From Flour Mill to Art Studio: Medina Electric Harnesses Hydroelectric Power When Renovating a Historic Structure
Minneapolis’ Pillsbury “A” Flour Mill building has witnessed a lot of transition since its construction next to Saint Anthony Falls in 1881. Its history reflects the early industrial growth and prominence of the Midwest. It was, in fact, the largest such operation in the world for 40 years. For much of its life, it was powered mainly by the Mississippi River. Now, its purpose has shifted to an affordable housing and work area for artists known as the A-Mill Artist Lofts.
In 2015, the construction team that conducted its renovation was tasked with converting this very industrial and historical building into a modern home and workplace for Minneapolis residents. The challenge was ensuring it had all the most modern, high-efficiency amenities while highlighting some of the features of the past.
Medina Electric Inc., Hamel, Minn., provided the electrical construction while Weis Builders was the general contractor. The developer was Dominium of Plymouth, Minn.
History of the mill
When Charles Pillsbury built the structure, he said it would be the most advanced mill the world had ever seen. The facility came with an underground canal that diverted river flow into a tunnel 5 feet under the building. That water then generated the heating and cooling for the mill’s operations. The hydroelectric turbine powered the building for half a century until the system was decommissioned in the 1950s.
Mill production continued until 2003, after which the building stood empty for more than 10 years. The building had been designed to accommodate the heavy equipment and operations inside, with wall thickness varying from 2 feet at the top to 8 feet in the basement. The main building has seven floors plus the basement.
Dominium bought the property, along with an adjacent warehouse, for $3.6 million. The building was designated at the time as one of Minnesota’s National Historic Landmarks. The developer’s goal was to create a residential facility offering housing and work spaces for artists, as well as a dance studio and several galleries. The renovated building would include 251 housing units in the space where milling once took place. Once again, the building would leverage the Mississippi River for much of its power.
Dominium wanted to preserve not only the hydropower but also some of the original grinders and conveyors. Once finished, the construction earned the facility LEED Gold certified project status.
Electrical challenges
Medina Electric was founded in 1973 to offer residential, commercial and industrial construction. It specializes in unusual design-build projects, such as the Schmidt Brewery that was also renovated from an industrial space into artists’ studios. None of Medina’s projects was quite like the A-Mill Loft, however, with its hydroelectric system.
When Medina arrived at the former Pillsbury building, the shaft for hydroelectric power had been closed, but a decommissioned turbine remained. Medina electricians helped remove the old turbine and a new one was installed, said Jason Ianfolla, Medina president and CEO.
The structure’s 500-foot hydro tunnel would support 600 kilowatts of energy generation with 480-volt (V) backfeeds through Medina’s switchgear, said Mike Dennis, Medina Electric general foreman. To accomplish this, the EC needed to install new piping as well as power for the sensors and gates to control water flow.
Medina hired an engineering firm to design the gate and sensor system. Barr Engineering consulted on the job for the control aspect of the hydroelectric power, and also provided wiring layout and startup, said Paul Kaeding, company vice president.
The new system consists of equipment from Canadian Hydro and an Alstom control system.
Kaeding described the system as a “run-of-the-river” configuration, meaning the force of the water spins the turbines to generate power. The project also required transmitters at multiple levels: head, trash rack and tail race. The sensors indicate any trash blocking the entrance, the amount of flow through pipe and how deep the water is in front of the gate.
“This would shut the gate in the event of low water in the river,” Dennis said.
Other components included control wicket gates and blades to manage water flow to meet the maximum capability of the generator. These hydraulically operated fins adjust to the building’s power-consumption needs. The hydro system’s 1,600-ampere (A) controller then feeds into the main power system. The hydro is capable of providing most of the power (typically 75 to 80 percent) for the complex. If the building load exceeds the generator capacity, power is imported from the local utility, Xcel Energy.
Medina Electric installed a 480V, 4,000A, three-phase switchgear with six privately owned transformers to convert power down to 120/208V for the building.
“The hydro voltage is 480V, so the system voltages match,” Kaeding said.
In fact, the switchgear and the hydro system communicate, so Xcel power and hydro power are always in sync.
Working underground provided some day-to-day challenges for electricians. The tunnel shaft itself was about 20 feet wide and 25 feet tall, and Medina’s crew worked inside it daily for about four months when wiring the gate controls and installing lighting and the generator. At any given time, about 10–15 people were in the shaft, two or three of whom were Medina electricians.
When they first got into the tunnel, Dennis said, they found it in good condition. In fact, he recalled, it looked almost like new. However, concerns about air quality while working in the tunnel, as well as potential for falls, meant the work was considered hazardous. Workers were equipped with oxygen sensors and harnesses; and an ambulance was parked above at all time, just in case.
For tunnel construction, Medina first installed temporary lighting consisting of 100-foot string lights anchored to the tunnel wall. These lights operated for about a year before they were replaced with permanent fixtures.
The permanent lighting consists of 4-foot, weatherproof fluorescent fixtures, which include battery-powered EM ballasts for life safety lighting. They installed 20 fixtures, one every 30 feet. Altogether, Medina installed 3,000 feet of pipe and wire in the tunnel that also served controls, general power requirements and main feeds out of the hydro system.
Modern lighting meets history
Above ground, A-Mill Loft consists of four buildings: the A-Mill where the millwork was conducted, the Clean House where flour packaging was done, and the Red Clay Tile building where storage silos have been renovated and preserved. A fourth building, Warehouse 2, served as a storage area for the finished product before shipping.
To provide power and light, Medina installed about 550,000 feet of wire. The buildings also needed about 80,000 feet of Cat 5e and RG-6 low-voltage cable. For each media panel, the contractor pulled a dual Cat 5e and RG-6 cable. In addition, about 40,000 feet of two-strand, fiber-optic, single-mode lines were also pulled to each media panel, Dennis said.
None of this was as straightforward as it might be in new construction. Lighting installation had to accommodate the thick cement walls as well as requirements from the Historic Preservation Society, including no visible cabling. To accomplish this, cable trays were installed in the corridors; however, any feeding cable had to run through the individual housing units rather than down the corridor. They were then concealed in joist spaces or through drop drywall areas.
On the other hand, Medina took a contemporary approach to the lighting, installing modern fixtures (about half of them LEDs) rather than historic ones. A Lutron system controls lighting, dimming and occupancy sensing and can be managed with a smartphone or tablet in all three buildings.
The contractor team also installed a fiber optic light fixture over the two-story lobby in the main building that is synchronized with music and a camera. When the camera observes a pedestrian walking by, the lighting and music begins its performance. It also can display their silhouette on the large screen as they move in front of the camera.
Outdoors, roughly 225 LED lights are installed on the building facade. About 175 of those fixtures are dedicated to signage and accenting historic features.
There is also an extensive security system installed in the buildings. Forty cameras are in use for security while the system also includes 62 door access control systems with card readers. The fire alarm leverages a Mircom FleX-Net control panel. Each stairwell serves as an area of refuge with voice capability for calling for help.
Residents began moving into the building in late 2015. Today, A-Mill Artist Lofts is filled to capacity with shared work and studio spaces. These spaces are available for special projects or daily work and are scheduled through the property manager. The building serves as one of only three Minneapolis structures designated as a National Historic Landmark and one of only 26 in Minnesota.