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Mazzotti, W., Lazzarotto, A., Acuña, J. & Palm, B. (2023). Calibration and Uncertainty Quantification for Single-Ended Raman-Based Distributed Temperature Sensing: Case Study in a 800 m Deep Coaxial Borehole Heat Exchanger. Sensors, 23(12), Article ID 5498.
Open this publication in new window or tab >>Calibration and Uncertainty Quantification for Single-Ended Raman-Based Distributed Temperature Sensing: Case Study in a 800 m Deep Coaxial Borehole Heat Exchanger
2023 (English)In: Sensors, E-ISSN 1424-8220, Vol. 23, no 12, article id 5498Article in journal (Refereed) Published
Abstract [en]

Raman-based distributed temperature sensing (DTS) is a valuable tool for field testing and validating heat transfer models in borehole heat exchanger (BHE) and ground source heat pump (GSHP) applications. However, temperature uncertainty is rarely reported in the literature. In this paper, a new calibration method was proposed for single-ended DTS configurations, along with a method to remove fictitious temperature drifts due to ambient air variations. The methods were implemented for a distributed thermal response test (DTRT) case study in an 800 m deep coaxial BHE. The results show that the calibration method and temperature drift correction are robust and give adequate results, with a temperature uncertainty increasing non-linearly from about 0.4 K near the surface to about 1.7 K at 800 m. The temperature uncertainty is dominated by the uncertainty in the calibrated parameters for depths larger than 200 m. The paper also offers insights into thermal features observed during the DTRT, including a heat flux inversion along the borehole depth and the slow temperature homogenization under circulation.

Place, publisher, year, edition, pages
MDPI AG, 2023
Keywords
distributed temperature sensing, DTS, uncertainty, fiber optic, Raman, borehole, temperature, deep coaxial BHE, DTRT, confidence intervals
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-332185 (URN)10.3390/s23125498 (DOI)001015764800001 ()37420665 (PubMedID)2-s2.0-85164021704 (Scopus ID)
Note

QC 20230721

Available from: 2023-07-21 Created: 2023-07-21 Last updated: 2023-07-21Bibliographically approved
Abuasbeh, M., Acuña, J., Lazzarotto, A. & Palm, B. (2021). Long term performance monitoring and KPIs' evaluation of Aquifer Thermal Energy Storage system in Esker formation: Case study in Stockholm. Geothermics, 96, Article ID 102166.
Open this publication in new window or tab >>Long term performance monitoring and KPIs' evaluation of Aquifer Thermal Energy Storage system in Esker formation: Case study in Stockholm
2021 (English)In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 96, article id 102166Article in journal (Refereed) Published
Abstract [en]

The majority of Aquifer Thermal Energy Storage (ATES) systems studies have been conducted in aquifer systems located in large sand aquifers. Esker formation present a more challenging geometrical complexity compared to typical sand aquifers. This study aims to conduct comprehensive and long term performance evaluation of doublet type ATES system in esker geological formation in Stockholm, Sweden. The total heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. The licensed total amount of water extraction and injection is 50 liters per second with undisturbed groundwater temperature of 9.5 degrees C. Over the first three storage cycles, the average injection and extraction temperatures for the warm side are 13.3 degrees C and 12.1 degrees C, and for the cold side 7.6 degrees C and 10.5 degrees C. The average temperature differences across the main heat exchanger from the ATES side are 4.5 K during winter and 2.8 K during summer which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. This was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is the oversizing of the heat pumps which were designed to be coupled to larger thermal loads as compared to the ones in the final system implementation. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the paper discusses the limitations of currently used energy and thermal key performance indicators (KPI) for ATES and propose an additional thermal KPI named heat exchanger efficiency balance (beta HEX) that connects and evaluate the optimum operational point of temperature differences from both the building and ATES prospective. In addition to ATES energy and hydraulic KPIs, beta HEX can contribute in providing more complete picture on the ATES-building interaction performance as well as highlights if the losses in energy recovery from ATES are due to the subsurface processes or building energy system operation which has been proven to be critical for the optimum ATES performance.

Place, publisher, year, edition, pages
Elsevier BV, 2021
Keywords
Aquifer Thermal Energy Storage, Performance Analysis, Renewable Energy, Shallow Geothermal Energy, Ground Source Heat Pump
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-303759 (URN)10.1016/j.geothermics.2021.102166 (DOI)000702860700002 ()2-s2.0-85109607839 (Scopus ID)
Note

QC 20211026

Available from: 2021-10-26 Created: 2021-10-26 Last updated: 2022-06-25Bibliographically approved
Fasci, M. L., Lazzarotto, A., Acuña, J. & Claesson, J. (2021). Simulation of thermal influence between independent geothermal boreholes in densely populated areas. Applied Thermal Engineering, 196, Article ID 117241.
Open this publication in new window or tab >>Simulation of thermal influence between independent geothermal boreholes in densely populated areas
2021 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 196, article id 117241Article in journal (Refereed) Published
Abstract [en]

Ground Source Heat Pumps (GSHPs) connected to Borehole Heat Exchangers (BHEs) are a fast-growing technology for thermally efficient buildings. Therefore, areas with several independent GSHP installations close to each other are becoming more and more common. To guarantee an optimal operation of these systems, it is necessary to design them considering the influence of the neighbouring installations. However, a tailored model for this scope has not been found in the literature. In this paper, we aim at filling this gap by proposing and validating a methodology to calculate the thermal influence between neighbouring independent boreholes. It is based on the Finite Line Source (FLS) model and prescribes novel boundary conditions, tailored to hydraulically independent boreholes. The methodology allows to prescribe different thermal loads to different BHEs and imposes uniform temperature boundary condition on each borehole wall. We also show how to implement and apply the model. Our application shows a thermal influence of up to 1.5 K during the lifetime of a GSHP and of up to 0.8 K during the first year of operation in an area with a relatively low number of installations, underlying the importance of considering the thermal influence and the usefulness of our proposed model. Finally, a sensitivity study on the ground thermal conductivity shows the importance of a correct estimation of this property for accurate simulation results.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2021
Keywords
Boreholes, Geothermal, Ground heat exchangers, Thermal influence, Neighbouring ground source heat pumps, Analytical modelling
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-300821 (URN)10.1016/j.applthermaleng.2021.117241 (DOI)000686757000005 ()2-s2.0-85109768739 (Scopus ID)
Note

QC 20210929

Available from: 2021-09-29 Created: 2021-09-29 Last updated: 2023-09-15Bibliographically approved
Mazzotti Pallard, W., Lazzarotto, A., Acuña Sequera, J. E. & Palm, B. (2020). Design methodology for laboratory scale borehole storage: An approach based on analytically-derived invariance requirements and numerical simulations. Geothermics, 87, Article ID 101856.
Open this publication in new window or tab >>Design methodology for laboratory scale borehole storage: An approach based on analytically-derived invariance requirements and numerical simulations
2020 (English)In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 87, article id 101856Article in journal (Refereed) Published
Abstract [en]

This paper presents a methodology for designing Laboratory Borehole Storages (LABS) intended to generate reference Thermal Response Functions (TRFs) for model validation. The design method is based on analytically-derived invariance requirements demanding the conservation of the Fourier and Biot numbers. Accordingly, convective boundary conditions (BCs) need to be up-scaled when downscaling the borehole field, especially for short boreholes. Indeed, numerical simulations show that natural convection as top BC leads to TRF values more than 14 % higher than a Dirichlet BC. In addition, this BC effect is proposed as a possible explanation for previously reported differences between experimental and analytical results. Finally, the numerical simulations are used to find suitable size – height and radius of twice the borehole length–and test durations for the LABS.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Borehole, Convection, Design of experiment, Downscaling, Invariance, Thermal response
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-276283 (URN)10.1016/j.geothermics.2020.101856 (DOI)000551469800018 ()2-s2.0-85083820328 (Scopus ID)
Note

QC 20200618

Available from: 2020-06-18 Created: 2020-06-18 Last updated: 2024-03-15Bibliographically approved
Aranzabal, N., Martos, J., Stokuca, M., Mazzotti Pallard, W., Acuna, J., Soret, J. & Blum, P. (2020). Novel instruments and methods to estimate depth-specific thermal properties in borehole heat exchangers. Geothermics, 86, Article ID 101813.
Open this publication in new window or tab >>Novel instruments and methods to estimate depth-specific thermal properties in borehole heat exchangers
Show others...
2020 (English)In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 86, article id 101813Article in journal (Refereed) Published
Abstract [en]

Standard thermal response tests (TRT) are typically carried out to evaluate subsurface thermal parameters for the design and performance evaluation of borehole heat exchangers (BHE). Typical interpretation methods apply analytical or numerical solutions, which assume that the ground is homogeneous, isotropic and infinite. However in reality, the underground is commonly stratified and heterogeneous, and therefore thermal properties might significantly vary with depth. Thus, novel instruments and methods are necessary to characterize thermophysical properties along the BHE. In this study, two novel in-borehole temperature measurement instruments, Geoball and Geowire, are assessed during the performance of a distributed TRT (DTRT). The latter is evaluated in comparison to the widely used fiber optical thermometers. Our results suggest that both novel instruments have several advantages. For instance, both devices are able to instantaneously measure temperature with a higher spatial resolution. In addition, our study evaluates two methods to estimate depth-specific thermal conductivities: (1) a computer program based on infinite line source (ILS) approach and (2) a recently suggested inverse numerical procedure. For the latter less data is required, while demonstrating an accurate resolution to even detect thin conductive geological layers. Moreover, the average value of the depth-specific local effective estimates for both methods is significantly close to the effective subsurface conductivity of 3.20 W/m-K calculated based on standard TRT: 1.27 % below for the computer program and 0.28 % below for the numerical procedure.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Ground source heat pump (GSHP), Borehole heat exchanger (BHE), Distributed thermal response test (DTRT), Layered subsurface, Thermal conductivity, Energy efficiency
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-275601 (URN)10.1016/j.geothermics.2020.101813 (DOI)000534152600026 ()2-s2.0-85078718113 (Scopus ID)
Note

QC 20200608

Available from: 2020-06-08 Created: 2020-06-08 Last updated: 2024-03-15Bibliographically approved
Fasci, M. L., Lazzarotto, A., Acuña, J. & Claesson, J. (2019). Analysis of the thermal interference between ground source heat pump systems in dense neighborhoods. Science and Technology for the Built Environment, 25(8), 1069-1080
Open this publication in new window or tab >>Analysis of the thermal interference between ground source heat pump systems in dense neighborhoods
2019 (English)In: Science and Technology for the Built Environment, ISSN 2374-4731, E-ISSN 2374-474X, Vol. 25, no 8, p. 1069-1080Article in journal (Refereed) Published
Abstract [en]

Ground source heat pumps (GSHPs) are a state-of-the-art technology for heating, cooling, and hot water production. They are already common in several countries and represent a promising technology for others. As the technology penetrates the market, the number of ground heat exchangers in densely populated areas may increase significantly. Therefore, it becomes important to consider the thermal influence of neighboring GSHPs while designing these systems in such areas. This question has become more frequent in some Swedish residential areas where the use of GSHPs is very common. This article proposes an easy-to-implement methodology to evaluate the thermal influence between borehole heat exchangers (BHEs) in areas with a high number of GSHPs installed. It also suggests two mitigation strategies to decrease the thermal interference so that the given limit for the ground temperature change is respected. The methodologies proposed are implemented using the programming language Julia and applied to fictional scenarios relevant for Sweden. It is found that neglecting the presence of neighboring systems might lead to an overexploitation of the underground heat. This can be avoided if, during the design phase, the presence of neighboring BHEs is taken into account and mitigation strategies are applied.

Place, publisher, year, edition, pages
Informa UK Limited, 2019
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-303303 (URN)10.1080/23744731.2019.1648130 (DOI)000483153000001 ()2-s2.0-85071044601 (Scopus ID)
Note

QC 20211013

Available from: 2021-10-13 Created: 2021-10-13 Last updated: 2023-09-15Bibliographically approved
Abuasbeh, M. (2018). Aquifer Thermal Energy Storage Insight into the future. Stockholm, Sweden
Open this publication in new window or tab >>Aquifer Thermal Energy Storage Insight into the future
2018 (English)Report (Refereed)
Abstract [en]

Underground Thermal Energy Storage (UTES) systems, such as Aquifer thermal energy storage(ATES) are used in several countries. The regulation and research on the potential impacts of ATESon groundwater resources and the subsurface environment often lag behind the technologicaldevelopment of an ever-growing demand for this renewable energy source. The lack of a clear andscientifically supported risk management strategy implies that potentially unwanted risks might betaken at vulnerable locations such as near well fields used for drinking water production. At othersites, on the other side, the application of ATES systems is avoided without proper reasons. Thisresults in limiting the utilization of the ATES technology in many occasions, affecting the possibilityto increase the share of renewable energy use. Therefore, further studies to characterizegroundwater resources, performance monitoring and identification of environmental impacts areneeded to understand the advantages and limitations of ATES systems.

The environmental impact and technical performance of a Low Temperature ATES (LT-ATES)system in operation since 2016 is presented. The system is called Rosenborg and is owned byVasakronan. It is located in the northern part of Stockholm, on a glaciofluvial deposit called theStockholm esker. The ATES system is used to heat and cool two commercial buildings with a totalarea of around 30,000 m2. The ATES consists of 3 warm and 2 cold pumping wells that are able topump up to 50 liters per second.

Analysis of groundwater sampling included a period of 9 months prior to ATES operation as well asthe first full season of heating and cooling operation. The sampling was conducted in a group ofwells in the vicinity of the installation and within the system. Means of evaluation constituted astatistical approach that included Kruskal-Wallis test by ranks, to compare the wells before and afterthe ATES was used. Then principal component analysis (PCA) and clustering analysis were used tostudy the ground water conditions change before and after the ATES. Aquifer Variation Ratio(AVR) was suggested as mean to evaluate the overall conditions of the aquifer pre- and post- ATES.

The results showed some variations in redox potential, particularly at the cold wells which likely wasdue to the mixing of groundwater considering the different depths of groundwater beingabstracted/injected from different redox zones. Arsenic, which has shown to be sensitive to hightemperatures in other research showed a decrease in concentration. A lower specific conductivityand total hardness at the ATES well compared to their vicinity was found. That indicates that theyare less subject to salinization and that no accumulation has occurred to date. It is evident that theenvironmental impact from ATES is governed by the pre-conditions in soil- and groundwater. ThePCA and clustering analysis showed very little change in the overall conditions in the aquifer whencomparing the ATES before and after operation. Temperature change showed negligible impact.This can be mainly attributed to the relatively small temperature change (+6 and – 5 degrees) fromthe undisturbed Aquifer temperature which is 10.5°C.

Performance of Aquifer Thermal Energy Storage (ATES) systems for seasonal thermal storagedepends on the temperature of the extracted/injected groundwater, water pumping rates and thehydrogeological conditions of the aquifer. ATES systems are therefore often designed to work witha temperature difference between the warm side and cold side of the aquifer without riskinghydraulic and thermal intrusion between them, and avoiding thermal leakage to surrounding area, i.e. optimize hydraulic and thermal recovery. The hydraulic and thermal recovery values of the first yearof operation in Rosenorg weres 1.37 and 0.33, respectively, indicating that more storage volume(50500m3) was recovered during the cooling season than injected (36900m3) in the previous heatingseason.

Monitoring the operation of pumping and observation wells is crucial for the validation of ATESgroundwater models utilized for their design, and measured data provides valuable information forresearchers and practitioners working in the field. After months of planning and installation work,selected measurements recorded in an ATES monitoring project in Sweden during the first threeseasons of operation are reported in this report.

The monitoring system consists of temperature sensors and flow meters placed at the pumpingwells, a distributed temperature-sensing rig employing fiber optic cables as linear sensor andmeasuring temperature every 0.25 m along the depth of all pumping and several observation wells,yielding temporal and spatial variation data of the temperature in the aquifer. The heat injection andextraction to and from the ground is measured using power meters at the main line connecting thepumping wells to the system. The total heat and cold extracted from the aquifer during the firstheating and cooling season is 190MWh and 237MWh, respectively. A total of 143 MWh of heatwere extracted during the second heating season. The hydraulic and thermal recovery values of thefirst year of operation was 1.37 and 0.33, respectively, indicating that more storage volume(50500m3) was recovered during the cooling season than injected (36900m3) in the previous heatingseason. The DTS data showed traces of the thermal front from the warm storage reaching the coldone. Only 33% of the thermal energy was recovered. These losses are likely due to ambientgroundwater flow as well as conduction losses at the boundaries of the storage volume. Additionally,the net energy balance over the first year corresponds to 0.12 which indicates a total net heating ofthe ATES over the first year. It is recommended to increase the storage volume and achieve morehydraulic and thermal balance in the ATES system. This can enhance the thermal recovery andoverall performance. Continuous monitoring of the ATES is and will be ongoing for at least 3 moreyears. The work presented in this report is an initial evaluation of the system aiming to optimize theATES performance.

Furthermore, data management and processing tool has been established for the ATES system in Rosenborg. Additionally, a conceptual model of the ATES area has been established. Current andfuture work is focussed on completing a full scale numerical model in FEFLOW and validated themodel (both hydraulically and thermally) with the available monitoring data. Furthermore,establishing recommendations for optimum design and operation of ATES system.

Abstract [sv]

Att lagra värme och kyla under markytan, exempelvis i grundvattnet i en akvifer, används världenrunt. Oftast arbetar dessa system med två brunnsgrupper, en kall och en varmgrupp, som viavärmeväxlare och eller värmepumpar till ett energisystem i en fastighet.

Syftet med ett säsongslager i en akvifer är oftast att arbeta inom rimliga temperaturer och vattenuttagoch garantera att det kalla och det varma lagret inte påverkar varandra, samt att systemet i sin helhetinte påverkar förhållanden i det omgivande grundvattnet.

Regelverk och forskning inom akviferlager ligger tyvärr några år bakom marknaden och dentekologiska utvecklingen, trots stort intresse för förnyelsebara energikällor. Bristen av vetenskapligtframtagen kunskap inom området medför därmed en ökad risk för fel i konstruktion, fel inom 

framtagning av underlag för bedömning av tillståndsansökningar samt för förorening avgrundvattnet. Det kan även hända att akviferlager förbjuds baserad på fel grunder. Eftersom dettakan resultera i en begränsad användning av denna förnyelsebara energikälla är det viktigt att utökakunskapsnivån inom karakterisering av grundvattenresurser, miljöpåverkan av akviferlager samtmätning och uppföljning av dessa system.

Miljöpåverkan och prestandauppföljning har under detta projekt utförts i ett lågt tempereratakviferlager, Rosenborg, som äggs av Vasakronan och som är i drift sedan 2016. Anläggningen ärplacerat i en del av Solnastad som passerar Stockhoms åsen.

Grundvattenkemi kan studeras med hjälp av regelbundna provtagningar och statistiska analyser.Provtagningar utfördes i observationsbrunnar placerade innanför och utanför lagret, och pågick frånoch med 9 månader innan anläggningen satts i drift till och med slutat av effsysprojektet, dvsprovtagningskampanjen inkluderade en helt kyl och värmelagringssäsong. Utvärderingen inkluderadeStatistiska metoder så som Kruskal-Wallis rangordningstester samt en data-driven metod så kalladPCA (från engelskan Principal Component Analysis) har använts, även klusteranalyser användes föratt studera och jämföra variationer i specifika kemiska komponenter i brunnarna före och efterdriftsättningen av akviferlagret. Varibeln AVR (Akvifer Variation Ratio) föreslogs som ett sätt attutvärdera kemisk påverkan i akviferen före och efter driftsättning på ett mer övergripande sätt.

Den kemiska analysen visade Redox variationer i de kalla brunnarna, som sannolikt berodde påblandning av grundvatten från olika djup (olika Redox potential). Arsenik, som är kännslig till högretemperaturer enligt tidigare utfört arbete, visade en minskning i koncentration. Akviferlagret visadeen lägre hårdhet (proportionell mängd kalcium och magnesium) och lägre konduktivitet än detomgivande grundvattnet, som betyder att lagret har varit mindre känslig till intrång av saltvatten frånomgivningen. PCA och klusteranalysen visade små ändringar före och efter driften. Detkonstaterades att temperaturändringarna (+6 K sommartid och -5 K vintertid) hade en försumbarpåverkan i relation till akviferens ostörda temperatur (10,5°C).

Eftersom energiprestanda i ett akviferlager är beroende av hydrauliska och termiska aspekter hardessa studerats i projektet genom att jämföra volymmängder grundvatten som pumpades ut och insamt utifrån temperaturbalansen över året, båda med hänsyn till akviferens hydrogeologiskaförhållanden. Begreppen hydraulisk och termisk återhämtning har använts för kvantifiering avakviferens prestanda. Resultatet för det första året blev en hydraulisk återhämtning lika med 1,37 ochden termiska återhämtningen 0,33. Den hydrauliska återhämtningen av 1,37 betyder att en störreandel (37%) av lagrets vattenvolym återanvändes under kyluttaget jämfört med värmeuttagsperioden.Den termiska återhämtningen, som är relaterad till den önskade temperaturnivån (10,5°C) ellerbörvärde har det första året visar att 67% mindre kyla har plockat upp i relation till värmeuttaget.Det är viktigt att hålla i åtanke att denna indikatör är starkt beroende på börvärdet somdriftpersonalen bestämmer. Mer förståelse kring hur det hydrauliska och termiska prestanda kan tasfram i fortsättningsprojektet med hjälp av uppföljning av vattenflöden, nivåer ochgrundvattentemperaturer i systemet som utförs via en state of the art mätsystem som har applicerasunder projektet. Av speciell relevans är det fiberoptiska systemet som har installerats i samtligapumpbrunnar samt i ett antal observationsbrunnar i akviferlagret. Systemet mäter var 25 centimeteroch täcker det mesta av lagrets volym. Mätningarna kan i fortsättningen användas för att validera ennumerisk modell som har tagits fram inom projektet med programmet FEFLOW.

Place, publisher, year, edition, pages
Stockholm, Sweden: , 2018. p. 42
Keywords
Heating, Free cooling, Heat pump, Thermal Energy storage, Aquifer, ATES, Groundwater, Monitoring, DTS, Värme, kyla, akviferlager, Termiska energilager
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-243835 (URN)
Projects
Effsys Expand P22: Heating and cooling from aquifer layers an insight into the future/Värme och kyla från akviferlager en inblick i framtiden
Funder
Swedish Energy Agency, Projektnummer 40942-1 Effsys Expand P22
Note

QC 20190211

Available from: 2019-02-06 Created: 2019-02-06 Last updated: 2022-06-26Bibliographically approved
Abuasbeh, M. & Acuña, J. (2018). ATES SYSTEM MONITORING PROJECT, FIRST MEASUREMENT AND PERFORMANCE EVALUATION: CASE STUDY IN SWEDEN. In: Proceedings of the IGSHPA Research Track 2018: . Paper presented at IGSHPA Research Track 2018.
Open this publication in new window or tab >>ATES SYSTEM MONITORING PROJECT, FIRST MEASUREMENT AND PERFORMANCE EVALUATION: CASE STUDY IN SWEDEN
2018 (English)In: Proceedings of the IGSHPA Research Track 2018, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Performance of Aquifer Thermal Energy Storage (ATES) systems for seasonal thermal storage depends on the temperature of the extracted/injected groundwater, water pumping rates and the hydrogeological conditions of the aquifer. ATES systems are therefore often designed to maintain a temperature difference possible between the warm side and cold side of the aquifer, without risking hydraulic and thermal intrusion between them or thermal leakage to surrounding area, i.e. maximize hydraulic and thermal recovery. Monitoring the operation of pumping and observation wells is crucial for the validation of ATES groundwater models utilized for their design, and measured data provides valuable information for researchers and practitioners working in the field. After months of planning and installation work, selected measurements recorded in an ATES monitoring project in Sweden during the first three seasons of operation are reported in this paper. The ATES system is located in Solna, in Stockholm esker, and it is used to heat and cool two commercial buildings with a total area of around 30,000 m 2 . The ATES consists of 3 warm and 2 cold pumping wells that are able to pump up to 50 liters per second. The monitoring system consists of temperature sensors and flow meters placed at the pumping wells, a distributed temperature-sensing rig employing fiber optic cables as linear sensor and measuring temperature every 0.25 m along the depth of all pumping and several observation wells, yielding temporal and spatial variation data of the temperature in the aquifer. The heat injection and extraction to and from the ground is measured using power meters at the main line connecting the pumping wells to the system. The total heat and cold extracted from the aquifer during the first heating and cooling season is 190MWh and 237MWh, respectively. A total of 143 MWh of heat were extracted during the second heating season. The hydraulic and thermal recovery values of the first year of operation was 1.37 and 0.33, respectively, indicating that more storage volume (50500m3 ) was recovered during the cooling season than injected (36900m3 ) in the previous heating season. The DTS data showed traces of the thermal front from the warm storage reaching the cold one. Only 33% of the thermal energy was recovered. These losses are likely due to ambient groundwater flow as well as conduction losses at the boundaries of the storage volume. Additionally, the net energy balance over the first year corresponds to 0.12 which indicates a total net heating of the ATES over the first year. It is recommended to increase the storage volume and achieve more hydraulic and thermal balance in the ATES system. This can enhance the thermal recovery and overall performance. Continuous monitoring of the ATES is and will be ongoing for at least 3 more years. The work presented in this paper is an initial evaluation of the system aiming to optimize the ATES performance.

Keywords
Heat Pump, Heating, Free Cooling, DTS, Thermal energy storage, Aquifer, ATES, monitoring
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-243836 (URN)10.22488/okstate.18.000002 (DOI)
Conference
IGSHPA Research Track 2018
Funder
Swedish Energy Agency, Projektnummer 40942-1 Effsys Expand P22
Note

QC 20190211

Available from: 2019-02-06 Created: 2019-02-06 Last updated: 2022-06-26Bibliographically approved
Mazzotti, W., Acuña, J., Lazzarotto, A. & Palm, B. (2018). Deep Boreholes for Ground-Source Heat Pump: Final report.
Open this publication in new window or tab >>Deep Boreholes for Ground-Source Heat Pump: Final report
2018 (English)Report (Refereed)
Alternative title[sv]
Djupa borrhål förbergvärmepumpar : Slutrapport
Abstract [en]

This report presents the obtained results and performed tasks during the project Deep Boreholes for Ground-Source Heat Pumps, within the framework of the research program Effsys Expand.

A price model for the investment of GSHP system with deep Borehole Heat Exchangers (BHEs) is derived from a survey submitted to Swedish drillers. Notably, it is shown that the price increases with the borehole depth in a cubic fashion. Up to 300 m depth, the model shows a good match with a linear correlation having a slope of 275 SEK/m, a figure that is close to commonly used estimates for the total installation price of a single BHE. For larger depths, however, the installation price becomes non-linear and deviates from this linear tendency. Examples of total installation prices, including heat pumps and BHEs installation, are given.

Measurements performed in three different installations with deep boreholes are reported. The first tests are performed in a 800 m deep borehole equipped with acoaxial collector. Five Distributed Thermal Response Tests (DTRTs) are performed inthis BHE of which four were heat-extraction DTRTs. It is shown that heat flux inversion happens along the depth of the boreholes, that is heat is extracted at the bottom of the borehole but lost at the top. The flow rate is shown to have a significant effect on the thermal shunt effect and the coaxial BHE is shown to have significantly lower pressure drops that more traditional BHE (e.g. U-pipes). The pressure drop vs. flow rate relation is experimentally characterized through a hydraulic step test. An effective borehole resistance of 0.21 m∙K/W was found. This value is relatively high and is explained as a consequence of limited flow rate and the large depth. More investigations as regards the measurement technique (DTS with fiber optic cables) are needed before performing further in-depth analysis.

In another installation, four 510 m boreholes are measured to deviate about 30% from the vertical direction, highlighting the importance of drilling precision for deep boreholes, more particularly in urban environment. The GSHP system, using 50mmU-pipe BHEs is monitored over a year and it is found that pumping energy consumption in the boreholes could be as high as 22% of the total energy consumption of the system (compressors and circulation pumps). The relevance of pressure drops and control strategies for the circulation pumps in the borehole loop is emphasized. The temperature profile with depth confirms the existence of stored heat in the top part of the ground in urban environment.

The results of two DTRTs performed in the same borehole (335 m) are reported, thelatter being first water-filled before being grouted. The obtained thermal conductivities differ from one case to another, possibly highlighting the effect of the filling material on the results. Several other explanations are proposed although none can be fully verified.

The design and construction phases of a laboratory-scale borehole storage model are reported. The design phase mainly focused on deriving analytical scaling laws and finding a suitable size for such a model. Through the design analysis, an explanation to the discrepancy observed in the only previous attempt to validate long-term thermal behavior of boreholes is proposed.

Investigations as regards the KTH heat pump system, optimum flow rates in GSHPsystems with deep BHEs and quantification of thermal influence between neighboringboreholes are discussed although the work could not be fully completed within thetimeframe of the project.

The dissemination of knowledge through different activity is reported.

Publisher
p. 87
Keywords
Deep borehole, Ground-Source Heat Pump, Coaxial, Borehole Heat Exchanger, Drilling cost, Heat transfer, Thermal shunt, Hydraulic performance, Pressure drop, TRT, DTRT, Thermal Response Tests, Distributed Thermal Response Tests, Performance monitoring, Optimum flow, KTH Heat pump, Numerical model, Downscaling, lab-scale borehole storage, Distributed Temperature Sensing, Fiber optics
National Category
Energy Engineering
Research subject
Energy Technology; Real Estate and Construction Management
Identifiers
urn:nbn:se:kth:diva-239937 (URN)
Funder
Swedish Energy Agency, 40934-1
Note

QC 20181210

Available from: 2018-12-08 Created: 2018-12-08 Last updated: 2024-03-15Bibliographically approved
Mazzotti, W., Jiang, Y., Monzó, P., Lazzarotto, A., Acuña, J. & Palm, B. (2018). Design of a Laboratory BoreholeStorage model. In: Jeffrey Spitler, José Acuña, Michel Bernier, Zhaohong Fang, Signhild Gehlin, Saqib Javed, Björn Palm, Simon J. Rees (Ed.), Research Conference Proceedings: . Paper presented at International Ground-Source Heat Pump Association Research Conference 2018 (pp. 400-410).
Open this publication in new window or tab >>Design of a Laboratory BoreholeStorage model
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2018 (English)In: Research Conference Proceedings / [ed] Jeffrey Spitler, José Acuña, Michel Bernier, Zhaohong Fang, Signhild Gehlin, Saqib Javed, Björn Palm, Simon J. Rees, 2018, p. 400-410Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the design process of a 4x4 Laboratory Borehole Storage (LABS) model through analytical and numerical analyses. This LABS isintended to generate reference Thermal Response Functions (TRFs) as well as to be a validation tool for borehole heat transfer models. The objective of thisdesign process is to determine suitable geometrical and physical parameters for the LABS. An analytical scaling analysis is first performed and importantscaling constraints are derived. In particular, it is shown that the downscaling process leads to significantly higher values for Neumann and convectiveboundary conditions whereas the Fourier number is invariant. A numerical model is then used to verify the scaling laws, determine the size of the LABS,as well as to evaluate the influence of top surface convection and borehole radius on generated TRFs. An adequate shape for the LABS is found to be aquarter cylinder of radius and height 1.0 m, weighing around 1.2 tonnes. Natural convection on the top boundary proves to have a significant effect on thegenerated TRF with deviations of at least 15%. This convection effect is proposed as an explanation for the difference observed between experimental andanalytical results in Cimmino and Bernier (2015). A numerical reproduction of their test leads to a relative difference of 1.1% at the last reported time.As small borehole radii are challenging to reproduce in a LABS, the effect of the borehole radius on TRFs is investigated. It is found that Eskilson’sradius correction (1987) is not fully satisfactory and a new correction method must be undertaken.

Keywords
Laboratory model, Borehole storage, Downscaling, Thermal response function, Experiment design
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-238595 (URN)
Conference
International Ground-Source Heat Pump Association Research Conference 2018
Projects
Deep boreholes for Ground-Source Heat Pumps
Funder
Swedish Energy Agency
Note

QC 20181106

Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2022-06-26Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3490-1777

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