How Does Geothermal Heating Really Work?

Story at a glance:

• Geothermal energy is utilized for heating and cooling systems that are renewable, easily maintained, and affordable in the long run.
• King Open/Cambridge Street Upper Schools & Community Complex uses geothermal heating and cooling to reach net zero.
• Geothermal can be harnessed around the world and can even be used for electricity—especially at plate boundaries, where geothermal reservoirs are especially hot and porous.

In an impressive community complex that houses administrative offices, a library, a public pool, and two schools, Arrowstreet, along with William Rawn Associates and the City of Cambridge, built Massachusetts’ first Net Zero Emissions school. The project, King Open/Cambridge Street Upper Schools & Community Complex, is an integral part of the city’s Net Zero Plan, which aims to attain carbon net zero throughout the city in just 25 years.

The school building uses 70% less energy than the average school in the US and 43% less energy than a typical Massachusetts school that meets the state’s energy code. “The project goal was to achieve Net Zero emissions, which means that the building systems are all-electric and the building has an ultra-low Energy Use Intensity,” says Kate Bubriski, director of sustainability and building performance and an architect at Arrowstreet. Accordingly, the building combines several forms of clean energy and energy-reducing technologies, including a geothermal heating and cooling system.

Bubriski says the Arrowstreet team chose geothermal wells for the school because “ground source heat pumps were the most efficient system and have reliable maintenance and durability.” Geothermal technology is proven, and sooner rather than later it also yields a substantial return on investment.

How Geothermal Heating Works

What is geothermal energy?

Geothermal energy is found in steam and hot water in the earth’s crust. It can be harnessed for heating, cooling, and clean electricity generation via wells that go deep into the ground to reach the geothermal heat and pump steam and/or hot water up to the surface, according to the US Office of Energy Efficiency and Renewable Energy.

Plus, geothermal technologies can’t be affected by surface conditions like weather. The technologies behind geothermal energy, particularly geothermal heating and cooling mechanisms, do not often break, reducing the cost of system maintenance.

How is geothermal best used?

Generating electricity from geothermal energy typically requires hotter water or steam, which is most accessible at tectonic plate boundaries where you find hot permeable hydrothermal reservoirs. This accounts for its popularity on the US’s West Coast, according to the Geothermal Energy Association.

Geothermal heating and cooling technologies use heat exchanges in a closed loop and can be utilized just about anywhere, from Kenya to Iceland. According to the International Renewable Energy Agency, geothermal energy answers more than 90% of the heating demand in Iceland.

This closed-loop heating and cooling technology is in place at King Open/Cambridge Street Upper Schools, where 190 closed-loop geothermal wells 500 feet deep supply a heat transfer fluid to electric heat pumps. Heat exchangers at the pumps extract or release heat from the geothermal well loop depending on the season, and from the heat pumps hot and chilled water lines supply radiant heating and cooling panels throughout the building, including the air handling units that support the displacement ventilation system.

When’s the payoff?

Geothermal wells typically pay off in 3 to 10 years depending on location, type of system, and how the technology is used. For this project, Bubriski says, “The technologies needed to design the building to net zero, including geothermal wells and photovoltaics, were less than a 1% increase in construction cost. The significant operational savings from the low energy building and onsite photovoltaics make the return on capital investment fairly immediate.”