Deep geothermal resources for heat supply and waste heat potentials were assessed and measured for a high-temperature dairy plant. For the industrial waste heat, a borehole heat exchanger (BHE) seasonal storage was configured and simulated after an extensive investigation of shallow geothermal resources. We developed a concept for the subsequent use of the residual and waste heat from the plant in a low-temperature heating and cooling (LTHC) grid for the neighbouring former military camp “Martinek-Kaserne” with a future use as mixed-use urban quarter were investigated in two projects. The modelling of the deep geothermal resources showed that of the three potential reservoirs one is most feasible for geothermal heat supply with temperatures between 129 and 146 °C, which could be used with a high-temperature heat pump for process heat. The waste heat in all sub-processes of the dairy plant were measured over 18 months to identify the most suitable waste heat streams with regard to temperature and continuity. The results showed that 25 % of the waste heat from a sub-process of the plant (fresh products logistics) is sufficient to provide heat for the adjacent LTHC grid with a total energy demand of 3428 MWh per year. The simulation of the BHE field resulted in 96 BHE with 180 m depth for a dis-/charging capacity of 643.7 MWh and 20 decentral heat pumps in the buildings. The BHE field operates quite balanced with only 12.8 MWh of difference in the annual balance. The results of the feasibility study for deep and shallow geothermal resources, and the assessment of the industrial waste heat show that the whole cascade of high-temperature heat for industry to low-temperature heat for the LTHC grid could be realized at the investigated site.

The focus of the experimental work was on shallow spiral geothermal heat exchanger configurations. Real-scale experiments were carried out for vertically oriented spiral collectors (helix) in sand and soil. One objective was to develop a measurement concept in laboratory environment to create a framework for a validated database. This database serves as the basis for further and new development of engineering design tools. To achieve the highest possible data-point density in the observed environment, temperature sensors and a fiber-optic temperature measurement system (DTS) were used. Soil probes were taken in situ before and after the measurements and analyzed at a thermophysical laboratory to determine material properties. The heat flow was controlled by an electric heating cable, which was installed in the form of a spiral-shaped heat exchanger in a 1 m³ container. To guarantee constant boundary conditions, the measurements were carried out in a climate chamber at a defined ambient temperature. The evaluation of the transient response behavior is spatially resolved. The results are coordinate-based temperature points, which describe temperature gradients in all axes of the container over time, which are combined with known soil properties. The collected data was used to develop computational fluid dynamic (CFD) models, which are used to extend the variety of geometry and soil configurations for developing new design tools.

The Velingrad geothermal field is one of the largest in Bulgaria. Its water is widely used for balneology, spa tourism, sports, heating and other purposes. An interesting problem related with the operation of thermal water is the process of scaling or corrosion of equipment when the water passes through it. Specifically, for the geothermal field, a saturation index is used to assess whether the water is saturated or unsaturated, with regard to the respective mineral phase. The obtained results for this coefficient are compared with those for the existing water sources from the geothermal field and, depending on the location, temperature and other physicochemical differences, their variation is analyzed.

Urban heat islands (UHI) occur especially in inner-city areas due to small green areas, an excess of high solar heat, and low air circulation. One solution is the “harvesting” of excess solar urban heat through shallow absorber ducts, which are then used in borehole heat exchanger (BHE) fields for later use for heat or cold storage. Knowing the thermophysical properties of the subsurface as accurately as possible is of great importance in the design and configuring of a borehole heat exchanger field as a thermal energy storage system. In this study, a subsoil drill core from a BHE, with a depth of 80 m, was used to determine temperature dependent effective thermal conductivity based on the heat flow meter method, the specific heat capacity based on differential scanning calorimetry, and thermal expansion based on dilatometry in moist and dry states. The results have shown that the actual moisture content of the subsoil sample has a strong impact on the thermal conductivity, as well as on the heat capacity. Thermal expansion measurements have shown the influence of the drying process on the shrinkage of drill core samples and the low thermal expansion of the dry subsoil itself.