• Energy Research

AbstractBuilding-Integrated Photovoltaic systems (BIPV) represent a promising solution for the local generation of clean electricity combined with cooling or heating through the exploitation of natural convection or mechanical ventilation. In this article we present, through the ADEME project “RESSOURCES”, such components developed on a large scale (and adapted for new builds and renovation projects). To date, the work has focused upon 3 prototype building envelopes comprising naturally-ventilated double-skin configurations installed on real buildings: two systems were developed for individual houses (Moret sur Loing, EDF R&D) and one for an office building (Toulouse, HBS-Technal). A comparative experimental evaluation of the three prototypes is presented in terms of the thermal response of the PV elements and the air cavity.

The temperature of photovoltaic (PV) cells is a critical factor in evaluating energy yield and predicting system degradation. Although thermo-electrical models allows predicting the evolution of the system over time, precise understanding of the thermal exchanges between the system and its environment is needed as they are implemented in the yield assessment using thermal correlations. These empirical correlations are based on heat transfer magnitudes undergone by similar PV set-ups.The aim of this study is to introduce a non-intrusive experimental methodology for precisely determining the convective heat transfer coefficient (CHTC) at the front of photovoltaic modules using two setups. The method integrates a heat flux sensor glued to the PV surface coupled with environmental data (e.g., irradiance, ambient temperature). This experimental method is applied to PV modules on a roof in an urban area and to a floating photovoltaic (FPV) system. It is demonstrated that the method significantly improves the accuracy of prediction of PV module temperatures in operating conditions compared to the conventional method based on the energy balance of a PV module. By using quantile regression, an empirical forced convection correlation is found based on the average wind speed. Compared to the traditional approach which relies on global transmittance, the CHTC is mainly dependent on the wind, whereas the global transmittance includes the radiative heat transfer which depends on the module temperature. The correlation for CHTC tailored for the floating photovoltaic system shows sensitivity to wind speed that is slightly higher compared to the inland setup in the literature.

Abstract A detailed mathematical models is developed for a fully wetted absorber photovoltaic thermal (PVT) collector with and without phase change material (PCM) under its absorber channel. Thermal and electrical investigations were carried out using PCM OM37 for typical winter and summer days in Lyon, France. The system is analyzed under energy and exergy performances. PCM incorporation in a water PVT absorber improves the performance of system in terms of electrical and thermal parameters. Enhanced electrical and thermal energy is attributed to dissipation of excess heat of PV module by latent heat absorption mechanism that reduces the PV module temperature and release heat at the night as well, provides better electrical and thermal stabilities to the system. Overall thermal energy and overall exergy of PVT system for a winter day as well as for a typical summer day, are found to be strongly in favor of adding PCM. The effects of mass of PCM on module temperature, outlet water temperature, and PV module electrical efficiency, have also been investigated. During sunshine hours, increment in the PCM mass up to its optimal value decreases temperature resulting in higher electrical efficiency and also allows providing higher water temperature at the nighttime.

AbstractThis paper addresses the numerical simulation of a partially transparent, ventilated PV façade designed for cooling in summer (by natural convection) and for heat recovery in winter (with the aid of mechanical ventilation). For both configurations, air in the cavity between the two building skins (photovoltaic façade and the primary building wall) is heated by transmission through transparent glazed sections, and by convective and radiative exchange. First we describe the model for the naturally ventilated envelope. Validation of the model and the subsequent simulation of a building-coupled system are then presented, which were undertaken using experimental data from the RESSOURCES project (ANR-PREBAT 2007). The dataset comprise measurements from a full scale prototype system installed on a real office building in Toulouse, France. Finally the heating and cooling needs of a simulated building were calculated and the impact of climatic variations on the system performance was investigated. The PV double-skin was found to result in a slight increase in cooling needs for all the French climates considered, whereas the impact of the façade on heating needs was found to be not predominant from point of view energetic.

Abstract This paper investigates an innovative earth-to-air heat exchanger (EAHE), namely the geothermal foundation Fondatherm®. This system solves numerous technical problems inherent to a traditional EAHE. However, an accurate understanding of its thermal behavior is crucial to ensure the best energy gain and its economic viability. This current paper focuses on a numerical study of the ventilated foundation. A time-dependent three-dimensional finite volume numerical model is developed. This model considers coupled heat and moisture transfers as well as complex boundary conditions such as the weather, the building and the water table simultaneous influences. A matric-head based system of equations is used to represent the heat, vapor and liquid transfers within the soil. It is combined to a capillary pressure-based formulation of the heat and vapor balance equation for the concrete foundation. Furthermore, a numerical method built on a switching from a potential- to a flux-based system of equations is proposed. It is added to a variable time-step method of resolution and allow to handle the greatest hygric loads variations at the ground surface. The numerical code is successfully validated against analytical solutions for simple cases, and against experimental and in situ measurements.

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.