DI-UMONS : Dépôt institutionnel de l’université de Mons

Recherche transversale
(titres de publication, de périodique et noms de colloque inclus)
2018-12-10 - Colloque/Présentation - communication orale - Anglais - page(s)

Quinten Julien , Feldheim Véronique , "Equivalent wall method for dynamic modelling of thermal bridges in low-energy building: application and parametric study" in 10th International Conference on System Simulation in Buildings, Liège, Belgium, 2018

  • Codes CREF : Recherche énergétique (DI2290), Transfert de chaleur (DI2211)
  • Unités de recherche UMONS : Thermique et Combustion (F704)
  • Instituts UMONS : Institut de Recherche en Energétique (Energie)

Abstract(s) :

(Anglais) Currently, scarcity and cost of fossil fuels increase and we are facing more and more problems due to pollutants emissions. In response, the European Union has set energy savings and greenhouse gases reduction targets of 20% by 2020, from the 1990 levels. As the building sector represents about 40% of the total energy consumption of the European Union, many energy efficiency measures are taken in this domain. Simulations are performed to evaluate, predict or improve energy performance of new buildings thanks to numerical tools. Their accuracy must be improved as the building energy consumption becomes lower and lower. This work focuses on the dynamic modelling of thermal bridges and multidimensional details of low-energy buildings. Thermal bridges may be responsible for 4% up to 39% of the heat losses of a building. In most of the building energy software packages, the heat flux is considered as being 1-D and the real dynamic and multidimensional effects of the thermal bridges are not considered. The aim of this work is to develop a simple model accurately evaluating the impact of these effects on the building energy performance and easy to integrate into existing building energy software. To meet these specifications, the equivalent wall principle is used in this paper: the multidimensional geometry is replaced by a 1-D three-layer equivalent wall, having a similar thermal behaviour. The following assumptions are made: the thermo-physical properties of materials are constant, the convective and radiative effects are not modelled but standard heat transfer coefficients are used and the phase changing materials are not considered. A new mixed method is proposed, using the transfer functions in the frequency domain in addition to the total thermal resistance, the total heat capacity and the structure factors, to determine the thermo-physical properties of each fictitious layer. These properties are thereafter introduced into the building energy software. Steady-state and dynamic simulations and an optimisation script are needed: the whole process takes less than two hours for one equivalent wall (drawing time is not considered). Heat flux accuracy is studied for the equivalent wall of some particular well-insulated 2-D thermal bridges in light or heavy construction by using hourly meteorological data. The impact of some parameters is analysed: the type of climate, the type of indoor temperature (constant or variable), the period of the year and the consideration or not of the solar heat flux. In each case, the average error on the heat flux through the inside surface is lower than 1 W/m and the error on the time integral of this flux is less than 0.65%. Results are significantly better than for a classical evaluation of thermal bridge considering only the static effects of the junction. Further work is to define some practical rules for an easier and quicker equivalent wall determination and to apply this method to some buildings to assess its impact on the evaluation of the energy performance of those buildings.

Mots-clés :
  • (Anglais) Thermal bridge