On the coupling between natural ventilation and sensible energy charge and discharge in buildings: an experimental and modeling approach

As part of the searching for solutions to reduce the energy consumption related to the cooling in buildings, a naturally ventilated test platform, located in Southwest France, has been heavily instrumented in terms of heat flux and temperature measurements. Here, we are interested in contributing to the improvement of the passive management of the thermal comfort of an existing building during the summertime, by controlling the mobile elements of its envelope, that is to say, the solar protections and the opening natural ventilation. These two mobile elements allow a priori to control the radiative and convective contributions, respectively. Then, the control of these two mobile elements vis-a-vis the dynamics of the thermal mass of the building (which in particular is subject to the charge/discharge process), will make more appropriate selections of natural ventilation strategies, this which will also minimize the need for air conditioning. Thus, such type of control should have the characteristic of being in function of the meteorology and the instantaneous thermal state of the building in order to be able to envisage a control in real time. For this type of control, it is necessary to define the necessary metrology and the control variables, as well as to describe the system to be controlled. This description must be sufficiently simple and light to solve in order to consider the implementation of such type of control. Thus, in this context, this thesis aims first of all to comprehend and highlight the charge/discharge process and its coupling with natural ventilation, and then to construct a simple model to describe this coupling. The test platform is a Plus Energy House prototype, called Sumbiosi, created to participate in the inter-university competition Solar Decathlon Europe 2012. It was designed in such a way as to promote the passive storage of daytime energy in the winter and the semi-passive night storage in summer. Three main elements allow a priori these functions of energy storage and discharge: a thermally heavy-weighted floor slab located behind of the South-facing glazed-facade, fixed or mobiles and programmable solar protections and openings on the South and North facades. On the one hand, three measurement campaigns were carried out in the summertime to characterize the energy charge-discharge process and identify their nature. For this, a semi-empirical model is developed for decoupling the superficial heat transfer into its convective and radiative components, using couples of black and shiny heat flux meters. Correlation analysis is employed, to spot relevant heat-transfer couplings between the indoor and outdoor environment. On the other hand, the natural ventilation in the platform is characterized in terms of the air flow capacity of the openings and the natural airflow rate. The former is determined in situ by performing airtightness tests, and the latter, by transient airflow simulation using CONTAM software. Finally, a thermal model is developed to describe the behavior of the platform, based on its thermal characterization. This model consists of representing the heat transfers in (1) the indoor air via a global energy balance and in (2) the concrete slab by non-uniform heat conduction, as well as, of representing (3) the natural airflow rate accounting for wind and thermal buoyancy effects simultaneously via a semi-empirical model. (author)