District heating is a technology that most people know very little about. Probably because the pipes that connect the energy source to the buildings are buried underneath the ground where most of us won’t see them. But these systems are all around us, serving cities, hospitals, and college campuses. In fact, 80% of downtown Saint Paul is connected to a district system. District heating systems are made up of a plant, distribution pipes, and energy connections at each building that is served. The energy plant (or plants) produces hot water or steam and then distributes the thermal energy through underground pipes to buildings connected to the system. Individual buildings connected to district heating do not need boilers or hot water heaters in their basements for their heating needs. Customers use the hot water provided by District Energy St. Paul to meet their space heating, water heating, snowmelt, and manufacturing heat processing needs. Once customer buildings have captured the thermal energy they need, the water is returned to the central plant for reheating and then recirculated through the closed-loop piping system. Buildings are all connected to one system but have complete control over the temperature inside their buildings.
District Energy St. Paul is the largest hot water district system in the United States and serves more than 200 buildings with heating in downtown Saint Paul. The system has 42 miles of supply and return piping. It circulates 1 million gallons of water per hour, with a supply temperature of 250 °F in the winter and 190 °F in the summer. The system in Saint Paul has the environmental benefits of system efficiency and 65% of its fuel is biomass from locally sourced wood waste.
District cooling is a technology that most people know very little about. Probably because the pipes that connect the energy source to the buildings are buried underneath the ground where most of us won’t see them. But these systems are all around us, serving cities, hospitals, and college campuses. In fact, 60% of downtown Saint Paul is connected to a district cooling system. District cooling systems produce chilled water at a central plant and then distribute the thermal energy through underground pipes to buildings connected to the system. Individual buildings connected to district cooling do not need chillers on their rooftops for their air conditioning needs. Chilled water is circulated to buildings where it removes heat from the internal spaces, which cools the air. The heat removed from the building is captured in the return water and returned to the plant to start the chilling process again.
District Energy St. Paul serves more than 100 buildings with cooling in downtown Saint Paul. The system has 13 miles of supply and return piping. District Energy circulates 2.5 million gallons of chilled water per hour, with a supply temperature of 42 °F. The chilled water provides air conditioning with better efficiency and environmental benefits than traditional stand-alone systems by reducing the use of ozone-depleting refrigerants, reducing potable water usage at the building, and using energy more efficiently. Chilled water is produced at night using off-peak electricity and stored in 2 larger thermal storage tanks like a battery, located at West Kellogg Boulevard and across town from the EcoDistrict at 10th Street. Chilled water stored in these tanks is dispatched to customers as needed, particularly to meet higher cooling demand, such as high humidity and high temperature conditions.
Where can I find district energy?
District energy heating and cooling pipes stretch all throughout downtown and even across the river. Visitors can see the pipes embedded in the river bluff when south of downtown. Or they can see the plant that is producing hot and chilled water at Market Street and Kellogg Boulevard. There are signs on the plaza along Kellogg that explain how this technology works.