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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
Fasci, M. L., Mazzotti, W., Lazzarotto, A. & Claesson, J. (2023). Temperature of energy boreholes accounting for climate change and the built environment - A new model for its estimation. Renewable energy, 202, 1479-1496
Open this publication in new window or tab >>Temperature of energy boreholes accounting for climate change and the built environment - A new model for its estimation
2023 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 202, p. 1479-1496Article in journal (Refereed) Published
Abstract [en]

Changes in the ground surface temperature, as it can occur in built-up areas or due to climate change, affect the temperatures of geothermal boreholes. Analytical models for the thermal simulation of boreholes and consid-ering this factor have been proposed. However, they all impose a uniform heat extraction boundary condition along the borehole walls. This boundary condition overestimates the temperature change in the underground caused by the borehole heat extraction and underestimates it in case of rejection. More accurate results are most often obtained by imposing a uniform temperature boundary condition.In this paper, we propose a new model to calculate the boreholes wall temperature taking into account both the heat extractions/rejections from all the boreholes in the area and the change in ground surface temperature. The model is tailored for areas with independent ground source heat pumps and imposes a uniform temperature boundary condition along the borehole walls, overcoming the limitation of the existing models.We apply the new model to a real Swedish neighbourhood and show that existing systems may already be significantly affected by the increased ground surface temperature due to urbanization. We also compare our new model with an existing similar model and show that while the two models provide similar results for smaller areas, their difference tends to be relevant for bigger areas - including the real Swedish neighbourhood analysed -thus making the application of our model important for neighbourhood-and city-scale studies.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Ground-source heat pumps, Geothermal boreholes, Thermal interference, Effect of the ground surface, Analytical modelling
National Category
Building Technologies Energy Engineering
Identifiers
urn:nbn:se:kth:diva-323416 (URN)10.1016/j.renene.2022.12.023 (DOI)000905157000006 ()2-s2.0-85144377238 (Scopus ID)
Note

QC 20230307

Available from: 2023-02-01 Created: 2023-02-01 Last updated: 2023-09-15Bibliographically 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. (2021). Thermal response tests: A biased parameter estimation procedure?. Geothermics, 97, Article ID 102221.
Open this publication in new window or tab >>Thermal response tests: A biased parameter estimation procedure?
2021 (English)In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 97, article id 102221Article in journal (Refereed) Published
Abstract [en]

Thermal response tests are used to estimate the thermal properties of the ground and the borehole heat exchanger being tested. They are thus important for the design of borehole thermal energy storages and ground source heat pump systems. In this study, a theoretical framework is proposed in order to investigate if noise on the heat rate leads to a bias in the parameter estimation. Under the sole assumption of a linear time-invariant system and the use of the sum of squared errors as cost function, it is shown analytically that estimates are in fact biased when the heat rate is corrupted by noise. To understand how large this bias can be, a Monte-Carlo study is performed. It includes more than 126,000 simulations with different noises, thermal parameters and heat rate profiles. Negative biases as high as -0.44 W/(m K) (11%) and -11.10(-3) m K/W (4.1%) are observed for the thermal conductivity and borehole thermal resistance estimates, respectively. In addition, the parameter estimation is stochastic due to randomness of measurement noises. This cannot be ignored since only one thermal response test is performed, in general. Population of estimates with 95% confidence intervals as large as 1.0 W/(m K) (25%) and 24.10(-3) m K/W (9.4%) appear in this study. Although the bias and confidence intervals are not significant in all simulated cases, they cannot be generally disregarded and one should therefore be mindful of this potential issue when analyzing thermal response tests. An observed trend is that the confidence intervals and bias are higher for higher parameter values, with a particular dependency on thermal conductivity. To reduce the bias and spread of the estimates, having larger heat rate per meter appears to be a good strategy. Having a higher sampling frequency and/or longer tests might also help, but only in reducing the spread of the estimates, not the bias.

Place, publisher, year, edition, pages
Elsevier BV, 2021
Keywords
Thermal response test, Parameter estimation, Error-in-variables, Bias, BTES, Monte-Carlo, LTI
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-304181 (URN)10.1016/j.geothermics.2021.102221 (DOI)000706996700001 ()2-s2.0-85115939772 (Scopus ID)
Note

QC 20211105

Available from: 2021-11-05 Created: 2021-11-05 Last updated: 2022-06-25Bibliographically 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
Fascì, M. L. & Lazzarotto, A. (2019). A novel model for the estimation of thermal influence of neighbouring borehole heat exchangers. In: EGEC (Ed.), EUROPEAN GEOTHERMAL CONGRESS 2019: THE HAGUE, 11-14 JUNE 2019. Paper presented at European Geothermal Congress 2019.
Open this publication in new window or tab >>A novel model for the estimation of thermal influence of neighbouring borehole heat exchangers
2019 (English)In: EUROPEAN GEOTHERMAL CONGRESS 2019: THE HAGUE, 11-14 JUNE 2019 / [ed] EGEC, 2019Conference paper, Published paper (Refereed)
Abstract [en]

Ground source heat pumps (GSHPs) connected to vertical boreholes are popular systems to provide heat and/or refrigeration in residential and commercial buildings. The diffusion of these systems poses the question on how to effectively and sustainably handle the underground thermal resource without overexploiting it. In particular, this question can rise in densely populated areas where either heat extraction or heat rejection is dominant.Although several models are available and used to estimate the thermal influence between individual boreholes or group of hydraulically connected boreholes, the development of models that can quantify the thermal influence of neighbouring boreholes having different boundary conditions (it is the case for individual GSHP installations located in the same neighbourhood) is still at its early stages. The availability of such tools is essential both to enable the legislators to set appropriate rules for the allocation of the underground thermal resource and to enable the designers to properly size these systems.In this paper, we develop a model based on the stacked finite line source method that is tailored to estimate the thermal interaction of neighbouring GSHPs. The model takes as input the heat load of each GSHP and imposes uniform temperature on every borehole. The model is applied to a fictitious densely populated area to calculate the temperature changes on the boreholes walls of the systems. The results are compared with the results obtained with another model previously proposed by the authors.

Keywords
Ground source heat pumps, thermal influence, neighbouring boreholes, stacked finite line source
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-255168 (URN)
Conference
European Geothermal Congress 2019
Note

QC 20190902

Available from: 2019-07-24 Created: 2019-07-24 Last updated: 2024-03-18Bibliographically 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
Lazzarotto, A. & Mazzotti Pallard, W. (2019). Thermal response test performance evaluation with drifting heat rate and noisy measurements. In: European Geothermal Congress 2019, Proceedings: . Paper presented at European Geothermal Congress 2019. The Hague, Article ID 295.
Open this publication in new window or tab >>Thermal response test performance evaluation with drifting heat rate and noisy measurements
2019 (English)In: European Geothermal Congress 2019, Proceedings, The Hague, 2019, article id 295Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
The Hague: , 2019
National Category
Energy Engineering Energy Systems
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-254536 (URN)
Conference
European Geothermal Congress 2019
Note

QC 20190826

Available from: 2019-07-01 Created: 2019-07-01 Last updated: 2024-03-15Bibliographically 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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0550-2769

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