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Monitoring of a borehole thermal energy storage in Sweden
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0002-5093-9070
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0002-3490-1777
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2016 (English)In: CLIMA 2016-proceedings of the 12th REHVA World Congress: volume 3 / [ed] Per Kvols Heiseberg, Aalborg University, Department of Civil Enginnering, 2016, Vol. 3Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the description of the first stage of a project consisting on the monitoring of a newly installed borehole thermal energy storage (BTES) system that started to operate during the autumn of 2015. The BTES system is designed for approximately 4 GWh per year of heat injection and 3 GWh per year of heat extraction and will provide heating and cooling to a set of institutional facilities at Stockholm University, Sweden. The energy storage system consists of a set of 130 borehole heat exchangers, 230 meters deep. Strategic locations within the bore field have been selected to carry out the measurements. The monitoring system comprises temperature and energy flow meters. The temperature measurements are performed using a distributed temperature sensing set-up which allows to measure temperature along the depth of the boreholes, providing a large amount of data for the characterization of the thermal processes in the ground. During the upcoming years, the measured data will be utilized to evaluate and optimize the actual operational condition of the system, and to test the validity of assumptions made during the design phase. Moreover, the measured data will be utilized for validation of current bore field design methods and to have a better understanding of the thermal interaction between neighboring boreholes.

Place, publisher, year, edition, pages
Aalborg University, Department of Civil Enginnering, 2016. Vol. 3
Keyword [en]
ground-coupled heat pump; multiple bore field; borehole heat exchanger; monitoring system
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-187482ISBN: 87-91606-28-4 (vol3) (print)ISBN: 87-91606-36-5 (set) (print)OAI: oai:DiVA.org:kth-187482DiVA, id: diva2:932875
Conference
12th REHVA World Congress CLIMA, 22–25 May 2016
Funder
Swedish Energy Agency
Note

QC 20160603

Available from: 2016-06-02 Created: 2016-05-24 Last updated: 2018-01-29Bibliographically approved
In thesis
1. Modelling and monitoring thermal response of the ground in borehole fields
Open this publication in new window or tab >>Modelling and monitoring thermal response of the ground in borehole fields
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This Ph.D. dissertation aimed at developing tools for the evaluation of ground response in borehole fields connected in parallel through modelling and monitoring studies.

A total heat flow and a uniform borehole wall temperature condition equal in all boreholes have often been accepted when mathematically modelling the response of vertical ground heat exchangers connected in parallel. The first objective of this thesis was the development of a numerical model in which the ground controls the temperature response at the borehole wall, instead of imposing heat flow or temperature conditions at this interface. The unavoidable fluid-to- borehole wall thermal resistance and the variation of the heat flux distribution along the borehole depth violates the assumption of uniform temperature at the borehole wall. This aspect, which is often disregarded, was taken into account in this model. The results obtained from the numerical simulations are believed to come closer to reality and can be used as a reference for other approaches.

When bore field sizing, the worst ground load conditions are usually assumed to occur after several years of operation, but these may occur during the first year of operation. The second objective of this work was the development of a general sizing methodology that calculates the total required bore field length for each arbitrary month during the lifetime of the installations. The methodology was also used to investigate to what extent the borehole spacing can be reduced without increasing the total required bore field length when the ground load condition is thermally quasibalanced.

The ground source heat pump community still lacks detailed and accurately measured long-term data for validation of modelling tools. In order to partially contribute to filling this gap, the last part of this Ph.D. study focused on state of the art monitoring activities. The main goal of this part is to provide a comprehensive description of the ground thermal loads and response measurements at a large bore field, that is being monitored from the beginning of its operation. Unique data sets, showing the thermal loads and ground thermal response during extraction and injection, along with measurement error analyses are reported in the thesis. 

Abstract [sv]

I denna doktorsavhandling presenteras nya verktyg för utvärdering av berggrundens respons i geotermiska borrhålslager där borrhålen är kopplade parallellt. Avhandlingen beskriver både modellering och fältstudier.

Ett givet totalt värmeflöde och likformiga väggtemperaturer i alla borrhålen har ofta varit accepterade randvillkor vid matematisk modellering av den termiska responsen av parallellkopplade borrhålsvärmeväxlare i grupper av vertikala borrhål. Det första målet i arbetet med denna avhandling var att utveckla en numerisk modell i vilken berggrunden tillåts bestämma temperaturresponsen vid borrhålsväggen, istället för att som randvillkor ange ett visst värmeflöde eller en viss temperatur. Det ofrånkomliga värmemotståndet mellan flödet i slangen/värmeväxlaren och bergväggen och variationen i värmeflöde längs borrhålet innebär att dessa förenklade antaganden inte stämmer. Denna aspekt, som ofta förbisetts, har inkluderats i den här presenterade modellen. Resultaten som erhållits med denna numeriska modell kan förväntas vara närmare verkligheten än tidigare modeller och kan användas som referens för andra beräkningar.

Vid dimensionering av borrhålslager antas vanligen de värsta berggrundstemperaturerna inträffa efter flera års drift, men i avhandlingen visas att de värsta förhållandena kan uppstå under det första driftåret. Det andra målet med arbetet var att utveckla en generell dimensioneringsmetodik som kan användas för att beräkna den totala nödvändiga borrhålslängden för varje månad under installationens hela livslängd. Metodiken användes också för att undersöka i vilken mån borrhålsavståndet kan minskas utan att den totala borrhålslängden behöver ökas, under förutsättningen att borrhålslagret är ungefär balanserat.

Forskarsamhället saknar fortfarande detaljerade och noggrant uppmätta långtidsdata som kan användas för att validera olika modelleringsverktyg. I avsikt att i någon mån bidra till att fylla detta tomrum, innehåller den sista delen av avhandlingen beskrivningar av god teknik för utvärdering av borrhålslager.  Huvudmålet för denna del av avhandlingen är att ge en utförlig beskrivning av värmelasterna och responsmätningarna i ett stort borrhålslager som studerats sedan det först togs i bruk. Unika data rörande termiska laster och berggrundens termiska respons under värmeuttag och värmelagring, samt felanalys, presenteras i denna avhandling.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 124
Series
TRITA-ITM-AVL ; 2018:1
Keyword
ground temperature response, borehole heat exchanger, modelling, monitoring, sizing, bergtemperaturrespons, borrhålsvärmeväxlare, modellering, övervakning, dimensionering
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-222007 (URN)978-91-7729-667-6 (ISBN)
Public defence
2018-02-23, Sal D2, KTH, Lindstedtsvägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial PlanningSwedish Energy Agency
Note

QC 20180130

Available from: 2018-01-30 Created: 2018-01-29 Last updated: 2018-02-07Bibliographically approved

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Monzó, PatriciaAcuña, José

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