In situ experimentation and numerical model validation of thermal flow in shallow crystalline rock, Otaniemi case

In situ experimentation and numerical model validation of thermal flow in shallow crystalline rock, Otaniemi case

Caballero Hernandez, Enrique (TU Delft Civil Engineering & Geosciences)

Heimovaara, T.J. (mentor)
Rinne, M. (mentor)
Siren, Topias (graduation committee)
Janiszewski, Mateusz (graduation committee)

Delft University of Technology

Applied Earth Sciences

Tackling the Challenges of a Solar Community Concept in High Latitudes

2017-11-14

Nowadays more attention to environmental-friendly sources of energy has been given, aiming to slow down and counteract the damage to the ecosystem product of the abuse of fossil fuels. Different technologies on energy production, solar, wind, tidal, geothermic, etc., have been researched with the additional challenge of how to store it.
From the different types of energy, heat represents a basic need in countries where the climate conditions lead to long and cold periods, namely countries at high latitudes where a big part of the produced energy is destined to household and district heating.
The Academy of Finland implemented the New Solar Community Concept project to research the development and application of alternative technologies for production and storage of energy. The use of the local geological domains has been considered as a possible solution for seasonal and long-term energy storage, specifically heat. Aalto University participates in Tackling the challenges of a Solar-Community Concept in High Latitudes by researching the seasonal storage of thermal energy in the ground simulating and assessing thermal flow for different borehole heat exchangers arrays.
To do this, numerical models have been implemented, special attention to the Weak Form Equations (WFE) and the Heat Transfer in Pipes (HTiP) models. These models are evaluated using the COSMOL® Multiphysics software, each of them with advantages and disadvantages over the other.
An in situ experiment has been performed in Aalto’s research tunnel to validate the results of the numerical models. The aim of the experiment was to assess the performance of the models based on the result comparison between the simulated and the observed data under controlled conditions.
The experiment consisted of a single U-pipe borehole heat exchanger operating under seasonal conditions. Two phases were defined, heating and cooling. In the first phase, a constant heat flux is provided to the rock by circulating a heated carrier fluid in the BHE. In the second phase, the circulation is stopped allowing the rock to cool down under normal conditions. The heat field in the rock was tracked with a monitoring borehole one meter away from the heat source. Several digital temperature sensors were installed at the monitoring point in customized equipment referred in this work as Thermal Multisensor Probes for this purpose.
The comparison made between model and observed results returned an acceptable accuracy of the predicted values of the models for the heat flow in the rock mass. Additionally, it was identified the WFE model can be improved by calibrating the borehole thermal resistance parameter in the equations, parameter that must come from experimental data. Finally, it was seen that the few discontinuities present across the boreholes had a low impact on the flow of heat through the rock for this experiment.
Currently, the tuning of the numerical models is being performed at Aalto University by increasing the weight of different parameters in the models matching the results of the experimentation process.

Borehole Heat Exchanger (BHE)
numerical modelling
model validation
in situ experiment
heat flow
seasonal storage

http://resolver.tudelft.nl/uuid:de329bb1-e218-40ff-9016-7c34b8ea5fd5

Student theses

master thesis

© 2017 Enrique Caballero Hernandez