Look up at the sun. (Ouch!) Now look down at the ground. (Ahhh.) That pretty much sums up architect Jeanne Gang's breathtakingly simple approach to reducing energy use in Windermere West, a 26-story condominium destined for Chicago's Hyde Park neighborhood. She tilted two-thirds of the south-facing floor-to-ceiling windows away from the sun, letting the structure make its own shade — no duckbill protrusions required. It's mainly a summertime strategy: The hottest sun of the year is also the highest in the sky — and typically coincides with the most expensive electricity. The sawtooth design creates balconies that block direct midday sun, decreasing the need for power-hungry air-conditioning. In winter, when the sun is lower, rays pass through the windows to warm the interior. Gang worked with engineering powerhouse Arup to calibrate the facade. Using a computer model, they gradually angled the glass until they hit the sweet spot — skewed enough to keep living rooms from baking, but not so much that they feel like the inside of a boat. The magic number for Chicago's latitude? Exactly 71 degrees. Which should also be the temperature inside.

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