Analiza obnavljanja toplote pri izkoriščanju plitve geotermalne energije z geosondo

Svetina, Janja (author), Brenčič, Mihael (mentor), Prestor, Joerg (comentor)

Za alpski svet je značilna zapletena, močno nagubana in tektonsko spremenljiva geološka zgradba s plastmi, ki so za uporabo odprtih geotermalnih sistemov običajno premalo izdatne. Primernejša in bolj dostopna je uporaba toplotnih izmenjevalcev ali geosond. Srednja letna temperatura tal, ki pomembno vpliva na zahtevano dolžino geosonde, je v alpskih okoljih relativno nizka, vendar pa je za alpski svet tipična tudi večja količina padavin, ki kot del hidrološkega cikla vpliva na porazdelitev toplote v Zemeljski skorji. Namen magistrske naloge je bil s pomočjo izdelave numeričnega modela analizirati obnavljanje toplote tal v okolici geosonde z upoštevanjem vpliva infiltracije in toka podzemne vode. Na osnovi predhodno izvedenega geološkega in hidrogeološkega kartiranja sem izdelala konceptualni model za območje Črnega vrha nad Novaki (občina Cerkno) in ocenila poenostavljeno hidrogeološko bilanco raziskovanega območja. S programom Earth Energy Designer (EED 4.19) sem ocenila dolžino geosonde, s katero lahko pokrijemo energetske potrebe enostanovanjske stavbe. Numerično modeliranje sem izvedla v programskem orodju FEFLOW 7.0, in sicer za osem različnih scenarijev, ki upoštevajo različne hidrološke pogoje. Rezultati modeliranja so pokazali, da infiltracija padavin geološko podlago ohlaja in znižuje geotermalni gradient, kar se odraža v nižjih temperaturah delovne tekočine, vendar ima lahko pozitiven učinek na stabilizacijo sistema. Infiltracija vpliva tudi na dvig gladine vode, zaradi katere se lahko vzpostavi hidravlični gradient in pojavi tok podzemne vode. Slednji po ugotovitvah predhodnih študij izboljšuje učinkovitost geosonde. Na podlagi rezultatov modeliranja lahko izboljšano obnavljanje toplote v okolici geosonde pričakujemo, ko Darcyeva hitrost dosega vsaj 0,046 m/dan, kar je pogojeno z boljšo prepustnostjo tal.

• Language: Slovenian
• Keywords: plitva geotermalna energija, geosonda, numerično modeliranje, obnavljanje toplote, infiltracija, tok podzemne vode
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2019
• PID: 20.500.12556/RUL-107779
• COBISS.SI-ID: 1485662
• Publication date in RUL: 25.05.2019

SVETINA, Janja, 2019, Analiza obnavljanja toplote pri izkoriščanju plitve geotermalne energije z geosondo [online]. Master’s thesis. [Accessed 4 July 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=107779

Secondary language

• Language: English
• Title: Heat recovery analysis while exploiting shallow geothermal energy with a borehole heat exchanger

Abstract

Alpine space is characterized by a complex, strongly deformed and tectonically variable geological structure with layers that are usually insufficiently productive for the use of open-loop geothermal systems. More suitable and accessible is the use of borehole heat exchangers (BHEs). Mean annual soil temperature, which significantly affects the required length of the BHE, is relatively low in the alpine environment. However, higher precipitation amounts, which as a part of the hydrological cycle affect the distribution of heat in the Earth's crust, are also typical for the alpine world. The purpose of the master's thesis was, by using numerical model, to analyze heat recovery while exploiting shallow geothermal energy with a BHE and in particular to show the effects of rainwater infiltration and groundwater flow. On the basis of previously performed geological and hydrogeological mapping, I set up a conceptual model for the area of Črni vrh above Novaki (municipality of Cerkno) and estimated a simplified hydrogeological balance of the investigated area. The required length of BHE, that can cover energy demands of one-dwelling building, was calculated in Earth Energy Designer (EED 4.19) software. Numerical modeling was performed in FEFLOW 7.0 software for eight scenarios that take into account different hydraulic conditions. The results showed that rainwater infiltration decreases geothermal gradient and cools the model, which is reflected in lower temperature of the carrier fluid, however, it can have a positive effect on the stabilization of the system. Infiltration also affects a rise of water table, which may establish a hydraulic gradient and groundwater flow. According to preliminary studies, the latter improves efficiency of BHE. Based on the results of modeling, improved heat recovery can be expected when Darcy's velocity reaches at least 0.046 m/day, which is conditioned by better permeability of the ground.

• Keywords: shallow geothermal energy, borehole heat exchanger, numerical modeling, heat recovery, infiltration, groundwater flow