On the other hand, creating that illusion demands an unusual amount of all-too-real work and preparation. Fortunately, a group of professionals have contributed their own talents to construct such a haven in the Nancy Lee & Perry R. Bass Performing Arts Center, a 2,000-seat horseshoe-shaped opera house in downtown Fort Worth. The versatile center is the area’s cultural heart; this month alone, a Flamenco dance troupe, acrobats from Peking, and soul legend Ray Charles are just three of the acts scheduled to appear.
Basic NotesProviding an exceptional level of indoor comfort for patrons at such a facility is well within the capabilities of today’s hvac industry. Mechanical equipment used for this project included two 375-ton centrifugal chillers for future ice storage, two boilers, two cooling towers, and ten pumps. Eleven air-handling units (AHUs) were also employed. Air is distributed through 400,000 lbs of ductwork to 16 various control zones.
The distribution system also includes seven steam humidifiers to protect stored instruments as well as assorted fine art and other delicate wood-finish materials. A custom direct digital controls (ddc) unit keeps tabs on temperature, humidity, and life safety, offering readout and reset for each zone of the audience chamber.
The Sound of SilenceFor this and other symphony homes, however, establishing the best possible acoustic environment becomes an unusually high priority. Eliminating all exterior noise is only a small piece of the battle; eliminating noise from essential equipment is another crucial struggle altogether. After all, Mozart never wrote anything for “string trio and rattling duct,” did he?
Working with design architect David M. Schwarz/Architectural Services, Inc. (Washington) and architect of record HKS, Inc. (Dallas), experts at Jaffe Holden Scarbrough Acoustics, Inc. (Norwalk, CT) raised the bar by setting an original target of NC-15. For reference, a typical modern office rates as NC-40, and an average concert hall comes in at NC-22.
Following an admirable round of cooperation between the acoustical engineer; general contractor Linbeck Construction Co. (Fort Worth); and engineering, mechanical contracting and maintenance firm Dyna Ten (Fort Worth), the final noise level measured a reverent NC-12. Consider some of the measures taken to achieve this level of success:
- The refrigeration system, chilled water pumping, and air-handling systems were all installed in the basement of a rehearsal hall across the street and ducted under the street to the performance hall. Impressively, all ducts were triple isolated from the hall and hung on spring isolators.
- Ducts were intentionally oversized to keep velocity under 350 fpm, and normal commercial velocity at 1,000 to 2,000 fpm. Because of the low velocity, grilles and duct accessories such as turning vanes and volume dampers were deleted to reduce regenerated noise in ducts and terminals.
- Supply and return air fans were selected to operate at about half of normal speed to reduce energy and noise.
- All ducts supplying the audience chamber were routed through two velocity reduction chambers to reduce residual low-frequency sound, then extended to the peak of the ceiling dome to reduce impact on the audience. The distribution system also uses a total of 31 sound attenuator banks.
- All penetration of high-density and con- crete sound walls required special sealing to prevent sound flanking.
- The return air system included custom- designed return grilles under the seats. After leaving the auditorium, the air is routed through two sound-deadening return air chambers, then under the street back to the AHUs.
Working in Tight HarmonyIt may not be historically accurate, but it seems like symphonies have been performing only slightly longer than technicians have been trying to figure out how to install hvac equipment within limited space. As usual, design was only half the battle. While the larger components reside across the street, limited space in the hall’s mechanical rooms and duct areas required carefully planned sequential installation. Once equipment was brought in, there was usually no room to reposition it.
These constraints also made placement of ductwork in relation to pipes and lighting grids more challenging. Nevertheless, innovation prevailed: in one instance, a telescoping duct section was created to allow access to light fixtures in the auditorium ceiling dome.
This level of expertise and commitment (Dyna Ten alone logged 107,970 “manhours” on the project) created what Fort Worth Symphony conductor John Giordano calls the “jewel” of the entire city. “Truly, this is beyond my wildest dreams,” he says. One can only suspect that such a beautiful and conducive arts center is helping to inspire the dreams of others as well.
Austin’s Honorable HvacIndoor air quality hasn’t made it into presidential campaign discourse so far in the proceedings, but at least one candidate has recent firsthand experience on the subject. About 180 miles south of Bass Performing Hall, some of the industry’s best consulting engineers, mechanical contractors, and equipment worked to reverse IAQ problems in Austin’s 143-year-old Governor’s Mansion. As a result, Gov. George W. Bush and his wife are now staunch air quality advocates.
“We all notice a significant difference in the quality of the air now that the retrofit has been completed,” reports Governor’s Mansion administrator Anne DeBois, who has served under four governors.
Previously, the 9,000-sq-ft, 27-room historic mansion suffered high levels of mold and mildew counts during Texas’ seasonably hot and humid summer months. The levels not only posed health concerns for inhabitants, state workers, and thousands of annual tourists, but they also created the expected unappealing odors.
Volz & Associates, Inc. (Austin, TX) spearheaded the renovation, which also included roof replacement and security updates. The firm put together an hvac team that had to:
- Ascertain how to increase outside air;
- Negotiate significant space limitations while getting that air into the distribution system;
- Update existing equipment; and
- Determine that all work meets historical building guidelines outlined by the Texas Historical Commission and the architect.
Constant Source of ComfortThe IAQ problems were solved by consultants William Holder, senior vice president of Assured Indoor Air Quality (Dallas); and Bill Harris, P.E., president of HMG & Associates (Austin). TDIndustries (Dallas), the largest employee-owned mechanical contractor in the nation, was the project’s mechanical contractor. While both consultants conceived the solutions, Harris’ firm performed the design work. Meanwhile, Holder developed the design criteria and served as commissioning authority.
“This was perhaps one of the most challenging and complicated design jobs that I’ve had in my 26 years in the hvac business,” said Harris, whose firm has provided mechanical and electrical consulting for projects ranging from large 15,000-sq-ft residences to 300,000-sq-ft, $50 million commercial buildings.
The existing hvac system consisted of a 20-yr-old double-duct, variable air volume (VAV) design with 15 zones. Equipment consisted of two 30-ton chillers (one as a backup), a 300,000-Btu boiler, and one built-up AHU. Although less than 10% of the system’s total 10,000 cfm consisted of untreated outside air, that “small” introduction of air during air conditioning season helped produce mold and mildew growth that propagated throughout the year.
For the new system, the designers opted for a constant-volume system. Equipped with three MagneTek (Nashville, TN) drives, the new approach would vary the speed of the fan to compensate for resistance caused by dirty air filters.
Harris’ firm also specified a safeguard new to the mansion: a building automation system. The new 600-NBC system from Siemens Building Technology — Landis Division (Austin) would consolidate supervision of the fans, VAV boxes, temperatures, humidity, building pressure, chillers, pumps, boilers, and dehumidifier.
Replacing existing equipment, the designers specified two boilers from Raypak (Westlake Village, CA), who had also handled the mansion’s hydronic system and domestic hot water needs. Two new, 30-ton, Trane (La Crosse, WI) chillers were also ordered. The existing AHU was not replaced, but it was renovated with new coils and filters. The IAQ aspect of the project, however, would provide the most unique challenges.
A Remote SolutionThe project’s onsite work started with a complete cleaning to rid building surfaces and ductwork of mold, mildew, dust, and other contaminants.
To eliminate the source of biological contaminants, Harris and Holder decided that a commercial dehumidifier combined with air purification was vital to the redesign. They specified a makeup air RK-100 Dry-O-Tron unit from Dectron; the dehumidifier brought a moisture-removing capacity of 137 lbs/hr and was able to provide about 40% (4,000 cfm of makeup air) of the building’s supply air volume.
As a further strike against existing IAQ problems, they had the unit fitted with a multistage, gas phase filtration system designed to remove outdoor air particulates and chemical contaminants produced by automotive exhaust.
“We started with the ASHRAE standard, but then our final numbers appeared to be enough to also satisfy our goal of reversing the negative pressure,” recalled Harris, referring to the “leakiness” inherent in 19th-century building techniques.
To achieve both of these goals, a 20 cfm/person calculation was specified for a capacity of 250 people. The building generally has less than 50 people in it at any one time, but as with most governors’ mansions, the site is a frequent gathering spot for large events that can attract that level of occupancy.
The mansion’s six-foot-tall crawl space mechanical area was hardly a hospitable destination for a new 12- by 7- by 6-ft packaged dehumidification unit. Furthermore, a rooftop placement would not have complied with the historical landmark criteria, and Harris doubted whether the roof was even strong enough to support such a burden.
Instead, designers chose to create a walled-off area 75 ft away from the building, where the unit could be custom-painted to match and then installed.
The new unit still needed to be connected to the mansion to do any good, and that was the job of a 75-ft, 24-in.-round PVC underground duct. Harris and TDI realized that it was important to pitch the duct toward the building and outfit it with a moisture trap in the event that any moisture entered the duct. TDI also soon realized that trenching for the duct would be difficult because stones, bricks, forgotten foundations, and other buried objects had to be circumvented to comply with the aforementioned historical landmark criteria. On several occasions, an arborist and/or archaeologist was called to the site to consult with the TDI crew. “We had to call (the Texas Historical Commission-appointed consultants) on three separate occasions because our trenching ran into roots or an old foundation,” says Ronnie Swingler, TDI project manager. Consequently, instead of a straight duct run, TDI had to use several custom-made PVC elbows ranging ranging from 30° to 35° to avoid various historical debris.
The design consortium also had to solve continual dryness in the winter months, especially since the mansion’s public areas showcase museum-grade artifacts dating back as far as Texas’ Republic period. Harris and Holder passed up a humidifier option on the Dectron unit, fearing complications from arranging running water and drains for the unit’s remote backyard location; instead, they installed an Armstrong International (Three Rivers, MI) duct humidifier, offering a 40 lb/hr-capacity on the supply side of the makeup air unit in the mansion’s basement.
All in all, the attention to detail, whether in design or underground, paid off.
“We all notice a significant difference in the quality of the air now that the hvac retrofit has been completed,” said DuBois. Even if the current residents don’t wind up relocating to Washington, they at least can survive the scorching Texas heat easier than Sam Houston ever did. ES