Completed in 1928, Midtown Exchange in south Minneapolis served as a retail and distribution center for Sears, Roebuck and Co. until closing in 1994. A year later, it was added to the National Register of Historic Places. For the next nine years, the building sat vacant, until the city, which acquired the property in 2001, awarded development rights to Ryan Companies US Inc.

In 2006, Midtown Exchange reopened as a mixed-use development consisting of retail and office space, residential units, and a hotel.

Midtown Exchange is the second-largest building in Minnesota, trailing only Mall of America.

Four hundred eighteen thousand of the building's 1.1 million sq ft serves as the headquarters of Allina Hospitals & Clinics, a not-for-profit network of health-care services. The building also includes 219 affordable and market-rate apartments, 88 condominiums, and 57 townhomes and flats. A 136-room, full-service Sheraton Hotel connected by walkways to Abbott Northwestern Hospital primarily serves hospital visitors, patients, and their families, as well as corporate guests.

New Hope, Minn.-based Horwitz/NSI was responsible for retrofitting the building's mechanical system.

“We chose super-efficient water-to-air heat pumps by ClimateMaster because — compared to traditional HVAC equipment — they can be installed for less money,” Bill McKoskey, PE, president of Horwitz/NSI, said. “The heat pumps also offer the flexibility of being easy to zone. And you can add heat pumps to the overall design as needed, so they give you an advantage in scalability.”

With hundreds of heat-pump components to connect, circulator pump stations were a key consideration.

In the bowels of Midtown Exchange are many ClimateMaster water-source heat pumps and several Taco pumps stations.

“We installed three large Taco pumping stations,” McKoskey said. “One is a variable-flow heating-water loop which matches flow to the building's loads through the use of variable-speed drives. The other loops serve the heat-pump core water loop and the cooling-tower loop.”

As Tom McCormick, product manager, commercial pumps, for Taco Inc., explained, “When the speed of the pump motor is varied to meet changing climate conditions — both inside and outside the building — the motor uses the least amount of energy.”

Meanwhile, “The pumping stations they chose provide the maximum wire-to-water efficiency, taking into account the combined efficiency of the pump and motor together,” McCormick added.

Chief among environmental considerations was noise.

“Several professionals involved in the project raised concerns about this,” McKoskey said, “so … we built a mock-up vertical heat pump at an older building here in town. And when it was operational, we led a group there to see and hear the system in operation. Everyone was favorably impressed.”