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New Bank of America Tower raises the standard for urban water reuse.
Rainwater, graywater, cooling tower makeup water—even groundwater under the basement slab will be tapped, piped, and continuously recirculated in an ultra-green skyscraper being built in midtown Manhattan. When completed in mid-2008, the gleaming, crystalline Bank of America Tower will redefine water efficiency in large commercial structures. Bank of America and its co-developer, the Durst Organization, are striving for a US Green Building Council Leadership in Energy & Environmental Design (LEED) platinum certificate—making this 52-story structure the first of such size ever to undertake that challenge. With its array of conservation technologies and green concepts, the billion-dollar tower is aptly being called “the world’s most environmentally responsible high-rise office building.”
“Our goal,” says Cook+Fox Architect and Project Director Serge Appel, describing the building’s wastestream strategy, “is to try not to reject any water into the stormwater system.”
n unprecedented 95% of the runoff will thus be collected for reuse. By means of this and several other measures, potable water use from the city will be reduced to about half. “We haven’t succeeded in reaching 100%,” he says of these figures, “but we’ve gone a long way.”
Multiple, custom-designed innovations incorporated into the 2.1 million-square-foot, nearly 1,000-foot-tall bank headquarters will conserve, overall, an estimated 10 million–plus gallons of fresh water yearly—an achievement particularly beneficial in this high-density urban setting prone to sewer backups.
Rooftop Rainwater
It’s a bit surreal-sounding, perhaps, and hardly the image one expects atop a sleek, 21st-century skyline. Gathering rainfall on a roof and shunting it to vats inside harkens back to ancient times and primitive rainspouts—but, apparently, some engineering concepts never grow old and obsolete.
Plumbing designers at the New York mechanical and plumbing engineering firm of Jaros, Baum & Bolles (JB&B) have taken their cues from the past and are devising a series of rainwater collection tanks and distribution piping. These will be positioned on the tower’s roofs and at strategic points amid the 52 floors. Collectively, they form a unique plumbing matrix that will integrate freshwater loops with graywater collection for reuse in all of the building’s water services. The design concept is principally that of JB&B partners Robert Benazzi and Project Engineer Scott Frank, along with Plumbing Engineer Mike Roberts.
As Frank explains it, the tower will feature “a complicated … articulated roof; there’s significant flat area … and very large cooling-tower installations,” together with flat-roofed penthouses. Nearer to the ground level there’s another 25,000-square-foot podium roof. “But in the end,” he says, “it’s all drained.”
Downspouts run to four stacked water tanks positioned about 10 feet apart and arranged, he says, “so that water from the upper tower roof kind of flows into the top tank—and then cascades down to the successively lower tanks,” filling each in turn, as rain volumes require.
From this tankage, the water will flow directly to the building’s 250 to 300 flush toilet fixtures (“five or six public ones in the building core, on each of the 50 floors,” notes Appel.) Frank points out that “it’s a complete gravity system, requiring no pumps,” and thereby saving lots of electricity that otherwise would be squandered: In green designs, he adds, gravity only makes good sense.
As for the innovativeness of it all, he notes: “We’re not aware that this has been done in a tall commercial building—and distributed by tanks all flowing by gravity—anywhere else.”
Blackwater from toilets will, of course, plumb to the sewer. But that’s about all the water that will, as most of the flow—including lavatory graywater, cooling tower condensate and blowdown, steam water condensate, and assorted other service graywater—will travel to a large basement storage tank for filtering, disinfection, and reuse.
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Photo: Durst |
| Estimates show tower water conservation of 10 million-plus gallons annually. |
Big Indoor Reservoir
One bit of ingenuity applied on this aspect, notes Appel, was the decision to use the building’s thick concrete core as siding for a massive water storage bin. “Instead of having to build an additional water tank or buy and install several huge ones,” he says, “all we had to do was waterproof those core walls and build the tank right into the building”—making for “a much cheaper system,” he adds.
Sizing this built-in, watertight pool was determined, says Frank, by evaluating New York City meteorological data, especially peak rainfall averages. “About 90% of precipitation happens in events of less than an inch of rain,” he points out. Hence, “the architects could maximize tank usage for that kind of rainfall.”
Total water storage capacity in all five tanks will come to about 330,000 gallons, Appel adds.
And, although the freshly falling raindrops need little in the way of filtering and disinfection, the tanks’ reusable mix does. Benazzi explains that it is filtered with a sand type system and it’s UV’ed (i.e., subjected to ultraviolet light on a ‘side street’ basis, then sent back out) to other storage tanks staggered around the building.
Cleaning of the filter will occur automatically via a backwash system designed to engage whenever the pressure drops to a certain point.
The water, thus reclaimed, is reusable, he says, for flushing toilets or cooling tower makeup or steam production. All of the building’s heating and cooling systems’ water (and much of the flush toilet water) will come from this basement source.
Heating and cooling each draw about 5,000 gallons a day; thus, the water level in the tank will never be allowed to drop below 18 inches or so, Benazzi notes. Tank water is also constantly recirculating: Wintertime steam condensate and summertime cooling tower blowdown are always replenishing the tank, along with graywater inflow from core lavatories.
All of this represents something of a “next-generation” advance for JB&B over its previous stormwater reclamation designs in that city water in that bottom layer is being allowed to mix with incoming graywater. Benazzi explains: “JB&B has utilized stormwater retention and reuse for cooling tower makeup for many years.” In these earlier systems, collected stormwater would “float” above a minimum amount of city water always captive in the tank. Thus, he says, “On those days of no rain, a city water makeup system kept the minimum reserve at level,” but on rainy days, “the float valve would close, allowing stormwater to fill the tank for reuse.”
A key consideration in this new, greener approach was the fact that the expanded use of nonpotable treated graywater could potentially foul some building systems. Thus, preventive measures had to be weighed. As Benazzi recalls, “We wanted to make sure we’re not sending a lot of ‘bugs’ up there,” referring to possible algae blooms in the cooling or heating plant loops, caused by organics in the graywater. “So,” he says, “the thought occurred to us, ‘Well, we are keeping a base of chlorinated water at the bottom of this tank.’ And if you go through the mass balance, you’ll see there’s probably enough chlorinated city water there to where we shouldn’t have any problems.”
However, he adds, if algae should ever arise, it could easily be chlorinated as required.
He notes, “If it doesn’t rain in New York [City] for a month, that tank will constantly be getting filled by domestic water at that level.” And again, on rainy days the tank becomes a big stormwater reservoir.
The previous-generation stormwater collection designs have proved reliable and problem-free in several other JB&B applications around New York, albeit without this new wrinkle of lavatory graywater.
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Photo: Falcon |
| Waterless urinals |
Potable/Non-Potable Loops
At any rate, the decision to utilize thousands of gallons of nonpotable water necessitated designing and installing two completely independent plumbing loops. These will ensure that the nonpotable output “should never come into contact with people,” Benazzi says. Safe potable water from the city circulates, of course, to all fixtures in the tower that might come into human contact, including drinking fountains, lavatories, and kitchens.
One critical factor in the graywater strategy was the decision to collect lavatory graywater only from the core restrooms rather than from the many private suites with kitchen pantries, washrooms, and showers, which typically produce a higher-strength graywater—soapier, with shaving cream, toothpaste, and a bit more sink debris. “We don’t see that kind of stuff in a typical core toilet lav,” he notes. “People just wash their hands, and that’s about it.” Core lavatories thus yield relatively low-strength graywater, easily filterable for reuse.
For added “insurance” that the two loops will never be confused, future building tenants who may want to remodel the executive washroom or kitchen won’t be given access to the graywater loop. There will be no capped outlets for it. And potable and non-potable loops will be distinctly color-coded.
In sum, he says, “We’ve taken a lot of steps to make sure that there’s no chance that we can get cross-contamination. That was our biggest fear in doing the system.”
Low-Flow Toilets, Waterless Urinals, and Automated Faucets
On the “business end” of all this reclamation use, water closets will be hung with Kohler low-flow toilets that meet the EPA’s green standard of 1.6 gallons per flush. Automated “Optima-Plus” battery-operated flushometer valves from Sloan Valve Co. are incorporated. Although not claimed “as a water efficiency product,” as Sloan’s Manager of Water Conservation Jim Allen notes, these are desirable on toilets “as a convenience and hygienic feature,” and to reduce housekeeping calls.
In the men’s rooms, several hundred of Sloan’s Waterfree vitreous china urinals will be installed. Urine is collected in a small sealed cartridge containing a biodegradable liquid that stores and degrades the waste in an odorless trap. The design eliminates the need for any water at all—as well as plumbing inflow or outflow pipes and associated costs.
Although these products have been on the market for some years now, waterless urinals are so exceptional in New York City, says Appel, that Cook+Fox, being cautious, decided to install them in its own building on a trial basis before recommending them to other clients. In that tryout, says Appel, “We found no problems at all. Most people wouldn’t even know they’re any different.” The urinals “work very well,” he reports, “as long as you change out the filter” every few weeks or so, depending on usage.
When filing permit applications at City Hall, Roberts recalls, the proposed Bank of America urinals raised some eyebrows: Such devices had never been seen before, let alone requested. New York City’s building code does not allow them. However, a new code (based on the international building code), which is scheduled to take effect in mid-2007, will permit them if they’re incorporated into larger water-saving designs, Roberts says. To allow installation in the Bank of America, a special variance had to be granted.
As for the bathroom lavatory sinks (Kohler under-counter models), these will, of course, be plumbed with potable water. For water efficiency they’ll be equipped with Sloan battery-powered electronically controlled low-flow faucets. The low-flow and electronics in tandem can reduce flow to just half a gallon per minute. By contrast, New York City’s code allows conventional faucets a profligate 2.2 gallons per minute or more, notes Roberts.
Sloan Valve’s Allen adds that the combination units “are tremendous water savers.” A recent study at Texas A&M University found the relative conservation advantage came to “about 70% over standard high-flow manual taps,” he reports. Any architect or plumbing designer can do a simple demonstration test, by using a sensor-equipped faucet side by side with a manual one, and then measuring the result in a bucket. Allen sums up: “Sensors are very water efficient, and we always encourage their use in a high-performance LEED building.”
The Bank of America tower will thus gain the distinction, says Appel, as “one of the first large-scale projects in New York” to use all three water technologies—automated faucets, low-flow toilets, and Waterfree urinals—together.
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Photo: Durst |
| Cold groundwater will provide the tower with cooling in the sumer months. |
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Photo: Durst |
| The tower is scheduled to open in mid-2008 |
Groundwater Sump Adds to the Mix
As if all this weren’t enough, the building’s nearby groundwater will also be tapped and used indoors, notes Roberts. Manhattan—an island in an estuary—enjoys copious underground currents, and in fact, “underground rivers are criss-crossing” beneath the land, he says. Soggy ground poses a challenge to structural engineers, who must plan on sump pumps for dewatering. “Under a normal scheme,” Roberts says, “you would take that water and just dump it into the city sewers.” However, this particular groundwater is relatively quite cold—and thus potentially valuable as a source of summer cooling. When the tower opens in mid-2008, the bank’s ground-level branch office will enjoy this unusual natural cooling, as groundwater loops will lift the cooling indoors. Heat exchangers will transfer the energy. “We’ll actually use that as a thermal storage sink,” says Roberts. After cooling is extracted from it, the warmer water will flow on into the basement reservoir. “We don’t waste it,” he says, adding: “I don’t know of any other building in the city that does anything like that.”
Taking the LEED
Those last two statements aptly summarize the entire design concept here, from top to bottom: First, the desire not to let a single drop of usable water escape if it can be reclaimed at reasonable cost; and second, the goal of being the first big project to demonstrate “green” in a big, skycraping way.
More specifically, as Roberts outlines the anticipated efficiency gains being sought: “At the end of the day, we predict we’ll save about 10.3 million gallons a year on city water.” Percentage-wise, that’s about 40% less than what would otherwise be used, or, in dollars, $60,000 a year at current rates. (And, notes Appel, reducing water usage will also put the property into a lower rating category—so that the net dollar savings actually works out to about 48%.)
Breaking down the total 10.3 million gallons per year into sub-parts, this works out to 2.3 million gallons per year savings from stormwater; 0.9 from cooling coil reuse; 2.6 from steam condensate; 1.1 from lavatories; and 3.4 from waterless urinals.
Offsetting all these water savings, though, are admittedly modestly higher first costs incurred with the dual piping for graywater and rainwater collection. “It’s more money,” Roberts concedes. But the primary design criterion here wasn’t to erect a cheaper building but a greener one. The owner-developers, Bank of America and the Durst Organization, gave all the designers the “green light” to incorporate whatever efficiencies they saw fit to, within reason. Besides these water innovations, other green features include heavy use of recycled materials; energy- and water-conservation; filtered under-floor displacement air ventilation; advanced double-wall technology; translucent insulating glass in floor-to-ceiling windows that permit daylight and views; and a 4.6-MW cogeneration plant—all of which will make the tower soar to prominence in green design circles worldwide.
Although the water system components, individually, aren’t unprecedented, Appel says, what’s probably most distinctive here is their use in combination on such a monumental scale. He adds, “In order to top this building in the future, you’d have to reject virtually no water into the stormwater system.”
He sums up: “These systems are getting to be more known now. They just make a lot of sense. They’re not complicated. They’re very easy to put in. It’s just the logical thing to do.”
David engle, a writer based in La Mesa, CA, specializes in construction-related topics.
OW - March/April 2007 |
