New projects show possibilities and limits of geothermal
Standing at the bottom of an 60-foot hole, Michael Purtell watched an ambitious and deeply challenging geothermal installation proceed.
Montgomery County had set bold sustainability goals for the 14-story government office building in Wheaton Town Center. Its energy infrastructure would include a geothermal loop that extended nearly 600 feet beneath four levels of underground parking.
“Putting a wellfield under a building is a major coordination challenge,” said Purtell, Senior Vice President of Gipe Associates. “There were weird footings and pilings that we had to work around. The team had to coordinate with a crane to lower the well drilling rigs down into the hole.”
Gipe had to carefully design and complete the installation in a way that would not risk bursting a pipe, then coordinate with other trades to protect and repair equipment as a parking garage and office tower were erected overtop of the wellfield. The effort succeeded and the building went on to win multiple sustainability awards, but it also left Purtell cautious about embarking on another geothermal installation on a tight, urban site.
The large majority of geothermal installations still happen on K-12 school sites with ample land. Yet the technology’s high efficiency and sustainability, its aesthetic benefits, and advances in equipment and system designs are convincing scattered other clients to adopt geothermal. From residences, office buildings and laboratories to data centers and community-scale installations, those uncommon projects are revealing possibilities and limitations for geothermal.
Over the past 30 years, a niche market has landed multiple geothermal projects for EBL Engineers. The niche is very high-end, single-family residences, typically measuring 20,000 to 30,000 square feet.
“Residences of this size perform more like commercial buildings than typical houses. Houses of this size typically require 40 to 50 tons of cooling capacity resulting in complex systems,” said Jamie Raithel, an associate at EBL.
By locating all heating and cooling equipment underground and within a mechanical room, geothermal systems meet an aesthetic requirement, where owners do not have to see or hear equipment.
Meanwhile, technology advances “essentially create unlimited flexibility in the system providing the ability to heat or cool individual spaces if desired,” Raithel said. “We have variable speed compressors, variable speed pumping available to us and controls have become very capable while being user friendly in the residential environment. From a flexibility standpoint, a geothermal loop can be pumped through a bank of water source heat pumps, which can generate heating or chilled water for delivery to various fan coil units, so you have a system that is capable of doing simultaneous heating and cooling in different areas of the home.”
Variable speed equipment combined with the new industry standard of decoupling the heating/cooling functions from the fresh air exchange has also made geothermal more effective and more efficient. Current, decoupled systems adjust temperature more quickly and, in most cases, have made auxiliary heating and cooling equipment unnecessarily, Purtell said. “For projects where we have concerns about geothermal load imbalance, intermittent high demands, or backup heating energy sources we have designed auxiliary boilers into the heating water systems. In most of those cases, we found that the boilers rarely energize.”
Advances in equipment and control technologies also allow for much more effective humidity control.
“We are able to run the compressor at just the right speed to match the fan and remove humidity without over-cooling the spaces,” Raithel said. “We can create much more comfortable indoor environments at higher dry bulb temperatures, ultimately reducing energy costs for owners.” People tend to be comfortable at higher dry bulb temperatures when the humidity is low.
Shifting technology and system designs are also enabling project teams to deliver added functions from a geothermal system. In addition to heating and cooling, the geothermal system at the new Crown High School, currently under construction in Gaithersburg, will also produce the building’s hot water supply.
James Posey Associates (JPA) designed a separate loop linking “the domestic water heater directly to the electric room which has a constant need for cooling,” said Mark Black of JPA. “We are trading heat back and forth between those two facilities, which is a great way to save energy. Because we have a geo loop available, we are able to tie into the heat exchanger. If our loop between the electric room and the domestic hot water demand gets out of balance, we can access the heat exchanger on the geo loop and compensate. Without the geothermal system, we wouldn’t be completely comfortable relying on this source for hot water.”
Despite those capabilities, geothermal still faces obstacles in most projects.
“There is a substantial first cost to a geothermal system and often it is difficult to make the return on investment work,” said Seonhee Kim, Director of Sustainability at Design Collective.
Accessing land for a wellfield can also be an obstacle, Kim said. “Geothermal doesn’t necessarily need a large area to accommodate the wells, but a large area will lower your costs and improve your return on investment.”
Some projects at schools and other sites clear those hurdles and deliver full return on investment in 10 years, said Justin Bem of JPA. When projects have goals of electrification, clients realize savings from significantly lower energy use and longer equipment lifespan. A wellfield can last over 50 years and indoor geothermal equipment, which is typically smaller and less costly than conventional equipment, typically lasts 20 years (compared to 15 years for more conventional equipment). Geothermal, Bem added, plays a key role in achieving or nearing net zero status by lowering energy needs and freeing up roof space for solar panels.
For a geothermal system to operate effectively long-term, it also “needs a balance of cooling needs and heating needs,” Kim said. “We think the ground is an unlimited, renewable, untapped resource for heating and cooling, but in reality if you dump a lot more heat into the ground than you take out, then the ground can be oversaturated with that temperature” and diminish the performance of the geothermal system.
Project planners need to complete detailed, year-long energy modelling for buildings to assess that balance then adequately design and space wells to accommodate imbalances, Bem said.
Projects with highly imbalanced heating/cooling loads, such as data centers, “can address that issue by adding a cooling tower to release energy out into the atmosphere,” Raithel said.
The expense, land requirements and load-balancing needs of geothermal systems, however, have also given rise to a new kind of geothermal development – community- or utility-scale geothermal. Massachusetts, New York and the federal Department of Energy are currently funding pilot projects for larger, multi-user geothermal systems.
In addition to tapping into economies of scale, shared systems can balance the higher heating needs of residences against the higher cooling needs of commercial buildings, Kim said. “If you balance all the different uses and different demands, then it makes sense to have a shared system because it would have a balanced load. In theory, that’s what makes community geothermal more promising than installing systems to serve individual buildings.”