Experimental study on heat transfer performance of double U-shaped buried tube heat exchanger

Authors

LI Lei, China Coal Research Institute, Beijing 100013, China; China Coal Pingshuo Group Co., Ltd., Shuozhou 036006, ChinaFollow
ZHANG Weidong, CCTEG Xi’an Research Institute(Group)Co., Ltd., Xi’an 710077, China
XU Shuanhai, China Coal Research Institute, Beijing 100013, China; China Coal Pingshuo Group Co., Ltd., Shuozhou 036006, ChinaFollow
ZHAO Yongzhe, China Coal Research Institute, Beijing 100013, China; China Coal Pingshuo Group Co., Ltd., Shuozhou 036006, China
DANG Dongsheng, CCTEG Xi’an Research Institute(Group)Co., Ltd., Xi’an 710077, China
WANG Qilong, CCTEG Xi’an Research Institute(Group)Co., Ltd., Xi’an 710077, China
GOU Li, CCTEG Xi’an Research Institute(Group)Co., Ltd., Xi’an 710077, China
LEI Yanzi, CCTEG Xi’an Research Institute(Group)Co., Ltd., Xi’an 710077, China

Abstract

Double U-shaped buried tube heat exchanger (DUBTHE) are prone to pipe crossing and thermal short-circuiting in the practical applications, resulting in the reduced heat transfer performance and directly affecting the operational efficiency of shallow geothermal heat pump system. Based on the initial line thermal average temperature, thermal conductivity theory and slope method, and taking a shallow geothermal heat pump project in Xi'an as the engineering background. Then, this study investigate the effects of initial average temperature, thermal conductivity and volumetric heat capacity of rock-soil, and tube clamp spacing on the heat transfer performance of DUBTHE through field geotechnical thermal response testing and different temperature measurement methods. The results show that the initial average temperature of rock-soil measured by the multi-point temperature measurement cable is 17.08℃, which is closer to the actual formation temperature. Besides, the comprehensive thermal conductivity and volumetric heat capacity of rock-soil in the formation are 1.65 W/(m·K) and 2.81×10⁶ J/(m³·K), respectively. In addition, the heat exchange per linear meter of DN25 DUBTHE in summer and winter increases with the decreasing tube clamp spacing, with the acceleration increasing firstly and then decreasing with the decreasing tube clamp spacing. Definitely, the heat exchange per linear meter of DN25 DUBTHE in summer is increased by 21.03%, 19.48%, 15.16% and 3.92% respectively compared with that without tube clamp, and that in winter is increased by 20.83%, 19.48%, 14.94% and 3.79%, respectively, in case that the tube clamp spacing is 1 2, 3, and 4 m. DN25 DUBTHE with a tube clamp spacing of 2 m or 3 m is the optimal arrangement in the project. Therefore, the results could provide experience and data support for the optimal design of shallow ground source heat pump systems in Guanzhong area.

Keywords

double U-shaped buried tube，geotechnical thermal response test，heat transfer performance，shallow geothermal heat pump，tube clamp spacing

DOI

10.12363/issn.1001-1986.22.09.0701

Recommended Citation

LI Lei, ZHANG Weidong, XU Shuanhai, et al. (2023) "Experimental study on heat transfer performance of double U-shaped buried tube heat exchanger," Coal Geology & Exploration: Vol. 51: Iss. 4, Article 14.
DOI: 10.12363/issn.1001-1986.22.09.0701
Available at: https://cge.researchcommons.org/journal/vol51/iss4/14

Reference

[1] SHAH A,KRARTI M,HUANG J. Energy performance evaluation of shallow ground source heat pumps for residential buildings[J]. Energies,2022,15(3):1025.

[2] LI Zhongjian,ZHENG Maoyu. Development of a numerical model for the simulation of vertical U−tube ground heat exchangers[J]. Applied Thermal Engineering,2009,29:920−924.

[3] BEIER R A. Transient heat transfer in a U−tube borehole heat exchanger[J]. Applied Thermal Engineering,2014,62:256−266.

[4] KERME E D,FUNG A S. Comprehensive simulation based thermal performance comparison between single and double U–tube borehole heat exchanger and sensitivity analysis[J]. Energy & Buildings,2021,241:110876.

[5] 杨卫波. 土壤源热泵技术及应用[M]. 北京：化学工业出版社，2015.

[6] 杨培志,陈嘉鹏,陈君文,等. 双U型地埋管换热器换热性能模拟分析[J]. 中南大学学报(自然科学版),2021,52(6):1733−1738.

YANG Peizhi,CHEN Jiapeng,CHEN Junwen,et al. Simulation and analysis of heat transfer performance of double U−tube ground heat exchangers[J]. Journal of Central South University (Science and Technology),2021,52(6):1733−1738.

[7] 邓军涛,张继文,郑建国,等. 不同形式和管径的地埋管换热器换热性能分析[J]. 太阳能学报,2015,36(11):2590−2596.

DENG Juntao,ZHANG Jiwen,ZHENG Jianguo,et al. Analysis on thermal performance of different type and diameter ground heat exchanger[J]. Acta Energiae Solaris Sinica,2015,36(11):2590−2596.

[8] 邓军涛,王娟娟,郑建国. 不同管径和埋深地埋管换热器换热性能分析[J]. 太阳能学报,2021,42(9):416−421.

DENG Juntao,WANG Juanjuan,ZHENG Jianguo. Analysis on thermal performance of ground heat exchanger with various diameters and depths[J]. Acta Energiae Solaris Sinica,2021,42(9):416−421.

[9] FLORIDES G A,CHRISTODOULIDES P,POULOUPATIS P. Single and double U−tube ground heat exchangers in multiple−layer substrates[J]. Applied Energy,2013,102:364−373.

[10] 沈国民,张虹. 竖直U型埋管地热换热器热短路现象的影响参数分析[J]. 太阳能学报,2007,28(6):604−607.

SHEN Guomin,ZHANG Hong. Parametric analysis of thermal interference in vertical U−tube heat exchangers for GCHP[J]. Acta Energiae Solaris Sinica,2007,28(6):604−607.

[11] PU Liang,XU Lingling,QI Di,et al. Structure optimization for horizontal ground heat exchanger[J]. Applied Thermal Engineering,2018,136:131−140.

[12] PU Liang,XU Lingling,QI Di,et al. A novel tree–shaped ground heat exchanger for GSHPs in severely cold regions[J]. Applied Thermal Engineering,2019,146:278−287.

[13] JAHANBIN A. Thermal performance of the vertical ground heat exchanger with a novel elliptical single U–tube[J]. Geothermics,2020,86:101804.

[14] LI Xinguo,CHEN Yan,CHEN Zhihao,et al. Thermal performances of different types of underground heat exchangers[J]. Energy and Buildings,2006,38(5):543−547.

[15] 穆玄,裴鹏,周鑫,等. 岩溶构造对地埋管群换热效率影响数值模拟研究[J]. 煤田地质与勘探,2022,50(10):131−139.

MU Xuan,PEI Peng,ZHOU Xin,et al. Numerical simulation of the influence of karst structure on heat transfer efficiency of buried pipeline group[J]. Coal Geology & Exploration,2022,50(10):131−139.

[16] 李娟,郑佳,雷晓东,等. 地质条件及埋管形式对地埋管换热器换热性能影响研究[J]. 地球学报,2023,44(1):221−229.

LI Juan,ZHENG Jia,LEI Xiaodong,et al. Study on the influence of geological conditions and heat exchanger type on BHE thermal performance[J]. Acta Geoscientica Sinica,2023,44(1):221−229.

[17] SCHIBUOLA L,SCARPA M. Ground source heat pumps in high humidity soils:An experimental analysis[J]. Applied Thermal Engineering,2016,99:80−91.

[18] LI Wenxin,LI Xiangdong,PENG Yuanling,et al. Experimental and numerical studies on the thermal performance of ground heat exchangers in a layered subsurface with groundwater[J]. Renewable Energy,2020,147:620−629.

[19] 朱红梅. 基于双U型地埋管的岩土热响应试验数据处理分析研究[D]. 西安：西安建筑科技大学，2014.

ZHU Hongmei. Study on the insitu soil thermal response test data processing methods of double U–tube BHE[D]. Xi’an：Xi’an University of Architecture and Technology，2014.

[20] GEHLIN S. Thermal response test：Method development and evaluation[D]. Lulea：Lulea University of Technology，2002.

[21] YOON S,KIM M J. Prediction of ground thermal diffusivity from thermal response tests[J]. Energy and Buildings,2019,185:239−246.

[22] American Society of Heating，Refrigerating and Air–conditioning Engineers. 2007 ASHRAE Handbook–HVAC applications (SI)[M]. New York：Stephen Comstock，2007.

[23] SPITLER J D,GEHLIN S E A. Thermal response testing for ground source heat pump systems:An historical review[J]. Renewable and Sustainable Energy Reviews,2015,50:1125−1137.