Geothermal potential and sustainable use of karst groundwater in urban areas–Belgrade, capital of Serbia case study

The increase in energy demand due to urban expansion and migration to urban areas has a negative impact on the environment and the city budget. Development plans of cities are more frequently based on the implementation of energy efficiency measures, which among other things include the use of renewable energy sources. In the area of Belgrade, research was conducted aiming for assessing the geothermal potentiality of the field and defining the possibility of groundwater exploitation. The research has been directed to groundwater formed in karst aquifers. Geothermal field evaluation was preceded by the formation of geological and hydrogeological bases, then, the development of a conceptual model of karst distribution in the city area and the systematization of data measured in the observation well network. The potentiality assessment is followed by defining of the conditions and possibilities of the exploitation of karst water as a form of geothermal energy in heat pump systems. In the exploitation of karst water in the city, it is significant to establish mechanisms of sustainable management, especially in terms of protection of resources. In recent years, there has been recorded a constant increase in the number of heating and cooling systems of buildings using groundwater as an energy source in the territory of Belgrade. Potential causes of the negative impact of exploitation of karst water are the overexploitation of resources, creating of the effect of "thermal feedback" as a result of incompetent disposition, namely restoring of groundwater to the aquifer.

Low-enthalpy geothermal energy resources from groundwater in fluvioglacial gravels of buried valleys

Low-enthalpy geothermal energy can be generated from groundwater in gravels infilling buried valleys formed during the Pleistocene glaciation, when the sea level was significantly lower than at present. Where buried valleys underlie floodplains of present-day rivers, flowing through major cities, a [`]heat island' effect can generate slightly enhanced temperatures in shallow groundwater. This groundwater can be utilised for space heating buildings by passing it through a heat pump, and the chilled water then used as a heat exchanger to satisfy cooling requirements of the building. For flow rates of 20 l s-1, and a temperature reduction of 8 °C in the heat pump, a 672 kW heating resource can be generated, sufficient to heat buildings of 11,000 m2 floor area. A cooling resource of 336 kW is also available. Potentially, this geothermal resource could be utilised without the [`]heat island' effect. Cost of the development is minimal and long-term economic benefits are significant.Low enthalpy geothermal energy Buried valleys [`]Heat island' effect Groundwater Gravels Space heating/cooling Heat pumps

Geothermal concept for energy efficient improvement of space heating and cooling in highly urbanized area

New Belgrade is a highly urbanized commercial and residential district of Belgrade lying on the alluvial plane of the Sava and the Danube rivers. The groundwater of the area is a geothermal resource that is usable through geothermal heat pumps (GHP). The research has shown that the “heat island effect” affects part of the alluvial groundwater with the average groundwater temperature of about 15.5°C, i.e. 2°C higher than the one in less urbanized surroundings. Based on the measured groundwater temperatures as well as the appraisal of the sustainable aquifer yield, the available thermal power of the resource is estimated to about 29MWt. The increasing urbanization trend of the New Belgrade district implies the growing energy demands that may partly be met by the available groundwater thermal power. Taking into consideration the average apartment consumption of 80 Wm-2, it is possible to heat about 360,000 m2 and with the consumption efficiency of 50 Wm-2, it would be possible to heat over 570,000 m2. Environmental and financial aspects were considered through the substitution of conventional fuels and the reduction of greenhouse gas emission as well as through the optimization of the resource use

Prospects for wider energetic utilization of subgeothermal water resources: Eastern Serbia case study

Intenzivno korišćenje fosilnih goriva širom sveta uzrok je ozbiljnih zagađenja prirode i utiče na globalno zagrevanje. Otuda je jedan od glavnih ciljeva energetske politike evropskih zemalja korišćenje efikasnije 'zelene' energije iz obnovljivih i sopstvenih izvora. Generalno, geotermalna energija predstavlja vid obnovljivih izvora energije. Ipak, i dalje se smatra da korišćenje subgeotermalne energije niske entalpije (temperature podzemnih voda od 30°C i niže) za potrebe grejanja nije u potpunosti ekonomski opravdano. Standardna tehnologija za primenu ovog vida energije zahteva velike površine pod panelima sa cevima koje provode toplu vodu i/ili upotrebu toplotnih pumpi sa visokim stepenom iskorišćenja. Razvoj kaskadne toplotne pumpe i njena šira primena omogućila bi daleko efikasniju upotrebu 'lako' dostupnih podzemnih vodnih resursa temperature između 10-30°C i stoga je u više projekata realizovanih poslednjih godina analizirana i razvijana ova tehnologija. Hidrogeološki uslovi u terenima istočne Srbije, su veoma povoljni sa aspekta eksploatacije subgeotermalnih resursa. Područje se odlikuje značajnim količinama podzemnih voda i terestičnim toplotnim tokom u okviru geoloških formacija u osnovnim geo-strukturnim jedinicama ovog regiona (Karpato-Balkanidi i Dakijski basen). Blizina urbanizovanih naselja i manjih gradova i postojanje razvijenog i centralizovanog grejanja su činjenice koje povoljno utiču na mogućnost eksploatacije subgeotermalnih vodnih resursa. Održivo korišćenje podzemnih vodnih resursa podrazumevalo bi i potrebnu termalnu rekonstrukciju i bolju izolaciju postojećih građevinskih objekata, kao i donošenje novih zakonskih propisa u Srbiji u cilju podsticaja korišćenja obnovljivih izvora energije. U području istočne Srbije, procenjene količine energije koje se mogu dobiti iz subgeotermalnih voda iznose oko 33 MWt, što bi predstavljalo oko 16% ukupnih energetskih potreba nekoliko odabranih većih naselja za koje je ova analiza vršena. I pored činjenice da se ne očekuje potpuno iskorišćenje ovog potencijala, evidentno je da je on daleko veći od 4 % koliko je u planovima energetskog razvoja predviđeno da bi moglo iznositi učešće geotermalnih vodnih resursa na nivou cele Srbije.Extensive worldwide usage of fossil energy sources causes high pollution and contributes to global warming. Hence, achieving energy independence by stimulating efficient use of energy and environmentally friendly exploitation of renewable sources is a main orientation of European countries. Geothermal energy is generally treated as a renewable and inexhaustible energy source. Nonetheless, direct use of low enthalpy subgeothermal resources, i.e. groundwater of 30.C or lower, for heating is commonly viewed as economically unjustified. To enable its usage, large panel surfaces or a high-temperature heat pump with excellent efficiency is required. The development of a cascade type heat pump and its wide application would enable more efficient utilization of widely available and easy replenished groundwater sources with temperatures of 10-30.C. The hydrogeological conditions in eastern Serbia are particularly favourable for exploitation of subgeothermal resources due to rich aquifer systems and notable terrestrial heat flow formed into the main geo-structures of the region (Carpathian-Balkan arch and Dachian basin). More intensive exploitation of subgeothermal sources additionally justifies the existence of a number of urbanized small and medium-size cities with a heating infrastructure already developed and centralized. Sustainable use of groundwater resources should be followed by thermal reconstruction of the previously constructed buildings as well as new legislation which supports and encourages development of renewable energy sources. It is estimated that the total potential thermal power which can be generated from subgeothermal waters in the study area is around 33 MWt, which corresponds to some 16 % of the total heat requirements

Site characterization for the design of thermoactive geostructures

This paper addresses the topic of site characterization for the design of Shallow Geothermal Energy (SGE) systems, namely of thermoactive geostructures, which are geotechnical structures, such as piles, retaining walls and tunnel linings, also used as heat exchangers as part of closed-loop SGE systems. Such solutions, being increasingly adopted for buildings’ and infrastructures’ heating and/or cooling, are considered sustainable and cost effective. For the design of the primary circuit of the SGE system, which is embedded within the superficial soil layers, a comprehensive knowledge of the ground condition at the site is mandatory. This includes the evaluation of the energy features and whether the system can provide the required energy needs during the operational period, as well as the verification of the structural and geotechnical safety and functionality requirements. The site characterization for SGE systems involves different stages, from desk studies to detailed characterization, including in-situ trials, laboratory testing of undisturbed soil samples and the study of possible interferences. The specific aspects that will be addressed are: (i) the assessment of the site undisturbed ground temperature and its hydrogeological features; (ii) the thermal and thermomechanical characterization of the different soil layers; (iii) the investigation of the ground-heat exchanger thermal resistance; (iv) the collection of information related to the environmental constraints and to potential interferences among multiple users, which are related to the service life of the structure. The overall aim is to ensure a proper design of the SGE system for guaranteeing its sustainability in the long term