Numerical investigation of energy potential and performance of a residential building-integrated solar micro-CHP system

International audienceThe studied micro-CHP unit converts concentrated solar energy into electricity and heat by coupling a 46.5 m² parabolic trough collector with an oil-free single-cylinder steam engine operating according to the Hirn cycle. Originalities of this system are two axis solar tracking and direct steam generation. The exhaust heat of the cycle is recovered to cover building's heat needs, while the electricity is either self-consumed or fed back into the electricity grid. Experimental studies have shown that it is impossible to achieve continuous operation of the facility without an additional heat source. Thus, we are studying solutions for integrating a backup heating system from dynamic thermal simulations performed with TRNSYS© software One of them consists in adding a 30 kW boiler to the primary circuit in order to ensure daily electricity production. However, this is restricted by the considered storage tank. A parametric study on the volume of the storage tank makes it possible to propose an optimal solution for heat recovery. The results indicate that a storage volume of 3 m 3 meets the needs of the building and limits the heat losses due to heat storage. In order to optimize the use of such a micro-CHP unit, a heat sharing between several buildings equipped with 3 m 3 storage seems therefore to be a coherent solution

ABSTRACT Logistics: A Step Towards Lean Construction LOGISTICS: A STEP TOWARDS LEAN CONSTRUCTION

Some factors are likely to impel a deep change in the construction industry in France. As in other European countries, this activity remains traditional in spite of a significant flow of innovations concerning both industrial products and execution of works on site. Experimental building operations have been carried out within the frame of a national five year programme focused on the improvement of the activity on site. The consequences of these experiments on the relations between actors have been studied from different points of view. Nearly one hundred operations will have been supported by the end of 1999. This paper is based on the evaluation of several of these experimental operations with a special emphasis on site logistics, which is considered as a step towards lean construction, because it clearly reveals where are the limitations to improvements. The variety of projects, of size of contracting companies, and of constraints of industrial products involved in these experiments allow concluding remarks concerning the conditions of development of lean construction in Franc

Sensitivity study of the energy balance to urban characteristics

International audienc

Modèles en thermique du bâtiment, réduction de modèles et approches inverses

International audienc

Sensitivity study of the energy balance to urban characteristics

International audienc

Le climat et la ville : la nécessité d’une recherche croisant les disciplines

With the observation of the urban climate and after the modeling of the physical phenomena, the climatologists are and were able to describe and to understand with more and more precision the formation of the urban climate. The first works were above all dedicated to the urban heat island observed globally on all the urban area. The climatologists were gradually interested in the other climatic parameters (pluviometry, wind, etc.) and in lower scales than the city, highlighting the importance of the urban geometry and the building materials. The urban climatology is a research thematic investigated at the same time by the climatologists and the geographers, but also by the architects and the town planners. This allows to set up a multidisciplinary approach and to integrate into the practice of the urban planning and the architecture some elements of urban climatology. So climatologists, geographers, town planners and architects could reflect together on the interest to take into account the urban climate in the urban planning and the architecture. We need some tools allowing to take into account the urban climate in the urban conception but priory has to be given to promote and to organize a better synergy between the various actions led in favour of the environment. Green infrastructures are a good example. Initially implemented to provide connexions between natural habitats of species by corridors, they can also improve the climatic quality of spaces

Solar panels reduce both global warming and urban heat island

International audienceThe production of solar energy in cities is clearly away to diminish our dependency to fossil fuels, and is a good way to mitigate global warming by lowering the emission of greenhouse gases. However, what are the impacts of solar panels locally? To evaluate their influence on urban weather, it is necessary to parameterize their effects with in the surface schemes that are coupled to atmospheric models. The present paper presents a way to implement solar panels in the Town Energy Balance scheme, taking account of the energy production (for thermal and photovoltaic panels), the impact on the building below and feedback toward the urban microclimate through radiative and convective fluxes. A scenario of large but realistic deployment of solar panels on the Paris metropolitan area is then simulated. It is shown that solar panels, by shading the roofs, slightly increases the need for domestic heating (3%). In summer, however, the solar panels reduce the energy needed for air-conditioning (by 12%) and also the Urban Hea tIsland (UHI): 0.2K by day and up to 0.3K at night. These impacts are larger than those found in previous works, because of the use of thermal panels (that are more efficient than photovoltaic panels) and the geographical position of Paris, which is relatively far from the sea. This means that it is not influenced by seabreezes, and hence that its UHI is stronger than for a coastal city of the same size. But this also means that local adaptation strategies aiming to decrease the UHI will have more potent effects. In summary, the deployment of solar panels is good both globally, to produce renewable energy (and hence to limit the warming of the climate) and locally, to decrease the UHI, especially in summer, when it can constitute a health threat

Méthodologie pour la quantification de l’impact d’aménagements urbains sur un climat urbain modifié

Dans le cadre du projet EPICEA (Ville de Paris, Météo-France et Centre Scientifique et Technique du Bâtiment), cette étude s’intéresse à un épisode climatique extrême – la canicule d’août 2003 – en tant qu’extrapolation dans le futur, puisque, si l’on considère le scénario le plus pessimiste (A2), un tel phénomène concernerait l’Europe de l’Ouest en moyenne un été sur deux d’ici 2070. Une simulation à 250 m de résolution de la période allant du 08 au 13 août 2003 est effectuée en utilisant le modèle de recherche numérique MésoNH, modèle non-hydrostatique à échelle très fine préfigurant la future génération de modèles numériques de prévision du temps, et le schéma de ville Town Energy Budget (TEB). TEB représente la ville de manière théorique sous la forme d’un canyon urbain dans lequel est modélisé le bilan d’énergie des surfaces élémentaires urbaines (route, toit mur). Il est ici employé en mode « couplage » avec le modèle MésoNH pour caractériser au mieux les conditions atmosphériques urbaines. Son homologue pour la végétation, Interactions Sol-Biosphère-Atmosphère (ISBA), est également utilisé. La ville de Paris est représentée en mode « réaliste » par le biais d’une base de données du couvert urbain parisien élaborée conjointement avec l’Atelier Parisien d’Urbanisme, intégrant l’altitude, les surfaces de végétation, de voirie, d’eau, les hauteurs des bâtiments, les différents types de toits et de murs et leur surface, etc. Les données de surface issues de cette base sont retravaillées et intégrées au modèle de ville TEB via un logiciel SIG. Les résultats sont très satisfaisants : le modèle reproduit bien les observations de température et de vent, ainsi que le cycle diurne d’humidité relative et les caractéristiques du climat urbain sont clairement identifiées. Les résultats permettent de discerner des micro-ICU au sein de Paris avec des différences de température de 2 à 4°C et mettent en évidence la vulnérabilité des arrondissements périphériques et de certaines communes limitrophes en liaison avec le panache urbain engendrant des différences de température de l’ordre de 2°C. Par ailleurs, différents leviers d’action sur le climat urbain ont été préalablement identifiés. Les plus pertinents sont l’albédo des surfaces (toits, murs et voirie) et la végétalisation des surfaces urbaines. Différents tests de sensibilité sont donc envisagés en modifiant ces paramètres, dans un contexte de canicule (août 2003) : éclaircissement des façades et des toitures, verdissement et humidification de la ville. Cette étude confirme l’intérêt d’utiliser ce type de schéma urbain en intégrant les spécificités complexes de l’occupation des sols en milieu urbain dans l’optique d’études sur l’adaptation d’un territoire au changement climatique, en comparant une situation de référence – présentée ici – à différents scénarios réalisables dans le futur