[zombielinux]

Thats how lots of large commercial buildings do it. Make huge blocks of ice in the middle of the night when energy is cheap and the building's heat load is at a minimum, then melt the ice and use the phase change of water to absorb as much heat as possible.

Also why its colder in the morning and it feels like the building is a bit too warm to be comfortable if you stay late. This, of course, varies from building to building.