Last year, District Energy St. Paul retained TKDA to provide planning, design and construction assistance for what would become the Midwest’s largest solar thermal project. The project, which was completed in March, offers additional energy output to District Energy’s distribution system, which heats 80 percent of the buildings in downtown St. Paul. It is the first project of its type in the United States to be integrated with a district energy system.
TKDA determined the size and configuration of the system to maximize performance. The solar thermal panels were placed atop the RiverCentre, the city-owned convention center, which offered more than one acre of unshaded rooftop. TKDA engineered a skeleton system where the panels were ultimately supported by the building columns, ensuring the weight was evenly distributed.
Each of the 144 solar thermal collectors was connected in a series on a structural skeleton and installed at a 45-degree tilt. A pump and piping network circulate a glycol solution that begins to flow once the sunlight level reaches a certain intensity. The liquid absorbs solar energy, which flows to heat exchangers located in a mechanical area of the RiverCentre, just under the roof.
From TKDA’s research and system modeling output, District Energy St. Paul was able to select a manufacturer that offered the highest performing solar thermal panels and had the ability to generate energy even during the colder months of the year.
The energy is used to heat water for the RiverCentre, as well as warm the 162,000-square-foot building. If the energy supply is insufficient, the process defers to the existing District Energy hot water system. If the supply exceeds demand, the excess energy is diverted into the hot water distribution loop servicing other buildings on the District Energy system.
The new system offers peak energy production of 1.2 megawatts. It also reduces carbon dioxide emissions by 900,000 pounds annually, which is the equivalent of eliminating the emissions of 90 vehicles per year.