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First Measurements of a Monitoring project on a BTES system
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
2017 (English)In: IGSHPA Technical/Research Conference and Expo, Denver, March 14-16, 2017, International Ground Source Heat Pump Association , 2017Conference paper, Published paper (Refereed)
Abstract [en]

Performance of Borehole Thermal Energy Storage (BTES) systems depends on the temperature of the secondary fluid, circulating through the ground-loop heat exchangers. Borehole systems are therefore designed in order to ensure that inlet and outlet temperatures of the secondary fluid are within given operational limits during the whole life-time of the system. Monitoring the operation of the bore fields is crucial for the validation of existing models utilized for their design. Measured data provides valuable information for researchers and practitioners working in the field. A first data-set from an ongoing monitoring project is presented in this article. The monitoring system comprises temperature sensors and power meters placed at strategic locations within the bore field. A distributed temperature sensing rig that employs fiber optic cables as linear sensors is utilized to measure temperature every meter along the depth of nine monitored boreholes, yielding data regarding both temporal and spatial variation of the temperature in the ground. The heat exchanged with the ground is also measured via power meters in all nine monitored boreholes as well as at the manifold level. The BTES system is located at the Stockholm University Campus, Sweden, and consists of 130 boreholes, 230 meters deep. After more than a year of planning and installation work, some selected measurements recorded in the BTES during the first months of operation are reported in this article.

Place, publisher, year, edition, pages
International Ground Source Heat Pump Association , 2017.
Keywords [en]
ground source heat pump, monitoring project, BTES
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-202532OAI: oai:DiVA.org:kth-202532DiVA, id: diva2:1077155
Conference
IGSHPA Technical/Research Conference and Expo, Denver, March 14-16, 2017
Note

QC 20170330

Available from: 2017-02-26 Created: 2017-02-26 Last updated: 2018-02-28Bibliographically 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
Keywords
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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