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Standing Tall in the Aleutians—A Challenging Project in a Remote Location

Nothing is easy in the Aleutians. Thus, a project to install necessary air handlers for a power station in Unalaska, AK, was a challenge for the engineer and the manufacturer, Governair Corp. Unalaska—the 11th largest city in the state—is a community of about 4,000 residents located on Unalaska Island in the Aleutian Chain, approximately 800 miles southwest of Anchorage.

The Aleutians separate the stormy North Pacific and the equally turbulent Bering Sea—an area that has become familiar thanks to the Discovery Channel program, “The Deadliest Catch.” The section of the city known as Dutch Harbor is the home port for the now-famous crab fishing fleet that takes high risks for high rewards in the stormy northern ocean waters. In recent years, changes in federal fishing regulations have created an extended fishing season, and the City of Unalaska has seen a rise in the construction of new commercial facilities—hence a growth in electrical demand.

To meet that need, the city made plans to purchase two 5.2-MW diesel units and begin an expansion of its power house, a $48-million project. The project engineer was Anchorage, AK-based Electric Power Systems. As part of the power-plant project, EPS specified air handlers to supply the power house with combustion air, cooling, ventilation and comfort conditioning. This element was a requirement of the Finnish generator manufacturer, Wartsila.

Space challenges
Arrangements for the design, construction and installation of the air handlers were handled by Bob Heym of Alaska Winter Inc.—a CES Group manufacturer’s representative in Anchorage. According to Heym, Wartsila had initially specified an indoor air-handler system, but there was no space available indoors for such a system and its associated ductwork in the new power house. Heym suggested a modular outdoor system with openings in the building wall for the required supply and exhaust ducts.

Heym and a city representative went to the Governair factory in Oklahoma City, OK, to go over the submittals and to assure that the finished product would meet the owner’s needs. A few changes were made at this point, including the addition of a rail system in case it was ever necessary to remove a 30-lb motor. Another addition was the installation of an aluminum tread plate floor.

Another requirement—one that had been missed in developing the initial specifications—was that the air handlers must be able to withstand 175-mph winds.. With winter storm winds officially recorded at 115 mph in December 2009 and a recent unofficial measurement at Dutch Harbor of 170 mph, the design had to be reconsidered to withstand such extreme conditions.

Coffman Engineering of Anchorage revised the plans to meet the changed wind-speed specifications. According to Coffman Engineering Contractor David Lunow, “Governair replaced standard 2-in. x 2-in. corner tubes with 6-in. x 6-in. tubes, and used additional 4-in. x 4-in. tubes for cross-bracing support. This kind of steel support, along with the stiff panel construction of the system, made it easy to meet the 175-mph wind load and Zone 4 seismic requirements.” Lunow added, “We have done vertically stacked units before this job, but nothing that had to meet such extreme requirements.”

Two air-handlers, each delivering 62,000 cfm, were designed to be stacked as four sections, simplifying transportation and site erection.
Viewing assembly process
Heym and the Lunow went to the Governair factory for a final walkthrough and to watch the units being assembled in the factory before disassembly and shipping.

“Given the conditions at the site and the challenge even getting the product there, we didn’t want there to be any mistakes,” Heym said. “I wanted the contractor to observe the erection process.”

After completion of the factory stage, the two units were each demounted into four stages and shipped by truck to Seattle, WA. From there they were shipped by barge to Unalaska and trucked to the power house. The four sections were stacked vertically against the rear-exterior wall of the power house. Each air handler is 20-ft wide, 12-ft deep and 40-ft high. Due to the climate conditions, there was no need to provide either heating or cooling coils for the power house.

Each unit is able to supply 62,000 cfm of supply air, and is designed to be able to mix in return air, depending on outdoor conditions. The units are designed in four levels:
• The first floor is a three-sided louvered section to provide outside air, and access to the unit;
• The second floor contains the filters and is the location of the control panel;
• The third floor has one of the exhaust fans with its VFD; and
• The fourth floor contains the supply fan, the second exhaust fan, along with the two fan VFDs.

The supply fan for each unit is a vertical-shaft plenum fan, which was assembled along with the fan frame at the factory. This fan type was selected because it fits the unit design and air-flow requirement the best. The exhaust fans are prop fans. The interior power wiring was done with a single-point power connection and a disconnect switch. The control contractor at the site installed the control wiring.

Project nears completion
The first unit is already up and operating and the second unit is nearly complete. Heym points out that because of the unique characteristics and remoteness of this region, projects such as this often take longer than expected.

“A single missing part or a failed tool can bring the project to a halt for days,” Heym said. “Add to that some very dynamic weather and a limited number of skilled workers, and it is a challenge.” These are some of the reasons that maximum factory assembly of the units was desired.

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