In this study, to investigate a method for reducing the linear thermal transmittance between windows and building walls, we used Taguchi’s method to calculate the linear thermal transmittance between PVC windows, FIX, Casements, Sliding, and the building wall in the wooden filling heat insulation construction method. We quantitatively evaluated the impact of the insulation performance and the position of the frame part on the building wall as well as the influence of the properties of the indoor casing (thermal conductivity) on the linear thermal transmittance. We presented a configuration that minimized the linear thermal transmittance, described the fabrication of test specimens, and reported the appropriateness of these specimens via performance verification. Our results are summarized as follows.
1) The linear thermal transmittance (
ψb) between the windows and building walls was similar in all cross sections. In each case, the numerical magnitude could be confirmed with a certain extent of difference, possibly because of the influence of the control factor on the heat flux between the windows and building walls.
2) From the average value of the SN ratio, configuration that minimized the linear thermal transmittance were found for the combination, (Case 18) which accounted for the third level of the control factor (control factor A being the second level) common to all cross sections.
3) From the average value of the SN ratio, we found that the linear thermal transmittance can be reduced by improving the heat insulation performance of the frame part and the indoor casing and reducing the distance of the installation position of the frame part on the building wall directed inside the room.
4) It is possible to clearly show the ranking of control factors contributing to the reduction in the linear thermal transmittance at each section site; however, when considering window species having different cross-sectional structures, it is difficult to clearly judge the hierarchy from the extent of the impact of the SN ratio for each section site depending on the location of Sliding as an example.
5) The precedence order for each control factor could be clarified as a window based on the impact of the SN ratio obtained using the average
ψb (
Aveψb) between the window and the building wall per aperture window.
6) Performance verification was conducted for the average linear thermal transmittance between the window and the building wall per aperture window in FIX by fabricating test specimens (Cases 1, 5, and 18). The measured values, similar to the calculated values, demonstrated a tendency of decreased linear thermal transmittance in the order of Case 1 → Case 5 → Case 18. Furthermore, in each case, the divergence between the two values was less than 10%, which exhibited good consistency and proved the validity of the calculated values.
7) The installation position of the frame part had a higher effect on the convection component compared with the radiation component of the heat transfer resistance on the outdoor side; however, the impact on the linear thermal transmittance was small.
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