Abstract
Shallow geothermal energy (SGE) is a part of geothermal resources and is mainly used through ground source heat pumps (GSHP). However, the potential of SGE varies from region to region due to different geological conditions. There is a lack of regulations and codes for assessing SGE, which makes the design and planning of GSHP restricted. In this study, an evaluation system of the suitability of GSHP in a region of Qingdao by using Analytic Hierarchy Process (AHP) is proposed, and the test area is divided into three suitability levels based on suitability scores. The evaluation system contains property indicators, elemental indicators, and their weights. The result shows that the highly suitable area for the application of GSHP in the test area is 110.04 km2, accounting for 41.8% of the whole test area. The area of moderately suitable area is 65.02 km2, accounting for 24.7%, and GSHP should be developed and utilized on the basis of full demonstration in this level. The unsuitable area for GSHP is 88.19 km2, accounting for 33.5%. The indicator weights in this article may only be applicable to the Qingdao area and cities with similar geological conditions to Qingdao. However, the indicators within this evaluation system can be applied to the vast majority of locations where GSHP are to be developed, as it provides a method of assessment in terms of geological conditions, groundwater conditions, construction conditions, and ecological aspects.
Highlights
Shallow geothermal energy (SGE) is a part of geothermal resources, which generally refers to the thermal energy resources in the interior of the earth with a temperature of less than 25°C from the thermostatic zone to 200 m burial depth, and has the value of development and utilization at present
The main application of SGE is ground source heat pumps (GSHP), the Analytic Hierarchy Process (AHP) system in this study will be built on all factors that affect GSHP
This study establishes an evaluation system based on the geographic conditions, urban characteristics, and geological conditions in Qingdao
Summary
Shallow geothermal energy (SGE) is a part of geothermal resources, which generally refers to the thermal energy resources in the interior of the earth with a temperature of less than 25°C from the thermostatic zone to 200 m burial depth, and has the value of development and utilization at present. In China, it has been proven that the SGE resources available within 1.69 × 105 km are equivalent to 7 × 1012 kg of coal (Xu et al, 2020). In 2021, 58.8% of geothermal energy resources was extracted through ground source heat pumps (GSHP) (Lund et al, 2021), which provide energy by the borehole heat exchanger (BHE) (Sarbu et al, 2014). Suitability of Shallow Geothermal Energy (GB 50366-2009, 2009), the ground temperature and thermal conductivity obtained from thermal response tests are essential parameters. These two parameters cannot represent the development potential of SGE and efficiency of GSHP in detail (Luo et al, 2016). Before designing GSHP, the local geological environment, thermophysical properties of the soil, groundwater conditions, and construction costs need to be evaluated to ensure the efficiency of GSHP (Casasso et al, 2017)
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