1. Geothermal is a Renewable Energy (RES) as it exploits the endless energy encompassed in geological formations
  2. The efficiency of a geothermal system is 400%. That is, for every 4 Kw of thermal power output, 3 Kw is free from the ground.
  3. With current oil and electricity prices it provides a steady 70% savings
  4. The depreciation of a geothermal system is 5-7 years, depending on the use.
  5. It is a common system for heating and cooling.
  6. No chimneys and no oil tank required
  7. Easy to operate.
  8. Minimum maintenance cost
  9. It is the most modern and efficient heating / cooling system in the world right now
  10. It is a widespread technology, as it has been used for decades. In North Europe and America since the 1950s (eg in Sweden 80% of new buildings use geothermal energy). Also in our country there are numerous applications in Public and Private buildings with amazing energy saving results.
  11. The performance of a geothermal system is stable regardless of the weather outside.
  12. According to the new European Union energy policy directives, the aim is to detach fossil fuels (oil, gas, etc.) and to integrate Renewable Energy Systems for heating and cooling buildings. National legislation and the National Energy Plan also require the gradual abolition of conventional building heating systems and their replacement with modern and efficient Renewable Energy Systems, primarily for all Public Buildings and subsequently for Private Buildings.
  13. It is therefore imperative for many reasons that we switch from using conventional heating systems to new systems that offer savings and reduce the environmental footprint.
  14. Especially for buildings of particular cultural heritage and to emphasize their sustainability, the use of Renewable Energy sources is mandatory, according to UNESCO guidelines.
  15. Given that fossil fuels must now be considered past for use in heating plants, geothermal is clearly the optimal solution.


The lexical meaning of "Geothermal", could create confusion, because it refers to the thermal energy that is released from the interior of the earth. In our case, we refer to the utilization of the energy existing in the ground. A geothermal heat pump allows the flow of heat from/to the ground in order to product refrigeration, heating and hot water for domestic use.


Practically is nothing else than a machine which can transport heat loads from cold places to hot, or in the language of engineers, from the "hot sink" to the "cold sink". The same action is executed by the fridge which is in our house and the split type room air-conditioner installed in our lounge and in our office. A difference between the fridge and the air-conditioner is that we can select the hot and cold sink depending on our needs. During the summer we select the environment as the hot sink and our house as the cold one (by selecting operation of refrigeration). The air-conditioner removes heat loads from the interior of our house and it rejects it outside. During the winter we select the interior of our house as the hot sink and the environment as the cold one (by selecting operation of heating). The air-conditioner pumps the heat existing in the environment to the interior of our house.


The Geothermal Heat Pump (GHP) instead of using the air of the environment to reject (summertime) or remove (winter) heat loads, is using the heat load that is contained into the hypogean water, lake water and sea water, or even the heat contained in the earth! A few meters under the surface of the ground the temperature is almost constant during the year. The GHP, using a network of water piping, suitably placed, is exchanging heat loads with the soil or with the sea depending on the type of installation.


A comparison with a conventional system of air conditioning with air-cooled exterior units as for example the, very known to all, split type room air-conditioners, the exterior units of which is placed on the balconies of apartments or on the rooftops of buildings. Everyone who has used them in the summertime during a very hot day (35°C or even 40°C), has probably noticed the high reduction of their output and their inefficiency to cool satisfactorily. This happens because the appliance is attempting to pump heat loads to an environment which is already overcharged with heat load and strains a useless effort consuming excessive sums of electric energy.

However, if our air-conditioner is pumping the heat load to a colder environment, such the soil, where during the hotter days of summertime the temperature does not exceed the 20°C, the output would be much bigger and the economy in electric energy considerable.

The usage of the geothermal exchangers is based on this principle of the thermodynamics. We can imagine that the heat pump, transports the underground environment of 20°C into our house. The electric energy consumption this way is the minimal possible.

Proportionately, in wintertime, the geothermal system is called to raise 15-17°C of the ground up to 20-22°C in order to heat the building. The energy saving obtained by this function is also very considerable compared with a conventional air-cooled heat pump. It is important to mention that a conventional air-conditioner is almost unable to warm our room when the outdoor temperature is below 0°C.


There are three basic installation methods available which are represented below:

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Installation utilizing drillings

Water is pumped out the borehole and reentered after passing through the exchanger of the GHP. The water absorbs or rejects the heat load and the heat pump refrigerates or heats the building. This system has increased cost of manufacture, because of the required equipment (submersible pumps). Moreover, the power consumption of the submersible pumps is considerable. The basic advantage is the minimal requirements in space on the building ground




Closed vertical loop with circulation of the heat carrier fluid

Closed vertical loop with circulation of the heat carrier fluid

Boreholes are drilled to relatively small depths pipes are installed creating vertical loops which constitute the geothermal exchanger. The method is used in cases of big buildings with extended needs of cooling and heating so a very big length of piping is required and the unoccupied building ground is small. The cost is comparable with case 1 because the necessity of drillings.

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Closed horizontal loop with circulation of the heat carrier fluid

Trenches of about 1,5m depth are created on the unoccupied building ground or a complete excavation is made. This method is used almost always when the unoccupied building ground is sufficient because is the most inexpensive solution.



Argyrios Bairaklilis
Electrical Engineer – Geothermal Engineer

Miaouli 42,
ΤΚ 546 42, Thessaloniki

Tel: 6972 206166

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