Judicious Design

By David Summers, P.E, Mechanical Engineer, Glumac, Portland, Ore. April 1, 2006

Home to the University of Oregon, the city of Eugene offers breathtaking scenic views and sprawling bike trails. But natural beauty isn’t all the city has to offer. Eugene also has its fair share of art and culture. Thus, when it came time to design a federal courthouse for this Pacific Northwest community, the goal was to showcase the latest in sustainable architecture, engineering and construction.

When completed later this summer, the 262,000-sq.-ft. Wayne L. Morse U.S. Courthouse will certainly capture the fancy of passers-by with its three sweeping curved metal and glass fa%%CBOTTMDT%%ade pods, which house courtrooms and judge’s chambers, or its atrium-linked two-story glass podium that contains the facility’s administrative departments. But what’s not readily detectable is the cooperation and coordination that made this smooth design and construction process a hallmark of the U.S. General Service Administration’s (GSA) Design Excellence program.

Valued value engineering

To be clear, fiscal responsibility is a big part of this program, which seeks to raise the design quality of federally procured buildings. In order to assist in keeping the project on target, the Portland office of general contractor J.E. Dunn Construction was selected early during the design development phase. Additionally, the subcontractors, Total Mechanical, Portland, Ore., and Cherry City Electric, Salem, Ore., bid the design development drawings and were also selected to participate in the design process. The selections were made through an interview process in which the “best value” contractors were chosen based on many factors including price and the ability to collaborate.

Consequently, cost controls were implemented early in the design, major pieces of equipment were pre-purchased and specific routing of the M/E/P systems was coordinated with the contractors. This allowed the final documents to be designed around these early selections and, ultimately, was crucial due to the limited space the building allotted for M/E systems.

“Through our collaboration with the design team, we were able to save significant dollars on the HVAC budget, which allowed money to be returned to the overall project budget to pay for mechanical upgrades and enhancements to other parts of the building,” says Chuck Foreman, vice president, Total Mechanical.

Along these lines, a major portion of the project’s success can be attributed to the collaborative tools employed. With the mechanical subcontractor taking the lead, all of the subcontractors created shop drawings in three dimensions using Autodesk Building Systems. This level of coordination allowed the team to really see what was in the tight spaces before the systems were built.

For example, the administrative levels had less than two ft. of space between the ceiling and post-tensioned slab. In this narrow space there are perimeter VAV boxes and ducts, heating and chilled-water piping, plumbing, conduits, cable trays, lighting and security control devices. In many areas, several systems were stacked on top of each other with a fraction of an inch clearance between them.

With post-tension construction, the layout of these systems and insertion of hanger supports is best done before concrete placement to eliminate the potential of drilling hangers into a tensioned cable later. This required the stakeholders in the M/E/P disciplines to provide accurate shop drawings early in the process.

As the project progressed, subcontractor coordination meetings included the use of a high-performance laptop, a projector, laser pointers and a real discussion of where the conflicts were and what needed to move to make everything fit. The computer did the calculations, identified the conflicts and automatically generated sections and isometric views so that the team could spend its time solving problems. Real-time changes to the shop drawings were made and printed out so each member could carry the latest information back to his crew.

The additional cost of the shop drawings and coordination was more than made up by avoided conflicts and changes in the field. In fact, the contractors have estimated that the 3-D shop drawing process identified 95% of potential conflicts, as compared to 80% for a standard 2-D process on a project of this complexity.

Another result of this team collaboration was the implementation of a new HVAC technology known as a “fan-wall.” Basically, an improved type of air handler, a fan-wall unit is smaller in size than, and acoustically superior to, other types of air handlers. Essentially used in lieu of large house centrifugal fans, fan-wall technology (by Huntair) utilizes an array, or wall, of centrifugal fans to increase fan efficiency and reduce horsepower by decreasing redundancy. Fan-wall technology also solves a major maintenance issue by allowing individual fan replacement even while the air handlers are operating.

The implications of LEED

Incorporating new energy-saving HVAC measures proved wise, as after design had begun, GSA implemented a new policy mandating LEED certification for all its projects. In the end this was not a major problem. The basic design did not have to change significantly as the HVAC system had already been designed to minimize energy use. In fact, energy modeling results confirmed that building energy use was more than 38% below ASHRAE Standard 90.1—a condition that alone earned six LEED credits.

Another technology that helped in achieving LEED certification was daylighting. Its story, however, was not so cut and dried. With the large amount of glazing on the courthouse, the potential for energy savings through daylighting control was enormous. Despite this potential, budget constraints initially kept it out of the design. For one, dimmable ballasts proved expensive. In fact, the initial ballast specified was twice the cost of the device eventually suggested by Cherry City. Furthermore, there was also the issue of control compatibility with zero- to 10-volt signals. Cherry City also recommended an alternative daylight sensor/powerpack combination that allowed the ballasts to be manually dimmed and programmed with a hand-held remote. Still, the total materials cost for ballasts, sensors and power packs, even with these savings, came to $52,523.64.

But the team was not deterred and continued to search for ways to incorporate daylighting during construction. Obtaining incentives from the local electric utility, Eugene Water and Electric Board (EWEB), and tax breaks from the state of Oregon proved to be the answer.

Working with EWEB and GSA, Glumac performed energy modeling of the building and determined that daylighting would save an estimated 160,000 kilowatt-hours per year. EWEB provided energy incentives to offset 75% of the initial cost of the system, with GSA picking up the remainder of the cost.

As a federal entity, GSA is not taxed by Oregon. However, it still qualifies for its Business Energy Tax Credit (BETC) program through the Oregon Dept. of Energy, using a third-party pass-through organization to capture the credit. After the BETC rebate is realized, GSA’s net cost for the daylighting system will be mimimal.

Other sustainable elements include a central plant that utilizes a heat-recovery chiller to reject heat from server room loads into the heating water system. Condensing boilers maximize the efficiency of the heating water system while keeping water loop temperatures low so that the heat-rejection chiller works efficiently. An underfloor air-distribution system was also incorporated to serve the majority of space, including six courtrooms.

Getting loopy with HVAC

Lobbies and public spaces, however, will be served by radiant slabs coupled with displacement ventilation. This technology helped earn additional LEED points, but just as important, it increases comfort and allows for seamless integration with the architecture. Furthermore, radiant systems are excellent at offsetting large radiation loads from glazing, which allows for comfort to be achieved within a more lenient air temperature range.

The radiant system consists of PEX tubes encased in a concrete floor slab (see “Radiant Conditions” below). The tubing distributes heating water or chilled water from the central boiler and chiller plants through the floor slab. The floor handles 100% of the heating load in winter. In the summer, the radiant floor is also used to provide partial cooling.

A supplemental air system provides ventilation air and a portion of the cooling capacity for these public spaces. The air system is also integrated into the architectural design, as the air is delivered down through the wall stud cavities to hidden grilles at the bottom of the walls. The air is supplied at a low level and low velocity—a classic displacement ventilation system. Any concerns of excess noise were dismissed, as the air distribution capabilities and noise level produced by the system were already tested during the design phase with a mock-up built by the contractor.

Finally, the entire air system is smaller by using radiant floor technology. The resulting reduction in shaft sizes and duct distribution proved another benefit to the architecture.

In the end, the success of the Morse Courthouse can be attributed to superior design collaboration. GSA’s unique initiative to bring together designers and contractors early in the design process allowed for the competitive pricing needed to produce a green building appropriate for Eugene’s equally unique environment.

Collaborative Commissioning

To minimize cost and maintain design integrity, Glumac was retained to provide commissioning services. The success of the process ultimately depends on the buy-in of all stakeholders including GSA, the general contractor, subcontractors and the design team. So far, GSA has laid the groundwork early with all involved parties, and the commissioning tasks have been incorporated into the overall schedule.

An important component in this process is ensuring the integrity of the raised-access floor plenums. Working together, GSA and Glumac developed a procedure for testing air tightness. An initial test was conducted on a 4,000-sq.-ft. mock-up area and indicated an excess of 70% leakage. Utilizing smoke machines, the leaks were located and repaired. Overall, a goal of less than 10% leakage for all floor plenums has been established for the project. This plenum leakage testing will become a new standard for raised-access floor commissioning.

Radiant Conditions

A historical concern with radiant floor cooling is condensation on the floor. Consequently, space humidity sensors and floor slab temperature sensors must be employed to prevent condensation and ensure comfortable operation.

Another consideration is that care must be taken to ensure the heat transfer is directed up to the conditioned space, rather than down, where it could be wasted on the space below. This is achieved by insulating underneath the radiant floor, but not on top of the floor.

Fortunately for the Morse Courthouse, the insulation under the floor was already part of the architectural design to maintain the floor level with adjacent spaces. In the non-UFAD public spaces, the tile floor is raised on a rigid-foam and concrete-topping slab construction in order to maintain a consistent finished floor level throughout the building. The tile floor covering provides very little thermal resistance to the heat transfer between the tubing and space, and the foam underneath prevents energy waste below.