Using sunlight to heat and cool our buildings is a smart way to save energy and live more comfortably. Special designs, like Trombe walls, which are thick, dark walls placed behind glass, are experts at this. However, sunlight is not just one thing; it’s made of different types of light energy called wavelength bands. Some bands carry a lot of heat, while others don’t. A true Solar Building CFD study helps us understand how these different bands interact with building materials. By using computer simulations, we can see exactly how a Trombe wall absorbs the heat from some light waves while letting others pass through. This helps engineers design buildings that stay warm in the winter and cool in the summer all by themselves. This study uses Computational Fluid Dynamics (CFD) to investigate a solar building with a Trombe wall, based on a reference paper [1], to see exactly how this amazing process works.

• Reference [1]: Fidaros, Dimitrios, et al. “Assessment of various Trombe wall Geometries with CFD Study.” Sustainability9 (2022): 4877.
• Reference [2]: Jiang, Bin, Jie Ji, and Hua Yi. “The influence of PV coverage ratio on thermal and electrical performance of photovoltaic-Trombe wall.” Renewable energy11 (2008): 2491-2498.

Figure 1: The physical model of the Trombe Wall CFD system investigated in the solar building analysis.

Simulation Process: Using the DO Model for Wavelength-Specific Radiation

To build our digital model of the Solar Building Fluent simulation, we first drew the room and the Trombe wall using Design Modeler, following the details in the reference paper. We then created a very careful grid using ANSYS Meshing, making the little boxes of the grid much smaller and denser near the Trombe wall (Figure 2). This ensures we get very accurate results where the most important action is happening. The biggest challenge in a SOLAR CFD simulation like this is modeling the sunlight correctly. We used a powerful tool in ANSYS Fluent called the Discrete Ordinates (DO) radiation model. What makes the DO Radiation Fluent model special is that we can tell it to split the sunlight into four different wavelength bands. This allows us to simulate how the glass and the wall react differently to each type of light, which is exactly what happens in the real world.

Figure 2: The high-quality structured grid with refinement near the Trombe wall for the Solar Building CFD simulation.

Post-processing: Analyzing Airflow and Thermal Performance

The simulation results provide a clear picture of how solar energy creates a comfortable indoor climate. First, looking at the airflow in Figure 3, we can see a beautiful, gentle circle of moving air. The cause is the sunlight warming the Trombe wall on the left. This heat is transferred to the air next to it. The direct effect is that this warm air becomes lighter and rises, creating an upward current that reaches a speed of 0.255 m/s. As the air moves across the ceiling, it cools, becomes heavier, and sinks back down on the right side of the room, completing the loop. This process, called natural convection, is perfectly captured by our simulation. This gentle air movement is a great achievement because it shows the system can distribute heat throughout the room naturally, without any noisy fans.

Figure 3: Velocity contour from the Solar Building Fluent analysis, clearly showing the natural convection airflow pattern.

Now, let’s look at how the radiation and temperature work together. The cause of all the heat is the powerful solar radiation shown in Figure 4. Our model accurately shows that the wall is hit with intense energy, over 4,300 Watts per square meter (the bright red area). The effect of this energy is a significant rise in temperature, as seen in Figure 5. The temperature gracefully changes from a warm 314 K (41°C) near the heated wall to a comfortable 300 K (27°C) deeper in the room. This smooth temperature change proves that the Trombe wall is working perfectly, storing heat and releasing it slowly. The most important achievement of this Solar Building Considering Wavelength Bands CFD simulation is the successful integration of all physics: our advanced DO radiation model accurately predicted the heat absorbed from different sunlight bands, which then correctly drove the temperature increase and the resulting natural airflow pattern. This holistic and validated model gives architects a powerful tool to design highly efficient passive solar buildings with confidence.

Figure 4: Incident radiation contour using the DO Radiation Fluent model, highlighting the intense solar energy distribution on the wall.

Figure 5: Temperature distribution contour showing the thermal gradient established by the passive SOLAR CFD heating system