In this CFD Analysis of Geothermal Heat Pump tutorial, we provide a complete training guide on designing efficient ground-source heating systems. A Geothermal Heat Pump is a machine that uses the stable temperature of the earth to heat and cool buildings cleanly. In winter, it extracts heat from the ground, and in summer, it puts heat back. However, installing pipes deep underground is very expensive. If the design is wrong, engineers cannot see underground to fix it. This is why a Geothermal fluent simulation is essential. It allows engineers to test the system on a computer before digging. By using ANSYS Fluent, we can predict exactly how the heat moves between the water pipes and the soil. This ensures the system works perfectly and saves money on electricity.

In this lesson, we perform a detailed Vertical Ground Loop CFD study using a U-tube heat exchanger. This is the most common design in the industry. We simulate the complex interaction between the fluid flow and different soil layers. Our goal is to verify if the pipe length and soil properties allow for enough heat exchange. This ANSYS Fluent heat exchanger analysis helps manufacturers design systems that are both cheap to run and environmentally friendly. For more training on sustainable systems, please explore our Renewable Energy tutorials.

• Reference [1]: Roshani, M., et al. “Enhancing geothermal heat pump efficiency with fin creation and microencapsulated PCM: A numerical study.” Journal of Energy Storage95 (2024): 112664.

Figure 1: Schematic diagram of the Geothermal Heat Pump ground loop system showing the main components as described in reference [1].

Simulation process: Multi-Zone Conjugate Heat Transfer Setup in ANSYS Fluent

For this technical CFD Analysis of Geothermal Heat Pump project, we created a precise 3D geometry of a U-shaped pipe. To make the simulation realistic, we used a multi-zone approach. We modeled the steel pipe, the fluid domain, and three distinct soil layers: Clay, Sandy Clay, and Silica Sand. We generated a high-quality mesh using ANSYS Meshing, ensuring the grid was fine enough to capture the Conjugate Heat Transfer. This is the physical process where heat passes from the moving water, through the steel wall, and into the solid ground.

We set up the physics in ANSYS Fluent by enabling the Energy Equation to solve for thermal changes. We configured the solver to handle the different thermal properties of the soil layers (conductivity and specific heat). We set the Inlet Boundary Condition for the water to enter at 300 K. The simulation was run until the flow and energy residuals reached a stable convergence. This setup allows us to accurately calculate the temperature distribution across the entire Geothermal fluent simulation domain.

Figure 2: An overview of the 3D geometry used in the Fluent CFD simulation, showing the multi-zone model of the U-tube heat exchanger and surrounding soil.

Post-processing: CFD Analysis of Geothermal Heat Pump and Thermal Efficiency

In this section, we analyze the engineering data to judge the success of the design. First, we examine the Hydraulic Performance using the Velocity contours in Figure 3. The results show that the water flows smoothly through the U-tube with a Maximum Velocity of 0.15 m/s. From an engineering perspective, this low speed is an excellent result. It confirms that the flow is laminar and stable. For a manufacturer, maintaining a low velocity is critical because it keeps the pressure drop low. A low pressure drop means the building owner can use a smaller, cheaper water pump, which significantly reduces the system’s electricity consumption over time.

Figure 3: Velocity Magnitude Contours inside the U-tube for Geothermal CFD Analysis, illustrating smooth laminar water flow (max 0.15 m/s).

Next, we evaluate the Thermal Efficiency in Figure 4. The temperature data shows that water enters at 300 K and exits at 299.57 K. This represents a temperature drop of 0.43 K. While this number looks small, it proves the CFD Analysis of Geothermal Heat Pump is successful. In a closed-loop system, the water circulates continuously, so a steady removal of 0.43 K per pass adds up to a large amount of energy transfer. The contour also shows that heat moves differently through the Silica Sand compared to the Clay, confirming that our multi-zone physics are working correctly.

Finally, we analyze the Thermal Footprint in Figure 5. This top-view contour is the most valuable data for a site designer. It displays circular rings of temperature change, which represent the Radius of Thermal Influence. This tells the engineer exactly how far the heat spreads into the surrounding soil. This is vital for planning a borehole field. If you place multiple U-tubes too close to each other, their thermal rings will overlap, and the system efficiency will crash. This Geothermal heat pump fluent simulation provides the exact spacing distance required to guarantee long-term performance without thermal interference.

Figure 4: Temperature Contours on the vertical plane, visualizing the Conjugate Heat Transfer between the fluid and the multi-zone soil layers.

Figure 5: Radial Temperature Distribution (Top View) showing the circular thermal footprint and radius of influence in this ANSYS Fluent simulation.