How to determine the depth of buried pipes for ground source heat pumps in Dalian?

The depth of buried pipes is a key parameter in the design of ground source heat pump systems, directly affecting the system's heat transfer efficiency, initial investment, and operating costs. The Dalian ground source heat pump system is an efficient and energy-saving technology that utilizes underground soil as a heat source or sink. One of its core components is the buried pipe heat exchanger. Determining the depth of buried pipes requires comprehensive consideration of various factors such as geological conditions, climatic characteristics, system load, and economy.

1. Basic concept of buried pipe depth

The depth of the buried pipe refers to the depth at which the buried pipe heat exchanger is buried vertically underground. Typically, the depth of the buried pipe ranges from 50 meters to 200 meters, depending on engineering requirements and geological conditions. The greater the depth, the more stable the soil temperature, but the higher the construction difficulty and cost.

II. Main factors affecting the depth of buried pipes

geological conditions

Soil type: Different soils have different thermal conductivity coefficients. For example, sandy soil has a higher thermal conductivity coefficient, making it suitable for shallow burial; clay soil has a lower thermal conductivity coefficient, potentially requiring deeper buried pipes.

Groundwater level: In areas with a higher groundwater level, the soil has better thermal conductivity, which can appropriately reduce the depth of buried pipes.

Rock formation structure: If there are hard rock formations underground, the construction difficulty will increase, and the depth of the buried pipes may need to be adjusted.

Climatic characteristics

Temperature variation: In cold regions, the surface temperature fluctuates significantly, necessitating deeper burial of buried pipes to ensure stable heat exchange efficiency.

Seasonal temperature difference: In areas with significant temperature differences, the depth of buried pipes should be sufficient to avoid the impact of seasonal temperature changes on the system.

system load

Heat load demand: The greater the heat load of a building, the larger the heat exchange area required for the buried tube heat exchanger, which may be achieved by increasing the depth or the number of tubes.

Ratio of cooling and heating loads: If the cooling and heating loads of the system are imbalanced, the depth of the buried pipes needs to be optimized to avoid soil temperature imbalance.

economy

Initial investment: Increasing the depth of buried pipes will increase construction costs, necessitating a balance to be found between system efficiency and investment.

Operating costs: Deeper buried pipes can enhance system efficiency and reduce long-term operating costs.

construction conditions

Site constraints: When the site area is limited, it may be necessary to increase the depth of buried pipes to meet the heat exchange requirements.

Construction technology: The drilling capacity and technical proficiency of construction equipment also influence the selection of the depth of buried pipes.

III. Method for determining the depth of buried pipes

geological exploration

At the initial stage of the project, conduct detailed geological exploration to understand information such as soil thermal conductivity, groundwater level, and rock stratum distribution.

By conducting borehole tests, soil temperature data at different depths can be obtained, providing a basis for design.

heat load calculation

Calculate the heat exchange area required for the buried tube heat exchanger based on the cooling and heating load demands of the building.

Based on the soil thermal conductivity and system efficiency, the depth of the buried pipes is preliminarily determined.

simulation analysis

Utilize specialized software (such as GLHEPRO, EED, etc.) to conduct simulation analysis on buried tube heat exchangers, optimizing the depth and arrangement.

Through simulation, we evaluate the impact of different depths on system performance and select the optimal solution.

Economic evaluation

Compare the initial investment and operating costs at different depths, and choose the scheme with high cost-effectiveness.

Taking into account the energy consumption and maintenance costs during long-term operation, we ensure the economic efficiency of the system.

Empirical reference

Drawing from the design experience of similar projects and taking into account the local climate and geological conditions, the depth of the buried pipes should be adjusted.

Consult a professional design team for more accurate advice.

IV. Common depth range of buried pipes

Shallow buried pipe (below 50 meters)

It is suitable for small-scale projects or areas with favorable geological conditions.

The construction cost is low, but the heat exchange efficiency is relatively low.

Medium-depth buried pipes (50m to 150m)

It is suitable for most ground source heat pump projects.

Taking into account both heat transfer efficiency and construction cost is a commonly used depth range.

Deep buried pipe (over 150 meters)

It is suitable for large-scale projects or areas with complex geological conditions.

The heat exchange efficiency is high, but the construction difficulty and cost increase significantly.

V. Precautions

Avoid over-design

The depth of buried pipes is not necessarily the deeper the better, as excessive design can lead to unnecessary costs.

Choose the depth reasonably according to actual needs to ensure the efficiency and economy of the system.

Soil temperature balance

During long-term operation, the soil temperature around the buried pipes may change, necessitating reasonable design to avoid temperature imbalance.

construction quality

The construction quality of buried pipes directly affects the system performance, thus it is necessary to ensure the standardization of drilling, backfilling, and pipe installation.

Subsequent monitoring

After the system is operational, regularly monitor the heat exchange performance of the buried pipes and changes in soil temperature, and adjust the operational strategy in a timely manner.

Determining the depth of buried pipes for ground source heat pumps is a complex process that requires comprehensive consideration of factors such as geological conditions, climatic characteristics, system load, and economy. Through geological exploration, thermal load calculation, simulation analysis, and economic evaluation, the depth of buried pipes can be scientifically and reasonably determined to ensure the efficiency and economy of the system. In practical engineering, optimal design should be carried out according to specific circumstances to avoid over-design or under-design, in order to achieve better operational effects of the ground source heat pump system.