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Commercial low-rise buildings are often characterized by weak energy performances, and heat transfers through roof and ground are prevalent. The roof design and its opening system is a key factor of the thermal performance. Skylights and radiative properties of roof coating have a direct impact on solar gains, thermal losses and natural ventilation potential. The overall performance depends on the combination of these design parameters (solar reflectance and opening size), on the weather conditions and on the inertia given by the slab on the ground. The roof design performance depends on the ground which determines the dynamic behavior of these buildings. A generic case study is modeled and an extensive parametric study (about 840 annual simulations) is performed to point out these key parameters’ impacts on energy demand and comfort. The combination of efficient roof techniques (skylights and cool roof) along with a high thermal inertia of the building can be an adequate passive cooling solution in summer, with a 99.8% drop in degree-hours above the discomfort temperature in summer. Nevertheless, we show that these passive strategies could not be totally efficient without taking care of the ground thermal inertia which account up to 58.6%. [ABSTRACT FROM AUTHOR]

Abstract: Predicting the indoor air relative humidity evolution is of great importance to evaluate people thermal comfort, perceived air quality and energy consumption. In building environments, porous materials of the envelope and furniture act on the indoor air humidity by reducing its variations. Solving the physical processes involved inside the porous materials requires the knowledge of the material hygrothermal properties that needs multiple and, for some of them, time-consuming experimental procedures. Recently, both the NORDTEST Project and Japanese Industrial Standard described a new Moisture Buffer Capacity index that accounts for surrounding air vapor concentration variation. The Moisture Buffer Value (MBV) indicates the amount of water vapor that is transported in or out of a material, during a certain period of time, when the vapor concentration of the surrounding air varies. The MBV evaluation requires only one experimental procedure and its value permits a direct comparison of the building materials moisture performance. However, two limitations can be distinguished: first, no relation between the MBV and the usual material hygrothermal properties has been clearly identified and second, no model has been proposed to actually use the MBV in building simulation. The present study aims to solve these two problems. First, the MBV fundamentals are introduced and discussed; followed by its relation with the usual material properties. Then, a lumped model for building simulation, whose parameters can be determined from the MBV experimental procedure, is described. To finish, examples of the use of this MBV-based lumped model for moisture prediction in buildings are presented. [Copyright &y& Elsevier]

Abstract: In recent years, several intensive studies have been carried out in order to reduce the energy consumption of buildings. One solution lies on whole building energy simulation that permits to enable the heat (and moisture) transfer through the building envelope and, consequently, is a way to understand how to improve the building performance. This article aims to analyze the modeling level needed to successfully evaluate the heat transfer through glazing parts of windows in such whole-building simulations as it is well-known that windows are the thermally weakest elements of the building envelope. In this way, predictions of glazing surface and zone air temperatures and energy demand obtained using both resistive and finite-volume based models are compared. Results show that for common window glazing structure and outdoor/indoor perturbations, differences between the two models are small. However, in the case of glazing presenting higher solar absorption and thermal inertia, the use of the finite-volume based model is required to accurately predict the glazing internal surface temperature and avoid errors up to 50% for energy consumption in the studied case. Those results put into relief a clear limitation of current whole energy simulation programs to correctly predict the energy consumption of buildings where high thermal inertia double- or triple-glazing windows are installed. [Copyright &y& Elsevier]