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unilogo Universität Stuttgart
Institute of Hydraulic Engineering

Research: VEGAS - Research Facility for Subsurface Remediation

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Influence of heat pump operation on potential freezing of bore hole heat exchanger grouts
Project manager:Jürgen Braun, Ph.D.
Research assistants:Dipl.-Ing. Simon Kleinknecht
Giulia Giannelli, M.Sc.
Duration:1.11.2014 - 31.12.2015

This project is part of the research area:
Measurement techniques and site investigation


Publications: Link


During the utilization of borehole heat exchangers (BHE) freeze-thaw-cycles may cause damages to the injected grout of the borehole heat exchangers and also to the surrounding porous media. To prevent a potential freezing of a BHE, the minimal inflow temperature of the BHE is restricted to minus 3°C. This minimal temperature was defined conservatively based on empirical values and numerical model calculations. However, no detailed experimental studies of temperature gradients and isotherms inside the BHE space are available, which could support (question) this regulation.
A new BHE, set up in one of the large VEGAS containers will be equipped with sensors at a high spatial resolution both within the BHE itself and its immediate surroundings. Based on a number of loading cases this new set up will for the first time allow for the detailed spatial and temporal investigation of temperature profiles and gradients in the BHE zone. Focus of the study is on the one hand to determine under which conditions a freezing of the BHE grout occurs and on the other hand to describe possible utilization scenarios, which ensure a frost-free use of the BHE while the heat pump is used at a very high capacity.