Geothermal heat pumps and heat piles are energy efficient means to heat and cool buildings. Heat piles are embedded in existing foundation elements, which generally store and conduct heat better than the surrounding soil. Geothermal heat pumps, on the other hand, are embedded directly in the soil, can be designed independently of the constraints existing foundation, and can take advantage of groundwater flow to help maintain a more constant temperature.
This planning visit to the Swiss Federal Institute of Technology, Lausanne (EPFL) will explore opportunities to collaborate on two important research questions regarding these technologies. The first is the effect of the repeated heating and cooling cycles on soil properties. Depending on the type and state of a given soil, these cycles may strengthen or weaken the soil, and may cause expansion or contraction of the soil, affecting the foundation and substructures of the buildings that use these systems. The second question is the comparative efficiency and cost effectiveness of these energy geostructures.
A planned outcome of the visit is competitive proposals on the US and Swiss sides for a collaborative numerical and experimental program to study these questions. Using an existing heat pile at the Swiss Federal Institute of Technology, Lausanne (EPFL), and heat pumps planned at University of Illinois at Chicago, we will monitor the performance and changes in soil properties over time. We will then develop models to capture the observed behavior. The broader impacts of the planning visit and follow-up research include: better understanding of the behavior of soil and changing conditions, improved computer models for this behavior, and tools to evaluate the efficiency and effects of different energy geostructures. Ultimately, this research will lead to more economical and more energy efficient ways to heat and cool buildings. In addition, the project will support a junior faculty member and provide an American undergraduate student with a first international research opportunity.
. The first was to learn more about the different technologies used in geothermal energy production on Switzerland. Secondly, we hoped to learn more about the specific research accomplished and in progress by Professor Laloui and his group at the Swiss Federal Institute of Technology (EPFL). Finally, we looked for significant ways to build a collaboration between our research group and his. We began by discussing the work that Professor Laloui and his group were conducting in the area of heat piles. These are foundation elements that support a building, but also contain pipes that circulate coolant fluid. As part of a heat pump system, they become a very efficient means of heating and cooling buildings. We were able to discuss the experimental project underway at EPFL. We examined diagrams of the setup and sensors distribution to monitor the structure, as well as photographs of the installation procedure. We also had an opportunity to visit their experimental lab and view their soil testing equipment. Along with standard soil testing equipment, there were some custom devices. The most important for our research was a temperature-controlled triaxial test, which could monitor the interaction of soil mechanical behavior such as shear strength with temperature changes. After several discussions, most of our effort turned the deep geothermal heating. For this method of extracting energy, shafts are drilled into the ground, often several miles, and fluid is circulated to recover heat from these depths. This heat may either be used to generate electricity or provide heating for large groups of buildings. Part of the process for creating these systems is to send highly pressurized fluid into the ground to open naturally occurring fractures or create new ones to improve the fluid flow and heat recovery in the system. Since the principal investigator has experience modeling propagating fractures and rock, this area appeared to be a good starting point for collaboration. It was agreed that the groups would submit joint proposals in this area, with our groupâ€™s proposal to the National Science Foundation (NSF) to be submitted in September 2012. There were several broader impacts to the proposal. The discussions resulted in an exchange of information on the state of geothermal energy production in the two countries. A minority undergraduate student participated in the project, as part of a yearlong investigation of geothermal heat pumps that he conducted. The student was exposed to research practices and computer modeling techniques for geothermal systems.