How Ground Source Heat Pump Systems Work

Ground source heat pump systems consist of three main components: the ground loop, the heat pump unit, and the building distribution system. Understanding how these components work together is essential for designing effective geothermal solutions.

The ground loop is a network of pipes buried underground that circulates a heat transfer fluid (typically water with antifreeze). In closed-loop systems, this fluid never comes into direct contact with the ground but exchanges heat through the pipe walls. The loop configuration depends on available land area and geological conditions.

Vertical boreholes are most common in urban settings where land is constrained. Holes are drilled 50-200 metres deep, with U-tube pipes inserted and the annulus filled with thermally enhanced grout. Horizontal loops require more land but shallower excavation, typically installed at 1-2 metres depth.

The heat pump unit sits inside the building and operates on the same principle as a refrigerator, but in reverse for heating mode. A compressor, evaporator, condenser, and expansion valve work together to transfer heat from the ground loop to the building distribution system. Modern heat pumps can also provide domestic hot water.

System integration with the building is crucial for efficiency. Underfloor heating and radiant panels work particularly well with heat pumps because they operate at lower temperatures. Fan coil units and ducted systems are also compatible but may require higher water temperatures.

Proper design requires understanding both the building's thermal loads and the ground's thermal properties. Thermal response testing provides site-specific data on ground thermal conductivity and borehole thermal resistance, enabling accurate system sizing.