Geothermie

• 1-2m horizontal collectors (“gound heat collectors”)

• 4-50m groundwater wells

• 40-250m borehole heat exchanger

• 40-250m borrhole heat exchanger fields

maximum possible output 𝑄𝐻 of a heat pump with electrical or mechanical

power 𝑃𝑝 theoretical optimum

Ec = Th / (Th- Tc)

Pp= Qh / Ec = 1 / Ec

1. borehole heat exchanger

2. BHE field

3. thermal use of spring water

4. thermal use of funnel

5. horizontal collectors

6. pile heat exchanger

7. surface water use

8. groundwater heat pump

9. trench collector

10. waste water usage

    
    

open system:

• ground water heat pump

  closed systems:

• BHE

• geothermal heat collector

• energy pile

  
  

• performance number ε does not take into account other needed electric power like the heat circulation pump or a water pump

• COP involves also other electric processes like the heat circulation pump or a water pump

𝐶𝑂𝑃=𝑄𝑊/𝑃𝑊𝑒𝑙

• ratio between the released heat energy under changing operation conditions and the used operating power in aspecific time intervall

𝛽𝑎=𝑄ℎ / 𝑊𝑒𝑙

1. soil characteristics

2. local climate

3. thermic regeneration in summer

4. laying depth

5. minimal operating temperature

   
   

1. due to its complicated geometry

2. due to the co-existence of different heat transport mechanisms (advection (advection = vertical convection) in the pipes and conduction in the ground)

3. different driving forces (thermal load, air temperature and its dampening at different depths below the ground surface, time varying water saturation etc.).

For these reasons, rule of thumb sizing tables are adopted

q [W/m²] = Q[W] / A [m²]

Q[W]= q [W/m²] x A [m²]

the cooling agent of the heat pump) flows directly in the pipes of the

ground heat collector

• lower efforts to build up

• higher SCOP

• higher amount of cooling agent

• seamless pipes needed

• higher costs for copper ) pipes

• higher distances between the piles because

EP are closed systems with thermal recovery.

EP use construction components (concrete piles or slabs).

In order to use EP we need…

IF no or low groundwater flux through:

• active thermal regeneration.

• heat extraction heating ): 25 30 W/ m pile , 50 80 kWh/( a∙m pile

  heat supply cooling ): max. of 30 W/ m pile , 20 60 kWh/( a∙m pile

IF high groundwater flux

• low seasonal depency between