the above-ground portion of the building dedicated for retail use (which consists of the ground floor, the three floors immediately above the ground floor as well as the two floors below ground), accommodates offices using two distinct floor shapes. from floors 7 through 46, the typical floor space is 36,350 square feet (3,376 square meters) in the shape of a parallelogram (which is designed to echo the configuration of the site). from floors 48 through 63 the floor space is 28,000 sq ft (2,600 square meters) in the shape of a trapezoid, shaped so that it opens toward the tip of manhattan island and also triangulated to face one world trade center. the tower includes five levels of mechanical floors. the new york power authority selected utc power to provide 12 purecell model 400 fuel cells that will be used to provide electricity, water and heat. according to the developer, the systems combined will rank as one of the largest installations of fuel cells in the world. the upper floors of the building have no interior columns.