The brine-to-water heat pump uses the ground as a heat source. An antifreeze-water mixture, known as brine, circulates through horizontal ground collectors or vertical geothermal probes, absorbing stored solar energy. The heat pump raises the temperature level via compressor, condenser, and expansion valve, transferring heat to the heating circuit. Since ground temperature remains relatively constant throughout the year, the system operates efficiently even at sub-zero outdoor temperatures. Typical seasonal performance factors range between 4.0 and 5.5. Installation requires official approval; probe depth and number depend on heating load and geological conditions.