Thermal response test for shallow geothermal applications: a probabilistic analysis approach

Thermal Response Test (TRT) is an onsite test used to characterize the thermal properties of shallow underground, when used as heat storage volume for shallow geothermal application. It is applied by injecting/extracting heat into geothermal closed-loop circuits inserted into the ground. The most common types of closed loop are the borehole heat exchangers (BHE), horizontal ground collectors (HGC), and energy piles (EP). The interpretation method of TRT data is generally based on a regression technique and on the calculation of thermal properties through different models, specific for each closed loop and test conditions. A typical TRT record is a graph joining a series of experimental temperatures of the thermal carrier fluid. The proposed geostatistical approach considers the temperature as a random function non-stationary in time, with a given trend, therefore the record is considered as a 'realization', one of the possible results; the random nature of the test results is transferred to the fluctuations and a variogram modeling can be applied, which may give many information on the TRT behavior. In this paper, a nested probabilistic approach for TRT output interpretation is proposed, which can be applied for interpreting TRT data, independently of the different methodologies and technologies adopted. In the paper, for the sake of simplicity, the probabilistic approach is applied to the 'infinite line source' (ILS) methodology, which is the most commonly used for BHE. The probabilistic approach, based on variogram modeling of temperature residuals, is useful for identifying with robust accuracy the time boundaries (initial time t 0 and the final time t f) inside which makes temperature regression analysis possible. Moreover, variograms are used into the analysis itself to increase estimation precision of thermal parameter calculation (ground conductivity λ g, ground capacity c g, borehole resistance R b). Finally, the probabilistic approach helps keep under control the effect of any cause of result variability. Typical behaviors of power, flows, and temperatures and of their interaction with the specific closed-loop circuit and geo-hydrological system are deepened by variogram analysis of fluctuations

Comparative life cycle assessment of renewable energy systems for heating and cooling

Renewable systems for heating and cooling (RES-HC) systems in last ten years have gradually increased their importance and their presence in the global heating ventilation and air conditioning (HVAC) market. Many energetic analysis and impact assessments have been made, which have demonstrated the convenience, respect to traditional HVAC systems, of solutions such as solar thermal or low enthalpy geothermal systems in terms of: energy consumption reduction, renewable energy use increase and emissions decrease. However, the several analysis made, up to date, only have considered the operation period of such systems, and consequently the comparison has been made only in terms of energy vectors used, omitting materials, components and processes. This paper aims to give a new perspective, showing how a correct environmental analysis should take into account all the life cycle of a system, from the cradle to grave, also if the system concerns a renewable energy source. In the specific case, a Life Cycle Assessment (LCA) will be presented, focusing on two currently popular RES-HC systems: solar thermal and low enthalpy geothermal, compared to the same functional unit. The results of this analysis could be a good starting point for future work on impact assessment of more complex and integrated HVAC systems

Integrated Underground Analyses as a Key for Seasonal Heat Storage and Smart Urban Areas

The design and performance of a shallow geothermal system is influenced by the geological and hydrogeological context, environmental conditions and thermal demand loads. In order to preserve the natural thermal resource, it is crucial to have a balance between the supply and the demand for the renewable energy. In this context, this article presents a case study where an innovative system is created for the storage of seasonal solar thermal energy underground, exploiting geotechnical micropiles technology. The new geoprobes system (energy micropile; EmP) consists of the installation of coaxial geothermal probes within existing micropiles realized for the seismic requalification of buildings. The underground geothermal system has been realized, starting from the basement of an existing holiday home Condominium, and was installed in dry subsoil, 20 m-deep below the parking floor. The building consists of 140 apartments, with a total area of 5553 m2, and is located at an altitude of about 1490 m above sea level. Within the framework of a circular economy, energy saving and the use of renewable sources, the design of the geothermal system was based on geological, hydrogeological and thermophysical analytical studies, in situ measurements (e.g., Lefranc and Lugeon test during drilling; Rock Quality Designation index; thermal response tests; acquisition of temperature data along the borehole), numerical modelling and long-term simulations. Due to the strong energy imbalance of the demand from the building (heating only), and in order to optimize the underground annual balance, both solar thermal storage and geothermal heat extraction/injection to/from a field of 380 EmPs, with a relative distance varying from 1 to 2 m, were adopted. The integrated solution, resulting from this investigation, allowed us to overcome the standard barriers of similar geological settings, such as the lack of groundwater for shallow geothermal energy exploitation, the lack of space for borehole heat exchanger drilling, the waste of solar heat during the warm season, etc., and it can pave the way for similar renewable and low carbon emission hybrid applications as well as contribute to the creation of smart buildings/urban areas

A METHOD TO EVALUATE THE IMPACT OF URBANIZATION ON GROUND TEMPERATURE EVOLUTION AT REGIONAL SCALE

Zamjena prirodnoga tla i vegetacije s „umjetnim” površinskim objektima ima za posljedicu promjenu temperature okolnoga zraka, ali i tla tijekom cijele godine. Razlozi su tomu neizravno Sunčevo zagrijavanje urbanih građevina, toplinski gubitci objekata te promjene i korištenje samoga tla. Takva pojava naziva se i „otokom urbanoga zagrijavanja” i lakše se opaža tijekom noći kada naselja oslobađaju toplinu nakupljenu tijekom dana. Tijekom dnevnoga razdoblja takva pojava također se dobro opaža u gusto naseljenim gradovima smještenim u pustinjskim i polupustinjskim područjima. U radu je opisana mješovita vjerojatnosno-deterministička metoda za procjenu temperature plitkoga podzemlja. Temelji se na geološkim, hidrogeološkim, klimatskim te urbanim (korelacija prekrivenosti zemljišta i gustoće naseljenosti) podatcima. Načinjeno je kartiranje na odabranoj mreži te su rezultati uspoređeni s temperaturama tla i vodonosnika (dostupni u literaturi). To je napravljeno za nekoliko gradova na Apeninskome poluotoku i u alpskoj zoni. Provjera je potvrdila kako su rezultati dobro polazište za znatno detaljnije, regionalno kartiranje promjene temperature tla.The replacement of natural soil and vegetation by artificial surfaces increases temperatures of the surrounding air and subsurface throughout the year, because of indirect solar heating of urban structures, building heat losses and land use change. This phenomenon is called Urban Heat Island and it can be better perceived during night-time, when the city releases the heat accumulated during the day. During day-time, due to relatively small amounts of solar radiation received by urban surface, especially in high-density cities in arid and semi-arid climates, Urban Cool Island can be identified as well. The present work illustrates a mixed probabilistic-deterministic method to estimate ground temperature at shallow depth, starting from information on geology, hydrogeology, climate, but also urban presence, through correlations with global land cover and population density. A dedicated mapping on regular grid has been produced. Results have been compared with ground and aquifer temperature available in the literature, for some representative cities of Italian Peninsula and Alpine Zone. Preliminary validations are encouraging and can be taken as a starting point for more comprehensive mapping of ground temperature evolution at regional scale

Exploitation of drainage water heat. A novel solution experimented at the Brenner Base Tunnel

Deep tunnels in permeable fractured rock-masses and under high piezometric levels can drain notable volumes of warm water, which are collected under gravity in specific conduits towards the portals, where heat can be exploited. The utilization of this energy source is generally narrowed by the limited presence of end-users near the portals, while other promising heating and cooling needs can be found directly along the tunnel length. The work presents the design, construction and installation of a geothermal system prototype exploiting the drainage water heat directly inside the tunnel. The prototype was named Smart Flowing due to the peculiarity of its heat exchange process. The system was realized and installed inside the exploratory tunnel of the Brenner Base Tunnel, near the border between Italy and Austria. The Smart Flowing modules were built outside and later moved inside the tunnel, where they were placed and assembled concurrently to the advancement of the Tunnel Boring Machine. A design procedure was proposed and validated against a testing and monitoring campaign. The data from the experimental activity confirmed that the drainage water flow guarantees long-term stabilization of circulating water temperature and fast heat recovery afterwards, thus securing the considerable power and performance values of a water-water heat pump connected to the system. A sensitivity analysis allowed the reproduction of different working scenarios, in order to generalize the application of Smart Flowing beyond the specific installation context

PRIMJENA STOHASTIČKOGA MODELA NA ODLAGALIŠTU JALOVINE KAO POTPORA DUGOROČNOJ PROIZVODNJI U OTVORENOME KOPU S CILJEM POVEĆANJA POSTOTKA RUDE U OBRADBI

This paper presents a chance-constrained integer programming approach based on the linear method to solve the longterm open pit mine production scheduling problem. Specifically, a single stockpile has been addressed for storing excess low-grade material based on the availability of processing capacity and for possible future processing. The proposed scheduling model maximizes the project NPV while respecting a series of physical and economic constraints. Differently from common practice, where deterministic models are used to calculate the average grade for material in the stockpiles, in this work a stochastic approach was performed, starting from the time of planning before the stockpile realization. By performing a probability analysis on two case studies (on iron and gold deposits), it was proven that the stockpile attributes can be treated as normally distributed random variables. Afterwards, the stochastic programming model was formulated in an open pit gold mine in order to determine the optimum amount of ore dispatched from different bench levels in the open pit and at the same time a low-grade stockpile to the mill. The chance-constrained programming was finally applied to obtain the equivalent deterministic solution of the primary model. The obtained results have shown a better feed grade for the processing plant with a higher NPV and probability of grade blending constraint satisfaction, with respect to using the traditional stockpile deterministic model.Rad prikazuje uporabu vjerojatnosnoga cjelobrojnog programiranja, temeljenoga na linearnome algoritmu, za dugoročno rješavanje proizvodnje u rudniku otvorenoga kopa. Obrađeno je jedno odlagalište jalovine sa „siromašnom” koncentracijom rude u cilju aktiviranja toga materijala u budućoj preradbi korisne sirovine. Takav projekt maksimizira trenutačnu vrijednost rudarenja uzimajući u obzir niz fizičkih i ekonomskih varijabli. Posebnost u odnosu na determinističke modele koji se danas uglavnom koriste za izračun granične prosječne vrijednosti koncentracije rude prije odlaganja kao jalovine izražena je stohastikom. Ona je uključila vjerojatnosnu analizu dvaju slučajeva, tj. za ležište željeza i zlata. U obama je dokazano kako se varijable određene na odlagalištu mogu opisati normalnom razdiobom. Stohastički model programiran je za rudnik zlata te je uzeta u obzir optimalna vrijednost rude razvrstane na različitim rudničkim razinama, a prije slanja na obradbu (mljevenje). Optimizirani model zatim je primijenjen za dobivanje usporednoga determinističkog modela. Rezultati su upozorili na to da je konačno rješenje pokazalo znatno bolji odabir granične koncentracije rude koja se mogla poslati na daljnju obradbu. Time je uvećana i ukupna vrijednost rudnika/ležišta

Key features of the novel geothermal heat exchanger prototype installed at the Brenner Base Tunnel

The design, installation, and testing of an innovative geothermal heat exchanger, tailored for tunnels excavated by Tunnel Boring Machines, will be presented. The prototype was developed by the joint efforts of BBT SE, involved in the construction of a new railway base tunnel system connecting Italy and Austria, and the University of Bologna, engaged in applied research over various aspects of the BBT system. The geothermal heat exchanger consists in a modular horizontal closed-loop system located in the exploratory tunnel of the BBT system, specifically in the space dedicated to collect the drained water at the lining invert. Due to the type of the heat exchange process, working with the drainage water, and for its compact design and simple installation procedure, the prototype was called “Smart Flowing”. Modules were built outside and later moved inside the tunnel, and eventually placed and assembled concurrently to the advancement of the Tunnel Boring Machine. Specific tests were performed to prove the reliability and the efficiency of the system, by simulating the work of a heat pump conditioning system in both heating and cooling modes. Finally, a preliminary assessment of the economic and environmental potential of this innovative prototype was carried out. First results showed the performance of the system for both heat dissipation and extraction. The drainage water flow guarantees a continuous recovery to the natural state, thus improving efficiency compared to classic geothermal heat exchangers. Economic savings and reduction of pollutants and greenhouse gases, as compared to burning fossil fuels, can reach up to 70%

A novel TRNSYS type of a coaxial borehole heat exchanger for both short and mid term simulations: B2G model

[EN] A dynamic model of a ground source heat pump system is a very useful tool in order to optimize its design and operation. In order to fairly predict the performance of such a system, the dynamic evolution of the fluid entering the heat pump and coming from the borehole heat exchanger (BHE) must be accurately reproduced not only in the long term but also in the short-mid term operating conditions, as it directly affects the coefficient of performance of the heat pump unit. In this context, the B2G model was developed to reproduce the short-term dynamic evolution of the fluid temperature inside the BHE. This work presents the new upgraded version of the B2G dynamic model for a coaxial BHE, which includes several new features to better reproduce not only the short-term but also the mid-term behaviour of the BHE. For that purpose, the model of the surrounding ground has been improved: vertical heat conduction in the grout and ground, heterogenous ground with different layers, and a higher number of ground nodes in the thermal network considered in the model were added, which are automatically located by means of polynomial correlations for any type of ground, geometry and operating conditions. This novel approach has been implemented in TRNSYS for accurately modelling the dynamic behaviour of a coaxial BHE with low computational cost (2.5¿s for a 24¿h simulation period in a modern computer). The model has been validated against experimental data from a dual source heat pump installation in Tribano (Padua, Italy) and has proven capable of accurately reproducing the short-mid term (up to five days) behaviour of the BHE, with a deviation lower than 0.12¿K.The present work has been supported by the European Community Horizon 2020 Program for European Research and Technological Development (2014-2020) inside the framework of the project 656889 –GEOTeCH (Geothermal Technology for Economic Cooling and Heating) and by the Generalitat Valenciana inside the program “Ayudas para la contratación de personal investigador en formación de carácter predoctoral (ACIF/2016/131)”.Cazorla-Marín, A.; Montagud- Montalvá, C.; Tinti, F.; Corberán, JM. (2019). A novel TRNSYS type of a coaxial borehole heat exchanger for both short and mid term simulations: B2G model. Applied Thermal Engineering. 164(114500):1-15. https://doi.org/10.1016/j.applthermaleng.2019.114500S11516411450

Macro-Scale Underground Geomechanical and Thermal Mapping for Very Shallow Geothermal Applications

The document is an extended abstract presented at "GeoENV 2016", the 11th International Conference on Geostatistics for Environmental Application Conference, 6-8 July 2016, Lisbon, Portugal

Long-range Radio for Underground Sensors in Geothermal Energy Systems

The paper presents the design of a temperature monitoring system in a very harsh environment, such as Shallow Geothermal Systems (SGS), where the information of underground temperature is necessary to assess the thermal potential of the soil, for maximizing the efficiency of the SGS. The challenge is to get information at different depths (sometimes up to - 100m), to transmit data wirelessly in rural areas where conventional wireless connections (e.g. WiFi, GSM) are not guaranteed and energy availability poses severe limits. Our design exploits a recent new modulation protocol developed for long-range transmission, at the minimum energy cost, and a two-tier hardware architecture for measuring underground temperature. Aggressive duty cycling permits to achieve lifetime of several years. Experimental results demonstrate the utility of such a system during the design and the operational activity of a SGS