Innovative Solutions for Improving the Heat Exchange in Closed-Loop Shallow Geothermal Systems

Giovanni Floridia,Giuseppe M Belfiore,Salvatore Iuculano,Marco Viccaro,Federica Blandini

doi:10.3390/en14010108

Giovanni Floridia, Giuseppe M Belfiore + Show 3 more

Open Access

https://doi.org/10.3390/en14010108

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Abstract

Thermal conductivity, hydraulics properties and potential use in low-enthalpy geothermal applications of single and double U geothermal probes enhanced with carbon fibre are discussed in this work. Although the efficiency of a shallow geothermal installation is chiefly based on chemical and physical characteristics of rocks and hydrogeological aspects of the subsurface, the total heat extracted from the subsoil also depends on the intrinsic thermal characteristics of probes. New configurations and solutions aimed at enhancing the performance of components are therefore of considerable interest in this field of research. As a consequence of the economic and versatility advantages of the components, geothermal probes have been generally developed with materials like polyethylene, which presents, however, isolating behaviour that does not allow ideal heat exchange in ground source heat pump systems (GSHP). Innovative combinations of different materials are therefore necessary in order to improve thermal conductivity and to preserve the exceptional workability and commercial advantages of the finest elements available on the market. This work presents results coming from experimental tests involving standard polyethylene geothermal probes integrated with radial rings of polyacrylonitrile-based carbon fibre (PAN). Our evaluations are aimed at finding the best solutions for thermal exchange and adaptability with respect to traditional systems. Hydraulic and thermal performances and the response in a geo-exchange system have been verified. The new solutions appear to be highly suitable as geothermal exchangers in shallow geothermal systems and contribute to significantly reduce the total costs pertaining to the drilling operations.

Highlights

Within the current global energy context, the constant increase in energy demand leads to a redefinition of the energy supply models [1,2]
The test circuit consists of a PN 16 polyethylene sample tube with diameter of 32 mm and length of 3 m, accompanied by 5 carbon fibre (CF) rings 2 cm wide, radially arranged and spaced at steps of 50 cm from each other (Figure 2)
Pure graphite and the hybrid allows a more exchange, compared toCF-I50 the standard probe allowed an increase in system heat exchange of a about

Summary

Introduction

Within the current global energy context, the constant increase in energy demand leads to a redefinition of the energy supply models [1,2]. The thermal energy stored in the shallowest portion of the Earth’s crust (100–150 m depth) is very high, since the soil temperature remains constant throughout the year with values comparable with the average annual temperatures at the surface depending on the latitude [1,3] This paradoxically represents an optimal condition for the supply of thermal energy through the use of heat exchanger systems with open or closed-loop configurations [3]. Significant thermal dissipation occurs between the soil, the bentonitic grout as filler and the heat exchanger, which causes reduction in performances of the entire system This means that higher performances of the whole SGS installation can be only accomplished if characteristics of each of the above-mentioned components turns out to be enhanced. Experimentation of new materials for improving the characteristics of standard geothermal probes has been extremely limited throughout recent years

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