| 1. |
- Kordas, Olga, 1970-, et al.
(författare)
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A phenomenological theory of steady-state vertical geothermal systems: A novel approach
- 2019
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Ingår i: Energy. - : Elsevier. - 0360-5442. ; 175, s. 23-35
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a novel approach for studying the stationary energy characteristics of vertical geothermal systems (VGS) using stationary two-dimensional phenomenological mathematical theory. The approach describes VGS as a single, strongly nonequilibrium thermodynamic system consisting of a soil, a borehole with secondary fluid and a ground source heat pump (GSHP). The model uses continuity conditions for temperature and local heat fluxes between VGS components. The theory includes a special class of nonequilibrium spatial scale of VGS that is independent of its geometrical parameters. It is determined by the energy characteristics of the heat pump and the thermodynamic properties of soil and secondary fluid. Spatial variables can be chosen so that the energy characteristics of the VGS depend on only one dimensionless parameter (a similarity parameter), the thermal conductivity ratio of soil to secondary fluid. This considerably simplifies interpretation of theoretical and experimental results obtained using similarity methods. We show that, under real conditions of VGS functioning, the value of this similarity parameter varies from 0.5 to 10. The approach can be used to optimise GSHP systems to obtain energy of the required amount and quality to capitalise on heat pumps as ‘flexible agents’ in Smart Energy Systems.
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| 2. |
- Mulder, Karel F., et al.
(författare)
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Motivating students and lecturers for education in sustainable development
- 2015
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Ingår i: International Journal of Sustainability in Higher Education. - 1467-6370 .- 1758-6739. ; 16:3, s. 385-401
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Tidskriftsartikel (refereegranskat)abstract
- Purpose - This paper aims at identifying factors that could contribute to the motivation of students in sustainable development (SD) education. The underlying idea of the paper is that SD education is not always as attractive among students and lecturers as many would like it to be. Design/methodology/approach - The paper briefly reviews literature regarding behavioral change for long-term benefits. It identifies four motivators that could be effective to make people pursue longer-term objectives. It identifies if these motivators were present in five cases of successful SD education. Findings - The four motivators for students that were identified in the literature review (a sense of autonomy, a challenge of reflection on the future role, connection with others, self-fulfillment, focus on the individual learning need) could be observed in the cases of successful SD education, although to various degrees. Individual autonomy in learning was not observed, but group autonomy was present in all cases. Research limitations/implications - The case studies were all electives. It is unclear how the motivators could work out in mandatory courses. Moreover, the curriculum as a whole will affect the success of single courses. Successful courses being "the exception" of the curriculum might be judged differently if they would be part of the curriculum in which such courses would be the main stream. Further research is required to check if the motivators are effective in mandatory and not specifically SD-targeted courses. It is also not clear how various motivators could be applied most effectively in a curriculum. Practical implications - The paper gives guidance to lecturers and educational managers to design attractive and effective SD education. Originality/value - The paper treats SD education from a novel perspective: how to convey a credible behavioral message, and how to motivate students for education for SD.
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| 3. |
- Nikiforovich, Eugene, et al.
(författare)
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Unsteady energy transfer in vertical geothermal systems
- 2017
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Ingår i: Proceedings of the 2nd Thermal and Fluid Engineering Summer Conference, TFESC 2017 and 4th International Workshop on Heat Transfer, IWHT 2017. - : Begell House Inc.. ; , s. 2299-2306
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Konferensbidrag (refereegranskat)abstract
- A comprehensive energy analysis was performed on a unsteady strongly nonequilibrium thermodynamic system comprising the ground, a borehole heat exchanger (BHE), and a ground heat pump. The analysis was based on a theory of vertical geothermal systems (VGS) developed by the authors. The novelty of the proposed approach, in comparison to the conventional mathematical modeling of VGS, derives from the description of VGS as a unsteady single strongly nonequilibrium thermodynamic system consisting of soil (source of energy), borehole (energy well) and ground source heat pump (energy transducer), with continuity of energy flow conditions between its components. It was found that the system studied was characterized by two dimensionless parameters: the ratio of thermal conductivity and thermal diffusivity of the ground and the secondary fluid. Introduction of these parameters can significantly simplify the interpretation of results of theoretical and experimental studies using methods of the similarity theory. Furthermore, a definition of energy well debit was devised, the limiting stages of heat exchange in the conducting soil system were identified and a physical interpretation was made of the results obtained. The mathematical model developed was used for studying quantitative and qualitative characteristics of extractable energy. Finally, it was shown that the energy efficiency of each individual ground source heat pump (GSHP) system requires its own analysis and that the suggested approach can be used for optimization of GSHP systems in terms of their energy efficiency.
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