In Situ Experiment and Numerical Model Validation of a Borehole Heat Exchanger in Shallow Hard Crystalline Rock

Mateusz Janiszewski,Lauri Uotinen,Enrique Caballero Hernández,Ilmo Kukkonen,Mikael Rinne,Topias Siren

doi:10.3390/en11040963

Mateusz Janiszewski, Lauri Uotinen + Show 4 more

Open Access

https://doi.org/10.3390/en11040963

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Journal: Energies	Publication Date: Apr 17, 2018
Citations: 8	License type: CC BY 4.0

Affiliation: Aalto University, University of Helsinki

Abstract

Accurate and fast numerical modelling of the borehole heat exchanger (BHE) is required for simulation of long-term thermal energy storage in rocks using boreholes. The goal of this study was to conduct an in situ experiment to validate the proposed numerical modelling approach. In the experiment, hot water was circulated for 21 days through a single U-tube BHE installed in an underground research tunnel located at a shallow depth in crystalline rock. The results of the simulations using the proposed model were validated against the measurements. The numerical model simulated the BHE’s behaviour accurately and compared well with two other modelling approaches from the literature. The model is capable of replicating the complex geometrical arrangement of the BHE and is considered to be more appropriate for simulations of BHE systems with complex geometries. The results of the sensitivity analysis of the proposed model have shown that low thermal conductivity, high density, and high heat capacity of rock are essential for maximising the storage efficiency of a borehole thermal energy storage system. Other characteristics of BHEs, such as a high thermal conductivity of the grout, a large radius of the pipe, and a large distance between the pipes, are also preferred for maximising efficiency.

Highlights

Solar thermal energy is a renewable energy source that can be used to cover space heating and domestic hot water demand in buildings
It has to be noted that the goal of this study was not to quantify the exact temperature field and its absolute values, but to compare the simulated and measured temperature changes caused by the thermal performance of a short single heat exchanger using the presented numerical modelling approach
The goal of this study was to validate the proposed methodology and compare it with other methods from the literature to evaluate its applicability for numerical simulations of seasonal thermal energy storage in rocks using boreholes

Summary

Introduction

Solar thermal energy is a renewable energy source that can be used to cover space heating and domestic hot water demand in buildings. The solution is to collect the thermal energy in low demand periods, store it seasonally using one of the underground thermal energy storage (UTES). Methods, and use it during times of high demand. A viable option for storing the energy is the borehole thermal energy storage (BTES) method that utilises an array of borehole heat exchangers (BHE) installed in the ground, which serve as the storage medium [1]. The goal of this study was verification of the Heat Transfer in Pipes (HTiP) modelling approach of BHE that will be used to model large BTES systems.

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