Jour | EPFL Graph Search

vignette|360px|Les moments de la journée. Le jour ou la journée est l'intervalle de temps qui sépare le lever du coucher du Soleil. Le jour est précédé par l'aube le matin, aussi appelée « petit jour » et laisse place au crépuscule le soir. Son début (par rapport à minuit heure locale) et sa durée dépendent de l'époque de l'année et de la latitude ; ainsi, le jour peut durer six mois aux pôles terrestres. Par extension, le jour ou la journée correspond à une rotation complète de la Terre sur elle-même par rapport à un point géographique donné, soit l'ensemble d'un jour, d'un crépuscule, d'une nuit et d'une aube consécutifs. Les jours sont traditionnellement regroupés en semaines et portent en français les noms lundi, mardi, mercredi, jeudi, vendredi, samedi et dimanche. Enfin, le jour est aussi le nom de l'intervalle qui sépare un moment de son lendemain à la même heure au même endroit, par exemple entre le à et le à la même année. On parlera parfois dans ce cas de jour courant o

Domestic hot water optimizing potential in existing or renovated multifamily residential buildings

Flourentzos Flourentzou, Joshua Pereira

In a Swiss case study of the ReCO2st research project, hot water optimization demonstrated a high potential for energy savings with low investment costs. The optimization started with the end user to reduce first hot water consumption. Energy-efficient showerheads and faucets reduced hot water consumption by 10 to 25%, notably from 65.2 [l/p.day] to 48 [l/p.day] for the period of September to October 2019. A multi-criteria selection of showerheads involved end users considering other qualitative aspects like rinsing efficiency, overall feel of use, noise, and material robustness. Strict control of pipe and storing tank insulation reduced storage and distribution losses. Day and night storage temperature setpoints, water recirculation time, switching off this process after 11.00 p.m., temperature differential of start and stop loading setpoints, creating long loading cycles, ensure that the pipes are not always hot. Reducing Legionella cycles at 60 degrees to once a day avoided the need for continuous high temperatures. The combination of all these soft measures in the Swiss case study resulted in a reduction of energy consumption for hot water of 20-30%. This is equivalent to the installation of expensive solar panels for hot water. A detailed two- year monitoring of the building's hot water consumption shows the contribution of each optimization measure. The encouraging results show that without perfect control of the entire process, it is impossible to avoid a performance gap between planned and actual energy consumption.

IOP PUBLISHING LTD2021

Preliminary Study of a Solar Trough/Tower Power Plant

Jorge López Moreno

The possibility of combining both the advantages of a solar tower thermal power plant and of a solar parabolic trough power plant could be interesting from an energetic point of view as well from an economic point of view. The preliminary study of this combination feasibility is the goal of this project. The study of the project viability consist first of all on the modeling of the trough system, the energy balance of the parabolic troughs will be established at first. Secondly, and choosing a perfect solar day simulating a day when the solar radiation is rather stable, with no cloudy periods along the day, the power available from the trough plant can be calculated. Once we have estimated the power that we can introduce into the cycle of the tower plant, the main issue consists on how and where it is better to use this energy in the cycle. Several possibilities seem to be interesting a priori, however a more detailed study of each one is to be done in order to get to the most economic and efficient layout. The work related to the tower thermal power plant will be done taking as starting point the master thesis of James Spelling, who did an incredible work in this field and whose work will be a valuable help to continue the research on the proposed concept in this project of combining two plants, tower and trough. The main advantage of the tower design compared to the parabolic trough design is the higher temperature. As it will be explained further, thermal energy at higher temperature can be converted more efficiently, the exergy efficiency is better. In terms of storage, the high temperature results in a cheaper and a more efficient storage system. Nevertheless, the set up of the field of heliostats is more complex than the set up of the parabolic trough lines even though the area for a trough plant must be previously flattened. The lower temperature level that entails an inconvenient itself for a parabolic trough power plant may become an advantage when combining both types of concentrating solar power plants. If the results are positive enough that it seems interesting to combine both types of power plants, another step forward will be done towards the use of the sun energy as a renewable source thus making it a more interesting choice for power generation. Sun potential has already shown as an important technology not only at the present time but also in the future. Commercial solar plants have already achieved levelized energy costs around 12-15 UScts/kWh, and the potential for cost reduction is expected to follow this trend even further, to costs as low as 5 UScts/kWh. In addition the taxes imposed for the non-green power should make even more interesting the use of concentrating solar power plants. The requirements of high beam normal radiation lead to a limited amount of suitable places where the implantation of this technology is possible. However many places exist on Earth where the conditions are perfectly adapted, we talk about regions such as United States (the country with more carbon dioxide emissions in the world), some regions in Mexico, North Africa, India, Australia, northeastern Brazil and some locations around the Mediterranean, especially in the south of Spain. The challenge is therefore set for a change in our energy production scheme.

2010

Taking the pulse of volcanic eruptions using plagioclase glomerocrysts

Stéphane Laurent Escrig, Anders McCarthy, Anders Meibom, Pierre Vonlanthen

Crystallization timescales in subvolcanic systems and the consequences of interaction between ascending magmas and gases remain largely unconstrained, as do links between these processes and monitoring signals at restless volcanoes. We apply diffusion chronometry to radially-oriented plagioclase and associated olivine in a glomerocryst from Tolbachik volcano (Kamchatka, Russia) to elucidate such processes. We show that cm-size glomerocrysts grow in a few days prior to, or during, eruption. Melt inclusions from these glomerocrysts show no compositional evolution during crystallization, implying growth in a melt-rich and dynamic environment. Volatile elements in melt inclusions show significant variability, with increasing CO2 as H2O decreases. This behaviour is inconsistent with normal degassing processes, and more likely reflects CO2-fluxing. On the basis of short residence timescales of glomerocrysts and sharp changes in melt inclusion volatile abundances, we propose that rapid (pre-)eruptive crystallization is controlled by rhythmic fluxing of magmatic H2O and CO2 through the sub-volcanic conduit. This implies that compositional zoning in plagioclase, from resorption textures to oscillatory zoning, record short-term CO2- and H2O-fluxing episodes, consistent with strombolian eruption dynamics. We propose that volcanic glomerocrysts represent the counterpart of vertical igneous layering (or comb layering) in shallow plutons. Magmatic layering and glomerocrysts dominated by radial plagioclase offer novel ways of targeting short-term crystallization and degassing processes in subvolcanic systems. (C) 2020 The Author(s). Published by Elsevier B.V.

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Preliminary Study of a Solar Trough/Tower Power Plant

Jorge López Moreno

2010