Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

Abstract

Increasing use of the ground as a thermal reservoir is expected in the near future. Shallow geothermal energy (SGE) systems have proved to be sustainable alternative solutions for buildings and infrastructure conditioning in many areas across the globe in the past decades. Recently novel solutions, including energy geostructures, where SGE systems are coupled with foundation heat exchangers, have also been developed. The performance of these systems is dependent on a series of factors, among which the thermal properties of the soil play a major role. The purpose of this paper is to present, in an integrated manner, the main methods and procedures to assess ground thermal properties for SGE systems and to carry out a critical review of the methods. In particular, laboratory testing through either steady-state or transient methods are discussed and a new synthesis comparing results for different techniques is presented. In situ testing including all variations of the thermal response test is presented in detail, including a first comparison between new and traditional approaches. The issue of different scales between laboratory and in situ measurements is then analysed in detail. Finally, the thermo-hydro-mechanical behaviour of soil is introduced and discussed. These coupled processes are important for confirming the structural integrity of energy geostructures, but routine methods for parameter determination are still lacking.

Energy performance of ground heat exchangers embedded in diaphragm walls: Field observations and optimization by numerical modelling

“…On the front and back faces, being symmetry planes, an adiabatic condition is prescribed. The In absence of both on-site and laboratory thermal characterization, the saturated soil properties are calculated as arithmetic means of the properties of solid and water components, weighed by the volume fractions [18,19]. An average porosity equal to 0.47 is assumed from surveying reports and the properties of the solid grains are based on literature data [e.g.…”

Explicit multipole formulas and thermal network models for calculating thermal resistances of double U-pipe borehole heat exchangers

“…The approaches to determine borehole thermal resistance include both experimental (Vieira et al 2017) and theoretical (Javed and Spitler 2016;Lamarche et al 2010) methods. The often-used experimental approach to measure the borehole thermal resistance is by means of an in situ thermal response test (TRT) (Spitler and Gehlen 2015).…”

Explicit Multipole Formulas for Calculating Thermal Resistance of Single U-Tube Ground Heat Exchangers

“…Ground thermal conductivity (λ) and borehole thermal resistance (R b ) are the two principal parameters that govern the heat transfer mechanism of a borehole heat exchanger, and thus influence the sizing and performance of the overall GSHP system [2]. The heat transfer outside the borehole boundary is dictated by the thermal conductivity of the ground, whereas the heat transfer inside the borehole is characterized by the borehole thermal resistance between the heat carrier fluid and the borehole wall.…”