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A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 2
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.ORCID iD: 0000-0001-7073-2600
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. Vol. 86, no 01, 1353-1361 p.
Keyword [en]
inclined boreholes, g-functions, superposition
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-166217DOI: 10.1016/j.renene.2015.09.057ISI: 000364248300130Scopus ID: 2-s2.0-84944048511OAI: oai:DiVA.org:kth-166217DiVA: diva2:809832
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
In thesis
1. Developments in Ground Heat Storage Modeling
Open this publication in new window or tab >>Developments in Ground Heat Storage Modeling
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
Borehole fields, g-functions, network, inclined, integrated design
National Category
Energy Engineering Building Technologies
Research subject
Energy Technology; Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-166219 (URN)978-91-7595-566-7 (ISBN)
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

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Citation style
  • apa
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