A Case Study Analysis on Green Building: The Hearst Tower

The Hearst Tower was the first skyscraper in New York after 9/11 event. It was designed by Sir Norman Foster and constructed in the year 2006.In the same year it received 2006 Emoporis skyscraper Award citing is as the best skyscraper in the world completed that year. This tower houses of the headquarters of the Hearst Publishing group. The tower located at the corner of Eighth Avenue and 57th Street in New York, United States, in the middle of Manhattan shopping business is 182 m in height, covering an area of 79,500 square meters. The building was initially a 6 storied Art Deco building designed by architect Joseph Urban as an international magazine building in 1928 and in the year 2001 Sir Norman Foster was awarded the contract to design a new tower keeping the old six storied cast stone as the base of new skyscraper. The construction work was started right after the completion of design work however it was postponed due to the great depression and was completed only in the year 2006.

Hearst Tower is a 46-storey office tower whose six-story cast stone base is ornamented with columns and allegorical statues, while the tower portion is dia-grid cladding profiled with stainless steel and low-E clear glass. The uncommon triangular framing pattern (also known as a diagrid) required 10,480 tons of structural steel — 20% less than conventional steel frame. The building is designed with long list of environmental consideration which lead to the designation of Hearst Tower as New York City's first LEED Gold certified skyscraper. Some of the environmental consideration like sustainable site, indoor air quality, water efficiency, sustainable materials and resources and innovation taken into the account will be discussed in the following pages.

Green building strategy

Sustainable site

The site is located two blocks south of Central Park and the building is within walking distance of Midtown Manhattan. It is easily accessible by the Columbus Circle subway station and several New York City Metropolitan Bus routes.

The building walls and facades (envelope) was designed to reduce glare from low angle sun during the early morning and evenings. The tower on the site was designed to ensure that all existing trees on site were protected, to ensure their long term vitality and they are now irrigated through the rainwater harvesting system (ARCH daily). The innovative landscape and exterior design increases building efficiency by 26%. The effective storm water management system in the tower reduces dumping of rainwater into New York City’s sewer system by 30%. Since the tower is constructed behind the preserved façade of existing six storied structure, 85% of the original structure was recycled.

Water efficiency

The tower is designed with rain water harvesting strategy, a grassed terrace designed to collect rainwater. Water collected from this roof is taken to the basement where a tank with 53 thousand liters tank is located.[image: ]This rain water harvesting system reduces the water discharged to the city drainage system by 25%. The water stored in the basement tank is used in a series of waterfalls located around the stairs that collaborate in cool temperatures and ensure a comfortable microclimate on the ground floor.

This water feature helps in maintaining an ideal relative humidity of 30 to 50 percent, depending on the season, and reduces the atrium's summer air-conditioning load by 5%. The embedded polyethylene pipes with the circulating water in the atrium floor provide radiant heating and cooling. In winter, this system warms the granite floor to 25.5 degree Celsius, cutting 36 percent of the atrium's heating energy. During the summer, it chills the floor to 22 degree Celsius, supplying 10 percent of the atrium's cooling. It is also used for landscaping irrigation, to water indoor plants and trees of avenue and to replace the evaporated water from the air conditioning system.

Apart from rain water harvesting system, low flow fixtures are used in the tower to reduce the portable flowing water. The tower recycles about 6.4 million liters of water annually which would be otherwise wasted.

Energy and atmosphere

Some of the energy efficiency strategy used in the tower is: use of glass coating to reduce solar radiation and therefore cooling load. The glass used is coated with ‘low –E’ which allows the internal space to be lighted with natural lighting while eliminating the invisible solar radiation that causes heat. To control the energy, sensors that control artificial light based on the amount of natural light and motion sensors to turn off lights and computers when an area is unoccupied are also used. Natural ventilation is used forFigure.6 special low E glass 75% of the year for the air conditioning of the tower. The mechanical equipment use for heating and cooling the tower are CFC refrigerant free equipments. Recycled water is used for cooling the ten-storey atrium. To maximize the penetration of light, limited amount of interior walls are used so as to block less light. Light sensors are used to measure amounts of natural light and react automatically depending on what is needed.

Building materials

The 20% building materials used in the construction of the tower were regionally available materials. The materials used were within the 500 miles from the site. The use of dia-grid façade reduces the amount of steel required (conventional steel frame) by 20%. The 80 % of the steel used were recycled steel.

To reduce the cost and improve the indoor air quality low-e carpet (Green Label), Millwork - composite wood low-e VOC sealants & adhesives and paints and clear wood finishes were used.

Conclusion

The Hearst Tower has a list of features that contribute to its gold LEED rating, which includes low-emitting glass, rain water harvesting system which helps in water management, light sensors to control the amount of artificial light used based on the amount of natural light available from outside, motion sensor to trun off computers and appliances when the spaces are unoccupied, high-efficiency HVAC systems, Energy Star appliances, and the use of outside air for cooling and ventilation during 75 percent of the year. Rainwater harvesting and reuse provides about half of the watering needs while also improving the indoor air quality by humidifying and chilling the 10-story atrium as necessary. Walls and concrete surfaces are painted with low-vapor and low-toxicity paints and furnishings are formaldehyde-free. Sustainable materials like recycled materials and wood from sustainable forests are used for manufacturing Floors and ceilings. Over all the Hearst Tower is designed to be 26% more energy-efficient than a standard office building.