The first realised test facility has been since 6. December 2023 in operation. The single-family house from the 90-ers was previously heated with an aging Gastherme. Just when the owners of the home in Altach, Austria decided to modernize the heating, separatus was looking for a suitable project nearby to realise a first drilling for test purposes.
In the previous planning, a nominal heating load of 7.5 kW was determined using an available energy certificate. The family opted for an IDM iPump T 3-13 modulating heat pump. The integration into the existing heat dissipation system combined with radiators and floor heating took place directly, without buffer storage. The heat pump also treats hot water in the integrated drinking water reservoir.
The surface is peaty in the upper layers. At depths between 9 and 30 metres, gravel and sand are predominant. Subsequently, alternating silt and gravel sand layers follow. On the last 10 metres, a layer of clay was encountered. Drilling was carried out in total to 70 metres depth. Groundwater came in from 4 metres – due to the hydrogeological situation in the entire environment, abundant flowing groundwater is expected.
The comparison bore is equipped with a double U-tube BHE with 32 mm pipe diameter. This double U-tube BHE can be switched to a single-U probe at any time by means of shut-off elements. In general, both borehole heat exchangers were made accessible via shafts to carry out temperature measurements or the like. In a distribution box manufactured by Geser Erdwärme, the probe feed lines are equipped with heat metres. Motorized regulating valves are also controllable – thus can be regulated according to volumetric flow rate or power as required. The data is continuously recorded and thus any comparisons and evaluations between the probe types are possible.
This embodiment allows the direct comparison of these two probe types and shows the impressive performance of the separatus probe.
Performance data
separatus in individual operation:
According to design guidelines, it is not intended to operate the geothermal installation with only one borehole heat exchanger (BHE). For test purposes, however, it is interesting to observe how well the separatus probe performs in individual operation. Even if the heat pump requires very high extraction capacities of 100 watts per metre, separatus delivers relatively high temperatures. If the heat pump then goes down to a level of about 50 watts per metre, separatus shows enormous stability. Temperatures recover again and again and do not drop further even after a longer period of time, which is of course also an indicator of good geology.
separatus in comparison:
separatus lies in this test system in the heat transfer between a single U and a double U.
In comparison between separatus and the double U, different scenarios were played, including different temperature spreads (“Delta-T”) between Vor- and return. Short-term fluctuations of the delta-T at the probe are not noticeable in the power ratio. This allows the conclusion that the internal heat transfer between the pre- and return via the web plays a minor role in practice. Factors such as well geometry, borehole grouting and runtime make a much bigger difference.
Findings:
In this test plant, the same drilling diameter was executed for the two compared probes (separatus and double U). In addition, the borehole grouting of the separatus probe was made thermally less conductive, so the probe is quasi “insulated”.Under all conceivable conditions, this is the “worst case” for separatus.Overall, separatus still delivers a very high performance even under these not entirely ideal operating conditions and thus shows its potential.
From the measurement results of the "Pernter" system, the design recommendations for the simulation with tools such as EED or GHEtool were finally derived. Based on the calculation model of a single U probe, it was determined which parameters must be used to obtain the same effective thermal resistance in the borehole as measured for separatus. A correction factor was introduced to account for the additional – albeit minor – thermal transition between the warm and cold sides inside the tube. More on the subject is on the pagePlanning“to be found.”
Basic parameters of the installation:
