Regional-Scale Assessment of the Potential for Shallow Geothermal Energy Development Using Vertical Ground Source Heat Pumps

Abstract

Shallow geothermal energy (SGE) is a widely prevalent geological resource underground, and its utilization offer significant energy conservation and emission reduction benefits, contributing to the achievement of carbon neutrality goals. Assessing the development potential of regional SGE can ensure sustainable development of these resources and prevent adverse effects induced by overexploitation. Jiangsu Province, a developed region in the eastern coastal area of China, has a strong demand for cooling and heating in urban buildings. The primary form of utilizing SGE in this area is through vertical ground source heat pumps (VGSHP). Based on the analysis of the impact of regional geological conditions on the development of SGE, this study specifically evaluated the suitability of developing SGE through VGSHP. After excluding areas unsuitable for development, the heat exchange capacity, heating or cooling area per unit area, and energy conservation and emission reduction benefits of VGSHP were calculated. The results indicate that the area suitable and moderately suitable for developing SGE through VGSHP in Jiangsu Province amounts to 76,453 km². The total heat exchange capacity for summer is 1.21 × 10⁹ kW, which can provide cooling for an area of 1.21 × 10¹⁰ m². The total heat exchange capacity for winter is 8.70 × 10⁸ kW, which can provide heating for an area of 1.09 × 10¹⁰ m². The annual available resource amount is 2.68 × 10¹² kWh, equivalent to 3.30 × 10⁸ tons of standard coal, and a CO² reduction of 7.86 × 10⁸ tons.

1. Introduction

Shallow geothermal energy (SGE) has significant advantages, such as wide distribution, large reserves, and cyclic regeneration. As an alternative to fossil fuels, it contributes to achieving carbon peak and carbon neutrality goals, offering broad prospects for development [1,2]. SGE is a type of thermal energy with a temperature usually below 25 °C that is contained in rock, soil, and water bodies within a certain depth range below the earth’s surface (generally from the constant temperature zone to 200 m below ground). It can be utilized for cooling in summer and heating in winter through ground source heat pumps (GSHP) [3,4]. Compared with traditional air-conditioning systems, GSHP have a relatively high heat transfer efficiency, and eliminate the costs of the transportation and storage of fossil energy. GSHP do not produce waste gases or residues, and they have outstanding energy conservation and emission reduction benefits [5,6].

Quantitative assessment of regional SGE is conducive to ensuring the rational and orderly development of the resource, avoiding the adverse effects induced by overexploitation [7,8]. In recent years, along with the rapid development of the SGE industry, especially in China, a series of resource and environmental issues have become increasingly prominent [9,10,11]. Typically, individual GSHP projects operate well, but large-scale utilization has not yielded ideal results, with low heat exchange efficiency. Several important reasons for this include ignoring the endowment characteristics of local SGE, adopting a one-size-fits-all development model, and overestimating the resource carrying capacity of SGE [12]. Essentially, SGE is a kind of geological resource, and its development potential is constrained by regional geological conditions [13]. Before large-scale utilization, it is crucial to conduct appropriate evaluations of the resource development potential and implement strategic planning based on local conditions [14,15]. Additionally, there are various methods of utilizing SGE, including buried pipe heat exchange systems (further divided into horizontal and vertical buried pipes), groundwater heat exchange systems, and surface water heat exchange systems [16] (see Figure 1). It is insufficient to support the efficient use of SGE through a generalized assessment of its development potential without distinguishing between utilization methods [17].

Jiangsu Province is located in the Yangtze River Delta region along the eastern coast of China, with a permanent population of 85.26 million. Situated in the transitional zone between subtropical and warm temperate climates, the province experiences dry and cold winters and hot and humid summers, resulting in strong demand for heating and cooling in urban buildings. To promote regional low-carbon development, local authorities have introduced several policies encouraging the development of SGE. Due to strict groundwater protection measures within the province, the application of groundwater source heat pump systems is significantly restricted, and the utilization of SGE in the region typically adopts vertical ground source heat pumps (VGSHP).

This study focuses on Jiangsu Province and, based on an analysis of the geological factors affecting SGE development, establishes suitability zoning standards for the development of SGE using VGSHP. Suitability zoning was completed using the ArcGIS platform 10.8, and a quantitative assessment of the potential for SGE development through VGSHP was carried out in terms of heat exchange capacity, heating or cooling area per unit area, and energy conservation and emission reduction benefits.

2. Overview of the Study Area

Jiangsu Province is located in the Yangtze River Delta region on the eastern coast of China, comprising 13 cities with a total land area of 107,200 km² (see Figure 2). In 2023, the province’s GDP reached 12.82 trillion RMB, ranking among the leading provinces in China. At the end of the year, the resident population was approximately 85.26 million, creating a strong demand for cooling and heating in urban buildings. The region’s topography is predominantly flat, with expansive plains covering 86.89% of the area, while the remainder consists of hilly and mountainous terrain. The province spans two tectonic units: the North China Plate and the South China Plate, with extensive and thick Quaternary deposits. The region experiences ample rainfall and is rich in rivers and lakes. Situated in a transition zone between the subtropical and warm-temperate climate zones, the area exhibits distinct monsoon characteristics, with cold, dry winters and hot, humid summers, and an average annual temperature ranging from 13.6 °C to 16.1 °C. The initial average soil temperature is between 17.0 °C and 18.1 °C (below 25 °C), which is favorable for the development of SGE. Through an analysis of typical SGE projects in Jiangsu Province (

Table 1. Statistics on VGSHP pipe configurations, burial depths, and spacing in typical projects across Jiangsu Province.

Project Title	U-Tube Configuration	Burial Depth (m)	Spacing (m)
Zhenjiang Intercity Railway	single	120	4.6–5
Suqian Star International Hotel	double	100	4.5
Yangzhou Sunshine Midtown Community	double	80	5
Taicang Yuexing Home Furnishing Plaza (Buildings 1–3)	single	80	—
Nanjing Bafao East Street Residential Project	double	80	5
Suzhou Railway Station	double	103	3–6
Nanjing Hexi New City G51 Parcel Project	double	85	4.2
Nanjing Tech University Houchong Green Low-carbon Industrial Park	double	100	4.5
Funing County People’s Hospital South New District Branch	double	100	5
Haimen Zhongnan Group Headquarters Office Building	single	100	4.5–6.3
Suqian Public Security Bureau Business and Technical Facilities	double	100	4.5–6
Lianshui Central City Buildings 24, 25, and 26	single	100	5
Changzhou Wujin Binhu City Commercial and Office Complex	single	100	5
Yixing Science and Technology Incubation Park Phase I	single	100	5
Changshu Shajiabang Hot Spring Resort Hotel	double	120	3–5
People’s Government of Hongqiao Town, Taixing City, Jiangsu Province	single	100	—
Jiangyin Zhonghua Garden Phase I	double	65–70	5
Bosch China Headquarters Phase I Building 1	double	100	—
Wuxi Lan Kwai Fong Commercial Project	single	100	5
Huai’an Qingjiang Family Residential Buildings 1–4	double	110	>4.5
Taizhou Municipal Government Logistics Service Center	double	70	4–6
Nantong Railway Station Building	double	68–71	4.5
Changzhou *	single	80	4
Taizhou *	single/double	80–120	4.5/5
Suzhou *	single/double	50–100	4.5/5
A Certain City in Jiangsu Province *	single	75	5

Note: “*” indicates that the project name is unknown, and “—” indicates that the data for this item are unknown.

), it was observed that SGE is primarily exploited using VGSHP, with a pipe spacing of 4–6 m and a burial depth of approximately 100 m.

3. Procedures and Methodology

SGE is carried by geological bodies composed of rock, soil, and water. Its resource potential is controlled by regional geological conditions. To conduct a resource potential assessment, it is first necessary to analyze the geological conditions of its occurrence. To achieve more accurate evaluation results, areas unsuitable for SGE development have been excluded. Therefore, before conducting the resource potential assessment, it is necessary to perform suitability zoning for resource development based on the analysis of geological conditions. For VGSHP, there are no unified suitability zoning standards, and this paper discusses this issue as well. The final estimation of resource development potential references previous research results and evaluates from three aspects: heat exchange capacity, heating or cooling area per unit area, and energy-saving and emission reduction benefits (see Figure 3).

3.1. Analysis of the Impact of Geological Conditions on SGE

The geological conditions affecting the development of SGE primarily include geological structure, topography and landforms, geological strata, and groundwater. The mechanisms by which these factors influence SGE development are as follows.

3.1.1. Geological Structures

Geological structures can influence various aspects of the geothermal field, including the temperature and depth of the isothermal layer and the geothermal gradient [18]. Typically, geological structures have a significant impact on the enrichment of deep geothermal resources. In large sedimentary basins, the structural morphology of the basement directly affects the distribution characteristics of the terrestrial heat flow, with heat flow values generally higher in uplift areas compared to subsidence areas [19]. Near major deep fault structures, there is a noticeable change in the geothermal field distribution, with the influence diminishing significantly away from the fault zones [20]. Additionally, geological structures also affect the homogeneity and water-bearing properties of geological bodies, as well as site stability [21].

In Jiangsu Province, the main geological structures and geothermal gradients are shown in Figure 4a. Multiple episodes of tectonic activity have resulted in the development of faults and folds, making this region one of the most geothermal resource-rich areas in eastern China. The largest fault systems trend northeastward, and the geothermal gradient lines generally follow this northeastward distribution pattern. These faults cause the geothermal gradient in southern Jiangsu to be significantly lower compared to other regions. Furthermore, east–west trending faults control regional uplift and subsidence, leading to a higher geothermal gradient in central Jiangsu compared to other areas, while the Xuzhou composite syncline crossing the Xuzhou urban area results in a lower geothermal gradient in the Xuzhou region.

3.1.2. Topography and Landforms

Topographical variations directly affect the construction costs of SGE development, especially for VGSHP, where costs are significantly higher in mountainous areas compared to flat plains. Typically, regions with significant differences in topography and landforms also exhibit variations in climate and hydrological conditions, which influence the inherent characteristics of shallow geothermal resources [22].

From Figure 4b, it can be seen that in the Ningzhenyang region and the Yishu region, which are characterized by hilly and mountainous terrain, the Quaternary cover layer is relatively thin, and in some areas, the bedrock is exposed on the surface. These factors impose limitations on the development and utilization of SGE, resulting in higher costs. In contrast, in the remaining flat plain areas, the thickness of the surface loose layer is greater, making the development and utilization of SGE less challenging and more cost-effective.

3.1.3. Geological Strata

The geological strata that compose the rock and soil bodies serve as the medium for the storage, transfer, and dissipation of SGE. Stratum characteristics have a significant impact on the occurrence of SGE. There are substantial differences in density, water content, and porosity among rock and soil layers [23]. Even within soil layers, different genesis types exhibit significant variations in their physical, mechanical, and thermal properties, which affect the static storage of SGE [24]. Additionally, the cost of drilling through different strata varies, which impacts the initial investment for the development and utilization of SGE.

In Jiangsu Province, the majority of the area is covered by Quaternary loose soil layers, with a thickness generally ranging from 100 to 200 m (see Figure 4c). In the transitional zone from the plain to the hilly terrain, the thickness of the soil layer decreases; for example, in the southwestern Nanjing area, the average soil layer thickness is around 40 m. In regions where the bedrock is exposed or shallowly buried, such as in the northwest and southwest, the potential for developing SGE is lesser compared to areas with thicker overlying soil layers.

3.1.4. Groundwater

Hydrogeological conditions largely determine the amount of SGE reserves and the efficiency of their development. Water serves as an excellent medium for heat storage and transfer, and the depth, thickness, and recharge-runoff-extraction conditions of aquifers are crucial for the design of GSHP and directly affect heat exchange performance [25]. Generally, regions with high precipitation, abundant groundwater recharge, and fast renewal rates are favorable for the construction of GSHP and can prevent heat (or cooling) accumulation effects [26].

In Jiangsu Province, the vast Quaternary loose soil layers in the plains exhibit significant variability in groundwater quantity and characteristics due to differences in ancient water systems and hydrodynamic conditions (see Figure 4d). The Yangtze River middle and lower reaches groundwater system is the most abundant groundwater resource area in Jiangsu, with thick aquifers, good permeability, and a direct hydraulic connection with the Yangtze River, making it an ideal area for the development of SGE. Conversely, in the hilly and mountainous regions, the clastic rock fracture aquifer groups have relatively poor groundwater resources and thus a smaller potential for SGE development. Although the groundwater system in the lower Huaihe River region has a considerable aquifer thickness, the sediment particles are relatively fine, resulting in moderate water richness and a development potential for SGE that is between that of the Yangtze River Delta region and the hilly and mountainous areas.

3.2. Suitability Zoning for SGE Development Using VGSHP

Environmental factors affecting the utilization of SGE are numerous. If GSHP are applied in unsuitable areas, it may lead to a series of adverse environmental effects, and the maintenance costs of the system could be excessively high, or the heat exchange efficiency may not meet expectations. The suitability zoning standards for different types of GSHP vary. Based on an environmental analysis of resource utilization, a set of suitability evaluation standards for VGSHP was established, and the suitability zoning was completed using the ArcGIS platform.

3.2.1. Suitability Zoning Standards

The purpose of suitability zoning for SGE is to ensure the technical feasibility and economic rationality of geothermal energy development in a given region. Therefore, the suitability zoning should be based on the geological conditions of SGE and adhere to principles that prioritize both economic efficiency and environmental protection. Based on the analysis of the geological environmental background’s impact on SGE development, the suitability indicators for VGSHP mainly consider the thickness of Quaternary strata, the thickness of gravel layers, the thickness of groundwater aquifers, and regional policy protection requirements.

• Thickness of Quaternary Strata

Drilling is the primary reason for the higher initial investment of VGSHP compared to traditional air conditioning systems. The difficulty of drilling through rock layers is significantly higher than that of the loose Quaternary cover layers, and the thickness of Quaternary strata greatly influences the economic feasibility of VGSHP. Moreover, most groundwater is found in Quaternary strata, where a greater thickness of Quaternary strata generally indicates better water-bearing properties and is more favorable for heat pump system performance. Hence, the thickness of Quaternary strata is a critical factor for the suitability zoning of VGSHP.

• Thickness of Gravel Layers

The thickness of gravel layers in the Quaternary strata is a crucial factor affecting the difficulty of drilling heat exchange wells. Drilling through gravel layers is challenging and can lead to well collapse accidents, significantly increasing drilling costs. Thus, the thickness of gravel layers is an essential indicator for the suitability zoning of VGSHP.

• Thickness of Groundwater Aquifers

Water has a specific heat capacity of 4.2 × 10³ J/(kg·K), while the specific heat capacity of rock and soil is around 1.2 × 10³ J/(kg·K). Water’s heat storage capacity is much greater than that of soil and rock. A thicker groundwater aquifer increases the capacity for heat storage, which benefits the heat exchange efficiency of the VGSHP. Additionally, groundwater flow enhances the heat transfer capacity of the soil and rock mass and reduces the time needed for the underground environment to reach thermal equilibrium, thereby improving heat exchange efficiency. Regions with thicker groundwater aquifers generally have higher groundwater flow velocities. Thus, the thickness of groundwater aquifers is a vital criterion for the suitability zoning of VGSHP.

• Environmental Protection Requirements

GSHP should be avoided in restrictive drilling areas, such as coastal regions with saline and freshwater aquifers where drilling could breach confining layers and cause cross-contamination. Additionally, certain water source protection zones should be avoided. When employing GSHP, local policies, laws, and regulations must be followed.

Based on the above analysis and in combination with the recommended standards in the “Specification for shallow geothermal energy investigation and evaluation” [27], the suitability zoning standards for developing SGE using VGSHP are detailed in

Table 2. Suitability zoning standards for developing SGE using VGSHP.

Zoning Results	Zoning Criteria (within the 200 m Depth Range)			Comprehensive Evaluation
	Thickness of Quaternary Strata (m)	Thickness of Gravel Layers (m)	Thickness of Groundwater Aquifers (m)
Suitable area	>100	<5	>30	All three indicators meet the criteria
Moderately suitable area	<30 or 50~100	5~10	10~30	When other comprehensive evaluation criteria are not met
High-cost area	30~50	>10	<10	At least two indicators meet the criteria
Restricted area	Important water source protection areas and special areas with drilling restrictions			Any one indicator meets the criteria

Based on data collected from the Jiangsu Provincial Geological Data Center, the thickness of the Quaternary strata, pebble layers, and aquifers in Jiangsu Province are shown in Figure 5.

.

The thickness of the Quaternary strata in Jiangsu generally decreases from east to west. Influenced by geological structures, the thickness of the Quaternary strata aligns well with geomorphological units. Most of Jiangsu’s area consists of alluvial and depositional plains formed by river and marine actions, characterized by flat terrain covered with thick Quaternary layers. The eastern region, a tectonic subsidence zone, has the greatest thickness due to long-term marine sedimentation. Due to tectonic activity and paleoenvironments, the Quaternary thickness in Yancheng, Nantong, and Taizhou generally exceeds 200 m. In contrast, thinner Quaternary layers are found in the northern and southwestern hilly regions of Jiangsu, such as the Ningzhen area and Lianyungang’s low hills, where bedrock is exposed in some parts.

The regions with significant thicknesses of pebble and gravel layers are concentrated in the Yangtze River floodplain, the northern hills of Lianyungang, and the urban area of Xuzhou. In large areas along the Yangtze River in Yangzhou and Zhenjiang, the pebble layers generally exceed 10 m in thickness. In Xuzhou and its surroundings, thick gravel layers present considerable drilling challenges. In the plains, sandy layers dominate the subsurface, with minimal or thin pebble layers and small pebble diameters, reducing the impact on drilling operations.

Most regions in Jiangsu have aquifer thicknesses exceeding 30 m. Hydrological geological zoning reveals poor aquifer conditions in the western hilly hydrogeological area, particularly in the southern Gaochun–Lishui belt. Northern areas of the Huaibei Plain hydrogeological zone also show poor aquifer conditions, characterized by hilly terrain with thin Quaternary layers and lacking loose rock aquifers. In contrast, thick sandy aquifers over 30 m are prevalent in the plains, especially in the coastal plain and Yangtze River Delta plain hydrogeological zones, providing excellent groundwater reservoirs.

3.2.2. Suitability Zoning Based on the ArcGIS Platform

The ArcGIS platform, known for its powerful data management, spatial analysis, and mapping capabilities, is widely used in natural resource evaluation [28]. In this study, the suitability zoning was performed using ArcGIS software, with the following specific steps:

• Data Input and Basic Information Editing

The coordinates of the study area were entered into the ArcMap module of ArcGIS to create and load data layers. Basic information about the region, including boundaries, administrative divisions, rivers, and lakes, was edited.

2.

Digitalization of Indicators and Interpolation Calculations

Maps of the regional distribution of various indicators were imported into the ArcMap module and digitized. Interpolation calculations for the digitized indicators were performed according to the suitability zoning standards to process the conditions for each indicator.

3.

Visualization of Results and Output

The calculation results were visualized, including the addition of legends and the output of standard maps to produce and export the suitability zoning results.

3.3. Evaluation of the Potential for Developing SGE Using VGSHP

The assessment of the potential for developing SGE is based on the suitability zoning results. For the areas deemed suitable and moderately suitable, the potential for SGE development is determined by calculating the heat exchange capacity, heating or cooling area per unit area, and energy conservation and emission reduction benefits.

• Heat Exchange Capacity Calculation

The method for calculating the heat exchange capacity is as follows. The total heat exchange capacity is determined based on the single-borehole heat exchange power and the number of available boreholes [27]:

H_t = H_s × n × 10⁻³

(1)

n = C_L × A ÷ A_B × 10⁶

(2)

where H_t is the total heat exchange capacity, kW; H_s is the single-borehole heat exchange capacity, W; n is the number of heat exchange boreholes in the area; C_L is the land utilization coefficient; A is the land area available for VGSHP, km²; and A_B is the land area occupied by a single heat exchange borehole, km².

In this study, the single-borehole heat exchange power is derived from field heat exchange test data, using the heat exchange rate per meter of depth. The data were collected from on-site tests conducted in various locations across Jiangsu Province (see

Table 3. Heat exchange capacity per meter of rock and soil in cities of Jiangsu Province.

City	Heat Exchange Capacity per Meter of Single U-Tube (W/m)		Heat Exchange Capacity per Meter of Double U-Tube (W/m)
	Heat Dissipation	Heat Extraction	Heat Dissipation	Heat Extraction
Nanjing	48/60	40/40	70/69.6	60/51.2
Wuxi	58/65	39/35	67/65.5	48/47
Xuzhou	—	—	69.3	46.8
Changzhou	67	53	—	—
Suzhou	53/58	34/50	65/81	50/64
Nantong	60/62.6	40/49.25	75	50
Huaian	52	45	66	45
Yancheng	—	—	70	50
Yangzhou	55.5	43	63.5/62.2	51/50.7
Taizhou	60.6/49	44.3/35.1	77.2/62.52	52.8/41.99

Note: “—” indicates that the single borehole heat exchange data for this city are temporarily unavailable and has been estimated using analogous conditions from similar regions.

). According to local conditions, the depth of vertical boreholes is set at 100 m.

To determine the number of heat exchange boreholes, it is necessary to consider the heat exchange pipe spacing, construction land area, and land utilization coefficient. Data on the average spacing of buried pipes from ground source heat pump projects in Jiangsu Province were used, with a spacing of 5 m assumed for calculations. The area for calculation includes only suitable and moderately suitable regions, with a land utilization coefficient of 0.3 applied to account for existing buildings and municipal facilities.

2.

Heating or Cooling Area per Unit Area Calculation

Based on the suitability zoning and heat exchange capacity calculations, and combined with the indoor thermal load indicators for buildings, the area available for heating and cooling per unit area is calculated:

A_h/c = H_t ÷ L_h/c ÷ A_t

(3)

where A_h/c is the heating or cooling area per unit Area, m²/km²; H_t is the total heat exchange capacity, kW; L_h/c is the heating or cooling indicators, W/m²; and A_t is the total area available for SGE utilization, km².

Jiangsu Province, spanning from the north to the south of China, is located in a region with hot summers and cold winters, requiring both summer cooling and winter heating. The GSHP in the study area are mainly used for commercial residential and office buildings. The cooling and heating load indicators for the calculation process are based on the design values in the “Practical Handbook of Heating and Air Conditioning Design” [29], which are 100 W/m² for cooling and 80 W/m² for heating.

3.

Calculation of Energy Conservation and Emission Reduction Benefits

Energy conservation is represented by converting the saved energy into its standard coal equivalent, and the emission reduction benefits are represented by converting the standard coal equivalent into the saved emission control costs.

The formula to convert the amount of SGE development into its standard coal equivalent is [30]:

E_c = Q_t ÷ q × 0.24

(4)

Q_t = (W_H × T_h + S_H × T_c) × t

(5)

where E_c is the amount of standard coal equivalent, tons; Q_t is the total amount of energy used for heating and cooling, kWh; q is the heating value of standard coal, 7000 kcal/kg; 0.24 is the conversion factor from kcal to MJ; W_H is the heat exchange capacity in winter, kW; T_h is the number of heating days; S_H is the heat exchange capacity in summer, kW; T_c is the number of cooling days; and t is the daily operating hours. The heating and cooling periods in Jiangsu Province are set at 90 days and 120 days respectively, with the system operating 12 h per day.

Using the standard coal equivalent method, the reductions in CO₂, SO₂, NOx, and particulate matter are calculated as follows [31]:

R = η × E_c

(6)

where R is the amount of emission reduction, tons; and η is the conversion factors between the amounts of CO₂, SO₂, NO_x, and dust and the equivalent amount of standard coal (in tons, E_c), with the conversion factors being 2.386, 0.017, 0.006, and 0.008, respectively.

The cost of emission control is shown in

Table 4. The unit cost of emission control.

Emissions	CO2	SO2	NOx	Dust
Treatment cost (Yuan/kg)	0.1	1.1	2.4	0.8

.

4. Results

4.1. Suitability Zoning Results

Based on the suitability zoning standards and using the ArcGIS platform, the suitability for VGSHP in Jiangsu Province has been divided into four categories: Suitable Area, Moderately Suitable Area, High-Cost Area, and Restricted Area (see Figure 6).

• Suitable area

Covering approximately 35,204 km², this zone is primarily located in the eastern plain region of Jiangsu Province. The surface is largely covered by thick Quaternary sediments, with some local areas having Quaternary thicknesses exceeding 300 m. The lithology is predominantly sand, offering good drilling conditions. The thick underground aquifers and excellent runoff conditions ensure high heat exchange efficiency and economic viability.

• Moderately suitable area

Spanning a total area of 41,249 km², this zone mainly encompasses the Ningzhenyang hilly region and the Xuhuai Yellow River alluvial plain area. The Quaternary thickness is relatively thin, and bedrock is present within the drilling depth range, affecting the economic feasibility of drilling. The aquifer conditions and recharge status are not as favorable as in the eastern plain area.

• High-cost area

Covering an area of 4756 km², this zone is predominantly distributed across the hilly regions where bedrock is exposed or shallow. The presence of gravel layers, poor groundwater conditions, and deep groundwater levels negatively impact the stability and economic viability of the system.

• Restricted area

These are mainly water source protection zones and areas where drilling is prohibited by policy. They are scattered throughout the region.

4.2. Potential Estimation Results

Based on the suitability zoning and excluding high-cost and restricted areas, using Formulas (1)–(6), the results of the heat exchange capacity, heating or cooling area per unit area, and energy conservation and emission reduction benefits of VGSHP in various cities in Jiangsu Province are shown in

Table 5. The results of heat exchange capacity of VGSHP in various cities in Jiangsu Province.

City	Calculation Area (km2)	Land Utilization Coefficient (%)	Area per Borehole (m2)	Number of Drilled Boreholes	Borehole Depth (m)	Summer Heat Exchange Capacity per Borehole (kW)	Winter Heat Exchange Capacity per Borehole (kW)	Total Summer Heat Exchange Capacity (kW)	Total Winter Heat Exchange Capacity (kW)
Nanjing	4897	30	25	1.60 × 107	100	6.98	5.56	1.12 × 108	8.89 × 107
Wuxi	3458	30	25	9.88 × 106	100	6.63	4.75	6.55 × 107	4.69 × 107
Xuzhou	9822	30	25	2.36 × 107	100	6.93	4.68	1.63 × 108	1.10 × 108
Changzhou	3631	30	25	1.02 × 107	100	6.70	5.30	6.80 × 107	5.38 × 107
Suzhou	4826	30	25	1.32 × 107	100	7.30	5.70	9.64 × 107	7.53 × 107
Nantong	6209	30	25	1.31 × 107	100	7.50	5.00	9.84 × 107	6.56 × 107
Lianyungang	4176	30	25	1.15 × 107	100	7.00	5.00	8.07 × 107	5.76 × 107
Huaian	8334	30	25	1.51 × 107	100	6.60	4.50	9.97 × 107	6.80 × 107
Yancheng	12,530	30	25	1.98 × 107	100	7.00	5.00	1.39 × 108	9.92 × 107
Yangzhou	4867	30	25	1.14 × 107	100	6.29	5.09	7.20 × 107	5.83 × 107
Zhenjiang	2765	30	25	7.80 × 106	100	6.40	4.50	4.99 × 107	3.51 × 107
Taizhou	4694	30	25	1.32 × 107	100	6.99	4.74	9.21 × 107	6.25 × 107
Suqian	6244	30	25	1.08 × 107	100	6.60	4.50	7.12 × 107	4.86 × 107
Total	76,453			1.76 × 108				1.21 × 109	8.70 × 108

,

Table 6. The results of heating or cooling area per unit area of VGSHP in various cities in Jiangsu Province.

City	Unit Cooling Load (W/m2)	Unit Heating Load (W/m)	Cooling Area in Summer (m2)	Heating Area in Winter (m2)	Cooling Area Served per Unit Area (m2/km2)	Heating Area Served per Unit Area (m2/km2)
Nanjing	100	80	1.12 × 109	1.11 × 109	2.28 × 105	2.27 × 105
Wuxi	100	80	6.55 × 108	5.86 × 108	1.89 × 105	1.70 × 105
Xuzhou	100	80	1.63 × 109	1.38 × 109	1.66 × 105	1.40 × 105
Changzhou	100	80	6.80 × 108	6.73 × 108	1.87 × 105	1.85 × 105
Suzhou	100	80	9.64 × 108	9.41 × 108	2.00 × 105	1.95 × 105
Nantong	100	80	9.84 × 108	8.20 × 108	1.58 × 105	1.32 × 105
Lianyungang	100	80	8.07 × 108	7.20 × 108	1.93 × 105	1.73 × 105
Huaian	100	80	9.97 × 108	8.49 × 108	1.20 × 105	1.02 × 105
Yancheng	100	80	1.39 × 109	1.24 × 109	1.11 × 105	9.90 × 104
Yangzhou	100	80	7.20 × 108	7.28 × 108	1.48 × 105	1.50 × 105
Zhenjiang	100	80	4.99 × 108	4.39 × 108	1.80 × 105	1.59 × 105
Taizhou	100	80	9.21 × 108	7.81 × 108	1.96 × 105	1.66 × 105
Suqian	100	80	7.12 × 108	6.07 × 108	1.14 × 105	9.72 × 104
Total			1.21 × 1010	1.09 × 1010	1.58 × 105	1.42 × 105

, and

Table 7. The results of energy conservation and emission reduction benefits of VGSHP in various cities in Jiangsu Province.

City	Available Resource Amount (kWh)			Equivalent Standard Coal (tons)			Emission Reduction (tons)
	Summer	Winter	Total Available Resources Amount	Summer	Winter	Total Equivalent Standard Coal	CO2	SO2	NOx	Dust
Nanjing	1.61 × 1011	9.60 × 1010	2.57 × 1011	1.98 × 107	1.18 × 107	3.16 × 107	7.53 × 107	5.37 × 105	1.89 × 105	2.53 × 105
Wuxi	9.43 × 1010	5.07 × 1010	1.45 × 1011	1.16 × 107	6.23 × 106	1.78 × 107	4.25 × 107	3.03 × 105	1.07 × 105	1.43 × 105
Xuzhou	2.35 × 1011	1.19 × 1011	3.54 × 1011	2.89 × 107	1.47 × 107	4.36 × 107	1.04 × 108	7.41 × 105	2.62 × 105	3.49 × 105
Changzhou	9.79 × 1010	5.81 × 1010	1.56 × 1011	1.20 × 107	7.15 × 106	1.92 × 107	4.58 × 107	3.26 × 105	1.15 × 105	1.54 × 105
Suzhou	1.39 × 1011	8.13 × 1010	2.20 × 1011	1.71 × 107	1.00 × 107	2.71 × 107	6.46 × 107	4.60 × 105	1.62 × 105	2.17 × 105
Nantong	1.42 × 1011	7.08 × 1010	2.12 × 1011	1.74 × 107	8.71 × 106	2.61 × 107	6.23 × 107	4.44 × 105	1.57 × 105	2.09 × 105
Lianyungang	1.16 × 1011	6.22 × 1010	1.78 × 1011	1.43 × 107	7.66 × 106	2.19 × 107	5.24 × 107	3.73 × 105	1.32 × 105	1.76 × 105
Huaian	1.44 × 1011	7.34 × 1010	2.17 × 1011	1.77 × 107	9.03 × 106	2.67 × 107	6.37 × 107	4.54 × 105	1.60 × 105	2.13 × 105
Yancheng	2.00 × 1011	1.07 × 1011	3.07 × 1011	2.46 × 107	1.32 × 107	3.78 × 107	9.02 × 107	6.42 × 105	2.27 × 105	3.02 × 105
Yangzhou	1.04 × 1011	6.29 × 1010	1.67 × 1011	1.28 × 107	7.74 × 106	2.05 × 107	4.89 × 107	3.48 × 105	1.23 × 105	1.64 × 105
Zhenjiang	7.19 × 1010	3.79 × 1010	1.10 × 1011	8.84 × 106	4.66 × 106	1.35 × 107	3.22 × 107	2.29 × 105	8.10 × 104	1.08 × 105
Taizhou	1.33 × 1011	6.75 × 1010	2.00 × 1011	1.63 × 107	8.30 × 106	2.46 × 107	5.87 × 107	4.19 × 105	1.48 × 105	1.97 × 105
Suqian	1.03 × 1011	5.24 × 1010	1.55 × 1011	1.26 × 107	6.45 × 106	1.91 × 107	4.55 × 107	3.24 × 105	1.14 × 105	1.53 × 105
Total	1.74 × 1012	9.40 × 1011	2.68 × 1012	2.14 × 108	1.16 × 108	3.30 × 108	7.86 × 108	5.60 × 106	1.98 × 106	2.64 × 106

, respectively.

The total heat exchange capacity in the suitable and moderately suitable areas of Jiangsu Province is 1.21 × 10⁹ kW in summer and 8.70 × 10⁸ kW in winter. The VGSHP systems benefit from a higher temperature difference in summer, resulting in greater heat exchange capacity compared to winter. In Nantong, the heat exchange capacity in suitable and moderately suitable areas during summer is approximately 50% higher than in winter, showing the largest difference. In Yancheng, the difference is smallest, with the summer heat exchange capacity being about 23% higher than in winter. This variation is primarily due to the temperature differences in the rock and soil.

After considering suitability and land use factors, it is estimated that the potential cooling area is 1.21 × 10¹⁰ m², and the heating area is 1.09 × 10¹⁰ m², with average cooling and heating areas per unit of 1.58 × 10⁵ m²/km² and 1.42 × 10⁵ m²/km², respectively. The area with the highest SGE resource potential in summer is Nanjing, reaching 2.28 × 10⁵ m²/km², while the lowest is Yancheng, at 1.11 × 10⁵ m²/km². In winter, Nanjing again has the highest potential at 2.27 × 10⁵ m²/km², with Suqian having the lowest at 0.97 × 10⁵ m²/km². Due to a higher proportion of construction land, Nanjing City boasts the largest unit area for both cooling and heating. It is important to note that the regions most suitable for shallow geothermal energy development are not necessarily those with the highest resource potential.

Without considering energy extraction efficiency, the maximum annual usable shallow geothermal energy resource is equivalent to 3.30 × 10⁸ tons of standard coal. Annually, the environmental benefits include reductions of 7.86 × 10⁸ tons of CO₂, 5.60 × 10⁶ tons of SO₂, 1.98 × 10⁶ tons of NOx, and 2.64 × 10⁶ tons of dust, significantly mitigating severe air pollution and slowing regional carbon emission growth. According to Table 4, the annual savings on environmental governance costs are approximately 91.6 billion yuan.

5. Discussion

• The results of this study reveal that the use of VGSHP for SGE development in Jiangsu Province is not only technically feasible but also holds substantial potential for energy savings and environmental benefits, which aligns with the province’s carbon neutrality goals. It is noteworthy that the geological environment and current development status vary significantly across different cities within the province, leading to differences in shallow geothermal energy resources and development potential. Therefore, it is essential to devise development policies tailored to the specific conditions of each city.
• While this study provides an assessment of SGE potential in Jiangsu Province, there are limitations that should be addressed in future research. The exclusion of certain areas due to high costs or policy restrictions may omit potential sites that could become viable with technological advancements or policy changes. Additionally, the current assessment does not account for the long-term sustainability of heat extraction, such as the impact of climate change on geothermal gradients and groundwater levels, which may affect the efficiency of VGSHP systems over time. Future studies should incorporate dynamic modeling of heat extraction and regeneration processes to provide a more comprehensive evaluation of SGE potential.
• Due to the limited number of cases involving groundwater-source heat pumps collected in the study area, this work focused solely on the quantitative evaluation of SGE development potential using VGSHP. Future studies could expand to include the potential of groundwater-source heat pumps. Additionally, this paper only discusses the positive effects of SGE development. However, issues induced by SGE development, such as thermal imbalance in the geotechnical body, land subsidence, groundwater pollution, and damage to the underground ecological environment, should not be overlooked [32,33,34].

6. Conclusions

The primary conclusions drawn from this study are as follows:

• The key indicators determining the suitability of developing SGE in Jiangsu Province using VGSHP include the thickness of the Quaternary strata, the thickness of the pebble layer, the thickness of the underground aquifer, and local protection policy requirements. The areas classified as suitable and moderately suitable for developing SGE using VGSHP are 35,204 km² and 41,249 km², respectively, accounting for 34.31% and 40.20% of the total provincial area.
• In Jiangsu Province, the total heat exchange capacity in suitable and moderately suitable areas for VGSHP is 1.21 × 10⁹ kW in summer and 8.70 × 10⁸ kW in winter. The potential cooling area available in summer is 1.21 × 10¹⁰ m², and the potential heating area available in winter is 1.09 × 10¹⁰ m².
• The potential for developing SGE in Jiangsu Province using VGSHP is substantial, with significant energy-saving and emission reduction benefits. Without considering energy extraction efficiency, the annual available resource amount is equivalent to 3.30 × 10⁸ tons of standard coal, nearly matching the province’s annual energy consumption. The emission reductions are equivalent to 7.86 × 10⁸ tons of CO₂, 5.60 × 10⁶ tons of SO₂, 1.98 × 10⁶ tons of NOx, and 2.64 × 10⁶ tons of dust, corresponding to environmental governance costs of approximately 91.6 billion yuan.