Naturally ventilated geothermal foundation modeling

AbstractThis work is concerning the modeling of a heat and mass transfer within a new kind of Canadian well, a geothermal foundation, and its coupling with a solar chimney. The foundation model is based on a 3D finite volume method. A long term simulation is necessary, aiming to precisely understand the behaviour of this combined system. Since this model requires high computational resources, we propose to use a domain decomposition technique and the balanced realization reduction method to speed up computational time. The studied case shows this system seems to be relevant to supply cold air to buildings during summer

Convection naturelle dans un canal vertical chauffé asymétriquement : stratification thermique externe et écoulements de retour (S23).

Le refroidissement passif d'une façade double-peau photovoltaïque est étudié expérimentalement par l'analyse de la convection naturelle dans un canal vertical chauffé ouvert dans une cellule en eau. Une paroi est chauffée à une densité de flux de chaleur uniforme, l'autre étant adiabatique. L'étude est réalisée pour un nombre de Rayleigh modifié élevé (Ra* = 2, 75.10^7 ). Les mesures de température de la paroi chauffée et de vitesse en sortie du canal par PIV (Particle Image Velocimetry) ont mis en évidence deux états dits "mélangé" "et "stratifié" qui sont caractérisés par la position du maximum de température de paroi situé, respectivement, à mi-hauteur et en sortie. Les mesures de vitesse montre que l'état stratifié est toujours associé à l'existence d'un écoulement de retour. Les trois expériences, réalisées pour différentes stratifications thermiques de la cellule en eau, montrent trois dynamiques différentes de changement d'état

Simulation study of a naturally-ventilated building integrated photovoltaic/thermal (BIPV/T) envelope

This paper addresses the simulation of a partially transparency, ventilated PV facade integrated into the envelope of an energy efficient building. Such an arrangement exploits the heat transfer between cavity air, the PV façade and the primary wall of the building for the purpose of PV cooling in summer (with natural convection) and heat recovery in winter (mechanical ventilation). A simplified physical model of the system is proposed for the summer operating configuration, which is more challenging from a numerical perspective. The model describes the active envelop in terms of a simplified geometry, and includes parameters such as density of PV cells, relative coverage of degree of transparency/opaque surfaces, and the ratio of height/width of the double-skin. For a given set of meteorological conditions, the surface and air temperatures, mass flow rate and PV power output are obtained by solving a system of thermal and aerodynamic balance equations. Validation of the model was undertaken using experimental data from a full scale prototype system installed in Toulouse, France as part of the RESSOURCES project (ANR-PREBAT2007). Coupling of the system to a simulated building was achieved with the aid of TRNSYS, and this combined system was evaluated in terms of heating and cooling needs for a range of French climates. It was found that the cooling needs are marginally higher for all locations considered, whereas the impact of the façade on the heating needs is weak as these needs are already low for these all locations

Overview and future challenges of nearly zero energy buildings (nZEB) design in Southern Europe

In times of great transition of the European construction sector to energy efficient and nearly zero energy buildings (nZEB), a market observation containing qualitative and quantitative indications should help to fill out some of the current gaps concerning the EU 2020 carbon targets. Next to the economic challenges, there are equally important factors that hinder renovating the existing residential building stock and adding newly constructed high performance buildings. Under these circumstances this paper summarises the findings of a cross-comparative study of the societal and technical barriers of nZEB implementation in 7 Southern European countries. The study analyses the present situation and provides an overview on future prospects for nZEB in Southern Europe. The result presents an overview of challenges and provides recommendations based on available empirical evidence to further lower those barriers in the European construction sector. The paper finds that the most Southern European countries are poorly prepared for nZEB implementation and especially to the challenge opportunity of retrofitting existing buildings. Creating a common approach to further develop nZEB targets, concepts and definitions in synergy with the climatic, societal and technical state of progress in Southern Europe is essential. The paper provides recommendations for actions to shift the identified gaps into opportunities for future development of climate adaptive high performance buildings. (C) 2017 Elsevier B.V. All rights reserved.info:eu-repo/semantics/publishedVersio

Dynamic study of a new concept of photovoltaic–thermal hybrid collector

International audienceThis work presents the development of a concept of solar Photovoltaic/Thermal (PV/T) hybrid air collector. This type of collector combines the preheating of air through a gap at the underside of the PV modules in addition to the ordinary function of electricity production. The cooling of PV modules by heat extraction can improve the electrical efficiency. In this paper, a simplified dynamic two-dimensional mathematical model of solar PV/T hybrid air collector with a metal absorber is presented. The validation of this numerical model with the measured data obtained with a full-scale test bench located near Lyon is proposed. Then, a numerical parametric study is undertaken to determine the effect of the air gap ventilation type on the system preheated air thermal production and electrical production. The results show that forced ventilation provides the higher value of thermal production but natural ventilation is sufficient to cool the integrated PV modules

Large-scale multicriteria sorting for the integration of photovoltaic systems in the urban environment

International audienceThis work proposes a multicriteria approach in order to evaluate the suitability of a building to be equipped with Photovoltaic (PV) systems. In the present case, technical (roof complexity), economic (payback period), environmental (CO2 reduction), energetic (selfconsumption) as well as social (heritage constraint) are considered. These criteria are evaluated for each building of the Great Geneva agglomeration, then a multicriteria methods, ELECTRE TRI, allows to sort these roofs in three categories that corresponds to "Very High", "High", "Moderate" suitability

Unsteady heated vertical channel flow in a cavity

International audienceThis experimental work investigates buoyant flow in a differentially heated vertical channel located inside a water cavity. The flow is found to be highly unsteady, and the key aspect of this study is to consider this unsteady behavior as a succession of states that turn out to be driven by the flow outside the channel. A conditional mean operator with respect to the average wall temperature is used to disentangle the different states through which the flow passes. Most of these states are characterized by a transition from laminar heat transfer in the bottom part of the channel to turbulent heat transfer, with a transition point that moves toward the exit as the average wall temperature increases. For the highest values of the average wall temperature, no transition is observed, and the heat exchange is found to be similar to that along a single vertical plate. For an intermediate range of wall temperature, a transition zone with turbulent heat transfer is observed in the upper part of the channel, and the heat transfer is found to follow the same laws as found for a symmetrically heated channel. For the lowest values of the wall temperature, the beginning of the turbulent zone is observed near the entry. The analysis is extended to several channel widths. The origin of the unsteady behavior is attributed to the flow in the whole cavity, and the conditional mean operator allows characterization of the flow inside the channel independently from the flow in the surroundings

Influence of thermal behaviour of photovoltaic module on its electrical performance,

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Transition to turbulent heat transfer in heated vertical channel - Experimental analysis

International audienceThis experimental study deals with natural convection flow in a water channel with a symmetrical isoflux wall heating. Wall temperature, velocity, bulk temperature and fluctuating quantities are measured for a modified Rayleigh number Ra *=6.7x10^7. The analysis of the mean values shows a changeof behaviour at the two-third of the height of the channel. This change turns out to be a transition from a laminar heat transfer in the bottom part of the channel to a turbulent one in the upper part. Due to isoflux wall boundary conditions, shear layers develop and thicken in each half-channel. It is shown that the meeting of these layers at the centre of the channel triggers the transition from a laminar heat transfer to a turbulent one. This experimental study is followed by a scaling analysis

Transition to turbulent heat transfer in heated vertical channel - Scaling analysis

International audienceA thermally driven flow in a vertical channel with heated walls is studied through a scaling analysis and results are compared with the experimental data reported in [1]. As the geometry is symmetrical with respect to the vertical axis, the half-channel is considered. The domain is split into seven zones in which the flow behaviour results from a balance between several phenomena. This zonal analysis exhibits the main phenomena that drive the flow in each zone. The study leads to an expression of the wall temperature profile below and above the transition. An expression is given for the driving pressure that is found to increase along the channel. The increase rate is much more important above the transition due to the fluid heating in the center of the channel. Finally, The maximum Reynolds stress is expressed in terms of the mean velocity values and is found to fit well with the experimental data