses ont démontré l’importance de la mise en application des techniques de décroissance de gaz traceurs sur l’incertitude des taux de renouvellement d’air avec notamment une forte influence des temps de mesure et des concentrations de gaz utilisées. Une méthodologie a été adaptée puis testée pour la mesure de l’efficacité de renouvellement d’air en ventilation mécanique, naturelle et mixte en s’affranchissant de mesures en bouches d’extraction (technique habituellement utilisée et préconisée par les normes).La deuxième partie est consacrée à l’évaluation expérimentale in situ du confort thermique sous différentes configurations de ventilation. Différentes méthodes, standards et techniques d’évaluation ont été testés et comparés avec la perception des occupants. Les résultats ont démontré la présence de plusieurs inadéquations lors de la mise en pratique des méthodes et normes existantes. Principalement, il s’agit de l’inadéquation des méthodes statiques (PMV PPD) pour l’évaluation du confort en présence de conditions thermiques fluctuantes, y compris en ventilation mécanique. Les analyses d’incertitudes liées aux erreurs de mesure ont démontré l’incohérence des normes actuelles dans la classification des catégories de confort

Detection of outliers and changepoints in time series. Applications over the management of electricity production

Continental est l'outil de référence utilisé par EDF pour la gestion d'électricité à long terme. il permet d'élaborer la stratégie d'exploitation du parc constitué de centrales réparties sur toute l'europe. l'outil simule sur chaque zone et chaque scénario plusieurs variables telles que la demande d'électricité, la quantité générée ainsi que les coûts associés. nos travaux de thèse ont pour objectif de fournir des méthodes d'analyse de ces données de production afin de faciliter leur étude et leur synthèse. nous récoltons un ensemble de problématiques auprès des utilisateurs de continental que nous tentons de résoudre à l'aide des technique de détection d'anomalies et de ruptures dans les séries temporelles.Continental is the main tool that edf uses for the long-term management of electricity. It elaborates the strategy exploitation of the electrical parc made up by power plants distributed all over europe. the tool simulates for each zone and each scenario several variables, such as the electricity demand, the generated quantity as well as the related costs. our works aim to provide methods to analyse the data of electricity production in order to ease their discovery and synthesis. we get a set of problmatics from the users of continental that we tent to solve through techniques of outliers and changepoints detection in time series