Down in the basement of the bustling Dining and Community Commons (DCC) lies the new geoexchange plant — a little-known facility that plays a crucial role in supporting campus life. Recently installed, it is gradually replacing the original high-pressure steam system with a more environmentally sustainable geothermal system to provide heating and cooling for Swarthmore’s campus. This transition is part of Swarthmore’s “To Zero By Thirty-Five” energy plan, which aims to achieve carbon neutrality.
On Wednesday, March 5, The Phoenix toured the geoexchange plant with Director of Sustainable Energy Services Jim Adams, who introduced the plant’s innovative energy systems and explained its operational impact in shaping an environmentally friendly future for the community.
The plant sits in a large grey room where a sprawling network of steel pipes spans the ceiling and converges to several pumps on the ground. Currently, the geothermal system serves Singer Hall, Pearson Hall, Lang Music, Mertz Hall, the DCC, and the third and fourth floors of Parrish Hall’s east wing. As the ten-year program progresses, the system will eventually heat and cool the entire campus: about 40 buildings.
The pipes are distinguished by color, each belonging to one of three systems. The green pipes are connected to the geoexchange wells beneath Mertz Lawn. Last year, 350 wells were drilled, each 800 feet deep and about six inches wide. These wells are distributed seventeen feet apart in a pattern of equilateral triangles, and they are all interconnected so that liquid in the green pipes can be gathered and returned to the plant. Adams notes that another 350 wells will be drilled from June through the end of this year: “It’s loud, but we do a lot of things to keep it as quiet as possible.”
Adams then showed The Phoenix the drill bit used in the program, made of solid steel. Each bit can drill about two wells before wearing down. After drilling to 800 feet, a plastic pipe with a U-bend at the bottom is placed in the well. Grout is poured into the well to create a connection between the pipe and the surrounding ground, allowing heat to flow in or out.
“Below 60 feet, it’s not dirt but granite rock,” Adams explained. “Think of this gigantic block of rock as a thermal battery storing heat. When we send warm water down the wells, it warms the ground a little. If the ground is warmer than the fluid in the pipe, the fluid warms up and brings the stored heat back into the plant for use in the winter.” The system is sealed off to prevent wastewater generation and ensure the fluid in the pipes never mingles with groundwater.
The blue and orange pipes connect to the HVAC system in individual buildings to supply cooling and heating. Like the geoexchange pipes, each of these systems is a closed circuit that transfers heat carried by water within the pipes.
The blue pipes are part of the chilled water system, which provides air conditioning in the summer by pumping 40°F water through the radiators to cool the air and collect heat from the buildings. The water then returns to the plant at around 50°F, where it is chilled again to 40°F and sent back out. The heat collected doesn’t go to waste: in the summer it is stored underground in the geoexchange wells, while in the winter cold water is sent down into the wells to retrieve and use the stored thermal energy for heating.
The orange pipes belong to the low-temperature hot water system. These pipes send out 125°F water, which circulates back to the plant at around 110°F. The water is reheated back to 125°F using stored heat from the wells and electricity-run chillers. By replacing the 400°F high-pressure steam system with low-grade heating, the new system reduces energy loss caused by the massive temperature difference between the steam pipes and the surrounding environment.
In the center of the plant, two heat-recovery chillers create a constant low-pitch hum. Each chiller functions as a heat pump, with eight compressors that cause the refrigerant to evaporate outside the tubes, cooling the water flowing inside. This mechanism is similar to a refrigerator that rejects heat into the room through refrigerant and compressors. Unlike a refrigerator, however, the heat generated by the chillers is not released into the air but is stored in the well field for winter use. The chillers are designed to automatically switch between heating and cooling modes based on the temperature needs of various buildings. “There are no people [required] here. We would get text messages if there’s a problem, but the system has run really well since it started up in November,” Adams explained.
Adams noted that these chillers consume most of the purchased renewable electricity. Each chiller delivers 750 tons of refrigeration (TR) and consumes about 700 kilowatts per hour at full capacity. Nonetheless, the electricity demand for heating and cooling is currently much lower due to the moderate temperature outdoors.
As more buildings are connected to the geoexchange system in the future, two more chillers will be installed. “In the end, we’ll have 3,000 tons of refrigeration, which will be enough to meet the campus’s needs,” Adams said.
Next to each pump is also a variable speed drive, a box-like device that modulates the pump’s turning speed based on the amount of water needed, making energy use more efficient. “Before they made variable speed drives, pumps used to run at full speed all the time, and you had to use a valve to slow them down — that was very inefficient,” Adams said. “Right now, the pumps only need to operate at about a quarter of their full speed, saving a lot of energy.”
Adams reflected on the past and future of the geoexchange plant: “We installed the plant with the dining hall [already] in operation, and we got no complaints from anybody,” he recalled proudly. “Swarthmore is one of many early adopters of geoexchange. The [basement] space makes for a good plant that will last a long time and is easy to maintain. This is an investment the college is making that should last 50 years. Our steam system was installed in 1911, and we’re still using it. We hope that this investment will continue to operate for a long time as well.”
Great article, very clear explanations! Thanks!
Correction: Instead of granite, the rock storing thermal energy is called schist. It started as shale, which, under high heat and pressure, re-crystallized or metamorphosed into schist.
Exciting!! Love this article