Do you have any control of the radiators? I have Velux GGU windows too and plan on doing Home Assistant integration for precisely the reasons you mention plus some automatic shading based on sun position or light sensors. For this I understand you need a KLF200 interface [1] and of course HA integration [2], then the integration possibilities are pretty much endless.

1. https://www.baubay.de/home-interface-velux-klf-200.html

2. https://community.home-assistant.io/t/velux-kfl200-ha-config...