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Arid Land Geography ›› 2022, Vol. 45 ›› Issue (3): 836-846.doi: 10.12118/j.issn.1000-6060.2021.355

• Earth Surface Process • Previous Articles     Next Articles

Occurrence conditions of shallow geothermal energy and suitability analysis of soil source heat pump system in Lanzhou New District

FAN Bin1,4(),DING Hongwei2(),ZHANG Linxin1,4,ZHANG Lingpeng1,4,ZHANG Yongjun3,4   

  1. 1. The Second Institute of Geology and Minerals Exploration, Gansu Provincial Bureau of Geology and Minerals Exploration and Development, Lanzhou 730020, Gansu, China
    2. Gansu Provincial Bureau of Geology and Minerals Exploration and Development, Lanzhou 730000, Gansu, China
    3. Gansu Geological Environment Monitoring Institute, Lanzhou 730050, Gansu, China
    4. Gansu Provincial Key Laboratory of Groundwater Engineering and Geothermal Resources, Lanzhou 730050, Gansu, China
  • Received:2021-08-08 Revised:2021-12-19 Online:2022-05-25 Published:2022-05-31
  • Contact: Hongwei DING E-mail:362428520@qq.com;zydhw8029@163.com

Abstract:

Exploitation of shallow geothermal energy can optimize regional energy structure, save fossil fuel resources, and reduce carbon dioxide emissions. Understanding the subsurface characteristics which determine the suitability of an area for shallow geothermal energy is essential to provide a scientific basis for development planning and government decision-making. This study examines the conditions for shallow geothermal energy in both the existing built-up area and planned area of Lanzhou New District (440 km2 in total) in Gansu Province of northwest China, based on many years’ actual exploration and test data. An objective evaluation of the applicability of soil source heat pump (SSHP) systems was undertaken using an improved analytic hierarchy process (AHP) and the comprehensive index method. The results are that: (1) Lanzhou New District has generally excellent conditions for shallow geothermal energy utilizing SSHP systems. Specifically, the area has a simple and stable stratigrafic structure, high thermal conductivity, high specific heat capacity, and relatively high geothermal gradient. However, there are some unfavorable factors for developping groundwater source heat pump systems in the district, include a weak water-rich property aquifer and poor water quality. (2) The suitability evaluation model is based on an AHP divided into three attribute criteria and seven element indexes. This approach avoids some discrepancies inherent in a traditional judgement matrix constructed with the 1-9 scale proposed by Saaty. In this study, the judgement matrices for target layer and attribute criterion layer were constructed using an index scale, obtaining the weight of each factor to the target. Simultaneously, dimensionless parameters for each factor were optimized to make the model more efficient and give the evaluation result higher credibility. (3) The key factors affecting the suitability of SSHP are the average thermal conductivity and the geothermal gradient, which in this area are 1.807-2.676 W·m-1·K-1 and 0.30-0.40 ℃·km-1, respectively. The evaluation shows that “suitable” and “relatively suitable” areas for SSHP in the Lanzhou New District amount to 359.46 km2, which is 81.70% of the extent of the study area. Those suitable areas are chiefly located on the plains of Qinwangchuan Basin; other hilly and mountainous areas are less suitable for the installation of SSHP systems. Changing the traditional judgement matrix approach to this improved AHP-based evaluation process gives more accurate results more efficiently. The specific evaluation results of this study have clear practical value in guiding development planning for deployment of SSHP systems in Lanzhou New District and other comparable areas.

Key words: shallow geothermal energy, soil source heat pump, analytic hierarchy process (AHP), suitability, Lanzhou New District