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What is geothermal energy?


What is geothermal energy? Earth heat

• Earth is a renewable heat source. The energy it contains comes from the sun and the natural heat of the crust.
This energy is free of charge and available in large amounts; it must only be transferred from the soil to the homes.
Geothermal energy and clean energy represent an essential source not only for the end user but also for the entire
ecosystem.

How to exchange heat between soil and homes

• Geothermal energy is available at a constant temperature (approximately 14 °C at between 20 and 100 m depth) throughout the year, but it is not enough to supply the entire heating system.
• GEO heat pumps transfer the heat from the soil, increasing the temperature of the thermovector fluid by means of the compressor powered solely by electricity.
• This process is particularly efficient; in fact, 1 kW of electricity can produce up to 5 kW of thermal energy.
Efficiency is ensured throughout the year, unlike air-heat exchangers.
• By reversing the cycle during summer, GEO heat pumps can cool your home by releasing the heat captured inside
to the outdoors, thereby settling the energy balance.

How does a geothermal system work?

• The soil on which the house is built can be a sufficient energy source to heat and cool your home.
• There are several solutions to exchange heat between an underground source and the thermovector fluid:
- horizontal heat exchanger probes buried 2 metres deep;
- vertical probes (buried 80 - 120 m deep);
- stratum, river or lake water.
• A thermovector fluid, usually water or a glycol-water mixture, flows inside the probes, transferring the heat to the GEO heat pump, thereby making it available for heating, cooling and sanitising.

Horizontal heat exchanger probes

• This type of probes must be buried 1 - 1.5 m deep (always 20 cm below the freezing limit) in the soil, which must be left unsown.
• PE probes (DN 25 o DN 32) require an average lawn surface equal to 2.5 – 3 times the area to be heated.
Indications:
- Ideal moist and clay soils.
- Do not divert rainwater through drains to optimise soil  regeneration.
- Do not pave over the surface of the manifold
- Avoid tree and bushes with deep roots.
- The circuit piping must be provided with a water vapour barrier to prevent condensation and ice dams from forming.

Closed circuit vertical probes (water-glycol)

• Vertical probes require a perforation of approximately 150 mm
diameter where a PE pipe circuit is placed (geothermal probe)
sealed with a bentonite mixture.
• PE probes (DN 32 for double-U pipes or DN 40 for U-pipes)
• According to the soil quality, for every thermal kW yielded by
the heat pump an average between 15 and 20 m probe is required.
Indications:
- Drilling depth ranges between 80 and 120 m. For larger demands, several parallel probes must be used.
- In the event of multiple drilling, keep the probes at a distance of at least 8 - 10 m (grid) to prevent thermal interference.
- When drilling vertical probes, always provide for an adequate distance from the building foundations in order to
prevent soil subsidence and thermal strain. It is advisable to consult a geologist.

Stratum-water wells

• Being located close to a water source or an underground stratum allows for a direct heat exchange. The water withdrawn is reintroduced through a second well after exchanging heat with the heat pump.
• The geothermal system flow rate is 4 l/min/kW (heating).
Indications:
- The use of groundwater strata requires prior mandatory authorisation by the Province of competence.
- Minimum water temperature must not drop below 7°C, whereas maximum water temperature must not exceed 20°C.
- The quality of the water must comply with the indications in the “chemical-physical properties” table at the end of the paragraph; otherwise, an external inspectable plate heat exchanger must be placed between the heat pump and the well water circuit.
- The level of the detected stratum must be measured by having it bleed continuously for 24 – 48 hours, making sure that after this period the level of the stratum has not decreased (if so, a deeper or larger stratum must be found).
- It is important to ensure a distance of at least 10-15 m between the suction well and the drainage well to prevent underground hydraulic short-circuits (unless water is reintroduced in a stratum at a different level from the suction well).

Heating systems

• Geothermal heat pumps are advanced energy systems that are integrated in systems with certain basic features e.g., good thermal insulation class, especially for cooling applications during summer. It is important to consider the operating temperatures: The economic convenience of using a geothermal heat pump is set to a
50°C flow temperature in domestic hot water production and at lower temperatures (35-40 °C) for the flow to the heating system.
• This is why a typical system to be installed downstream a geothermal system (except for heated towel rails and radiators for bathrooms) can be:
- a low temperature floor radiant heating system
- a low temperature radiant wall heating system
- a low temperature ceiling radiant heating system
- low temperature radiant plate heating system (e.g. as a replacement for old radiators)
- medium temperature convection heating systems (e.g. as a replacement for old radiators)
- medium temperature fan coil heating system (e.g. as a replacement for old radiators)
- oversized heated towel rails with auxiliary heating element or bleeding of the primary boiler circuit.
In the event there are several areas designed on the (floor or wall) radiant system i.e., in the event the heating system does not have enough water content/thermal inertia, it must be provided with a hydraulic breaker or a heat storage device to ensure adequate water circulation in the geothermal pump for a regular operation.
Technische Daten

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