PSI - Issue 13

Barbara Šubic et al. / Procedia Structural Integrity 13 (2018) 503–510 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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without reinforcements and windows with aluminium reinforcements in the mullion (WB2_AL) was made. The WB2_AL design was used because its influence on the thermal transmittance of mullion, and consequently on the thermal transmittance of the window, is most pronounced. It can be seen Fig. 5 that U w decreases with increasing width and height. The reason for this is that area of the insulated glass increases with increase of the height and the width of the window. The glazing has much lower thermal transmittance (U g =0.6 W/m2K) than window frame (U f,WB2_Al =1.8 W/m2K), and this directly affect the final U w . The percentage of glass area (A g ) in window increases with window size and represents 42 % in case of 1000 mm × 1000 mm sized window and 82 % in case of 3000 mm × 6000 mm window. In addition, reinforcing material affects U w much more at slim and tall windows (up to 11 %) than at wide and small windows (3 %). This is due to increase of the mullion surface area (A f,m ) in narrow and tall windows. The percentage of A f,m at window of size 1000 mm × 1000 mm is 14 %, whereas in 1000 mm × 6000 mm window it is 18 %. Although the value of U f of WB2_AL design increases for 50 % compared to the reference window and the influence on the U w of the whole window is at maximum 11 %.

Fig. 5. U w of double casement window without reinforcing profiles (a) and with aluminium reinforcing profiles in the mullion WB2_AL (b).

4. Conclusion

Cross-sectional reinforcement of window mullions improves the mechanical performance of the window beams, but also decreases energy efficiency of the window frames. Since all reinforcing profiles used in this study have higher λ than wood, the reinforced mullions yield higher U f than reference mullion. Nevertheless, the observed effect on U w is relatively low and is especially lower in case of wider and smaller windows. However we should not neglect the effect of reinforcing material on local thermal bridges and importance of limit inside surface temperature of 13 °C, under which a condensation and mould growth appears, which can lead to bad indoor climate. The only reinforcing material that has showed acceptable results regarding U f of the mullion as well as T min , was GFRP, independent of reinforced layout.

Acknowledgements

The authors would like to acknowledge the support of European Commission in the scope of Horizon 2020 project XtremelY (739524) and the support of Slovenian Ministry of Education, Science and Sport and European Regional Development Fund, European Commission project TIGR4smart (grant number 5441-1/2016/116).