Heat Transfer Analysis of Timber Windows with Different Wood Species and Anatomical Direction

Abstract

When assessing the hygrothermal performance of timber windows, it is important to apply the unique thermal conductivity of wood by each wood species as well as an anatomical direction within the same material as they affect the performance and long-term durability of products. A series of heat transfer analyses of window frames using THERM and WINDOW along with measurements on the thermal conductivity of five hardwoods using laser flash apparatus (LFA) was performed to compare and evaluate heat transmittance (U-value) and condensation resistance (CR) of three types of timber and hybrid timber windows. For each window type, 6.1 to 10.3% of the maximum difference in the heat transmittance among cases was calculated. Besides, a linear correlation was found between the U-value and the CR for most cases; thus, the selection of wood species and anatomical direction would improve the hygrothermal performance of timber windows overall. The results also indicated that there were some cases where the overall CR of windows did not improve because the U-value of the glazing system was not sufficiently low.