Optimizing the thermal performance of window frames through aerogel-enhancements

Windows are often considered the weakest point in building envelopes, especially in buildings with high window-to-wall ratios, where the windows exhibit much higher thermal transmittance than the opaque portion of the walls. The poor thermal performance of windows can largely be attributed to their frames which have higher thermal transmittance than the glazing portions. This study investigates the thermal transmittance of 48 commercially-available high-performance aluminium, fibreglass, polyvinylchloride (PVC) and wood-composite window frames. Then, it focuses on the possible improvements of each frame by inserting aerogel in the frame cavities. Several modifications of the frame cavities are assessed through two-dimensional numerical modelling done according to the ISO 10077-2 standard. This research concludes that filling existing empty cavities of window frames with aerogel granules could reduce the frame thermal transmittance by 4–29% depending on the frame type. Moreover, the complete filling of the cavities with aerogel can further reduce the thermal transmittance by 35%. Finally, for each investigated material, window frames with a thermal transmittance as low as 0.5 W/m2 K are proposed.