Closed-Loop Water-Source Heat Pump Guide

Closed-loop water-source heat pumps offer an energy-efficient way to heat and cool buildings by exchanging heat with a contained groundwater or surface loop. This guide explains how closed-loop systems work, compares common configurations, outlines design and maintenance best practices, and covers costs and incentives for U.S. projects.

Feature	Typical Values/Benefits
Energy Efficiency	High — COPs often 3.0–5.0 depending on design
Loop Types	Horizontal, vertical (borehole), submerged
Applications	Residential, commercial, multi-family, institutional
Typical Lifespan	Heat pump 15–25 years; loop field 50+ years
Maintenance	Low to moderate — annual checks recommended

How Closed-Loop Water-Source Heat Pumps Work

A closed-loop water-source heat pump (WSHP) transfers heat between a refrigerant loop inside the unit and a closed hydronic loop circulating water or antifreeze. The loop exchanges heat with the earth, groundwater, lakes, or ponds rather than open environmental water. A compressor, expansion device, evaporator, and condenser operate as in any heat pump, but the hydronic fluid provides a stable thermal source or sink.

Key Point: Because the loop is closed, there is minimal risk of corrosion, biological growth, or contamination compared to open-loop systems.

Types Of Closed-Loop Systems

Horizontal Ground Loop

Horizontal loops are installed in trenches 3 to 6 feet deep. They require more land area but are cheaper to install per linear foot than boreholes. Horizontal loops work well where soil thermal conductivity is adequate.

Vertical Borehole Loop

Vertical loops use drilled boreholes spaced 10 to 25 feet apart and reach depths of 150 to 500 feet. They are more expensive per foot but require less surface area. Vertical loops are preferred in dense urban lots or where soil depth is inadequate.

Pond/Lake Loop

Pond or lake loops deploy coils submerged in a body of water. They offer excellent thermal performance when the water body is deep and well-mixed, but require access and suitable aquatic conditions.

Surface or Slab-Integrated Loop

Some systems integrate closed loops with building slabs or shallow bedrock where drilling is impractical. These require careful thermal modeling to avoid seasonal imbalance.

Benefits Of Closed-Loop Water-Source Heat Pumps

High Efficiency: Stable ground or water temperatures yield higher coefficients of performance (COP) than air-source heat pumps, especially in extreme weather.

Longevity: Closed-loop piping (PE or HDPE) resists corrosion and can last 50+ years, reducing lifecycle replacement costs.

Low Operating Cost: Lower electrical consumption for heating and cooling leads to smaller utility bills and reduced carbon emissions when electricity is clean.

Quiet, Reliable Operation: With fewer extremes in source temperature, compressors operate in favorable conditions, lowering wear and noise.

Design Considerations And Best Practices

Thermal Load Analysis: An accurate heating and cooling load calculation is essential. Oversizing the heat pump or undersizing the loop can reduce system efficiency and life.

Loop Sizing: Loop length and configuration depend on soil thermal conductivity, building load, and allowable fluid temperature range. Ground thermal response tests (TRT) or published conductivity data inform design.

Fluid Choice: Closed loops commonly use water with propylene glycol or methanol when freeze protection is required. Propylene glycol is less toxic and often preferred for building-adjacent systems.

Material Selection: High-density polyethylene (HDPE) piping is standard due to flexibility and long-term durability. Fittings and manifolds should match pressure and temperature ratings.

Loop Field Balance: Flow balancing and proper pump selection maintain consistent loop temperatures and maximize heat pump performance.

Sizing, Performance, And Efficiency Metrics

Coefficient Of Performance (COP): COP describes heating efficiency (heat output divided by electrical input). Closed-loop WSHPs can achieve COPs of 3 to 5 under favorable conditions.

Seasonal Performance: Use Seasonal Energy Efficiency Ratio (SEER) for cooling and Heating Seasonal Performance Factor (HSPF) for heating evaluations when available for unit types.

Loop Thermal Response Test (TRT): TRT measures in-situ ground thermal properties to optimize bore length and spacing. It reduces risk of underperforming loops and is recommended for larger installations.

Metric	Typical Range
COP (Heating)	3.0–5.0
SEER (Cooling)	14–24 (system-dependent)
Loop Lifespan	50+ years
Heat Pump Lifespan	15–25 years

Installation Steps And Considerations

Installation begins with site assessment, geotechnical review, and permitting. For horizontal systems, excavation and trenching are required. Vertical systems need drilling equipment and grouting of boreholes to enhance heat transfer.

Connection And Commissioning: After loop placement, pressure testing verifies integrity. The hydronic loop is filled, flushed, and treated. Heat pumps are installed, refrigerant charged if necessary, and the entire system is commissioned with flow, temperature, and electrical checks.

Local Codes And Permits: Permits for drilling, excavation, and mechanical work are typically required. Environmental reviews may apply for lakes or wetlands.

Maintenance And Troubleshooting

Closed-loop WSHPs require less maintenance than many HVAC systems, but regular tasks preserve efficiency and reliability.

• Annual inspection of the heat pump, controls, and electrical connections.
• Check loop pressure and glycol concentration every few years.
• Replace filters and verify airside coil cleanliness to maintain heat exchange.
• Monitor system performance metrics—flow rates, Delta-T across the loop, and energy consumption—to detect issues early.

Common Issues: Air in the hydronic loop, pump failures, or fouling of internal coil surfaces can reduce efficiency. A sudden rise in loop pressure can indicate blockage or thermal expansion issues.

Costs, Incentives, And Lifecycle Economics

Installed costs vary widely: residential closed-loop GSHP systems typically range from $20,000 to $50,000 depending on loop type and house size. Commercial installations scale by tonnage and site complexity.

Operating Savings: Energy savings often pay back a portion of the premium investment over time, with payback periods of 5 to 15 years depending on energy prices and incentives.

Incentives: Federal tax credits, such as the Energy Efficient Home Improvement Credit and commercial incentives, may apply. Many states and utilities offer rebates, performance incentives, or low-interest financing for geothermal/ground-source heat pump installations.

Cost Component	Typical Range
Horizontal Loop Installation	$5,000–$15,000 (residential)
Vertical Boreholes	$10,000–$40,000 (residential and up, depending on depth)
Heat Pump Unit	$5,000–$20,000 depending on capacity
Total Installed Residential	$20,000–$50,000+

Applications And Case Studies

Closed-loop WSHPs suit a variety of building types. Multi-family buildings benefit from decentralized WSHP units with a shared ground loop to provide tenant-level control and improved efficiency.

Schools and municipal buildings often use vertical closed loops to conserve land while achieving substantial energy savings. Hospitals and labs value the reliability and predictable thermal source for critical environments.

Example: A mid-sized school replaced boiler and rooftop units with a centralized closed-loop GSHP system. The school reported annual energy reductions of 30–50% and maintained comfortable indoor conditions with lower maintenance costs.

Comparing Closed-Loop To Open-Loop Systems

Open-loop systems withdraw groundwater or surface water, exchange heat, and discharge the water. Closed-loop systems circulate a contained fluid. Each has advantages.

Criteria	Closed-Loop	Open-Loop
Water Quality Risk	Low	High (scaling, corrosion, biofouling)
Permitting Complexity	Lower	Higher (discharge permits often required)
Efficiency	High (stable source)	Very High (if groundwater is ideal)
Maintenance	Lower	Higher

Frequently Asked Questions

How Long Does A Closed-Loop System Last?

The loop piping can last 50 years or more; the heat pump typically lasts 15 to 25 years. Proper maintenance extends life and performance.

Is A Closed-Loop System Suitable For Small Lots?

Yes. Vertical boreholes or pond loops are good options for small lots. Modern drilling techniques make vertical closed-loop installations feasible in urban settings.

Are Closed-Loop Heat Pumps Renewable?

They rely on stable ground or water heat, which is renewable at the building scale and produces lower emissions than fossil-fuel heating when paired with clean electricity.

Can Closed-Loop Systems Provide Domestic Hot Water?

Yes. Many installations incorporate a desuperheater or dedicated heat exchanger to preheat domestic hot water, improving overall system efficiency.

Selecting A Contractor And Next Steps

Choose contractors with experience in geothermal or ground-source heat pump projects. Verify references, request thermal response testing for larger systems, and compare turnkey bids that include loop installation, equipment, controls, and commissioning.

Next Steps: 1) Conduct a site assessment and load calculation. 2) Obtain permits and explore incentives. 3) Perform a loop thermal test if required. 4) Proceed with installation and commissioning guided by an experienced mechanical contractor.

Important: Proper design and commissioning are critical to realize the energy, cost, and comfort benefits of closed-loop water-source heat pumps.