Development of a tool for the design of geothermal systems

Shallow geothermal energy is a promising renewable energy source for the sustainable, environmentally friendly, and economical use of the theoretically inexhaustible thermal energy available underground for heating and cooling buildings. Geothermal energy is therefore considered to be of great importance for decarbonizing the heating and cooling demand for buildings.
Especially in urban contexts, different geothermal systems can be utilized, but the knowledge about the applicability of the different systems is not widespread enough. The technologies for geothermal energy use are well established and show a high market maturity, but there is currently no widely accessible information platform that gives interested users an overview of the existing possibilities, offers a rough design or potential assessment and therefore allows for an initial feasibility analysis.
Currently, either project-specific, individual approaches are developed for geothermal systems, which require a profound expertise and represent a time-consuming planning task, or commercial programs are used, which usually only cover few isolated cases.
The project therefore essentially pursues two primary goals:

  1. To provide information as low-threshold as possible also for planners and contractors who are not specialized in the field of geothermal energy.
  2. The consideration and representation of as many systems as possible for the use of shallow geothermal energy in a single planning tool.

Site-specific data are required for the planning and design of geothermal systems. These include climate data (air temperature, solar radiation) on the one hand and (hydro-) geological subsurface data on the other.
The required climate data are available throughout Austria and are provided to the project by GeoSphere Austria. In the course of the project, the data is processed so that it is available as a simplified time series based on statistical parameters such as the mean value, standard deviation and amplitude for each grid cell.
The required subsurface data are currently not available for the whole of Austria. For this reason, a study area in the form of the Vienna metropolitan area (The city of Vienna and the greater Mödling-Baden-Schwechat area) are defined for the project. Within the project period, the subsurface data for the mentioned investigation area shall be collected (evaluation of the Viennese subsoil cadastre, evaluation of already performed thermal response tests, etc.). 
As a result, all site-related data (climate data and subsurface data) are available to potential users in the defined study area.
For the design of geothermal systems, the heating and cooling demand of the users is required by means of a time series. In the project, usage profiles are defined based on representative scenarios that EVN, as an energy supplier, can provide to the project.
In order to create an interface between the demand to be met (e.g. hourly heating and cooling demand in the annual cycle) and the actual geothermal system (borehole heat exchangers, energy geostructures, etc.), an energy flow scheme is used in the project. In the energy flow scheme, different operating scenarios can be modeled to determine how much energy must be provided from the modeled geothermal systems to meet the total energy demand.
Regarding the various possibilities of geothermal energy use, the planning tool provides for the integration of the following types of systems by modeling and simulating the individual types:

  • Energy geostructure: energy bottom slab
  • Energy geostructure: energy pile
  • Energy geostructure: energy diaphragm wall
  • Borehole heat exchanger
  • Thermal groundwater utilization
  • Thermal energy storage
  • Horizontal (slinky) collector

Users do not have to decide in advance for a certain type of geothermal energy system, but can determine the most suitable system for the respective application or evaluate different types of geothermal energy systems.
In the actual planning tool, the site-related climate data (air temperature, solar radiation) and (hydro-) geological subsurface data are linked with the energy demand in the form of a utilization profile as well as the described modules for different types of geothermal energy systems via the modeled energy flow scheme.
A validation of the planning tool is carried out on the basis of actual geothermal plants that are already in use or are in a late design stage.

Schematic representation of the design of the planning tool

© TU Wien, Institut für Geotechnik