The first test facility has been in operation since December 6, 2023. The single-family home, built in the 1990s, was previously heated with an aging gas boiler. Just as the owners of the home in Altach, Austria, decided to modernize their heating system, separatus was looking for a suitable project nearby to drill the first borehole for test purposes.
During the preliminary planning phase, a nominal heat load of 7.5 kW was determined using an available energy performance certificate. The family opted for an IDM iPump T 3-13 modulating heat pump. It was integrated directly into the existing heat distribution system, which combined radiators and underfloor heating, without a buffer tank. The heat pump also produces hot water in the integrated drinking water storage tank.
The subsoil is peaty in the uppermost layers. Gravel and sand predominate at depths between 9 and 30 meters. This is followed by alternating layers of silt and gravelly sand. A clay layer was encountered in the last 10 meters. Drilling was carried out to a total depth of 70 meters. Groundwater ingress occurred at depths of 4 meters – due to the hydrogeological situation in the entire area, abundant groundwater flow is to be expected.
The reference borehole is equipped with a double-U probe with a 32 mm pipe diameter. This double-U probe can be switched to a single-U probe at any time using shut-off valves. Both geothermal probes were made accessible via shafts for temperature measurements and similar purposes. The probe supply lines are equipped with heat meters in a distribution box manufactured by "Geser Erdwärme." Motorized control valves can also be controlled, allowing for adjustment based on volume flow or power as needed. The data is continuously recorded, enabling any comparisons and evaluations between the probe types.
This version allows a direct comparison of these two probe types and demonstrates the impressive performance of the separatus probe.
Performance data
separatus in individual operation:
According to design guidelines, the geothermal system is not intended to be operated with just one geothermal probe. However, for testing purposes, it is interesting to observe how well the separatus probe performs in standalone operation. Even when the heat pump is required to achieve very high extraction rates of around 100 watts per meter, separatus delivers relatively high temperatures. When the heat pump then reduces to a level of approximately 50 watts per meter, separatus demonstrates tremendous stability. The temperatures continually recover and do not drop further even after extended operation, which is of course also an indicator of good geology.
separatus in comparison:
In this test system, separatus lies between a single U and a double U in terms of heat transfer.
In comparing separatus and the double-U, various scenarios were run, including different temperature spreads ("delta-T") between the flow and return lines. Short-term fluctuations in the delta-T at the probe are not noticeable in the performance ratio. This suggests that the internal heat transfer between the flow and return lines via the bridge plays a minor role in practice. Factors such as borehole geometry, backfill, and runtime make a much larger difference.
Findings:
In this test facility, the same bore diameter was used for the two probes compared (separatus and double-U). Furthermore, the backfill of the separatus probe was designed with less thermal conductivity, making the probe essentially "insulated. " Under all imaginable conditions, this is the worst case scenario for separatus. Overall, even under these less than ideal operating conditions, separatus still delivers very high performance, demonstrating its potential.
The measurement results from the "Pernter" system were ultimately used to derive design recommendations for simulation using tools such as EED and GHEtool. Based on the calculation model of a single-U probe, the parameters needed to be used to achieve the same effective thermal resistance in the borehole as measured for separatus were determined. A correction factor was introduced to account for the additional—albeit small—thermal transition between the warm and cold sides inside the pipe. More information on this topic can be found on the " Planning " page.
Key data of the system:
| Borehole and heat exchanger parameters | ||
| separatus | Double U 32 | |
| Borehole diameter | 146 mm | |
| Drilling method | Wash drilling | |
| depth | 70 m | |
| Dimensions (diameter x wall) | 50 x 3.1 mm | 32 x 3.0 mm |
