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Long-Term Thermal Performance Modelling and Simulations of a Borehole
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
2005 (English)In: Proceedings of the 7th Symposium on Building Physics in the Nordic Countries, Reykjavik, Iceland., 2005, 1-8 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the long-term thermal performance modelling and simulation of a single heat extraction borehole with a U-shaped pipe, by applying the Macro Element Modelling (MEM) method, developed by Schmidt (2004). The dynamic thermal performance of the ground around the borehole is analysed in the frequency domain. Thereafter, the ground properties are transformed into a network of discrete resistances and capacitances (RC’s) that together with the pipe, models the thermal performance of the borehole. The method allows the parameters of the RC- network components to be estimated and optimised for time domain simulations. The advantage of this modelling method is that it establishes a simplified yet accurate thermal borehole model, which requires less computing time and power compared to a traditional finite difference/element model. This makes it easier to perform several decades of long-term thermal performance simulations. In this paper the U-pipe was modelled by applying a star resistance network that calculates the weighted heat fluxes between the solid borehole and the U-pipe. The presented work shows that at small temperature increases and at relative large fluid velocities the U-pipe fluid temperature can be seen as rising linearly. This provides the borehole modelling with the possibility to model the entire borehole construction by using only one macro element. To compensate for any errors when using the linearly increasing fluid temperature for calculating the energy extraction from the borehole, the total U-pipe star resistance network is compensated. The U-pipe star network was also compared with a FEM (Finite Element Method) simulation, showing that the correspondence between the two models is good. The half 5-node network that was used by Schmidt (2004) for modelling the solid construction of the borehole was modified in this paper, with an additional resistance to ensure the stability of the network when simulation long-term heat extraction periods. The borehole RC-network was optimised for a time period of 100 years. The results from the long-term performance simulation made with the derived borehole model, were also compared to other presented borehole simulations. The model proved to have, at a first stage of comparison, a good correspondence with the other presented results.

Place, publisher, year, edition, pages
2005. 1-8 p.
Keyword [en]
Borehole, long-term thermal performance, Macro Element Modelling (MEM), simulations.
National Category
Building Technologies Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-19456OAI: oai:DiVA.org:kth-19456DiVA: diva2:338081
Note
QC 20100810Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-11-17Bibliographically approved
In thesis
1. Lifetime Performance Assessment of Thermal Systems: Studies on Building, Solar and Disctrict Heating Applications
Open this publication in new window or tab >>Lifetime Performance Assessment of Thermal Systems: Studies on Building, Solar and Disctrict Heating Applications
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main questions today concerning thermal systems are their economical and environmental impacts. These entities are generally, at present, assessed on the basis of operation performances of newly installed/designed systems, during an assumed lifetime period. While this is the common way of perceiving thermal systems, performance-over-time will change as an effect of degradation, and not solely of different operation scenarios. How and to what extent is the question that needs assessing in order to evaluate if these changes will jeopardise the intended system performance requirement, hence service life (SL). The lack of knowledge/approaches and tools for assessing durability and performance-over-time of thermal systems complicates the task of incorporating these aspects in engineering. In turn, this pro-active assessment and analysis is in line with today’s performance based directives, laws and regulations; of which the working life is an essential part. The durability of materials, components and systems is not a topic that is an end in itself, but becomes a vital part in a comprehensive perspective as sustainability. The lifetime performance assessment of thermal systems, as presented in this thesis, shows that it is a vital part of the R&D in the quest of sustainable energy/thermal systems and energy use.

This thesis gives knowledge to the thermal (energy) system/technology R&D and engineering sector, regarding durability and lifetime performance assessment methodologies; but also to the durability of construction works sector, regarding the needs for assessing lifetime performance of materials and components in relation to system performance. It also presents descriptions of requirements on construction works. Specifically, the studies presented in the thesis show how durability and lifetime performance assessment of thermal systems may be sought, with knowledge on: methodologies, exposure test set-ups, modelling and the attainment and use of adequate tools. The main focus is on performance-over-time modelling, tying material/component degradation to altered thermal performance, thereby attaining performance-over-time assessment tools to be used in order to incorporate these aspects when engineering thermal systems; hence enabling the forecasting of SL. The presented work was predominantly done in association to the EU project ENDOHOUSING. The project developed a solar-assisted heat pump system solution, with heat storage, to provide the thermal energy to meet space heating, cooling and hot water requirements for domestic houses in different regions of the EU. The project constituted the platform for the work presented in this thesis, thereby outlining the main context with studies on durability and lifetime performance of:

  • flat plate solar collectors
  • ground heat sources/storages and interaction with a heat pump system
  • evaluation of the ENDOHOUSING solar-assisted heat pump system

The thesis also presents a study of SL prediction and estimation of district heating distribution networks (an additional thermal system application). In this particular context, the Factor Method is proposed as a methodology. The main issue of lifetime performance of thermal systems is how and to what extent performance reduction in individual materials or components influence the overall system performance, as the essence of energy/thermal system sustainability is system performance.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xvi, 112 p.
Keyword
Lifetime performance, degradation, assessment, modelling, field exposure, thermal components and system
National Category
Building Technologies Materials Engineering
Identifiers
urn:nbn:se:kth:diva-10967 (URN)978-91-7415-384-2 (ISBN)
Public defence
2009-09-11, Gävle Teknikpark, Hörsalen, Nobelvägen 2, Gävle, 10:00 (English)
Opponent
Supervisors
Note
QC 20100810Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2012-03-23Bibliographically approved

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