The geothermal heat pumps (or ground heat pumps) (not to be confused with heat-actuated heat pumps) can be used regardless of the outside temperature, maintaining a constant heating temperature throughout the year as the sensors are installed at the required depth.
The types of geothermal heat pumps
There are three types of geothermal heat pumps based on the habitat:The geothermal sensors buried horizontally
The horizontal sensors (tubes made of polyethylene or polyethylene coated with copper) are buried in the soil horizontally at shallow depth (0.60 m to 1.20 m). They flow to the heat pump in a closed circuit of water mixed with antifreeze or coolant, depending on whether the expansion is direct or indirect.
The land must not be too steep and the sunniest surface above the sensor must be permeable (not paved).
The sensors must be at least 2 m deep on surfaces covered with trees, 1.5 m deep in the case of non-hydraulic underground systems and 3 m deep for foundations, wells, septic tanks and drains.
They are less expensive than the vertical sensors but require a larger area of land (1.5 to 2 times the surface to be heated).
They are mainly reserved for heating homes.
The vertical geothermal sensors
The vertical sensors (two polyethylene tubes forming a U are also called ground probes) are buried up to 80 m deep and sealed in a borehole with cement. They circulate in a closed circuit of water mixed with antifreeze since the heat pump fluid can only be fitted with intermediate vertical sensors.
The vertical sensors are not only suitable for heating individual houses but also for small dwellings or buildings with a limited surrounding surface.
The vertical sensors involve higher costs than the horizontal sensors, the additional costs are related mainly to drilling. However, they require a smaller land area.
The geothermal water layer (or water heat pump)
The heat pump does not capture the energy in the ground horizontally or vertically, but the shallow water, which is picked up by drilling.The water heat pump requires one or two water wells 30 to 100 m deep.
In systems with a single borehole, the collected groundwater is rejected into a river or a storm water system after the necessary calories are taken. In two-hole systems, the water used for heating is injected after a second drill. This system is costly but avoids the waste of groundwater.
The temperature of the water has the advantage of being consistently high all year round (between 8 ° C and 12 ° C). It is also possible to capture the heat of surface water such as lakes, rivers, streams and that of wastewater.
However, the quality and flow of water often pose technical difficulties, which make this option not recommended for some types of constructions.
There are three kinds of technologies implemented for heat pumps:
The DX system: it uses a single circuit. A considerable amount of liquid refrigerant (HCFC) circulates in the pump, sensors and transmitters of heat (heated floors) in a closed circuit.
This is called a ground heat pump for geothermal heating.
Investment cost: 70 to 100 EUR per square meter of hot water and cool water
Cost range: 2.3 to 3.5 EUR per square meter per year
The mixed system: it uses two circuits (the sensor circuit and the heat pump and the hot water emitters). It comes to a water heat pump/geothermal ground for heating.
The intermediate fluid system: it uses three circuits: the refrigeration circuit of the heat pump, the sensor circuit with circulating water mixed with antifreeze, the circuit that supplies hot water emitters (radiators or coil). The refrigerant is contained in the geothermal heat pump. There is talk of brine water for geothermal heating.
Investment cost: 85 EUR/square meter heated (optional heating) to 135 EUR/square meter heated (heating and cooling option) for horizontal sensor systems and 145 to 185 EUR/square meter heated for vertical sensor systems
Cost range: 2.3 to 3.5 EUR per square meter per year
Geothermal heat pumps can also provide geothermal heating of hot water or cooling through the floor (reversible geothermal heating) and can also be used for heating a swimming pool.
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