Search

Knowledge of thermal behaviour around and throughout Borehole Heat Exchangers (BHEs) is essential in designing a low enthalpy geothermal plant. In particular, the the kind of grout used in sealing the space between BHE walls and the pipes is fundamental to optimize the heat transfer and minimize the thermal resistance, promoting the reduction of total drilling lengths and installation costs. A comparison between grouts with different thermal conductivities coupled with simplified hydro-geological contexts were modelled over 212 days (typical one-year heating for continental climates). These data allowed for a sensitive analysis taking into account a different flow rate through pipes, as well. In groundwater transient conditions, porous lithologies enabled obtaining obtaining greater heat power extractions with increasing the thermal conductivity of grouts (until 105.91 W/m) if compared with limestone (until 32.09 W/m) or clayey silt deposits (until 6.74 W/m). Increasing of the inlet flow rates through the pipe greatly improves the final heat power extraction. In other hydro-geological contexts the situation is different and may depend on different factors for which using more performing grouts does not increase the final heat power extraction.

Several soil improving systems are available to increase the geotechnical properties of low resistance soils and increase the stability of overlaying constructions. Most of the already available methods make use of injections of more compacted material inside the ground, like: micro-piles, sand compaction piles, stone columns or grouting. Most of these solutions requires vibrations and rotary drilling, which could compromise soil properties and overlaying building integrity. Recently an innovative soil improving system by injections of a sand/gravel mixture was developed by Novatek® through mechanical preload of the mixture by compression adopting a hydraulic jack. The advantage of this last system with respect to available methods is the absence of vibrations and rotary drilling operations. In this study, the application of this system is documented in a first trial test site in the central Po plain (Italy). Description of the system and of the executed injections are reported. Characteristics of the ground before and after injections are compared, using both geotechnical and geophysical tests, in order to evaluate the system performances, which were also ascertained with direct verification through an explorative trench. The first results reported, even if for limited application depths, highlight the good potentialities of the improving system with respect to the increase of geotechnical parameters in the treated soil.

Underground Thermal Energy Storage systems have showed to be a useful and increasing technical solution for covering heating and cooling and domestic hot water buildings' demand. Thermal influence of these plants is however not still debated as it deserves and correct monitoring strategies appear to be of major importance both to better understand processes and to highlight their environmental effects into high populated areas. Litho-, hydro- and bio-sphere can indeed be adversely affected by temperature variations induced in the underground by heat storage applications. For this purpose, a geophysical monitoring approach using time-lapse electrical resistivity measurements contemporary to analogical simulations is here tested at laboratory scale. Results of the experiments are reported comparing measured apparent resistivity with direct temperature measurements and numerical simulations of heat propagation. Data presented confirmed that electrical resistivity has powerful relation with temperature variation in monitored media. In addition, they showed that also without performing data inversion valid temperature estimation can be carried out. Post-processing calibration of apparent resistivity data showed to be in acceptable agreement with both temperature measurements and numerical simulations. Simple apparent electrical resistivity variations appear therefore to be a promising, economic, quick and non-invasive tool for mapping thermal modifications induced in the underground by shallow geothermal applications.

The seasonal storage of thermal energy in the ground is a useful application able to provide H&C and DHW demand of commercial or residential buildings. Several examples in Canada and Northern Europe demonstrated the reliability and convenience of these systems in terms of both energy and economic savings, but more demonstration sites are however necessary. The surrounding litho-, hydro- and bio-sphere are influenced by the plant's activity and a trustworthy supervision of the temperature field would bring advantages to both the environment and the system's efficiency. Usually numerical modeling is used to forecast the system behavior but results of simulations can be strongly dependent from assumed material characteristics and should be strictly calibrated on real data. To better understand thermal processes in the ground related to thermal injection and thermal storage, a field scale BTES living lab was build up nearby Torino (Northern Italy) within unsaturated alluvial deposits. Results show that approximately 9.1 GJ were transferred to the ground during the first year, raising the undisturbed temperature by 2 °C, and that a correct comparison of monitoring data and numerical simulations can be obtained following a specific site characterization.