Geothermal Energy: How exactly does that lake heat and cool the hospital?

Manifold Building

You’ve heard that the new Sherman Hospital’s 15-acre lake not only provides beautiful views from the patient rooms, but it helps to heat and cool the entire hospital, saving $1 million in energy costs per year. And you know it’s a pretty big deal–it’s the largest geothermal system in Illinois and one of only 2 currently heating and cooling medical centers in the US. But you might not know the answer to the most basic question about the lake: How exactly does it work?

What is Geothermal Energy?

Pressure Gauges

Geothermal energy is energy that is derived from the temperature of the earth. The earth absorbs 50 percent of all solar energy and traps it as heat just below the frost line. Using a heat pump, this natural and renewable resource trapped below the earth’s surface is transformed into a harnessable form of energy. This energy –geothermal energy– provides buildings with a dependable, eco-friendly and economic heating and cooling system.

The tools that make it happen:

Lake Loop Pipes

• The temperature at the bottom of the lake—a constant 55 degree F in all climates. The ground absorbs almost 50% of the sun’s heat as it hits the earth’s surface. Regardless of the season, this solar energy maintains a relatively constant 55 degree temperature at the bottom of the lake, around 17-18 feet deep.
• A lake loop heat-pump system under the water, including 185 miles of pipes that are placed at the bottom of the lake to harness the energy. The pipes hold a heat-absorbing solution, and the heat pumps move heat from one place to another.
• A “manifold” building that houses over 170 pressure gauges connected to the pipes. This piping is channeled into supply and return pipes that are run to the building and fan out to individual heat pumps.
• Heat pump units housed just outside patient rooms that allow each room to be temperature controlled individually.

In the winter, the 55 degree temperature at the bottom of the lake is absorbed into a heat-absorbing fluid that constantly runs through the pipes. That heat is harnessed from the pipes through the pressure gauges, and pulled into the building. There it is concentrated and released into the building at a higher temperature. The heat is distributed through a conventional duct system as warm air. In the summer, the process is reversed–the heat from inside the hospital is pushed back down and stored in the cooler earth. Like in a refrigerator, cold air is not pushed into the hospital–rather, the heat is removed from the air.

Learn more about Sherman’s geothermal lake.