10 October 2010

Cook vs Gehry on designing the best NYC skyscraper

Last August Paul Goldberger, The New Yorker’s architecture critic, spoke with Richard Cook, founder and partner in Cook+Fox Architects and the designer of the new Bank of America Tower.  The Manhattan skyscraper, a.k.a. One Bryant Park, was completed earlier this year and is the largest commercial building to receive a LEED Platinum certification, the highest standard set by the U.S. Green Building Council. Cook and Goldberger indulge in a polite conversation about sustainable design, LEED certification and the meaning of green consciousness for architects nowadays.The critic does not perform as a critic; he seems convinced by the elegant, soft-spoken and well-educated leader of Cook+Fox Architects. My impression - I must admit it - was not so positive. There is something about this glazed tower that seems rather opposite to the concept of a sustainable building, and that's the huge amount of vision glass that covers the facade top to bottom. A similar percentage of vision glass than at the Lever House or the Seagram Building, to name just two icons of New York curtain walls in the 20th century.

The message in the video was well packaged and sent though. A quick review to the Bank of America Web page brings some more info:

Bank of America Tower at One Bryant Park is the heart of our New York operations - and a striking example of our environmental commitment. The 55-story tower, having obtained the U.S. Green Building Council's LEED® (Leadership in Energy and Environmental Design)- CS Platinum certification, is one of the world's most environmentally responsible high-rise office buildings.

Unlike most large buildings, the tower will generate a significant portion of its power on site through a 5.1 megawatt cogeneration system. It also will save about half the energy used by most buildings its size; will filter out about 95 percent of the particules in the air drawn into the building; will use less expensive night-time power to produce ice used to cool the building; and will conserve millions of gallons of water every year through methods such as green roofs and waterless urinals.

Even the Huffington Post, a reliable NYC politics and socialite Web page (not precisely conservative) seems to have joined the praise.

There is another tower in Manhattan, still under construction, which is not known by its sustainable credentials but by its designer, Frank Gehry. The Beekman tower, located just south of City Hall, has recently received a positive review at the art & design pages of The New York Times. The 76-story tower is recognizable by its crinkled stainless steel skin, bringing a new look to an imposing cluster of landmarks from a hundred years ago commanded up to now by the Woolworth Building.

The design of the Beekman tower has evolved through an unusual public-private partnership. In an agreement with New York education officials, the tower’s developer, Forest City Ratner, agreed to incorporate a public elementary school into the project. Forest City was responsible for the construction of the school; the Department of Education then bought the building from the developer. The Beekman tower is thus a curious fusion of public and private zones. Clad in simple red brick, the school will occupy the first five floors of the building. Atop this base will be the elaborate stainless-steel form of the residential tower.

As IBM ads tell, it's time to ask smarter questions. From the available literature, Cook+Fox are the nice, responsible guys whilst old Gehry, in his Southern Californian mood, has come to Manhattan just for the money. Is it as simple as that? Not really.

Let's have a look at the vertical section of One Bryant Park:

Two-thirds of the facade surface - floor to ceiling - are covered with vision glass, only one-third - the edge of slab - is opaque glass with a back-panel insulation. The tower has been clad with Viracon insulated glass with a low-e coating and a silk-screen pattern made of fritted dots on the #2 surface. To allow for higher transparency, the glass is low iron (extra clear). At eye level (sit or standing) the glass has no pattern, providing great views of the New York skyline. The silk-screen pattern extends graduately below eye level to the floor and above eye level to the ceiling to reduce radiant heat gains. These are the best data I could find from the glass supplier, not from the project, so take it as a guess (the glass coating is a project specific combination of VE 15-2M and VRE 15 -59 from Viracon): U-value 1.6 W/m2ºK or 0.30 BTU/hft2ºF, solar heat gaining coefficient between 0.36 and 0.39, visible trasmittance between 55% and 73%.

“Bringing in more daylight deep into the building reduces electricity costs. But it also increases the efficiency of the people that work in the builiding – and that's the greatest cost savings,” says a spokesperson from the developer, adding that financial firms' personnel costs are several factors higher than their energy needs. “If you're 10% more efficient on energy, it's not the same dollar amount as a 2-3% in personnel savings"

This sounds familiar to most of us involved with glass and energy efficient buildings. The architects seem to have convinced the developer that lots of light are good for tenants, and energy losses (or gains) through the glass are secondary. The solar passive behaviour of a glazed tower must be relative, since it doesn't impede the building to achieve a LEED platinum certification. It is true if you use LEED as the only metering system, but it is not true if you really try to minimize the total heat exchange through your facade. Lets have a look now at the curtain wall unit system detail (vertical section through the top-bottom interlocking transom):

The glazing contractor for the project, by the way, is Permasteelisa USA. Do you miss anything in this section? I do: a good old thermal break in the transom profiles. OK, so we have here a non-thermally broken unit system with a combination of 2/3 vision glass (U-value of 1.6 W/m2K centre pane) and 1/3 opaque glass (100mm of mineral wool plus insulated glass, that should be around 0.6 W/m2K centre pane).

We Europeans may be a bit pesimistic when doing U-value calculations, but the combination of those three elements (profiles, vision and spandrel glass), according to our standards, delivers an overall U-value between 1.9 to 2.3 W/m2K. Let's add to it the radiant heat gains: all orientations have the same glass, there are no external shading systems, and 2/3 of the glass is vision, with an average solar heat gain coefficient of around 0.35 (deducting the profiles but adding the radiant heat that enters through the non-thermally broken aluminium). What does this mean? Two things: important heat losses in winter and very important heat gains in summer, both along the whole working day. As a result, a) services must have been designed to cover peak loads, at an important extracost, and b) energy consumption along the year will be clearly higher than if designed otherwise. The energy performance of this curtain wall is much better than the Seagram or the Lever House from the 50s, of course, but it's nothing extraordinary nor any example of energy efficiency in buildings. I will skip the glare issue here, but I bet not all Bank of America clerks are happy about their transparent facade when they try to read their computer screen at the office.

But then, who is wrong? Wasn't it an example of environmental commitment? According to LEED, yes it is. According to some of us, there is much room for improvement - both in the design of this facade and in the way LEED points are measured and obtained. You can find more on the matter at this interesting webpage, written by Steve Mouzon: One Bryant Park and the LEED problem. I completely agree with his point of view about LEED: the US Green Building Council has made a lot for achieving better buildings and deserves our praise, but it's time for a change in the way LEED points are given. One sole change to begin with, please: all Gold and Platinum pre-qualified buildings should measure their energy output once they are built and occupied, and compare real life results against simulations, if they want to receive the final medal.

Time to come back to our old Frank Gehry and his slender residential Beekman tower. The developer here has not opted for a LEED certification (at least that I know). Compared to One Bryant Park, though, the project is quite reasonable in terms of facade energy performance.

The stainless-steel folds that now drape all but the top few floors of the Beekman Tower have already created a new landmark on Lower Manhattan. “I designed this building for New York,” says Gehry. “I’m a deeply rooted contextualist regardless of what anybody says. I stair-stepped the building like a New York skyscraper. It fits in without pandering to, or copying, its neighbors”.

To produce the tower’s wavy skin in a cost-efficient process, the facade concept is based on a flat, unitized curtain wall with a back-ventilated rain-screen cladding attached to its front. Permasteelisa (once again) was selected as the facade contractor. You will read lots of papers about the computer design process, Rhino, Catia, etc. This is not our stuff right now, we are just onto sustainable performance today.

Let's have a look at a the facade plan section. The folds of the facade become something as bay windows for the apartments, providing top and lateral shadows along the day. The residents will feel they are living within thick walls, at least that's the impression one gets from the plan section. This is a good feeling, don't you think?

The amount of opaque surfaces in this facade is much bigger than at One Bryant Park. All columns, partitions and parapets are clad with 16-gauge stainless steel face sheets, hiding a thick mineral wool insulation behind. The curtain wall elements are thermally broken. I haven't found any data about the glass yet, but I bet it's a low-e double glass unit without any additional coating.

The external wall looks really well from a nearby position. OK, stainless steel is not cheap, and these flumsy shapes are not easy to do. Even though, if we conducted a life cycle analysis of this facade, I wouldn't be surprised to find out that the low energy transmission - both during winter and summer - plus a low maintenance operation cost can offset the extra construction cost in a few years, making this facade more sustainable in the long term than the Bank of America's one. LEED permitting, of course.

Who knows? Maybe Gehry is more aligned with the real spirit of New York facades than Cook+Fox: a spirit that favours tall, vertical windows, stepped-back volumes and decorated external walls. There's nothing wrong about it, after all...


Anonymous said...

To some degree (although I'd be very interested to see further analysis into the cost effectiveness of Ghery's facade... if you know anything about his work, you know it is outrageously expensive and has absolutely no structural rationale... something that is typically highly desirable in tall a building) your argument makes some sense. In order to really understand the sustainability of One Bryant Park you need to look MUCH further beyond the facade to understand how truly sustainable it is (complex rainwater collection and ice storage system is one example). Ghery's building does nothing to push the tall building typology... it is a wedding cake skyscraper in different clothes... it may be pretty, but is lacking any kind of substance.

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