Evaluating the Thermal Impacts of Different Masonry Wall Tie Designs Using FEM

• Author / Creator

  Shao, Yue

• Building’s space heating system accounts for more than half of the total building’s energy consumption, reducing the energy use of space heating of buildings can decrease the national energy consumption of Canada and is helpful for sustainable development of the buildings. Improvement of thermal resistance of the wall is a reliable approach to decrease the energy consumption of the building. Masonry cavity walls is a commonly used type of exterior wall in Canada. It can provide reliable structural performance, considerable durability, and excellent thermal resistance. However, the presence of masonry ties, as a typical source of repeated thermal bridging, in the wall assembly significantly reduces the thermal resistance of the wall assembly.
  Ties are considered a typical source of repeated thermal bridging in masonry cavity wall assemblies. Thermal bridging can cause thermal resistance reduction due to its high conductivity material penetrating the thermal insulation layers. Ties thermal bridging effect provide additional heat transfer pathways in the wall assembly. Codes and industry catalogues require the thermal impact of thermal bridging to be considered when calculating the thermal resistance of exterior walls. Although a few studies have been conducted on the effect of ties in reducing the thermal performance of walls, the thermal impact of ties has not been comprehensively studied. Incomplete thermal bridging reduction effect evaluation will make insufficient HVAC system design and lead to energy consumption increase of the buildings. Also, the ties thermal impact on the thermal resistance of the ventilated air gap has not been determined.
  In this study, the effective thermal resistance of the ventilated air gap in masonry cavity walls considering ties thermal bridging impact was investigated, and the impact of ties on the thermal resistance of wall assemblies was addressed with different influence factors. Based on the parametric analysis, effective methods to reduce ties thermal bridging effect were suggested. The effective thermal resistance of the ventilated air gap in masonry cavity walls was studied by using coupling computational fluid dynamics (CFD) and steady-state thermal analysis in Finite element method (FEM) modelling. In addition, a parametric analysis of the impacts of ties on the effective thermal resistance of a unit wall area was performed by using FEM with variations in ties material, insulation R-values, tie depth, tie spacing, grouting in concrete masonry blocks, and the effect of adding insulation around the tie. Based on the results, the tie’s thermal bridging effects and ventilation in the air gap affect the thermal resistance of the air gap. And according to the parametric analysis, the tie material is the most influential factor of the ties’ thermal bridging effect. The thermal resistance of the wall assemblies varies greatly with the change of tie material, ranging from 14.68%~41.85%. Using a low thermal conductivity material (e.g., GFRP tie) can almost eliminate the thermal bridging effect of the tie. Enlarging the tie spacing also can improve the overall thermal resistance of walls up to 12%. Using a low thermal conductivity tie material such as GFRP is recommended for effective thermal resistance improvement for the masonry wall cavity wall assembly.

• Subjects / Keywords

  • Masonry tie
  • Thermal bridging
  • FEM

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-hnnr-4661

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.