Evaluation of the thermal efficiency and a cost analysis of different types of ground heat exchangers in energy piles

Abstract This paper presents an experimental and numerical study of the results of a thermal performance test using precast high-strength concrete (PHC) energy piles with W and coil-type ground heat exchangers (GHEs). In-situ thermal performance tests (TPTs) were conducted for four days under an intermittent operation condition (8 h on; 16 h off) on W and coil-type PHC energy piles installed in a partially saturated weathered granite soil deposit. In addition, three-dimensional finite element analyses were conducted and the results were compared with the four-day experimental results. The heat exchange rates were also predicted for three months using the numerical analysis. The heat exchange rate of the coil-type GHE showed 10–15% higher efficiency compared to the W-type GHE in the energy pile. However, in considering the cost for the installation of the heat exchanger and cement grouting the additional cost of W-type GHE in energy pile was 200–250% cheaper than coil-type GHE under the condition providing equivalent thermal performance. Furthermore, the required lengths of the W, 3U and coil-type GHEs in the energy piles were calculated based on the design process of Kavanaugh and Rafferty. The additional cost for the W and 3U types of GHEs were also 200–250% lower than that of the coil-type GHE. However, the required number of piles was much less with the coil-type GHE as compared to the W and 3U types of GHEs. They are advantageous in terms of the construction period, and further, selecting the coil-type GHE could be a viable option when there is a limitation in the number of piles in consideration of the scale of the building.

[1]  Stephen P. Kavanaugh,et al.  Ground Source Heat Pumps : Design of Geothermal Systems for Commercial and Institutional Buildings , 1997 .

[2]  Jalaluddin,et al.  Thermal performance investigation of several types of vertical ground heat exchangers with different operation mode , 2012 .

[3]  Seung-Rae Lee,et al.  Design of spiral coil PHC energy pile considering effective borehole thermal resistance and groundwater advection effects , 2014 .

[4]  Seung-Rae Lee,et al.  Life Cycle Cost Analysis for Ground-Coupled Heat Pump Systems Including Several Types of Heat Exchangers , 2013 .

[5]  Olcay Kincay,et al.  Comprehensive thermodynamic analysis of a renewable energy sourced hybrid heating system combined with latent heat storage , 2014 .

[6]  Fleur Loveridge,et al.  Influences on the thermal efficiency of energy piles , 2015 .

[7]  Philipp Blum,et al.  Greenhouse gas emission savings of ground source heat pump systems in Europe: A review , 2012 .

[8]  Xu Zhang,et al.  Thermal performance and ground temperature of vertical pile-foundation heat exchangers: A case study , 2008 .

[9]  Gao Jun,et al.  Evaluation of heat exchange rate of GHE in geothermal heat pump systems. , 2009 .

[10]  Arif Hepbasli,et al.  A review of heat pump water heating systems , 2009 .

[11]  G. Hellström,et al.  Multipole method to compute the conductive heat flows to and between pipes in a composite cylinder , 1987 .

[12]  Yasuhiro Hamada,et al.  Field performance of an energy pile system for space heating , 2007 .

[13]  Jong Min Choi,et al.  Heating performance characteristics of the ground source heat pump system with energy-piles and energy-slabs , 2015 .

[14]  Marc A. Rosen,et al.  Three-Dimensional Analysis of the Thermal Interaction of Multiple Vertical Ground Heat Exchangers , 2015 .

[15]  Daniel Pahud,et al.  Comparison of the thermal performance of double U-pipe borehole heat exchangers measured in situ , 2001 .

[16]  F. Kuwahara,et al.  A numerical model for thermal systems with helically-coiled tubes and its experimental verification , 2002 .

[17]  Seung-Rae Lee,et al.  Thermal transfer behavior in two types of W-shape ground heat exchangers installed in multilayer soils , 2014 .

[18]  M. Moreni,et al.  Comportement d'un pieu bi-fonction, fondation et échangeur de chaleur , 2003 .

[19]  Pingfang Hu,et al.  Performance study of a ground heat exchanger based on the multipole theory heat transfer model , 2013 .

[20]  H. Brandl.  Energy foundations and other thermo-active ground structures , 2006 .

[21]  J. Beck,et al.  Field Test of a New Method for Determining Soil Formation Thermal Conductivity and Borehole Resistance , 2000 .

[22]  H. Thomas,et al.  Ground heat transfer effects on the thermal performance of earth-contact structures , 2000 .

[23]  G. Florides,et al.  First in situ determination of the thermal performance of a U-pipe borehole heat exchanger, in Cyprus , 2008 .

[24]  Yi Man,et al.  Development of spiral heat source model for novel pile ground heat exchangers , 2011 .

[25]  Alvin C.K. Lai,et al.  New temperature response functions (G functions) for pile and borehole ground heat exchangers based on composite-medium line-source theory , 2012 .

[26]  Donggen Peng,et al.  A review on thermal response test of ground-coupled heat pump systems , 2014 .

[27]  O. J. Zobel,et al.  Heat conduction with engineering and geological applications , 1948 .

[28]  Hyunku Park,et al.  Evaluation of thermal response and performance of PHC energy pile: Field experiments and numerical simulation , 2013 .

[29]  S. Kavanaugh,et al.  Simulation and Experimental Verification of Vertical Ground-coupled Heat Pump Systems , 1985 .

[30]  Frank P. Incropera,et al.  Fundamentals of Heat and Mass Transfer , 1981 .

[31]  Jungwoo Choi,et al.  Numerical simulation of vertical ground heat exchangers: Intermittent operation in unsaturated soil conditions , 2011 .

[32]  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 .

[33]  Xu Zhang,et al.  Numerical and experimental assessment of thermal performance of vertical energy piles: An application , 2008 .

[34]  Jean L. Cornillot,et al.  Annual Book of ASTM Standards , 2016 .

[35]  Yusuf Ali Kara,et al.  Evaluation of low temperature geothermal energy through the use of heat pump , 2001 .

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