Hot Sun, Cold Justice
November 01, 2002
Appeared in Consulting-Specifying Engineer
Unlike Manhattan, Islip, N.Y., is not noted for its mountainous edifices. To the contrary, it's really one cell of Long Island suburban sprawl that dots an ordinary landscape. Therefore, it was ripe for some architectural justice, so to speak. And that's just what was served with the commissioning of its new U.S. courthouse and federal building.
Dominating the skyline, the $190 million, 870,000-sq.-ft., 235-ft.-tall structure is punctuated with a white cylindrical tower at its core--a feature meant to inspire all who see it. "It's a giant, in-your-face landmark that grabs your attention to the point that you know that it's the entrance," says Renny Logan, an associate partner at Richard Meier & Partners, New York, the building's architect.
In fact, if it weren't for the tower, the building, with its extensive glass facade, might be mistaken for a luxury high-rise condominium, as opposed to the traditional granite-clad look typical of many courthouses. And that was purposeful, says Logan, explaining the justice facility was designed within the parameters of the General Services Administration's (GSA) Design Excellence Program, whose goal is to change the face of public architecture in this country.
Of course, beauty often comes at a cost, and in this case, the architecturally pleasing visage presented a handful of HVAC concerns to the engineering team.
Shading a blazing sun
Designed to be open and inviting, the courthouse's public areas span the building's exterior walls, while the courtrooms and other spaces are clustered toward the center of each floor (see "Controlled Circulation" at right).
"With this courthouse, we felt it was particularly important to have clear glass, so that it didn't seem intimidating," Logan says. "We also wanted it to be something the general public feels is accessible, physiologically and spiritually."
Naturally, daylighting was also a goal, but with a 600-ft. long, 235-ft.-tall glass curtain wall that would span the building's south face, the architect knew he'd have problems with heat gain. A high-quality, low-emissivity insulating glass was specified, but the M/E/P engineering team knew it was just the beginning.
"When we started looking at the designs in the schematic phase, we realized that there was no way we would be able to cool that space without some way of controlling the sun," recalls John Lennon, project manager for M/E/P engineer, Syska Hennessy Group, New York.
A variety of calculations were performed by the engineering team to determine how much power would be necessary to cool the structure's southern exposure at different times of the day. The numbers were astronomical. In considering their options, the only viable solution was to create a sunshade.
"If you want to reduce the building's heat gain, you really need to stop the sun from hitting the glass in the first place," Logan says.
initial scheme, which strove to preserve the feel of the original
design, specified 2.5-ft. wide horizontal screens, spaced
on 6-ft. centers, floor to floor. However, after setting up
several computer models to
detail the sun's cycle, its intensity, and the subsequent effect on the building's waiting areas--for purposes of determining the angles of the shade-- Syska Hennessy found that screens on 3-ft. centers would decrease peak cooling
loads by 22%. This, in turn, allowed perimeter HVAC systems to be reduced in size, providing for greater energy savings from the reduced solar load.
The revised shade was composed of a series of modular units, each 30-in. deep and 9 and 12 ft. high, constructed of white-coated aluminum tubes and pipes that were attached to the curtain wall as it went up.
on that HVAC savvy
While the shading system was certainly a major step in reducing the building's cooling load--and a success in reducing glare--it was only the first component in keeping the space comfortable. Such a large, multi-functioning building required a well thought-out building automation scheme: Thermostats regularly report room temperatures back to the building automation system, which in turn controls variable-air-volume boxes installed in both the courtrooms and hallways (see figure below). The VAV boxes are programmed to automatically adapt the temperature to the load and occupancy of the space. The direct digital control system also allows GSA staff to read and control all the building's systems as an entity or separately, as needed. Furthermore, variable-frequency drives control the output of the building's fan system, which helps cool many of the interior spaces as well.
As far as HVAC basics, the building is cooled by three 830-ton electric centrifugal chillers. During off-peak and low-load periods, a smaller 300-ton chiller serves the facility.
For further energy efficiencies, free cooling is achieved via a plate heat exchanger. Furthermore, a condenser-water riser was installed and provided with capped valves on each floor.
This system serves as a contingent for future load increases, which will likely result in the installation of a planned computer/server room.
Other special HVAC concerns that arose in considering the facility's evolution involved noise--something judges are renown for being sensitive to. "There are cases I've heard of where a judge has called a mistrial because of too much noise in the courtroom," Lennon says.
In this case, it was an issue because office space in the complex, as the need for courts increase, will be converted over the next 30 years into additional courtrooms and judges' chambers.
This is obviously a challenge, Lennon says, as activity in courtrooms ranges from hosting a great deal of people-- including TV personnel and equipment--to only judges, lawyers and the defendants. In the former instance, heating or air conditioning kicking on might not be an issue; however, in instances involving the latter, it might be quite noticeable.
With this in mind, ductwork was created to be adaptable so it can be increased to reduce noise. The size of the VAV boxes in these areas were also built smaller and hung inside the ceilings, with controls outside the courtrooms. This way, when the rooms are changed over, larger VAV boxes will be built and stored outside the courtrooms, near their controls, further reducing noise.
However, in order to make the smaller VAV scheme work now, a low temperature air system had to be employed. In this system--somewhat unique to the courthouse's HVAC design--the air temperature off the coil is 44deg.F. This much colder supply air stream also proved a great economic move, as GSA's life-cycle analysis determined the system would shave approximately $1 million off the building's construction cost.
A final and unusual HVAC consideration in the building was dealing with the lead-filled air in the marshals' pistol range. Located in the basement, the two-lane room required a special exhaust system to simultaneously flow air away from shooters and minimize lead composition. Negative pressure prevents lead-contaminated air from leaving the room--a major concern, according to Lennon, as the "consequences could be damaging."
For example, six months after the building was in operation, lead content was too high. It turned out there were leaks in both the ceiling's ductwork and the room's vents. Fortunately, a readjustment of the diffuser blades, along with resealing the ducts, allowed the supply and exhaust system to be rebalanced, allowing the room to function as it was designed.
Although much of the HVAC system was driven by architectural considerations, maintenance and operation were also heavily factored. For example, due to the essential nature of the court function and inherent security requirements, the location of mechanical equipment, VAV boxes and controls were carefully selected so as not to present a security risk or interfere with routine maintenance.
- Access doors for duct cleaning and equipment inspection were strategically located.
- Two supply fans under one casing on the air-handling units provides a degree of flexibility in the maintenance schedule.
- The layout of the mechanical equipment room allows for sufficient access for equipment removal and routine maintenance.
This last point, according to Lennon, is really a testament to Logan and his firm. "The key to adequate maintenance space is an architect sensitive to the building owner's need to operate and maintain equipment once the design team is no longer involved."
This spirit of teamwork made the architect's demanding aesthetic requirements much more palatable, as Lennon recalls the tribulations of selecting and placing materials that matched the architectural theme. "You couldn't just spot recepticals or diffusers anywhere. The whole building had to go together," Lennon says. In the end, all customers were satisfied, as GSA had both a high caliber architectural statement and a high-performing building. "It's a legacy-quality building," says Ed Feiner, GSA's chief architect. "And I get a thrill every time I realize that a building of this substance and import has emerged out of public architecture. It's something we're not used to."