Inertie thermique | EPFL Graph Search

L'inertie thermique d'un matériau est sa résistance au changement de température lorsque intervient une perturbation de son équilibre thermique. Lorsqu'un matériau se trouve à l'équilibre thermique, sa température est fixe et les échanges de chaleur (par conduction, convection, rayonnement) qu'il entretient avec son environnement sont équilibrés (autant de chaleur reçue que de chaleur cédée). Lorsqu'une perturbation thermique l'amène vers une nouvelle température d'équilibre, l'inertie thermique est mise en évidence par le temps nécessaire pour atteindre ce nouveau point d'équilibre : si le matériau a une faible diffusivité thermique, il atteindra le nouvel équilibre au bout d'un temps long, si à l'inverse elle est élevée, il l'atteindra au bout d'un temps bref. Le temps mis pour atteindre le nouvel équilibre est nommé temps caractéristique. Il dépend de la diffusivité thermique du matériau, mais aussi de l'écart entre les deux températures d'équilibre. La notion d'inertie thermiq

Energy modeling of the Solar Decathlon pavilion: development and fine-tuning of solar passive strategies

Mathieu Desmarescaux, Mélanie Isabelle Gaillet-Tournier

The objective of the project is to evaluate the possible improvements of the design of the Solar Decathlon pavilion. In particular, this project aims at determining the effectiveness of passive systems (e.g. insulation, thermal mass, shading devices) in providing visual and thermal comfort.

2017

Refurbishment of Existing Envelopes in Residential Buildings: assessing robust solutions for future climate change

Giorgia Chinazzo

Evaluating the energy consumption of different design solutions during the design process is essential to reach energy targets. Conventionally, building energy performance is evaluated with energy simulations using a single input weather file (design or typical year) referring only to present weather conditions. Recent works, for example by Gaterell at al. for sites in the United Kingdom, suggest, however, that it is necessary to also include weather files describing climate conditions in future years. That is, the effect of predicted climate change on building performance. Buildings have a life span of 50 to 100 years and so must perform satisfactorily under both current and future climate, adjusting to take advantage of opportunities and to moderate potential damage caused by a changing climate (Wilde et al. 2008). Given the fact that climate is a singularly stochastic phenomenon and that we cannot predict the weather in future years with complete certainty, weather inputs necessarily have intrinsic uncertainties. Using a single weather file in building simulations, regardless of its source or generative algorithm, could lead to inaccurate energy consumption forecasts, and therefore wrong design decisions. In any case, the development of typical weather files was not always done keeping in mind forecasting, but rather what-if analyses. The innovation in our study consists in the introduction of more than one input weather file in building simulation to represent both present and future years. Our methodology aims to assess the robustness of different design solutions over many possible future climate projections, i.e. the sensitivity of a design or device to uncertain climatic outcomes. We focus on the robustness of refurbishment measures compared to the robustness of the non-refurbished building. We assess each intervention in terms of energy consumption. We decided to focus on existing buildings since they represent the biggest opportunity to reach energy targets today in Europe. In fact, the majority of the European building stock was constructed before any energy regulations and tends to perform poorly for energy consumption and comfort. We propose three indices to make comparisons between refurbishments. The Robustness Index (RI) compares the robustness of the each solution in terms of its range of energy usage. The Energy Saving Index (ESI) assesses the refurbished models in terms of energy usage difference in comparison with the non-refurbished model or base-case. The Gather Index (GI) summarizes the results of the two previous indices to compare the performance of the different refurbishments in terms of both robustness and energy efficiency. As a case study, we evaluated the robustness of an existing dwelling with twenty-two realistic refurbishments in Turin, Italy. The retrofit solutions focus on the thermal properties of the envelope by varying the U-value, the solar heat gains, the thermal mass and the air tightness of the envelope. The main outcome of our study is that interpreting numerical simulations of future energy consumption based on single-point estimates of input/output data (i.e. one typical weather file) is risky. Results are better treated as being probabilistic rather than deterministic, as is the norm today. Discussing outcomes in terms of ranges instead of single values improves estimates of outcomes, making it possible to identify robust design solutions for policy and investment decisions.

2014

On the Influence of Thermal Mass and Natural Ventilation on Overheating Risk in Offices

Jérôme Philippe Bonvin, Arianna Brambilla, Flourentzos Flourentzou, Thomas Bernard Paul Jusselme

Free cooling strategies are gaining importance in design practice due to the increased risk of overheating in well-insulated buildings with high internal loads such as offices. The state of the art highlights that the most efficient passive solution for indoor temperature stabilization and control is the integration of thermal mass with an optimized ventilative cooling profile to enhance the thermal cycle of heat storage. Due to its cyclical behavior, thermal mass effects are difficult to predict and quantify with the traditional steady-state approach to building thermal performance. Dynamic thermal simulations help to assess a building’s behavior under transient situations, including the thermal mass influence. However, building codes usually include thermal simulations based on standard assumptions: typical meteorological year (TMY), standard occupancy, standard daily-based lighting and appliances profiles, and standard weekly-based occupancy. Thus, when assumptions change, the actual behavior of the building may vary consistently from the predicted conditions. In this paper, we focused on the ability of thermal mass to contrast the influence of variations from the standard assumptions, especially in relation to climate and ventilation profiles. The results show the necessity of encompassing different risk scenarios when evaluating a free cooling solution performance. Among the different scenarios simulated, natural ventilation misuse shows greater influence on the thermal indoor environment, especially if coupled with low thermal mass.

2018

Refurbishment of Existing Envelopes in Residential Buildings: assessing robust solutions for future climate change

Giorgia Chinazzo

2014