The southern Alaska city of Seward plans to install a ground source CO2 (R744) heat pump serving four municipal buildings that could save $1.3 million over 50 years in heating costs, reduce carbon emissions from diesel oil and ensure a constant, reliable heat supply.
Details of the geothermal heat pump installation, tentatively planned for the summer of 2025, were shared by Griffin Plush, Vice-Chair of Seward Alaska Heat Loop Project Committee, during the end user panel at the ATMOsphere (ATMO) America Summit 2023 on natural refrigerants. The conference was held in Washington, D.C., June 12-13, 2023 and organized by ATMOsphere, publisher of R744.com.
Technical aspects of the project were presented at the conference by Andy Baker, Owner of Seattle, Washington-based YourCleanEnergy, who is working as a consultant on the project.
This isn’t just about building the technology, Plush noted, but also about establishing the community’s ability to support and maintain this system, with the potential to expand to other applications.
“This implementation of the ground source heat pump [GSHP] is more than just an upgrade; it is an essential move towards a greener and more sustainable future,” said Plush.
“By eliminating the risk associated with synthetic refrigerant leaks and reducing reliance on heating oil, we are not just cutting costs; we are protecting our environment for future generations,” he added.
The Seward GSHP was one of 11 projects to receive funding from the U.S. Department of Energy (DOE)’s Community Geothermal Heating and Cooling Design and Deployment program.
Leveraging Resurrection Bay
Presently, the four city buildings concerned – a library/museum, city annex, city hall and fire hall – are providing space and domestic hot water heating with traditional oil boilers. However, next year this will change to a rack-mounted transcritical CO2 heat pump system. This GSHP is expected to meet an impressive 90% of the heating needs for these buildings, which represent half of Seward’s municipal buildings.
Situated in southern Alaska, Seward benefits from bordering on Resurrection Bay, which is fed by the northern Pacific Ocean, and from the abundant heat energy that ocean currents bring. Resurrection Bay maintains temperatures of 34–54°F (1.1– 12.2°C) at 100ft (30.48m) below the surface.
The GSHP project will tap into this energy via 4in (0.1m) piping descending 40ft (12m) via several wells into deep gravel around the tidal area along the shoreline. Glycol will absorb heat and transfer it to the CO2 heat pump system residing in the basement of the library/museum.
The heat pump will generate 180°F (82°C) hot water, which will be shared with the city hall and fire hall, and then, at 150°F (66°C), with the annex before returning to the library/museum, in effect “cascading between buildings,” said Baker.
The supplier of the CO2 heat pump system, with a planned heating capacity of 120TR (422kW), has not yet been selected, noted Baker.
The use of CO2 in this project underlines an important aspect of eco-friendly heat pumps. Unlike synthetic refrigerants (notably HFO-1234yf) that can leak into the atmosphere and get converted into trifluoroacetic acid (TFA), CO2 is a natural refrigerant that is absorbed by trees when released, said Baker.
Furthermore, Seward’s GSHP reduces operating costs and greenhouse gas emissions by minimizing the reliance on heating oil. “Decarbonization is a simple word but a complex process,” said Baker. “We need to transition away from high carbon emission fossil fuels, heading towards cleaner energy.”
Inspiration for project
Baker highlighted that the Alaska SeaLife Center, also located in the city, served as a blueprint for the Seward project. Back in 2016, Baker designed a CO2 heat pump cascade hydronic system for the center, demonstrating the “gliding” nature of CO2 heat levels according to demand.
The system uses a fractal branching design for hot-side hydronic loops, serving heat loads that cascade downward to the required supply temperature. Large heat loads (like domestic hot water preheating and outdoor slab heating) are connected to draw down the return temperature of water before returning it to the CO2 heat pumps.
“By eliminating the risk associated with synthetic refrigerant leaks and reducing reliance on heating oil, we are not just cutting costs; we are protecting our environment for future generations.”Griffin Plush, Vice-Chair of Seward Alaska Heat Loop Project Committee