Natural Convection in nonuniformly heated channel investigation – Application to photovoltaic facades

International audienceThis paper investigates an active component of the building envelope: a photovoltaic-thermal double-skin facade. This element consists of a vertical open air channel bound by two parallel walls: one is made of photovoltaic panels and one is the main frame of the building. Integrating this system in a building facade is not an easy matter because the electrical output is strongly dependent on the operating temperature of the photovoltaic component. The aim of this study is to promote better cooling of the photovoltaic facade working on its typical geometrical arrangement. This consists of an alternation of photovoltaic cells (localized heat sources) and semitransparent window panes (unheated zones). Fundamentally, the flow of natural convection that develops within the vertical channel appears to be subjected to boundary-localized thermally active areas and adiabatic areas, evenly distributed throughout the height. This requires investigations of parametric variations of magnitude and space frequency of the heated areas as well as intermediate spacing. Two complementary experimental apparatuses were developed, namely, at CETHIL and at the CFD Research Laboratory UNSW in collaboration with the DIPTEM. Experiments were conducted on both. For these experiments, Grashof numbers, based on the channel width and the convective heat flux, are about 1010. The results obtained constitute an important database, which allows characterization of convective heat transfer. Some of the results concern the dynamic boundary conditions that are required for the numerical investigation. The present study compares (on a common operating range) both experimental and numerical investigations focusing on the CETHIL experiments