Geothermal Heat Pumps: Closed-Loop Surface Water Ground Heat Exchangers & Hybrid Systems

Closed-Loop Surface Water Ground Heat Exchangers

A closed-loop surface water ground heat exchanger can cleverly utilize an existing pond or a newly created one as a heat source or sink. The system operates with loop fluid circulating through pipes that are anchored at the pond's bottom. Typically, individual pipe coils are integrated into a single circuit and securely fixed to a frame.

Installation Process

This frame can be floated to the desired location on the pond, filled with fluid, and then carefully sunk. Concrete blocks are used to anchor the frame to the pond's floor to ensure stability. The frame is designed to hold the pipes slightly above the bottom surface, promoting effective circulation and preventing sediment accumulation over the pipes.

System Operation

The loosely coiled pipes enable water to flow across the bundle, facilitated by the buoyancy force caused by the temperature differences between the pond water and the pipe fluid. In heating applications, this system is efficient because water reaches its highest density at 39°F. Consequently, in a well-sized system, the water surrounding the pipes at the pond's bottom remains sufficiently above freezing, allowing easy heat extraction.

Regional Considerations

For the Virginia region, a pond with a depth of at least 12 feet is necessary to meet heating and cooling demands. Generally, about one 300-foot coil of pipe is required for each ton of peak block load. Successful operations have been recorded with ponds sized to accommodate 60 tons of installed heat pump capacity per acre at a 20-foot depth.

Comprehensive Thermal Analysis

A comprehensive thermal analysis that includes solar influx, evaporation, surface convection, inflow and outflow dynamics, ground conduction, and the thermal mass of the water is essential to determine the system's effectiveness. These elements contribute to the accurate sizing and efficient operation of the pond-based heat exchange system, ensuring sustainable and reliable thermal management.

Hybrid Systems

Hybrid systems offer innovative solutions for efficient thermal management by integrating diverse heat sources and sinks. These systems leverage ground heat exchangers within unique infrastructures, such as structural pilings of buildings, or utilize effluent from wastewater treatment plants to establish a connection with the environment. Ground Heat Pump (GHP) systems showcase their versatility by efficiently operating wherever moderate temperature heat sources or sinks, ranging from 40ºF to 90ºF, are accessible.

Key benefits of hybrid systems include:

• Reducing the load on ground heat exchangers, optimizing their performance.
• Decreasing initial investment costs due to reduced ground loop requirements.
• Saving valuable land space may be a significant constraint in urban environments.
• Incorporating additional components that, while adding complexity, enhance system efficiency and flexibility.