(Julia Halperin, ARTINFO) Reminder: the Whitney isn’t the only marquee art name opening a giant new space in Chelsea in the coming years. The Dia Art Foundation confirmed yesterday that it has completed an $11.5 million purchase of a new building at 541 W. 22nd St., adding some extra legroom to the 50,000-square-foot expanse next door that it has been planning to transform into a ground-floor exhibition venue.