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Developments in Ground Heat Storage Modeling
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ground heat storage systems can play an important role for the reduction of green house gases emissions by increasing the exploitation of renewable energy sources and “waste heat” with a consequent diminution of the use of fossil fuels.

A ground heat storage consists in an array of vertical boreholes placed in such a way that promotes the mutual thermal interaction between the ground heat exchangers creating the necessary conditions required to effectively store and retrieve heat. Suitable modeling tools for the estimation of the thermal behavior of these systems are very important to build installations yielding economical performance compatible with what expected during the design phase.

This thesis aims at giving a contribution in the development of the thermal modeling of borehole heat storage systems. The main objective is introducing in the modeling process a few features that are not usually considered in state of the art models, with the goal of improving the representation of the physical phenomena. These features are the mathematical description of the topology of the borehole heat exchangers network, and the modeling of borehole fields with arbitrarily oriented boreholes.

The detailed modeling of the topology of the borehole heat exchangers is approached with a network model. The overall geothermal system is discretized into smaller systems called components. These are linked between each other in a network fashion to establish the logical relations required to describe a given boreholes connections arrangement. The method showed that the combination of a sufficient level of discretization of the system and of a network representation yields respectively the granularity and the flexibility required to describe any borehole field connections configuration.

The modeling of non-vertical borehole fields is approached by developing a method for the calculation of g-functions for these configurations. The method is an extension of a recent work done by Cimmino on the computation of g-functions for vertical borehole fields. This modeling technique is based on describing boreholes as sets of stacked finite line sources and on the superposition principle. This approach requires the computation of response factors relative to couples of finite lines. A procedure for the fast computation of these response factors for the case of arbitrarily oriented lines is given. This yields computational performance that guarantees the practical feasibility of the methodology.

The last part of the thesis deals with the modeling of the storage system from a broader perspective. The borehole field is considered as part of a larger system constituted by several interacting components (i.e. heat pump, building, etc.). Interactions play a key role in the resulting overall performance of these systems. The analysis of the mutual relations between building envelope and borehole field design is utilized as an example to highlight advantages and challenges of strategies yielding a more integrated design.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 73 p.
Series
Meddelande. Institutionen för byggvetenskap, ISSN 1651-5536 ; 2015:01
Keyword [en]
Borehole fields, g-functions, network, inclined, integrated design
National Category
Energy Engineering Building Technologies
Research subject
Energy Technology; Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-166219ISBN: 978-91-7595-566-7 (print)OAI: oai:DiVA.org:kth-166219DiVA: diva2:809862
Public defence
2015-05-29, Kollegiesalen, Brinnelvägen 8, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
VINNOVA
Note

QC 20150507

Available from: 2015-05-07 Created: 2015-05-05 Last updated: 2015-05-07Bibliographically approved
List of papers
1. The application of the parametric analysis for improved energy design of a ground source heat pump for residential buildings
Open this publication in new window or tab >>The application of the parametric analysis for improved energy design of a ground source heat pump for residential buildings
2013 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 63, 119-128 p.Article in journal (Refereed) Published
Abstract [en]

Energy use in buildings represents a major share of the overall energy used in developed countries. The reduction of the energy demand and the efficient energy use are often seen as feasible ways for a more sustainable energy use in the built environment. Ground source heat pumps (GSHPs) are efficient systems to supply heating and cooling energy to buildings but their design is critical for their performance. Furthermore, their performance depends on the cooling and heating demand and on the environmental conditions. The need for the end-use energy for a building supplied with GSHP has been studied with regard to four parameters in two different locations. The effect of two building performance parameters, roof and external walls insulation, and of two parameters affecting the performance of GSHP, boreholes spacing and number of boreholes, have been investigated by means of factorial analysis. Results show that from an energy point of view the optimal configurations of the boreholes change depending on the variation of building parameters such as insulation. The methodology proposed allows to quantify the impact of different design configurations on the need for end-use energy.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Parametric analysis, GSHP, Energy, Residential buildings
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-105421 (URN)10.1016/j.enbuild.2013.03.050 (DOI)000320909500012 ()2-s2.0-84877789247 (Scopus ID)
Funder
Swedish Research Council FormasVINNOVASwedish Research Council
Note

QC 20130812. Updated from submitted to published.

Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2017-12-13Bibliographically approved
2. A network-based methodology for the simulation of borehole heat storage systems
Open this publication in new window or tab >>A network-based methodology for the simulation of borehole heat storage systems
2014 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 62, 265-275 p.Article in journal (Refereed) Published
Abstract [en]

The optimization of strategies to operate borehole thermal energy storage systems can play an important role for the exploitation of this technology. Available tools utilized for the design of borehole fields don't consider these aspects in the calculation. For this reason a network-based methodology which gives a sufficient level of detail to describe different system operation strategies has been developed. In particular, the method allows to calculate how the heat is distributed among the borehole heat exchangers in the field according to the way the brine is supplied to the borehole heat storage system. This enables to test the same borehole field configuration pattern for different piping arrangement. An example of application where a simultaneous need of heating and cooling is met by extracting and injecting heat in different region of the ground storage is considered to illustrate the potential of the method.

Keyword
Borehole heat exchanger, Finite line source, Ground heat storage
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-139252 (URN)10.1016/j.renene.2013.07.020 (DOI)000328095000030 ()2-s2.0-84881256923 (Scopus ID)
Funder
Vinnova
Note

QC 20140109

Available from: 2014-01-09 Created: 2014-01-08 Last updated: 2017-12-06Bibliographically approved
3. A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 1
Open this publication in new window or tab >>A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 1
2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 86, 1380-1393 p.Article in journal (Refereed) Published
Abstract [en]

This article is part of a two paper series presenting a development in the methodology for the calculation of response functions for geothermal fields with arbitrarly oriented boreholes. In the method utilized, boreholes are represented as sets of stacked line sources and the borehole temperatures are calculated by means of a superposition procedure. This particular paper is focused on the efficient computation of the building block of this approach, which is the non dimensional mean temperature response g~(t) along a finite line due to a step heat injection along a second finite line, where the lines are arbitrarily oriented. The speed in computing this function is critical for the applicability of the method. The solution proposed to achieve the required performance is a hybrid approach involving analytical, numerical and implementation aspects: an analytical procedure to simplify the expression of g~(t) was developed, the resulting problem was solved with a tailored numerical method, and the algorithm was implemented using a high-performing programming language. Each of these aspects showed to have a great impact from a performance perspective. The performance achieved in the calculation of g~(t) enables the integration of this method within the scheme utilized for g-functions calculation.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
inclined boreholes, g-functions, computational efficiency
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-166216 (URN)10.1016/j.renene.2015.09.056 (DOI)000364248300133 ()2-s2.0-84943614039 (Scopus ID)
Funder
VINNOVA
Note

Updated from Manuscript to Article. QC 20160126

Available from: 2015-05-05 Created: 2015-05-05 Last updated: 2017-12-04Bibliographically approved
4. A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 2
Open this publication in new window or tab >>A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 2
2016 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 86, no 01, 1353-1361 p.Article in journal (Refereed) Published
Abstract [en]

In the modeling of shallow geothermal systems, the accurate representation of the borehole field configuration is important for a proper estimation of the long term thermal behavior of borehole field systems. Modeling tools based on the so-called g-functions method, utilized for the design of borehole fields, assume that boreholes are vertical. This is a limitation since this condition might not apply in a real installation. This paper is focused on the calculation of g-functions of borehole fields featuring non-vertical boreholes. The strategy utilized consists in representing the boreholes as stacked finite line sources. The temperature along these finite lines, can be calculated by superposition of the effects of each linear heat source in the field. This modeling technique allows to approximate uneven heat distribution among the boreholes and along the axis of each individual borehole. This is a required feature for the calculation of g-functions according to Eskilson's boundary conditions. The test cases presented show that the method yields results that are compatible with the expected physical behavior of the system, and similar to previous results by Eskilson. The computational performance achieved indicates that the method proposed could be potentially utilized during the design phase of these systems.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
inclined boreholes, g-functions, superposition
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-166217 (URN)10.1016/j.renene.2015.09.057 (DOI)000364248300130 ()2-s2.0-84944048511 (Scopus ID)
Funder
VINNOVA, 2009-04475
Note

Updated from Manuscript to Article.

QC 20160204

Available from: 2015-05-05 Created: 2015-05-05 Last updated: 2017-12-04Bibliographically approved

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