Survey of the existing approaches to assess and design natural ventilation and need for further developments

ISBN : 978-0-947649-40-1 Disponible à l'adresse : www.ibpsa.org/proceedings/BS2009/BS09_0220_227.pdfInternational audienceIn the last years many building designers have turned their attention to natural ventilation, due to the potential benefits in terms of energy consumption related to ventilation and air-conditioning, especially in mild and moderate climates. Consequently, several calculation techniques have been developed to design and predict the performance of natural ventilation. This article presents a review of the existing approaches to predict natural ventilation performance, including simple empirical models, nodal models (mono-zone and multi-zones), zonal models and CFD models. For each approach, we analyse the physical basis, the main modelling assumptions, the necessary input data and the area of applicability. Thus, the integration of these methodologies in the available simulation programs is examined, with reference to the different phases of the natural ventilation design process and some examples of application are given. The aim of the review is to identify the main practical limits of existing programs in designing natural ventilation and in predicting its performance and the consequent need for further developments

Towards a better understanding of clogged steam generators: a sensitivity analysis of dynamic themohydraulic model output

Communication available online at http://hans.wackernagel.free.fr/article_ICONE_final_140311.pdfInternational audienceTube support plate clogging of steam generators affects their operating and requires frequent maintenance operations. A diagnosis method based on dynamic behaviour analysis is under development at EDF to provide means of optimisation of maintenance strategies. Previous work showed that the dynamic response to a power transient of the wide range level measurement contains informations about the clogging state of steam generators. The diagnosis method consists of comparisons of the measured dynamic response with simulations on a mono-dimensional dynamic steam generator model for various input clogging configurations. In order to assess the potential of this method, a sensitivity analysis has been conducted through a quasi-Monte Carlo scheme to compute sensitivity indices for each half tube support plate's clogging ratio. Sensitivity indices are usually defined for scalar model outputs. Principal component analysis has been used to determine a small subset of variables that condense the information about the shape of the response curves. Finally, estimation variability was assessed by construction of bootstrap confidence intervals. The results showed that half of the preselected input variables have negligible influence and allowed to rank the most important ones. Interactions of input variables have been estimated to exert only a small influence on the output. The effects of clogging on the steam generator dynamics has been characterised qualitatively and quantitatively

Simulation Based Assessment of Heat Pumping Potential in Non-Residential Buildings – Part 3: Application to a typical office building in Belgium

peer reviewedThe purpose of this paper is to describe the application of the tools presented in a companion paper [1] to a typical office building located in the Walloon Region of Belgium. This building is a mid-size (7000 m² on seven floors) office building constructed in the eighties and equipped with a classical HVAC solution: boiler and air-cooled chiller; all-air VAV system. An energy audit was conducted in this building and featured a number of management problems. Among the Energy Conservation Opportunities considered to improve the energy performance of the building, the move to a heat pump solution was considered. The identification of energy savings potential offered by the implementation of heat pumping strategies confirmed what was already shown by the parametric analysis: in temperate climates, reversibility offers a by far higher potential than condenser heat recovery given the dominant non simultaneity of the yearly heating and cooling demands profiles. Calculations show that theoretically half of the heating demand could be satisfied by the reversibility of the chiller to run in heat pumping mode. In a second step, a number of practical implementations of heat pumping solutions were evaluated by means of another software tool: reversible air/water HP, exhaust air HP, double condenser and water loop heat pump systems. These solutions are compared to the reference existing situation (boiler + chiller working independently) in terms of energy, CO2 emissions and cost on a 20 years life-cycle basis. Calculations show that the air/water reversible chiller solution offers the most important energy savings and CO2 reduction while staying at a reasonable level concerning the additional cost.IEA-ECBCS Annex 4

Influence Of Building Zoning On Annual Energy Demand

Simulation tools are widely used to assess the energy consumption of a building. In the modeling process, some choices should be made by the simulation tool user such as the division of the building into thermal zones. The zoning process is user dependent, which results in some difference in energy consumption results and model set-up and computational times. The aim of this work is to assess the influence of building zoning on the results of the dynamic thermal simulation including airflow and thermal transfers between zones For this purpose, several different building zonings are applied to the same office building, and then the results of the dynamic thermal simulations are compared in terms of energy consumption (heating, cooling, and auxiliaries) and computational and set-up times. To assess the impact of thermal zoning, five cases are studied (from the most to the least complex): - 1) *49-zone model* : each zone gathers the premises with the same air handling system, the same occupancy profile, at each floor and building orientation. - 2) *44-zone model* : the premises containing the same air handling system are gathered at every floor, even though their occupancy profile is different. - 3) *26-zone model*: all floors are merged, except for the first and the top floors (under-roof). - 4) *21-zone model* : the first and the under-roof floors are merged with the others if the premises have the same occupancy profile and handling system. - 5) *11-zone model* : the premises with a different orientation but with the same occupancy profile and handling system are gathered. The importance of airflow coupling is evaluated by using the most detailed model (49 zones) and comparing the cases with or without considering air transfer from offices to corridors and toilets (from which air is extracted). Then, to study the impact of thermally connecting juxtaposed zones, the “21-zone model” with and without thermal transfer are compared. Finally, the impact of merging the floors is analyzed by considering different roof and floor insulations and the impact of merging the orientations is studied by using different glazed surface ratio

ISUPFERE: une formation Ingénieur en énergétique des Mines de Paris en prise directe avec les enjeux de la rénovation des bâtiments

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Simulation Based Assessment of Heat Pumping Potential in Non-Residential Buildings – Part 2: Parametric Study

peer reviewedThis paper is the second one in a series of three papers presenting the assessment methodology of heat pump systems developed in the frame of the IEA-ECBCS Annex 48 project. A package of simulation tools is developed in order to assess the energy and environmental performances and costs of various reversibility and heat recovery solutions dedicated to space heating and cooling. This paper presents the results of an extended parametric study aiming in assessing the potential of the considered heat pump systems in the European building stock.IEA-ECBCS Annex 4

Simulation Based Assessment of Heat Pumping Potential in Non-Residential Buildings – Part 1: Modeling

peer reviewed1 Introduction A solution to reduce the energy consumption in office and health care buildings consist in better exploiting the potential of the heat pump technology. This can be done by recovering heat at the condenser when the chiller is used to produce cold (simultaneous heating and cooling demands) or by using the chiller in heat pump mode (non-simultaneous heating and cooling demands). Both strategies appear particularly feasible when cooling and heating needs and the heat pump technology are, at least partly, present in the building, which is often the case in the tertiary sector. The analysis of these reversibility and recovery potentials is one of the subjects of the IEA-ECBCS Annex 48 project. 2 Simulation tools A package of simulation tools is developed in order to assess the energy and environmental performances and costs of such solutions. A first tool allows a quick estimation of the potential of recovery and reversibility options, starting with limited information and using a limited amount of parameters. It consists in simulating the considered building and its secondary HVAC system in order to generate hourly values of heating and cooling system loads and to compute theoretical reversibility and recovery potentials. This first simulation run can be performed by mean of a calibrated building energy simulation tool (Trnsys, Energyplus…). Hourly values of heating and cooling loads of a given building can also be obtained through in-situ measurements. A second tool allows to simulate the behavior of the heat pump plant and to compute its performances using the previously computed heating and cooling load profiles as inputs. The considered heat pump configuration is then compared to a classical HVAC primary system (composed of a boiler and a chiller) in terms of primary energy consumption, CO2 emissions and costs. In this first paper, the development of such models and their implementation in an equation-based solver are described. The considered heat pump configurations are presented and the models of the main components (heat pump, boiler, thermal storage system, cooling tower and ground heat exchanger) are described. Five general configurations are considered: (1) reversible air-to-water heat pump, (2) exhaust air heat pump, (3) dual condenser heat pump, (4) water loop systems and (5) ground coupled heat pump. The modeling hypotheses, the control algorithms and the connection of these models into global heat pump systems simulation models are discussed. Finally, it is shown how simple equation-based simulation models can be connected to allow quick and robust assessment of the potential of complex heat pump systems.IEA-ECBCS Annex 4

Optimisation de l'intégration de solutions énergétiques dans les bâtiments

Pour atteindre les objectifs ambitieux de réduction des consommations énergétiques dans le bâtiment que s’est fixé l’Europe, il est nécessaire non seulement de développer des systèmes à très haute efficacité énergétique et des solutions passives pour le confort intérieur mais aussi de développer des méthodes de dimensionnement et de conduite des équipements adaptées aux différents usages des bâtiments. La démarche proposée repose sur une caractérisation expérimentale des solutions Chauffage-Ventilation-Climatisation (CVC), leur modélisation simplifiée et enfin leur couplage aux bâtiments dans des outils de simulations énergétiques afin d’évaluer leurs performances saisonnières. Des modèles physiques réduits des systèmes sont privilégiés afin de pouvoir les paramétrer à partir de données facilement accessibles et de réduire le temps de calcul notamment pour les coupler à des algorithmes d’optimisation. Mes travaux de modélisation sur la ventilation naturelle, la climatisation par dessiccation et la micro-cogénération illustrent la démarche.La perspective de bâtiments à énergie positive nécessite de faire évoluer la simulation énergétique des bâtiments. D’une part, l’intégration de méthodes statistiques dans les outils de simulation et d’autre part une meilleure prise en compte des interactions multi-physiques, de la régulation des systèmes et du comportement des occupants sont des éléments contribuant à la fiabilisation des outils

Urbanisme en milieu tropical pour favoriser la ventilation naturelle

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