The outside water's temperature hovers around 4°C (39°F). TENka City's spheres start to cool from the outside first (obviously) so the worst place to be during a prolonged power out is near the outside windows. On the other hand, those outside windows are the only places where you can see what's going on during a power out and most of the main hallways are on the outside edge as well.
All assembly points are situated deep inside the spheres, though. It helps to conserve as much heat as possible. And the arrival of lots of bodies helps, too. And that's when they get to focus on another fast approaching problem: the depletion of oxygen in the air (or rather, too much carbon dioxide overwhelming the available oxygen).
Also, I'm traveling today, so comments may be slow in showing up.