Thermal and physical characteristics of soils in Cyprus for use in shallow geothermal energy applications

Abstract

Ground heat exchangers in conjunction with shallow geothermal energy system applications have received significant attention in the case of renewable energy. Soil thermal properties such as thermal conductivity and specific or volumetric heat capacity are important aspects for the design of such systems, affecting the performance. They can be obtained with the use of empirical prediction models, laboratory tests and/or in situ tests. Laboratory tests can be performed either under steady-state or under transient conditions and have the advantage of requiring small volumes of soil and producing fast results. There are many types of heat probes commercially available, with limited—though—comparative assessment available in the literature. The current paper deals with the assessment of ground characteristics of seven samples of soil and rock collected from a certain area in the Mediterranean island of Cyprus. Such properties are the thermal conductivity, the thermal diffusivity, the volumetric heat capacity, but there are some other physical properties also. The laboratory testing was done under transient conditions and included measurements taken by two needle probes and one surface probe from two different commercial apparatuses. Comparison of the obtained results for the thermal properties of the samples was made and was also supported by numerical simulations using the COMSOL Multiphysics software through a finite element analysis method on the convection–diffusion equation for heat transfer. Laboratory testing on physical properties of the samples such as moisture content, specific gravity, permeability and particle size distribution was also performed, yielding useful results related to the assessment of the thermal properties.

Keywords

Ground thermal conductivity / Thermal conductivity methodology / Thermal conductivity laboratory thermal test / Soil thermal properties / Heat probe comparison

References

[1] Abu-Hamdeh N, Khdair A, Reeder R. A comparison of two methods used to evaluate thermal conductivity for some soils. Int J Heat Mass Transf, 2001, 44: 1073-1078

[2] Alrtimi A, Rouainia M, Haigh S. Thermal conductivity of a sandy soil. Appl Therm Eng, 2016, 106: 551-560

[3] Aresti L, Christodoulides P, Florides G. A review of the design aspects of ground heat exchangers. Renew Sustain Energy Rev, 2018, 92: 757-773

[4] ASTM (2014) D5334-14, Standard test method for determination of thermal conductivity of soil and soft rock by thermal needle probe procedure. ASTM International, West Conshohocken, PA. https://www.astm.org/

[5] Christodoulides P, Florides G, Pouloupatis P. A practical method for computing the thermal properties of a ground heat exchanger. Renew Energy, 2016, 94: 81-89

[6] Christodoulides P, Aresti L, Florides G. Air-conditioning of a typical house in moderate climates with ground source heat pumps and cost comparison with air source heat pumps. Appl Therm Eng, 2019

[7] De Vries D. Van Wijk WR. Thermal properties of soils. Physics of plant environment, 1966 2 Amsterdam North Holland Publishing Company

[8] DeGroot D, Ostendorf DW, Judge A. In situ measurement of hydraulic conductivity of saturated soils. Geotech Eng J SEAGS AGSSEA, 2012, 43: 61-72

[9] Farouki OT (1981) Thermal properties of soils. Hanover NH

[10] Florides G, Kalogirou S. First in situ determination of the thermal performance of a U-pipe borehole heat exchanger, in Cyprus. Appl Therm Eng, 2008, 28: 157-163

[11] Gehlin S. Thermal response test: method development and evaluation, 2002 Sweden Luleå Tekniska Universitet

[12] Gemant A. The thermal conductivity of soil. J Appl Phys, 1950, 21: 750-752

[13] Gemant A. How to compute thermal soil conductivities. ASHVE J Sect Heat Pip Air Cond, 1952, 24: 122-123

[14] Gustafsson (1991a) Device for measuring thermal properties of a test substance-the transient plane source (TPS) method. Patent no. 5,044,767

[15] Gustafsson SE. Transient plane source techniques for thermal conductivity and thermal diffusivity measurements of solid materials. Rev Sci Instrum, 1991, 62: 797-804

[16] Iosif Stylianou I, Tassou S, Christodoulides P Measurement and analysis of thermal properties of rocks for the compilation of geothermal maps of Cyprus. Renew Energy, 2016, 88: 418-429

[17] Jiřičková M, Pavlík Z, Fiala L, Černý R. Thermal conductivity of mineral wool materials partially saturated by water. Int J Thermophys, 2006, 27: 1214-1227

[18] Kalogirou SA, Florides GA, Pouloupatis PD Artificial neural networks for the generation of a conductivity map of the ground. Renew Energy, 2015, 77: 400-407

[19] Kerstan MS. Thermal properties of soil, 1949 Minneapolis University of Minnesota

[20] Koohi-Fayegh S, Rosen MA. Optimization of seasonal storage for community-level energy systems: status and needs. Energy, Ecol Environ, 2017, 2: 169-181

[21] Li H, Song J, Sun Q A dynamic price model based on levelized cost for district heating. Energy Ecol Environ, 2019, 4: 15-25

[22] Low JE, Loveridge FA, Powrie W, Nicholson D. A comparison of laboratory and in situ methods to determine soil thermal conductivity for energy foundations and other ground heat exchanger applications. Acta Geotech, 2015, 10: 209-218

[23] Mickley AS. The thermal conductivity of moist soil. Am Inst Electr Eng Trans, 1951, 70: 1789-1797

[24] Midttømme K, Roaldset E. Thermal conductivity of sedimentary rocks: uncertainties in measurement and modelling. Geol Soc Lond Spec Publ, 1999, 158: 45-60

[25] Mogensen P (1983) Fluid to duct wall heat transfer in duct system heat storage. In: Proceedings of the international conference on subsurface heat storage in theory and practice. Stockholm, Sweden

[26] Nusier OK, Abu-Hamdeh NH. Laboratory techniques to evaluate thermal conductivity for some soils. Heat Mass Transf und Stoffuebertragung, 2003, 39: 119-123

[27] Ramos R, Aresti L, Christodoulides P Assessment and comparison of soil thermal characteristics by laboratory measurements. Springer Ser Geomech Geoeng, 2018

[28] Rees S, Adjali M, Zhou Z Ground heat transfer effects on the thermal performance of earth-contact structures. Renew Sustain Energy Rev, 2000, 4: 213-265

[29] Singh DN, Devid K. Generalized relationships for estimating soil thermal resistivity. Exp Therm Fluid Sci, 2000, 22: 133-143

[30] Smith WO. The thermal conductivity of dry soil. Soil Sci, 1942, 53: 435-440

[31] Tokoro T, Ishikawa T, Shirai S, Nakamura T. Estimation methods for thermal conductivity of sandy soil with electrical characteristics. Soils Found, 2016, 56: 927-936

[32] van Rooyen M, Winterkorn HF. Theoretical and practical aspects of the thermal conductivity of soils and similar granular systems. US Highw Res Board Bull, 1957, 159: 58-135

[33] Vieira A, Alberdi-Pagola M, Christodoulides P Characterisation of ground thermal and thermo-mechanical behaviour for shallow geothermal energy applications. Energies, 2017

Funding

COST Action(TU1405)