Harnessing Earth's Energy: Exploring Open and Closed Loop Ground Source Heat Pump Systems

Ground Source Heat Pumps (GSHPs) have a decades-long track record of dependable performance, making them one of the most effective and trusted solutions reshaping the built environment. By leveraging the earth’s stable underground temperatures, GSHP systems provide a reliable, efficient and low-carbon approach to heating and cooling buildings.

As with any transformative technology, maximizing its benefits requires a deeper understanding of the systems at play. Open-loop and closed-loop systems each bring distinct advantages and challenges, requiring a nuanced approach to achieve optimal performance and sustainability. Understanding these differences is essential to integrating GSHPs successfully within a broader energy strategy.

Understanding Ground Source Heat Pumps

At their core, Ground Source Heat Pumps harness thermal energy stored below the earth’s surface. As air temperatures fluctuate seasonally, the ground remains a constant temperature, providing a reliable source of heating and cooling.

GSHP systems transfer heat between buildings and the earth through underground piping networks. By capitalizing on this steady geothermal temperature, GSHPs offer efficiencies that far exceed those of conventional HVAC systems. As the demand for decarbonization and energy resiliency continues to grow, GSHPs are emerging as a foundational solution to modern infrastructure challenges.

Closed-Loop Systems: Reliability and Efficiency

Closed-loop systems circulate a water-antifreeze mixture through underground pipes, exchanging heat without direct contact with groundwater. This self-contained design ensures consistent performance, making closed-loop systems ideal for projects with limited land area or uncertain groundwater availability.

These systems can be installed in horizontal, vertical or pond/lake configurations, depending on the site’s characteristics and space availability. Horizontal loops are most effective in rural or suburban settings where land is abundant. Vertical loops, requiring deeper boreholes, excel in urban environments with space constraints—typically ranging from 300 to 500 feet deep, with some systems now reaching depths of up to 1,500 feet. Pond or lake loops provide a cost-effective option when suitable water bodies are accessible.

The SIERR Building in Spokane exemplifies the power of a closed-loop system to deliver ultra-efficient, sustainable performance in a historic structure. Originally a locomotive repair facility, the building has been transformed into a vibrant medical and health sciences hub. McKinstry and Emerald Initiative deployed a modern closed-loop GSHP system that leverages the Spokane River’s proximity to provide heating and cooling year-round. Despite the building’s challenging features, including 30-foot ceilings in the main common areas, the system has enabled the SIERR Building to achieve LEED Gold certification. Today, it supports tenants like EWU’s Nursing and Communication Sciences & Disorders programs and Fred Hutchinson Cancer Center, making it a cornerstone of Spokane’s Health Peninsula.

Open-Loop Systems: Leveraging Available Resources

Open-loop systems operate by extracting groundwater or surface water, transferring thermal energy directly before discharging it back into the environment. This approach can offer remarkable efficiency gains in areas where groundwater is plentiful and accessible. A key advantage of these systems is their spatial efficiency, making them ideal for projects with site land constraints that prohibit closed loop systems.

By drawing from a stable temperature source such as an aquifer, open-loop systems provide consistent performance throughout the year. However, water availability, quality and environmental regulations must be carefully managed to ensure long-term viability.

The Washington State Public Health Lab (PHL) in Shoreline, showcases the power of an open-loop system to enhance efficiency and resilience. As the PHL campus expanded, the need for a sustainable heating solution became evident. McKinstry’s design-build approach resulted in a new all-electric heating and cooling plant featuring an open-loop ground source system. With 130 and 180-degree water loops providing gradual transitions to lower-temperature systems, this solution exemplifies how open-loop technology can drive efficiency in high-energy environments.

The University of Washington School of Medicine-Gonzaga University Health Partnership building in Spokane demonstrates the efficiency and adaptability of open-loop systems. Developed by Emerald and McKinstry, the 90,000 square-foot facility utilizes an open-loop ground source heat pump system that draws from the Spokane aquifer. The result is a modern, ultra-efficient building designed to meet stringent energy and sustainability goals while serving as a state-of-the-art hub for healthcare education and research.

Comparing Systems: How to Choose the Right Fit

Choosing the right GSHP system requires careful consideration of multiple factors. Closed-loop systems offer greater control, consistency and generally easier permitting, while open-loop systems can deliver exceptional efficiency when water resources are readily available. Key considerations include:

• Efficiency: Closed-loop systems are highly efficient but require more extensive infrastructure. Open-loop systems offer similar performance where water sources are available, with the added benefit of reduced installation and infrastructure costs.
• Installation Costs: Open-loop systems are often less expensive to install but can incur additional costs related to water management and permitting.
• Maintenance: Closed-loop systems generally require less maintenance due to their sealed design, while open-loop systems may face issues related to water quality and fouling.
• Environmental Impact: Both systems can contribute significantly to decarbonization goals when properly designed and maintained, though closed-loop systems may carry higher embodied carbon due to the greater number of wells and piping required.

The Impact of GSHPs on Sustainability Goals

GSHP systems are proving their value as a critical component of resilient infrastructure. By reducing reliance on fossil fuels and enhancing energy efficiency, GSHPs offer a powerful tool for achieving carbon reduction targets. Compared to air source heat pumps, they deliver superior reliability and consistent efficiency—especially in extreme temperatures—making them an ideal solution across diverse climates and site conditions. Their performance advantages make them essential for future-proof buildings. The financial return on investment (ROI) for GSHPs can be substantial, particularly when factoring in long-term energy savings, reduced maintenance costs and alignment with evolving sustainability standards.

Future Trends and Innovations

The future of GSHP systems lies in continued innovation. Hybrid systems combining GSHPs with other renewable technologies, advanced monitoring and control systems and improvements in drilling and installation techniques are all contributing to enhanced performance and broader adoption.

Furthermore, urban environments present a unique opportunity for GSHP integration, especially when paired with district energy systems or other shared infrastructure models. As cities strive to reduce their carbon footprints, GSHPs are poised to play an increasingly pivotal role.

Successfully implementing GSHP systems requires a strategic approach tailored to each project’s unique characteristics. By understanding the differences between open-loop and closed-loop systems, stakeholders can make informed decisions that balance efficiency, cost and sustainability.

As the demand for decarbonization grows, GSHP systems provide a proven pathway toward a more resilient, adaptable and environmentally responsible future. Contact us to learn how our expertise can help you unlock the full potential of geothermal technology.

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