Investigation of different collector and probe types for heat absorption in wells and/or in the soil

Description of the general operational principle of collector probe types for a heat pump technology

The heat pump "lives" from the total source output of a geothermal probe, the energy storage and contacted ground volume per m³. Source output of geothermal probes and/or a collector system is crucially influenced by the following factors: changes in temperature, heat flow per metre length of tube, thermal conductivity, distance from the centre of the tube, laminar or turbulent flow, time, thermal conductivity and viscosity of the heat carrier agent.

Antifreeze/brine fluid is pumped to the heat pump evaporator. The heat pump evaporator uses the incoming brine liquid/heat flux from the geothermal probe to vaporise a refrigerant on the cooling technical side. In this process heat is extracted from the brine liquid.

The return flow from the evaporator is therefore colder than the flow of the brine pipeline. The cold brine liquid is pumped, with the help of a circulation pump, back to the return flow of the geothermal probe system. In this case, the brine liquid absorbs the ambient heat from the soil and the cycle starts once more.

Heat pumps are usually installed, as a rule, near the surface, e.g. geothermal probes installed at a depth of 50-150 metres in prefabricated holes. They are fitted for use at an average soil temperature of about + 10-11° C. With aid of a circulation pump an antifreeze circulates in the geothermal probes to prevent the brine liquid from freezing.

Venturi stainless steel probe (memory probe)

The Venturi stainless steel probe can be used in situations where there is groundwater in the so-called first aquifer. This is the top layer of ground water, which has not been used to obtain drinking water yet. The probe forms the heat exchanger and uses the groundwater temperature. The temperature difference between inflowing and backflowing heat transfer medium is sufficient to deliver up to 75% of the energy. The remaining approximate 25% usually has to be supplied as electricity in order to power the heat pump. As to how many such probes (memory probes), available in different lengths, are required to supply sufficient energy for the object to be heated and which fluid is the best suited as a heat absorbing liquid (fluid), must all be determined on an individual case by case basis.

The required drilling depth is about 50% lower than for geothermal plants with comparable capacity.

The Venturi stainless steel probe reaches its high efficiency with the use of stainless steel, which has good thermal conductivity and with the inner structure of the probe, which allows a quick absorption of the heat taken from groundwater. The stainless steel probe is not made from an empty pipe. A rigid Archimedean screw is located inside with a coaxially mounted second tube. Through this inner tube the fluid is pumped into the Venturi probe. The outer diameter of the Archimedean screw is slightly smaller than the inner diameter of the outer tube. Thus, a part of the backflowing fluid passes with a higher speed (the Venturi effect) along the wall of the tube and is mixed by swirling with the slower flowing liquid in the inner area of the screw. This mixing causes the rapid heat transfer from the wall on the entire cross-section of the stream.

The Venturi stainless steel probe is at the heart of a modern, environmentally friendly heat production solution, with its main source of energy being renewable thermal energy from near-surface water. Within one yearly cycle the energy extracted from the ground is balanced by sunlight and infiltration of rain water into the soil.