Key Takeaways
- Water vs. Air: Geothermal heat pumps use water instead of air for heat transfer, providing consistent 55°F entering temperatures for superior efficiency
- Loop Types: Open loops (“pump and dump”) offer consistent temperatures but waste water, while closed loops recycle water with antifreeze but require proper sizing
- Sizing Matters: For optimal performance, size closed loops at 200 feet per ton rather than the outdated 100-150 feet standard
- Service Simplicity: Most geothermal systems use thermistors and error codes for easier troubleshooting compared to traditional heat pumps
Many of you in the industry have heard of geothermal heat pumps and their potential benefits, high installation costs, or available rebates. You may also be confused about their operation: Where does water come in? What do you mean there’s no outside fan? This article covers the basics of geothermal heat pumps—how they function, what applications they serve, and the differences between those applications.
Understanding Geothermal Heat Pump Operation
Geothermal systems are remarkably similar to standard air-to-air heat pumps you’ll find in homes or commercial buildings. The main difference is that instead of air, geothermal systems use water as the medium for heat absorption and rejection. This fundamental change delivers several advantages:
- Lower high-side pressures and saturated temperature conditions
- Better compression ratios in cooling mode
- More consistent heat output in heating mode
- Relatively stable entering water temperatures (around 55°F year-round)
When you understand that you have roughly 55-degree water entering the system regardless of outdoor conditions, it becomes clear why geothermal systems achieve such impressive efficiency ratings. Unlike air-source heat pumps that struggle with extreme outdoor temperatures, geothermal units maintain consistent performance throughout the year.
Open Loop vs. Closed Loop Systems
The water for geothermal systems comes from two types of loops: open and closed. Both have distinct advantages and drawbacks that affect installation, maintenance, and long-term operation.
Open Loop Systems (“Pump and Dump”)
Open loops pull water from a well using a well pump. After the water passes through the system, it’s deposited into another location or well. Water flow is regulated via:
- External solenoid valve and flow restrictor (older systems)
- Internal actuator valve (newer systems)
Advantages:
- Consistent water temperatures entering the system
- Simple design concept
- Lower initial loop installation costs
Drawbacks:
- Water waste concerns
- Requires strainer installation to prevent mineral deposits
- Needs routine strainer cleaning
- Dependent on adequate well water supply
Closed Loop Systems
Closed loops function like hydronic systems—water moves via one or two circulators through the system and then through an extensive underground loop. The water naturally cools or warms back up before returning to the system, depending on your operating mode.
Advantages:
- No water waste
- No strainer needed
- Independent of well water quality
- More environmentally friendly
Drawbacks:
- Requires antifreeze solution (typically glycol) to lower freezing point to 10°F
- Higher initial installation costs
- Loop sizing critical for performance
- Potential for temperature drift during extended run times
Critical Loop Sizing Considerations
Proper loop sizing makes or breaks closed-loop system performance. Many well drilling contractors rely on outdated rules of thumb that can compromise efficiency:
- Old Standard (Too Small): 100 feet of loop per ton of cooling
- Current Standard: 150 feet of loop per ton
- Recommended Best Practice: 200 feet of loop per ton
Oversizing loops in residential applications allows for better heat rejection and absorption, preventing temperature drift during extended run times. As someone with a geothermal system in my own home, I strongly recommend the 200 feet per ton standard for optimal performance. When calculating proper heat loads for equipment sizing, remember that geothermal systems maintain efficiency even in extreme conditions, unlike traditional heat pumps.
Learn more about geothermal heat pumps on this episode of the HVAC Know It All Podcast:
Package vs. Split System Configurations
Geothermal systems come in both package and traditional split system configurations, each suited to different applications.
Package Systems
In residential and commercial applications utilizing closed loops, package systems dominate the market. These units offer several advantages:
- All components housed in one cabinet for convenient servicing (similar to commercial RTUs)
- Factory-charged and ready for commissioning upon installation
- Simplified installation process
- Reduced potential for refrigerant leaks
- Ideal for scheduled maintenance programs
Split Systems
Split systems appear less frequently, typically in homes with multiple systems or commercial buildings utilizing open loop configurations. These systems require standard installation best practices:
- Brazing with nitrogen flow
- Proper evacuation procedures
- Refrigerant charge adjustment based on lineset length
- Careful attention to refrigerant leak prevention
Service and Troubleshooting
On the service side, many geothermal manufacturers utilize thermistor networks for sensing temperatures throughout the system. This design philosophy makes troubleshooting more straightforward compared to traditional systems:
- Systems lock out to prevent damage when issues arise
- Error codes display for quick diagnosis
- Temperature readings available at multiple points
- Protection for both the system and surrounding equipment
Unlike reversing valve issues in standard heat pumps, geothermal systems typically have fewer mechanical failures due to their protected indoor installation and consistent operating conditions. The thermistor-based control systems also integrate well with modern building management systems for commercial applications.
Working with geothermal systems becomes straightforward once you understand these fundamentals. The technology isn’t drastically different from air-source heat pumps—it simply uses a more stable heat transfer medium.
Looking Forward
The geothermal market faces interesting changes as rebates and tax programs evolve. However, existing systems will continue requiring professional service for decades to come. Understanding these systems expands your service capabilities and positions you as a comprehensive HVAC professional in markets where geothermal has gained traction.
Growing your geothermal service business requires reaching the right customers at the right time. Property.com’s ‘Know Before You Go‘ tool helps you identify homes with existing geothermal systems or properties ideal for geothermal retrofits by providing detailed property insights including permit history and home characteristics. This exclusive platform connects top HVAC professionals with homeowners actively seeking specialized services. Learn how Property.com helps HVAC pros build their reputation and secure more high-value geothermal projects.
Whether you’re troubleshooting an existing installation or helping customers understand their options, geothermal heat pumps represent a proven technology that delivers consistent comfort and efficiency when properly designed and maintained.
