Angles on Art

The geometrically unconventional spaces in the new 146,000-sq.-ft., $90.5 million Frederic C. Hamilton Building at the Denver Art Museum may not satisfy everyone's architectural tastes, but there's one thing that everyone can agree on: Each gallery in the new wing is well-designed for the protection of art.

By Erin McConahey, P.E., and Murat Karakas, P.E., Arup, Los Angeles, and Tim Junker, P.E., MKK Consulting Engineers, Denver November 1, 2006

The geometrically unconventional spaces in the new 146,000-sq.-ft., $90.5 million Frederic C. Hamilton Building at the Denver Art Museum may not satisfy everyone’s architectural tastes, but there’s one thing that everyone can agree on: Each gallery in the new wing is well-designed for the protection of art. M/E/P system engineers not only rose to the challenge of a demanding architectural configuration, but also met the test of creating the ideal environment for the museum’s patrons and its collection.

Architect Daniel Libeskind won the international competition to design the new wing. No newcomer to museum design, Libeskind’s high-profile projects include the Jewish Museum in Berlin and the Imperial War Museum North in Greater Manchester, England. But what really brought the architect to popular attention was his receiving the commission to create the master plan for the reconstruction of the World Trade Center in New York.

Libeskind’s trademark style is characterized by eccentric geometries and angles. Contracts for the project were developed with a full awareness that the Studio Libeskind vision of “two lines taking a walk” would explode upwards into a crystalline form of interlocking sloped planes, reminiscent of the nearby Rocky Mountains (see “Inspired by the Rockies,” p. 44).

Idiosyncratic architectural design, however, wasn’t the only factor affecting engineered systems design. The HVAC system of any museum in the Mile High City must hold to tight internal temperature and relative humidity (RH) conditions, despite the generally dry, sunny, high-altitude climate occasionally pummeled by winter snowstorms and visited by sudden summer rainstorms. (The chart on p. 48 tells the story in a glance.)

The staff at the museum was already intimately aware of the challenges that this type of climate posed for protection of an art collection, trying to maintain, in the existing 1971 North building, an RH stable enough to qualify for large-scale loans from international institutions.

In fact, a new state-of-the art wing was a key component in the museum’s strategy to attain a key placement on the American art scene, as it would provide rooms large enough and environmental systems sophisticated enough to capture a regular spot on the New York-Chicago-West Coast tour circuit of blockbuster traveling exhibitions.

And so began a quest for the ideal mechanical systems to achieve this goal.

In the district

Early-phase life-cycle cost analyses indicated that a connection to Denver’s downtown district-steam and chilled-water systems would be more economical than a building-based central plant. Moreover, the use of the district utilities would reduce the number of exterior penetrations, preserve more of the building as net occupiable space, and ultimately, allow the unique building exterior to remain unblemished by flues and refrigerant vent pipes. District steam was to be used for the local production of hot water for heating and the unfired generation of humidification clean steam from reverse osmosis water.

Also, it became clear to system designers that discussions with the North building’s on-the-ground staff—and the lessons they had learned over the years—would serve as the basis for the new project’s HVAC design goals, which included the following:

  • Close control over temperature and relative humidity in the galleries.

  • No water or steam piping within the galleries themselves.

  • Mechanical rooms that allow for the consolidation of equipment for ease of maintenance.

  • Outside-air intake louver physically inaccessible to prevent tampering.

  • Outside-air unit with centralized gas-phase filtration and preheat.

  • Dual airstream and fans in each gallery-related unit to allow partial air-conditioning during maintenance.

  • Room within gallery units to add gas-phase filtration for specific exhibition.

  • Stand-alone systems for retail and entry lobby/cafeteria.

  • Multiple monitoring and control zones in large “open” gallery spaces.

With these goals in place and a developing plan, it became quite obvious that it would be necessary to homerun the zonal ductwork back to the main mechanical rooms so that reheat coils and humidifiers could reside in a location far away from the gallery spaces.

In a gallery faraway

The gallery systems are designed as recirculation units with minimum ventilation air injected from a centralized outside-air system that tempers the incoming outdoor air content. The gallery air handlers contain two variable-speed supply fans running 50% duty, each in a cooling configuration with independent valving for the two independent cooling coils so that essentially the system can run as face/bypass. The control system uses CO2 monitoring in the galleries to control the ventilation air content in order to reduce the maintenance cost associated with replacing gas phase filters, as well as reducing the running cost of humidification. Additionally, the fans have VFDs to maintain constant volume supply, regardless of filter loading, and to provide setback airflow quantities to capture energy savings in the evenings when the galleries are in a low-load condition.

Every gallery incorporates a set of bypass dampers that allow pressure-relief air to escape into the central atrium. This allows the galleries to remain at positive pressure with respect to the outdoors and with respect to the lobby. A set of central exhaust fans near the roof run on VFDs to volumetrically track against the total known outside-air intake to the building minus the known toilet exhaust and pressurization leakage.

Temperature and relative humidity sensors are located throughout the gallery spaces in order to ensure that no monitoring zone is larger than 5,000 sq. ft. As the exhibit designers reconfigure display partition walls over time and create compelling, but oddly-shaped air volumes, the density of sensors will allow the facilities staff the ability to monitor for the unintentional byproduct of microclimates. Based on a prior agreement with the museum, and in order to ensure flexibility for shows not yet envisioned, the main gallery spaces incorporate a 20-ft. x 20-ft. grid of hard ductwork terminations. Through flexible ductwork, the grid allows supply diffusers to be moved another six to eight feet in any direction to resolve any unforeseen airflows that arise from the acute angles generated by the juxtaposition of the vertical temporary walls and the sloping permanent structural surfaces.

Lastly, with a view toward art protection, the electrical and HVAC design teams sequenced the diesel generator to accommodate both backup power in an emergency life-safety capacity and to provide sufficient power to keep the art-area air handlers running at a very low fan speed in an “art-preservation” mode during power outages.

Leftover spaces

Once the building program was incorporated and the structural elements were anchored to the foundations and cross-braced against one another, the mechanical area footprints were deeded to the mechanical team—in other words, the space leftover. But the layout of the rooms and risers are a testament to the power of design phase 3-D coordination for optimization of routing in a non-orthogonal volume (see Figure 1 above).

Starting at the top of the building, the penthouse contains a dual-fan outside-air system with pre-filtering, pre-heating and pre-humidifying of the dry Denver ventilation air to the gallery and art-storage recirculation air handlers. The penthouse also contains the main toilet exhaust fans, as well as the atrium exhaust fans, that serve the dual purpose of providing over-pressure relief under normal conditions and smoke control in the event of fire.

A main mechanical room is stacked in the southwest corner from the second to third floors, taking advantage of the increasing volume that is created by the expanding floorplate as the out-leaning walls of the building grow out of the ground. This location allowed for the double-stacking of air handlers with access from catwalks flush with the adjacent occupiable slabs, with zonal coils accessible from the mechanical room “minimal footprint” below the suspended air handlers. With a straight ducted run into the sloped ceilings of the double height galleries and a riser drop into the first floor, all the temporary galleries could be served from this position, again with no HVAC water or steam piping in any gallery.

With the majority of the public gallery spaces located at ground level and above, the basement was the most logical area for mechanical equipment. Besides serving as the main entry for chilled water and steam from the utility loops, the basement mechanical rooms house air handlers for the back-of-house art storage zones and the auditorium. There is also an air handler that serves the majority of the main lobby, which is supplemented upstairs by a small ceiling-hung air handler in the first floor zone, reserved for a possible future cafeteria/kitchen and fan coil units serving the retail shop. A small mezzanine at the southern mechanical rooms enables all zonal reheat coils and humidifiers to be easily serviced without leaving the mechanical room, as well as the fan coil units serving down into the electrical rooms.

In addition to the air handlers listed above, a final pair is located in the northern basement mechanical room, directly below the sloped riser wall that serves as a common return. The nine permanent gallery reheat/humidifier zones are ducted to both vertical and sloped risers for extension to the second, third and fourth floor galleries immediately above. With mechanical rooms somewhat remote from the zones they serve and the desire to “homerun” ductwork, sheet metal routing was a key challenge.

Geometric chaos

Due to the nature of the building’s unique geometry—walls that slope at 32.4° on the outside also slope at 32.4° on the inside—only three truly rectilinear elevator and stair cores were available. Consequently, the intensity of zonal ductwork for the north permanent galleries required that ductwork be run in sloped risers created through the thickening of pre-existing structural wall. Add to the sloping risers a need to exit onto some horizontal floor plates and into some severely sloped roofs, and the designers were presented with a geometrical nightmare as far as sheet metal and pipe routing is concerned. To produce 3-D sheet metal construction documents, every corrective transitional angle for each x, y and z axis rotation had to be calculated and then documented. With walls and roofs that run at angle for up to 200 ft., a 0.1° error in elbow angle is the difference between remaining within the ceiling cavity or not, and clashing with the structural members or not.

After the ductwork runs were complete, 3-D modeling was utilized to determine the best routing of piping for the hydronic, fire-protection and plumbing systems to ensure proper slope for drainage, to fit within the sloping structural constraints, to avoid conflict with the other services and to minimize piping over gallery and art display areas. Dry-pipe fire protection systems also utilized the 3-D software to ensure positive drainage to a point outside each gallery, to allow immediate drainage of the individual double interlock pre-action systems after a false alarm event.

The fantasy about 3-D work, of course, is that all parties are simultaneously working in a common environment, but that somehow, every other discipline should be done with their work before you have to start your own. But even in 2-D, integrated multidisciplinary design requires iteration and change that must be communicated and accommodated by others. For instance, Arup structural engineers used a variety of 3-D analysis programs to design the building — all the programs created line models as opposed to models with extruded 3-D wide flange shapes due to the processing power required to regenerate the shapes within the CAD environment. Moreover, some programs had the lines defined as the centerline of the web height, while others automatically defined the centerline on the plane of the upper flange. And lastly, some of the beams supporting the sloping roofs had flanges parallel to the roof slope, while others were parallel to the horizontal plane. Mix that in with a little structural “design iteration” and there was the need for a regular interpersonal collaborative accounting exercise by the combined Arup team of revisiting every beam and brace to check current ductwork clearances.

Throw in some value engineering measures to shrink the first floor ceiling void and to tighten the sloped roof sandwiches, and then steel beam web penetrations were necessary. This required that each duct adjust its route twice in order to minimize hole size: once to approach the web at a perpendicular angle, and again to ensure that the top of duct was purely parallel to the beam flange. The structural drawings were exactly dimensioned for hole position and size, and the holes were all cut in the factory. Of the coordinated 33 penetrations, there were only two holes required to shift slightly during shop drawings in order to accommodate some elongated bolted connections preferred by the steel detailers.

The real benefit of the 3-D design phase coordination, as a result, was during construction.

The careful detailers at mechanical subcontractor U.S. Engineering of Loveland, Colo., essentially “traced” into their 3-D CNC program the duct runs and angles pre-determined in the contract documents. Shop drawing review went quickly as Arup super-imposed the mechanical subcontractor’s actual 3-D models onto the original CD models and the reviewer could immediately see any deviation (see Figure 2 above). Once approved, those same 3-D shop drawings were downloaded directly into the sheet metal cutting machines, which meant that each shop-fabricated piece fitted up easily and exactly in the field, through each steel beam penetration, and along each unique slope. All in all, the sheet metal work had a total of 21 RFI’s associated with structural-ductwork conflicts, a feat on any orthogonal building, much less a building of this geometrical complexity.

Outside Design Conditions Indoor Gallery Conditions
Summer: 90°F dry bulb/ 59°F wet bulb 70
Winter : -11°F dry bulb/ -11°F dewpoint
per 1% exceedance from ASHRAE Fundamentals 2001

Inspired by the Rockies

Design of the museum’s new wing began in 2000 when architect Daniel Libeskind won the international competition sponsored by the museum, city and county of Denver. Through a joint venture formed between Studio Libeskind and the Davis Partnership of Denver, building engineers were contracted to perform subconsultant design services. Included was the requirement for final construction documents to be delivered as a three-dimensional model, with two-dimensional drawing provided for ease of reference and a repository of clarifying annotations.

Studio Libeskind’s vision was a design that explodes upwards into a crystalline form of interlocking sloped planes, reminiscent of the nearby Rocky Mountains. Arup’s Los Angeles office provided structural, air side mechanical and acoustics design services while MKK Consulting Engineers, Denver, provided design engineering services for hydronics, plumbing, fire protection, telecommunications/data and electrical work.

Setting the Stage

A city and county bond measure approved by voters in 1999, and a simultaneous private donation fundraising effort conducted by the museum’s non-profit organization, set the ball in motion for construction of the Denver Art Museum’s new Frederic C. Hamilton Building.

The public/nonprofit partnership was committed to the beauty of the designers’ original concept, but was strict in its requirements that the design be delivered in a way that would meet the new building’s functional requirements. Back-of-house spaces for art storage, protected art movement corridors, loading, crating, registrar and analysis were all to occur in the new museum wing.

Furthermore, it was essential that all building management, security and remote environmental monitoring systems be seamlessly compatible with those already present at the North building.