**Abstract:** This paper provides a comprehensive overview of ground-source heat pump systems, including their categories, features, and applications. It also reviews the current development status and future potential of ground-source heat pumps both globally and within the country.
**Keywords:** Ground Source Heat Pump; Energy Saving; Sustainable Heating and Cooling
In recent years, with the continuous growth of society and the improvement of living standards, enhancing the thermal comfort of buildings has become a major concern. Air conditioning systems have become an essential part of daily life, with a significant number of households in cities like Shanghai owning at least one unit. However, as air conditioning becomes more widespread, building energy consumption rises sharply, leading to increased atmospheric pollution. The challenge now is how to improve thermal comfort while reducing energy use and environmental impact. To address this, the HVAC industry must implement effective technical and management strategies, such as improving energy efficiency in new constructions and retrofitting existing buildings. This not only helps save energy but also contributes to environmental protection and better quality of life [1].
As an environmentally friendly, energy-efficient, and cost-effective heating and cooling technology, ground-source heat pumps are gaining increasing attention. These systems utilize the relatively stable temperature of the underground soil to provide heating in winter and cooling in summer. Unlike traditional systems that rely on energy conversion, ground-source heat pumps operate through a "handling" process, resulting in high efficiency and low operating costs [2-4].
Additionally, ground-source heat pumps offer an effective solution for regions with extreme weather conditions—hot summers and cold winters. In areas like the middle and lower reaches of the Yangtze River, where summer temperatures can be significantly higher and winter temperatures much colder than other regions at the same latitude, thermal comfort is often compromised. The humidity levels are also high, making it uncomfortable for residents. Traditional heating and cooling methods, such as electric heaters and air conditioners, are inefficient and energy-intensive. By leveraging the stable underground temperature, ground-source heat pumps can efficiently manage seasonal energy needs, offering a sustainable and cost-effective alternative.
### 1. Classification of Ground Source Heat Pumps and Their Characteristics
Ground-source heat pumps, also known as ground-coupled heat pumps, are classified based on the type of geothermal resource they use. There are three main types: ground-coupled heat pumps (GCHP), groundwater heat pumps (GWHP), and surface water heat pumps (SWHP) [7, 8].
#### 1.1 Ground-Coupled Heat Pump
A ground-coupled heat pump uses the ground as a heat source or sink. The heat exchanger is buried underground, allowing heat exchange with the soil. The system typically includes a water-to-water or water-to-air heat pump unit. Depending on the layout of the underground heat exchangers, there are three common types: vertical, horizontal, and snake-shaped.
Vertical borehole heat exchangers are usually U-shaped and categorized by depth: shallow (<30m), medium (30–100m), and deep (>100m). Deep systems benefit from more stable ground temperatures and require less land area, but they involve higher drilling and installation costs. The advantages include a small footprint, minimal temperature fluctuations, and high energy efficiency, although the initial investment is higher due to the need for specialized equipment.
Horizontal buried heat exchangers come in single-tube and multi-tube configurations. While the single-tube version covers the largest area, the multi-tube design reduces the footprint but increases pipe length to avoid thermal interference. These systems are generally more affordable and easier to install, especially in residential areas with sufficient space. However, performance can vary due to seasonal changes in ground temperature and moisture levels.
Snake tube heat exchangers are ideal for limited spaces and are more economical. They require about 20–30% less excavation than horizontal systems but allow for greater pipe capacity. Their performance is similar to horizontal systems, so some sources classify them under the same category.
#### 1.2 Groundwater Heat Pump System
Before the rise of ground-coupled systems, groundwater heat pumps were widely used in Europe and the U.S. Today, they are mainly found in commercial buildings. A typical system uses a plate heat exchanger to transfer heat between groundwater and the heat pump’s cooling water. Early systems used a single-well setup, which led to groundwater wastage and subsidence risks. Later, a double-well system was introduced, with one well for extraction and another for recharge.
Groundwater heat pumps are cost-effective and compact, requiring no additional site space. However, challenges include regulatory restrictions on groundwater use, limited availability of suitable water sources, and the risk of poor water quality or inadequate treatment. Additionally, if the pumping system is oversized or located far from the building, energy consumption can increase significantly.
#### 1.3 Surface Water Heat Pump System
Surface water heat pumps operate using either open or closed-loop systems. Open systems are not recommended in cold climates, where they may freeze. Closed-loop systems, on the other hand, are more reliable and commonly used. These systems are generally cost-effective, with low pump energy consumption and maintenance requirements. However, they are vulnerable to damage from debris in public waterways. Additionally, if the water body is too small or shallow, its temperature can fluctuate significantly, reducing system efficiency.
This classification highlights the diversity of ground-source heat pump technologies and their suitability for different environments and applications. Each system has its own set of advantages and limitations, making it important to choose the right type based on local conditions and energy needs.
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