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Evaluation of Solar Chimney Height Effect on the Airflow Rate and Temperature Inside the Pig House Using Computational Fluid Dynamics (CFD)

This study utilizes Computational Fluid Dynamics (CFD) to demonstrate that increasing solar chimney height significantly enhances airflow rates and reduces temperatures in naturally ventilated pig houses, with the CFD model showing over 95% accuracy against theoretical predictions.

Original authors: Siboniso Zakwe, Tilahun Seyoum Workneh, Sipho Sibanda

Published 2026-07-13

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Siboniso Zakwe, Tilahun Seyoum Workneh, Sipho Sibanda

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a pig house as a giant, cozy oven that needs to stay cool without plugging in a single electric fan. In this study, researchers asked a simple question: If we build a taller "solar chimney" on top of the pig house, will the air move faster and the temperature drop?

Think of a solar chimney like a giant, sun-powered straw. When the sun heats the air inside the straw, that air gets light and rises, sucking fresh, cool air in from the bottom to replace it. The researchers wanted to see if making this "straw" taller would make the suction stronger.

The Experiment: Five Different Straws

The team didn't just guess; they built five digital models of a pig house, each with a chimney of a different height: 0.85 m, 1.2 m, 1.70 m, 2.13 m, and 2.55 m. They used two methods to check the results:

Math Magic: Using old-school equations to calculate what should happen.
Digital Twins: Using a super-smart computer program called CFD (Computational Fluid Dynamics) to simulate the air moving and the heat shifting inside the house, just like a video game physics engine.

The Big Discovery: Taller is Sweeter

The results were crystal clear. As the chimney got taller, the air started moving faster, and the pig house got cooler.

The Airflow: The taller the chimney, the more air rushed through. The study found a strong positive link (a correlation of 0.95) between height and airflow. It's like opening a wider window; the taller the chimney, the stronger the "stack effect" (the natural rising of hot air), creating a powerful suction that pulls heat out.
The Temperature: As the air moved faster, the temperature dropped. There was a strong negative link (a correlation of -0.97) between height and temperature. In the simulations, raising the chimney from 0.85 m to 2.55 m dropped the inside temperature from 24.1°C down to 23.1°C.

The Computer vs. The Math

How much can we trust these digital simulations? The researchers put the computer's predictions against their math equations to see if they matched.

For Temperature: The computer was spot on. It predicted 95% of the data correctly, with a tiny error margin of just 0.43°C.
For Airflow: The computer showed a 97% agreement with the math (R² = 0.97) and a very low error of 0.01 m³/s. However, the study notes a small caveat: at the very tallest chimney heights, the computer slightly underestimated the airflow compared to the math, though the overall difference was still negligible.

The study suggests that this RNG k-ε turbulence model (a specific type of math used in the computer) is a very trustworthy tool for designing these systems.

What This Means (and What It Doesn't)

The paper confirms that taller chimneys work better for natural ventilation in pig houses, offering a free, energy-saving way to keep pigs comfortable without using electricity.

However, the study is careful not to claim this is the only thing that matters. The researchers note that airflow also depends on other things they didn't change in this specific test, like how much sun is shining, the material of the chimney, and the angle of installation. They also didn't test a chimney that was too tall (like 100 meters), so we don't know if there's a limit where it stops helping.

In short, if you are designing a pig house and want to save energy, this study suggests that building a taller solar chimney is a smart move. It creates a stronger draft, cools the pigs down, and does it all without a single watt of electricity. The computer simulations back this up with high confidence, giving engineers a reliable map for building better, greener farms.

Technical Summary: Evaluation of Solar Chimney Height Effect on Airflow Rate and Temperature Inside the Pig House Using CFD

Problem Statement
The thermal environment within livestock facilities, particularly pig houses, is critical for animal growth and development. Pigs are highly sensitive to thermal fluctuations, necessitating stable indoor conditions. While mechanical ventilation is common, it is a major energy consumer and contributor to carbon emissions, a concern exacerbated by global energy crises. Solar chimneys offer a passive, energy-free alternative for natural ventilation. However, while various parameters such as material and installation angles have been studied, there remains a significant gap in research regarding dimensional optimization. Specifically, few studies have isolated the effect of solar chimney height on ventilation rates and heat load removal to determine the optimal design for livestock housing.

Methodology
This study employed a dual approach combining mathematical calculations and Computational Fluid Dynamics (CFD) simulations to evaluate the impact of varying solar chimney heights on indoor airflow and temperature.

Experimental Design: Five distinct pig house models were developed using Autodesk Inventor 2024, featuring chimney heights of 0.85 m, 1.275 m, 1.70 m (baseline), 2.125 m, and 2.55 m. These heights represented modifications of the baseline by ±25% and ±50%.
Mathematical Modeling: Theoretical airflow rates and indoor temperatures were calculated using established equations. Stack pressure drive was determined based on ambient and chimney temperatures (Equation 1). Airflow velocity was derived by balancing the driving pressure against friction and minor pressure losses (Equations 2–4). Indoor temperature was modeled accounting for evaporative cooling, heat transfers, and internal heat loads (Equation 5).
CFD Simulation: Simulations were conducted using ANSYS Workbench 2025 R1. The geometry was meshed using a tetrahedral method with a maximum element size of 0.04 mm. The Reynolds-Averaged Navier-Stokes (RANS) RNG k-ε turbulence model was selected, as it is recommended for indoor turbulent flows. Boundary conditions included an inlet air velocity of 0.95 m/s at 22°C. Simulations ran for 2000 iterations with a time step of 0.025 s over a total duration of 5 seconds to capture temperature and airflow profiles.
Validation: The CFD results were validated against the theoretical data derived from the mathematical models.

Key Results
The study established clear correlations between chimney height and thermal/airflow performance:

Airflow Rate: There is a strong, significant positive correlation ( $r = 0.95, p < 0.01$ ) between chimney height and airflow rate. As the chimney height increased from 0.85 m to 2.55 m, the airflow rate increased from 0.13 m/s to 0.22 m/s. The regression analysis yielded an $R^2$ of 0.99, indicating chimney height is the dominant factor influencing airflow.
Indoor Temperature: A strong, significant negative correlation ( $r = -0.97, p < 0.01$ ) was observed between chimney height and indoor temperature. As height increased, the indoor temperature decreased from 24.1°C to 23.1°C. The regression coefficient ( $R^2 = 0.95$ ) suggests that nearly all variation in indoor temperature is explained by chimney height.
Mechanism: These trends are attributed to the stack effect. Taller chimneys generate a higher pressure differential between the inlet and outlet due to thermal buoyancy, creating stronger suction that drives airflow and enhances heat removal.
Model Validation: The CFD model demonstrated high accuracy when compared to theoretical data.
- Temperature: The model predicted temperature with an $R^2$ of 0.96 and a Root Mean Square Error (RMSE) of 0.43°C.
- Airflow: The model predicted airflow with an $R^2$ of 0.97 and an RMSE of 0.01 m³/s.
- While the model slightly underpredicted airflow at the highest chimney heights (2.125 m and 2.55 m), the overall agreement was strong, with over 95% of the data variation accurately explained by the model.

Significance and Claims
The paper asserts that optimizing solar chimney height is a crucial, low-cost, and passive strategy for improving microclimate conditions in pig houses without relying on mechanical systems. The findings highlight that increasing chimney height directly improves ventilation efficiency and heat load removal, thereby supporting animal welfare and reducing the carbon footprint of agricultural operations.

Furthermore, the study validates the reliability of the CFD RNG k-ε turbulence model for simulating airflow and temperature distribution in livestock facilities. Despite the known limitations of RANS models compared to Large Eddy Simulations (LES) regarding computational cost, the study concludes that the RNG k-ε model provides a dependable balance between computational resources and accuracy for this application. The results offer practical insights for engineers and designers to develop energy-efficient, climate-smart livestock infrastructure.

The Experiment: Five Different Straws

The Big Discovery: Taller is Sweeter

The Computer vs. The Math

What This Means (and What It Doesn't)

Technical Summary: Evaluation of Solar Chimney Height Effect on Airflow Rate and Temperature Inside the Pig House Using CFD

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