The air distribution system has several energy-saving features: a heat recovery loop, a cascade air system and a low-flow VAV fume hood exhaust system. All depend on the flexibility of the extended-size Vision air handling unit. Facility officials at St. Olaf and the project design team worked closely with Schwab-Vollhaber-Lubratt, Inc., St. Paul, the Daikin rep firm, to design a system that exactly met their requirements.

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The first of these features is a glycol heat recovery loop that recovers heat from the laboratory fume hood exhaust air stream. A standard water coil is located in the laboratory exhaust manifold upstream of the exhaust fans and a similar coil is strategically located in the air handling unit. Energy is transferred from the warm exhaust air to the glycol loop and transported to the air handling unit coil where it is used to preheat the outside air coming into the unit. Even during very cold outdoor conditions, the need for steam heat is greatly diminished due to the heat provided by the heat recovery coil. If necessary, a reheat coil on the VAV boxes will reheat the air when it reaches the space.

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The second feature, a cascade air system, is an efficient way to provide the high air exchange rate required for the laboratories. "We can't recirculate lab air; we have to bring in outside air and large amounts of it. Once air enters a lab, it must be exhausted to the outdoors," said Brett Gorden, design engineer, MEP Associates, Rochester (formerly with Holabird & Root). "So we mix all of the outside air required for the laboratories with the return air from the offices and classrooms and supply that to both types of spaces. This essentially provides the necessary ventilation air to the offices and classrooms for free. One large mixing box manages each half of the building."

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According to Gorden, these energy-saving benefits can be accomplished because of the design flexibility of the Daikin Vision air handling units. "The air handling units required a lot of custom modifications, such as isolating sections through the use of integral dampers to make all of these systems work. An additional challenge was designing an economical air handling unit capable of the large amount of airflow and high static pressure requirements. Daikin was willing to work with us on these needs."

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Vision AHU designed for flexibility

Regents Hall is divided into east and west wings joined by an atrium. The extended-size Vision air handling unit serves the entire east wing. Five smaller Vision air handling units serve the west wing and a single, stacked Vision unit serves the Link, which connects Regents Hall to the newly remodeled Old Music Building. Originally, nine air handlers were specified, but the extended-size Vision unit replaced three of them, significantly reducing installed and operating costs.

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The building's original HVAC plans specified custom air handlers, but Greg Pumper, project manager with HiMEC Mechanical, Rochester, Minnesota, had other ideas. "This was a design-assist project, meaning that all disciplines had input," he said. "We worked off the plan and gave our ideas for what could be done to cut costs. We used ProPress fittings on the copper pipe rather than soldering everything, and we used a different kind of stainless duct. We were able to use a low-VOC caulk on the stainless steel exhaust duct rather than weld it. The biggest cost savings came from being able to replace the three air handlers for the east side into one extended-size unit."

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The extended-size Vision unit, with a coil face area of 142.5 square feet, is built on a custom-modular platform. Compared to custom units, the Daikin single unit reduces cost in part by eliminating a common wall and minimizing space requirements. The Daikin Variable Dimensioning^® feature lets engineers specify cabinet sizes in increments of two inches high and four inches wide, making it easier to configure a short-and-wide unit for Regents Hall's high-air-volume requirement. Dual plenum fans in the unit also help reduce energy consumption as well as ensure quiet operation.

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The modular construction simplified installation, according to Pumper. Vision units are assembled at the factory and shipped in sections. The units are built with a patented splice collar to simplify section-to-section fit and seal without additional nuts, bolts, screws, gasketing or caulking. "Our foreman said that the units were well built and easy to put together compared to some others he's done," said Pumper.

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Energy-saving results

With so much attention to energy savings, Sandberg knew the operating data would be positive, but even he is surprised. "We're operating at one-third of the predicted costs," he said.

Yet thinking green is nothing new at St. Olaf. "Ten years ago, we started developing our own sustainable design guidelines and made them part of our design and construction contracts," said Sandberg. "Regents Hall is the building we would have built even if LEED didn't exist. It's that important to St. Olaf to provide the best teaching environment it can."