Numerical and experimental validation of a new hybrid model for vertical ground heat exchangers

Abstract A numerical and experimental validation of a new simplified model to simulate single U-tube ground heat exchangers is presented in this paper. The model is based on the use of the electrical analogy to model heat transfer within the borehole and thermal response factors (short and long time-step g-functions) to estimate heat flow to the surrounding ground. The substitution of ground nodes with short and long-term g-functions allows the simulation with short time steps, keeping the possibility of simulating periods of several years. The model has been validated experimentally by using the reference data sets drawn from two tests (constant heat input rate and interrupted tests) made under controlled laboratory conditions. The results have also been compared with the simulated data from a detailed Computational Fluid Dynamics model of the experimental system. A very good agreement has been observed for the modeled outlet fluid and borehole temperatures, with root mean square and relative error values smaller than 0.2 °C and 0.3%, respectively.

[1]  Marc A. Rosen,et al.  An analytical approach to evaluating the effect of thermal interaction of geothermal heat exchangers on ground heat pump efficiency , 2014 .

[2]  Philippe Pasquier,et al.  Short-term simulation of ground heat exchanger with an improved TRCM , 2012 .

[3]  Mehmet Esen,et al.  Experimental investigation of using ground source heat pump system for snow melting on pavements and bridge decks , 2010 .

[4]  Hongxing Yang,et al.  Vertical-borehole ground-coupled heat pumps: A review of models and systems , 2010 .

[5]  Ismael R. Maestre,et al.  Performance assessment of a simplified hybrid model for a vertical ground heat exchanger , 2013 .

[6]  Michele De Carli,et al.  Analysis of operating modes of a ground source heat pump with short helical heat exchangers , 2015 .

[7]  R. Al-Khoury,et al.  Efficient finite element formulation for geothermal heating systems. Part II: transient , 2006 .

[8]  Stanislaw Kajl,et al.  A review of methods to evaluate borehole thermal resistances in geothermal heat-pump systems , 2010 .

[9]  R. Al-Khoury,et al.  Efficient finite element formulation for geothermal heating systems. Part I: steady state , 2005 .

[10]  Michele De Carli,et al.  Performance of heat pumps with direct expansion in vertical ground heat exchangers in heating mode , 2015 .

[11]  J. Spitler,et al.  Reference data sets for vertical borehole ground heat exchanger models and thermal response test ana , 2011 .

[12]  Jong Min Choi,et al.  Current status of the performance of GSHP (ground source heat pump) units in the Republic of Korea , 2012 .

[13]  Min Li,et al.  Short-time performance of composite-medium line-source model for predicting responses of ground heat exchangers with single U-shaped tube , 2014 .

[14]  Thomas Kölbel,et al.  CO2 savings of ground source heat pump systems – A regional analysis , 2010 .

[15]  Simon J. Rees,et al.  Transient Analysis of Snow-Melting System Performance , 2002 .

[16]  Biagio Morrone,et al.  Energy and economic savings using geothermal heat pumps in different climates , 2014 .

[17]  O. J. Zobel,et al.  Heat conduction with engineering, geological, and other applications , 1955 .

[18]  Abdeen Mustafa Omer,et al.  Ground-source heat pumps systems and applications , 2008 .

[19]  Amanda Pertzborn,et al.  Experimental validation of a ground heat exchanger model in a hybrid ground source heat pump , 2011 .

[20]  Michele De Carli,et al.  A computational capacity resistance model (CaRM) for vertical ground-coupled heat exchangers , 2010 .

[21]  Georgios A. Florides,et al.  Ground heat exchangers—A review of systems, models and applications , 2007 .

[22]  Mehmet Esen,et al.  Experimental evaluation of using various renewable energy sources for heating a greenhouse , 2013 .

[23]  Jeffrey D. Spitler,et al.  A short time step response factor model for vertical ground loop heat exchangers , 1999 .

[24]  S. Patankar.  Numerical Heat Transfer and Fluid Flow , 2018, Lecture Notes in Mechanical Engineering.

[25]  Alvin C.K. Lai,et al.  Analytical model for short-time responses of ground heat exchangers with U-shaped tubes: Model development and validation , 2013 .

[26]  Mark A. Halverson,et al.  Integrating Renewable Energy Requirements Into Building Energy Codes , 2011 .

[27]  Li Shao,et al.  Simulation of a domestic ground source heat pump system using a three-dimensional numerical borehole heat exchanger model , 2011 .

[28]  J. C. Jaeger,et al.  Conduction of Heat in Solids , 1952 .

[29]  Hans Müller-Steinhagen,et al.  Thermal resistance and capacity models for borehole heat exchangers , 2011 .

[30]  Hongxing Yang,et al.  Numerical analysis and experimental validation of heat transfer in ground heat exchangers in alternative operation modes , 2008 .

[31]  Per Fahlén,et al.  Vertical ground heat exchangers: A review of heat flow models , 2009 .

[32]  Per Eskilson.  Thermal analysis of heat extraction boreholes , 1987 .