Numerical modeling of heat loss from residential foundation to surrounding soils in freezing environment

Dominique Beaulieu, Jean Cote

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Cold Regions Geotechnics

ABSTRACT: By adapting a numerical model recently developed at Laval University, it was possible to evaluate the heat flow through the foundation built in different typical soils. This paper will focus on clay and sand. This study is a numerical analysis of heat transfer including, pure conduction and freezing/thawing. Its aim is to determinate if phase change has an influence on the heat flow. Results show an increase in heat flow of about 0.5 W/m2 at maximum caused by phase change. RÉSUMÉ En faisant l'adaptation d'un modèle numérique récemment développé à l'Université Laval, il a été possible d'évaluer le flux thermique à travers une fondation construite dans différents sols typiques. Cet article se concentre sur l'argile et le sable. L'étude consiste en une analyse numérique de transfert thermique incluant la conduction et le changement de phase. Son objectif est de déterminer si le changement de phase à une influence sur le flux de chaleur. Les résultats montrent une augmentation du flux thermique d'environ 0,5 W/m2 au maximum provoqué par le changement de phase. 1 INTRODUCTION In the past 30 years, the key in improving residential insulation and energy efficiency was the enhancement of the exterior envelope, which leads to significantly increase the relative importance of heat loss trough building foundation. Nowadays, the recorded heat loss trough the foundation and surrounding soil is about 30% to 50% of the total heat loss [Deru and Laboratory, 2003]. Heat transfer through soil is often a complex combination of different mechanisms. Their relative influence on the heat loss through foundations has yet to be quantified. The aim of this paper is to evaluate the importance of phase change mechanism in soil for residential foundation insulation. The recently developed numerical model by Maghoul et al. [2012] allowed an analysis of the heat flow through a residential foundation in sand and clay. This paper compares the results of a model of pure conduction and a model of conduction and phase change. Numerical calculi were performed using a finite element model builder (FlexPDE 6). 2 MODEL 2.1 Equations This section briefly present the equations used in this paper. Eq (1) describes the energy conservation formulation used in the pure conduction model. represents the total volumetric heat capacity of the soil and is the total thermal conductivity of the soil. Both these variable are defined in section 2.3. [1] The energy conservation formulation for the model using conduction and phase change is given in Eq (2). is the apparent heat capacity of the frozen soil. This variable is also defined in section 2.3. [2] In order to take into account the phase change that occurs during freezing/thawing of soil, the Clausius-Clapeyron equation needs to be integrated in the model which required the knowledge of liquid water content. Water content in this paper is determined using Van Genuchten [1980] formulation shown in Eq. (3). ˘ˇˆ˙˝ˇ˛˚ˆ˜ !"#$%$%" [3] is the water content at suction . ˙˝ is the water content for the saturated soil and ˇ is the residual water content of the soil. 'a', 'n' are constant. The 'freezing = drying' assumption is considered [Miller, 1965] and is used along Clausius-Clapeyron equation to evaluate the pressure induced by the freezing/thawin of soils (&'()) (Eq.4). &'()˘*+,- [4]

RÉSUMÉ: ical modeling of heat loss from residential

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Dominique Beaulieu; Jean Cote (2014) Numerical modeling of heat loss from residential foundation to surrounding soils in freezing environment in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper147,author = Dominique Beaulieu; Jean Cote,title = Numerical modeling of heat loss from residential foundation to surrounding soils in freezing environment,year = 2014}