The two main components of a geoexchange system are the ground loop or ground heat exchanger and the Ground Source Heat Pump (or geothermal heat pump), which is typically located within the building or plant room. The ground loop provides the passive component of the system, whereas the Ground Source Heat Pump provides the mechanical component.
Ground Source Heat Pump
The first component of the geoexchange system is the Ground Source Heat Pump (or geothermal heat pump). It is the Ground Source Heat Pump which receives the water returning from the loop and transfers it to either hot/cold air via ducts (water to air) or as hot/cold water for hydronic heating, chilled beams, pools, spas etc (water to water). It achieves this through conventional (water source) heat pump technology. The main difference is that a Ground Source Heat Pump can operate on a conventional condenser water loop, whereas a conventional water source heat pump cannot operate off a ground loop. This is due to the higher temperature ranges present in a ground loop.
The Ground Source Heat Pump is typically controlled by a thermostat and can be connected to a Building Management System (BMS).
An optional component of a Ground Source Heat Pump is the desuperheater. The desuperheater is a simple connection between the Ground Source Heat Pump and a domestic hot water storage tank. It provides pre-heating of domestic hot water while the geoexchange system is operational. Depending on system usage, the desuperheater provides between 20% and 80% of the domestic hot water requirements of a typical home.
The desuperheater option is adopted on approximately 80% of residential installations. On a commercial installation, the desuperheater option can be used, or the hot water supply can be integrated into the geoexchange system.
Ground Heat Exchanger
Closed ground loops are constructed of Polyethylene (PE) pipe in a vertical (borehole) or horizontal (trench) configuration and water is used as the heat transfer fluid. The heat transfer fluid may also include small percentages less than 30% of additives for water treatment or anti-freeze in colder regions.
The loop fluid is simply circulated through the ground loop and returned to the Ground Source Heat Pump. In accordance with the Zero Law of Thermodynamics, the loop fluid and the ground will endeavour to reach a thermal equilibrium.
Thus during its passage through the ground, the loop fluid is equilibrating with the stable ground temperatures either by extracting heat from the ground (winter) or rejecting heat to the ground (summer). The extent of this equilibration is determined by the residence time in the ground, the temperature differential between the loop fluid and the ground and other ground properties such as thermal conductivity and thermal diffusivity.
Open loops utilise ground or surface water directly, pass it through a heat exchanger and then return the water to either its origin or a secondary application such as irrigation, industrial water etc. Open loop sources are varied and include groundwater, rivers, oceans, dams and treated effluent.