Background

Near-surface geothermal energy offers an ideal, sustainable source for heating and cooling, with very high, largely untapped potential, both as a standalone technology for supplying individual buildings and in cold local heating networks with decentralized energy supply in settlements and districts. With collector systems at depths of up to five meters, these geothermal installations benefit from advantages such as straightforward, low-cost installation and simplified permitting requirements. The use of near-surface geothermal energy in cold local heating has increased rapidly in recent years as part of the energy transition. However, because of the limited knowledge about the condition of the heat transfer medium in geothermal systems, and insufficient safeguarding, reservations about using glycol-based fluids are growing. The MoniGeoFluid project aims to introduce quality assurance tools for automated monitoring of geothermal collector systems, including long-term control of the source side, or brine loop. Based on measured signals, the system triggers an alarm and safeguards the system if critical values are exceeded, as required under AwSV. Comprehensive system monitoring, together with the integration of forecast values, makes it possible to intervene in a targeted way during operation and to improve overall system performance. The MoniGeoFluid measurement system to be developed is intended for use not only with glycol-based fluids, but also with new glycol-free heat transfer media. The project aims to deliver a cost-effective and reliable all-in-one solution.

Project Objective

The MoniGeoFluid project will be submitted under the 29th call of the IraSME program. The German-Austrian project consortium consists of Salzburg University of Applied Sciences, the planning firm RGK e.U., and TB Stampfer GmbH (all Austria), together with AQUA-CONCEPT Gesellschaft für Wasserbehandlung mbH (aqua-concept) and ipLON Solutions GmbH with its associated partner Stadtwerke Schleswig-Holstein GmbH (Stadtwerke SH) (all Germany). The project partners will jointly determine the baseline parameters using existing systems. Building on the physical and chemical parameters defined by aqua-concept, the consortium partners, including ipLON and Stadtwerke SH, will work closely together to develop a concept for selecting and implementing suitable measurement technology in geothermal systems. In parallel, measurement systems and a prototype geothermal installation will be set up in Austria, tests will be carried out, and measurement data will be collected. During the operational optimization phase, control limits will be defined, interfaces to the building will be established, and the measured values will be verified. The system will be filled with several heat transfer fluids, and the thermal output will be compared with the measured parameters. In addition, the aging behavior of the heat transfer fluids will be monitored to assess their sustainability. A radio-controlled early-warning system will be designed and integrated. Interface optimization and the scaling of individual systems will be used to evaluate transferability to cold local heating or anergy networks.

Insights

The project showed that the heat transfer fluids used in the systems studied maintain largely stable thermophysical performance over multiple years of operation. Deviations from manufacturer specifications, as well as differences between individual products, are measurable, but generally remain within a moderate range and can largely be attributed to different inhibitor packages and temperature ranges. Certain key parameters, such as speed of sound, viscosity, and electrical conductivity, proved particularly sensitive to changes and are therefore well suited as indicators for aging processes and condition assessments of the fluids.

Using a laboratory test rig, the measurement accuracy of heat meters was systematically analyzed. The evaluations show that uncertainty in flow measurement has a dominant impact on the overall deviation in heat quantity determination, while temperature measurement errors play a smaller role within typical operating ranges. In addition, real-world systems, ranging from single-family homes to multifamily buildings and a cold local heating network, were instrumented with extended sensor technology and a structured monitoring system. The evaluation of these field data demonstrates that operational anomalies, such as gradual pressure losses, energetically unfavorable operating strategies, or potentially corrosion-critical conditions, can be detected at an early stage. Overall, the results make clear that a purpose-designed monitoring and evaluation concept, consisting of suitable sensors, automated data acquisition, and systematic analysis, can make a significant contribution to improving operational safety, efficiency, and predictive maintenance planning for geothermal systems, even if certain sensor principles in cold brine have limited long-term applicability and therefore need to be supplemented by targeted laboratory testing.