Buried Pipe Ground Source Heat Pump
A buried pipe ground source heat pump system uses the soil as a heat source or heat sink. The core components include a heat pump unit and a set of heat exchangers buried underground. These heat exchangers are typically made of high-density polyethylene or polybutene pipes, and achieve effective heat exchange between the system and the ground through a fluid (such as water or antifreeze) circulating in the closed underground pipes.
Figure: Working principle of a buried pipe ground source heat pump (winter heating)
In a buried pipe ground source heat pump system, the dynamic changes in building load and the heat exchange with the underground soil are closely linked and interact, which makes this heat pump system also known as a soil-coupled heat pump. During implementation, there are two main choices for the burial method of the buried heat exchangers: horizontal burial and vertical burial.
Horizontal burial usually uses shallow burial, which is simple to construct and has a relatively low initial investment. However, this method occupies a larger area, and the temperature of the shallow soil is easily affected by the surface air temperature, resulting in a relatively small heat exchange per unit length of pipe.
In contrast, while vertical buried pipes have a higher initial investment, their deep underground location ensures a relatively stable temperature in the deep soil throughout the year, thus guaranteeing the stable operation of the heat pump system, and is therefore widely used.
However, a potential problem exists for vertical buried pipe heat pump systems: if the heat absorbed by the buried heat exchanger in winter is not balanced with the heat released in summer, the underground thermal balance will be disrupted, leading to a continuous rise or fall in underground soil temperature, ultimately affecting the heat exchange efficiency of the buried heat exchanger.
