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Limitations of using uniform heat flux assumptions in sizing vertical borehole heat exchanger fields.

Number: pap. 475

Author(s) : MALAYAPPAN V., SPITLER J. D.

Summary

Models of ground heat exchangers and the surrounding ground are essential for design, optimization and energy analysis of ground heat exchangers (GHE) used with ground source heat pump (GSHP) systems. These models can account for ground thermal response of GHE in timescales ranging from hours to as long as years. A commonly used, computationally efficient method utilizes a dimensionless response function known as a g-function. The heat extraction and rejection loads on the GHE are devolved into a series of step inputs, then the g-function is used to determine the response due to each step input, and the temperature responses are superimposed to determine the evolution of borehole temperatures with time. G-functions for specific borehole configurations are calculated by superimposition of single borehole responses and have been obtained with both numerical and analytical approaches. The numerical approach offers the most flexibility and does not require the approximation that all boreholes have uniform heat fluxes. However, the numerical approach requires significant computation time and the only practical approach at present is to pre-compute a library of g-functions. This paper examines the limitations of the uniform heat flux assumption as embodied in one analytical approach with a parametric study.

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Pages: 10 p.

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Details

  • Original title: Limitations of using uniform heat flux assumptions in sizing vertical borehole heat exchanger fields.
  • Record ID : 30009226
  • Languages: English
  • Source: Clima 2013. 11th REHVA World Congress and 8th International Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings.
  • Publication date: 2013/06/16

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