Analysis of Thermal Bridges in Concrete and Cross-Laminated Timber (CLT) Constructions: A Numerical Study

Abstract

The thermal efficiency of a building envelope relies on various factors, including insulation resistance, continuity, the thermal conductivity of structural materials, and the presence of thermal bridges. This study focuses on studying the thermal performance of thermal bridge details in two construction types: concrete and Concrete and Cross-Laminated Timber (CLT). For the study, two common building envelope details with significant thermal bridges are considered, balcony and intermediate wall-to-floor connections. Utilizing the finite element program COMSOL Multiphysics, hourly transient simulations were conducted over a one-year period to assess the heat loss/gain associated with thermal bridges, considering daily, seasonal, and annual heat flow for two diverse climatic conditions (hot weather Houston-Climate Zone 2 and cold weather Toronto-Climate Zone 6). The findings demonstrate that thermal bridges constructed from CLT outperformed those made of concrete. In Toronto, the annual heat flow for the concrete balcony was 146% higher compared to CLT, while in Houston, it was 67% higher. However, this trend was significantly reduced for the wall-to-floor detail, with a concrete detail showing a 13% increase in heat flow for Toronto and a 7% decrease in annual heat flow for Houston. Furthermore, the dynamic analysis revealed notable heat flow magnitude changes in the balcony detail, highlighting the importance of thermal conductivity, while the wall-to-floor detail exhibited dampening fluctuations in heat flow, emphasizing the material's heat capacity importance in this context.

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