Discovering the Water's Edge
An aerial panorama from the shores of Lake Michigan reveals Discovery World at Pier Wisconsin as the place where clear skies meet blue waters. Standing on top of the building's Pilot House even uncovers a 360° view of the City's skyline and the vast lake below. The view is so unobstructed that one must—at least an M/E/P engineer must—wonder where the building is hiding its me...
An aerial panorama from the shores of Lake Michigan reveals Discovery World at Pier Wisconsin as the place where clear skies meet blue waters. Standing on top of the building's Pilot House even uncovers a 360° view of the City's skyline and the vast lake below.
The view is so unobstructed that one must—at least an M/E/P engineer must—wonder where the building is hiding its mechanical systems. They're certainly not on the roof, and they're not beside the building.
That's because, in part, they dwell deep below the lake itself. Preserving this scenery and the facility's outdoor public gathering areas was so crucial to its owners that engineers at the local office of Hammel, Green and Abrahamson Inc. (HGA) had to come up with a very unusual mechanical system, one that notably features an innovative heat pump design and that uses lake water to cool the building, earning Discovery World at Pier Wisconsin the 2006 ARC Award in the HVAC category.
“Pier Wisconsin was chosen for this award because of the many unique challenges facing its HVAC systems design,” said Kevin Pope, associate vice-president with HGA and the project's lead mechanical engineer. “We were able to meet the challenges with creative HVAC systems applications.”
Pump it up
To understand its M/E/P systems, one first has to understand Discovery World's architecture. The 120,000-sq.-ft. Discovery World facility is bursting with exhibit areas, classrooms, meeting and event rooms, exploration laboratories and an aquarium.
“Because of the architectural layout of the building, we were forced to locate all the heat pumps in two mechanical rooms, each positioned at opposite ends of the couple-hundred-foot-long facility,” said Pope. “This created long duct runs in the form of loops and forced us to figure out a way to get as much static pressure off the fans as possible.”
HGA accomplished this by using the mechanical room as a mixing plenum for both return and outdoor air. By installing a centralized return air system and dedicated make-up air units, HGA was able to remove the static pressure drop from the return air system, the outdoor air intake and the air filtration from the heat pump units.
“This mixture was then drawn out of the room by the heat pumps and supplied to the building,” said Pope. “The result is the only static pressure drop the heat pumps have to overcome is the supply ductwork downstream. This was the uniqueness of our HVAC design.”
A cooling lake effect
Without a cooling tower or fluid cooler on the roof, keeping Discovery World comfortable during the hot Milwaukee summers posed a challenge for HGA mechanical engineers.
“Fortunately, we had a giant lake underneath us,” said Pope.
And that's exactly what they used.
Extracted at 15 feet below lake water level and elevated to two feet beneath the building's basement floor, lake water is brought into Discovery World's mechanical room and used to cool its heat pump loop.
Here's how: Once in the building, the lake water is pumped through two plate and frame heat exchangers, which transfer warmth from the water in the loop to the extracted lake water that is subsequently discharged back into Lake Michigan.
“The colder the lake water is, the cooler we're able to keep the loop,” said Pope. “This works because the heat pump is able to reject heat to the loop, and therefore cool the space.”
HGA engineers designed the intake system based on a maximum lake water temperature of 75°F. However, the majority of the cooling season records lower water temperatures, which only result in more efficient heat pump operation.
Sealing the site where the lake water pipe penetrates the building was another hurdle for the team, as sheet pile that holds the earth back from falling into the lake straddles the building's concrete foundation and the water.
“We were told this sheet pile will move during the change of seasons,” said Pope. “We had to come up with a way to penetrate it, allow it to move and still successfully seal the penetration.”
HGA specified a steel pipe sleeve with flanges welded to the sheet pile. This is attached to a flexible bellows and connected to the fixed intake pipe. The flexible bellows works by absorbing movement in the sheet pile, while allowing the intake pipe to remain still, without creating any stress on its joints.
In order to meet the tight construction schedule set for Discovery World, designers and contractors worked simultaneously to get the job done.
“They were building the facility before we were done designing it,” Pope said. “They had the foundation completely constructed while we were still planning the HVAC system.”
This gave HGA's engineers significant involvement during the construction process, a phase they aren't typically engaged in.
“The most enjoyable aspect was the collaborative effort between the design team and the contractors to work through the many hurdles encountered as a direct result of their construction completed prior to the conclusion of our design,” said Pope. “It's not very often that engineers get to do a project like this; it was really fun.”
The result is Discovery World at Pier Wisconsin, Milwaukee's new hands-on center featuring an aquarium, interactive science and technology exhibits and is the docking site for Wisconsin's Flagship S/V Denis Sullivan schooner, a 1880s-era educational sailing vessel. As the 2006 ARC winner in the HVAC category, the facility employs an innovative heat pump design and uses Lake Michigan water to cool its spaces.
Cure for the Milwaukee cold
The outdoor design temperature for Milwaukee's winters is -10and architectural designers.
Make-up air units were installed to treat 100% of the outdoor air with heat or dehumidification in order to maintain 35% humidity during the winter and a 50% humidity level in the summer. The units are continually reset as the outdoor air temperature fluctuates throughout the year.
The facility's exterior glass curtainwall system was specified with a condensation resistance factor of 68 as well. Panel radiators are located at the base of the curtainwall and supply air grilles are directed at the glass.
Stop the invasion
One final note: Tiny, fingernail-sized water inhabitants that grow on metal surfaces in Lake Michigan proved to be a significant challenge in cooling Discovery World.
Called Zebra mussels, these slippery creatures are native to Asia's Caspian Sea, but were brought to the Great Lakes in the late 1980s and have since spread rapidly throughout U.S. waterways.
To prevent Zebra mussels from clinging onto the pipes and potentially blocking the flow of water entering Discovery World, high-density polyethylene piping material was specified along with a customized lake water inlet screen coated with Z alloy and manufactured by Johnson Screens, New Brighton, Minn.
With the exception of the lake water channel, all other plumbing was isolated to prevent potential infestation. But, with the lake water pipe still at risk, 100% redundant plate and frame heat exchangers were specified to ensure continual operation of the lake water cooling system.
The seamless integration of engineered system in a way that protects the aesthetic integrity of the architectural design is a standout success and innovative adaption of systems to this unique project.