Document Type : Research Paper
Natural ventilation is one of the most effective and energy-efficient approaches for greenhouse climate control, playing a key role in regulating temperature, humidity, carbon dioxide concentration, and excess heat accumulation. Among natural ventilation strategies, wind-driven natural ventilation (WDNV) and buoyancy-driven systems have attracted considerable attention because they can reduce dependence on mechanically powered climate-control equipment. In particular, solar chimney-assisted natural ventilation (SCNV) has emerged as a promising passive technology in hot and sunny regions, where solar energy can be utilized to strengthen buoyancy forces and enhance airflow through the greenhouse. Previous studies have generally evaluated greenhouse ventilation performance based on air exchange rate (ACH) or average indoor temperature reduction. Although these indicators provide valuable information regarding ventilation capacity, they do not necessarily reflect the actual microclimatic conditions experienced by crops. A ventilation system with a higher ACH may still create non-uniform airflow distribution, thermal gradients, and localized heat accumulation within the crop zone. Consequently, greenhouse ventilation performance should be assessed not only by airflow quantity but also by airflow organization, temperature distribution, and the thermal conditions surrounding the crop canopy. Despite extensive research on wind-driven ventilation and solar chimney applications, direct comparisons between these two natural ventilation mechanisms under hot-arid climatic conditions remain limited. Furthermore, the relationship between ventilation capacity and crop-zone microclimate quality has not been sufficiently clarified. Therefore, the present study aimed to compare the performance of WDNV and SCNV in a greenhouse located in Ahvaz, Iran, during representative transitional-season conditions. The investigation focused on both aerodynamic and thermal behavior using three-dimensional CFD simulations and evaluated the systems through a set of complementary indicators describing ventilation capacity, thermal performance, energy efficiency, and crop-zone microclimate quality.
The study employed validated three-dimensional Computational Fluid Dynamics (CFD) models to compare wind-driven natural ventilation (WDNV) and solar chimney-assisted natural ventilation (SCNV) in a greenhouse located in Ahvaz, Iran. Simulations were conducted under representative transitional-season conditions corresponding to March, April, and October, using local meteorological data including solar radiation intensity, ambient temperature, prevailing wind speed, and wind direction. The numerical model incorporated greenhouse geometry, crop canopy, porous pad walls characteristics, and the solar chimney structure. In addition to evaluating the external airflow field around the greenhouse complex, detailed analyses were performed on airflow patterns, temperature distributions, thermal stratification, and ventilation pathways inside the greenhouse. Performance evaluation was based on a comprehensive set of indicators. Air exchange rate (ACH) was used to quantify ventilation capacity, while temperature reduction effectiveness (TRE) and canopy temperature were employed to evaluate crop-zone thermal conditions. Temperature Uniformity Index (TUI) was used to assess the homogeneity of temperature distribution within the cultivation zone. Sensible Heat Removal Rate (SHRR) was calculated to determine the ability of each system to remove excess heat from the greenhouse environment. For SCNV, solar collector thermal efficiency was also evaluated to quantify the effectiveness of solar energy utilization in driving buoyancy-induced airflow. The combination of these indicators enabled simultaneous assessment of ventilation performance, greenhouse microclimate quality, thermal behavior, and energy efficiency, providing a more comprehensive evaluation than approaches based solely on air exchange rate.
The CFD simulations revealed substantial differences in airflow organization and thermal behavior among the investigated ventilation strategies. Analysis of the external airflow field demonstrated that the prevailing wind interacted strongly with the greenhouse geometry, producing localized pressure variations that influenced ventilation performance. Solar radiation analysis further showed that the solar chimney received significant solar energy throughout the investigated months, providing favorable conditions for buoyancy-driven airflow generation. Qualitative analysis of airflow patterns indicated that the control greenhouse exhibited weak air circulation, extensive stagnation zones, and pronounced thermal gradients. In the WDNV configuration, airflow entered through side openings and exited through roof vents, generating greater air exchange but also producing localized recirculation regions and flow instabilities. In contrast, SCNV created the most organized and directional airflow structure. The solar chimney generated a continuous suction effect that promoted stable airflow from the porous wall toward the chimney outlet, reducing stagnation zones and improving airflow distribution throughout the greenhouse. One of the most important findings was the development of controlled thermal stratification in the SCNV system. Warm air accumulated near the roof and was continuously removed through the chimney, while cooler air remained in the crop zone. This behavior reduced thermal stress around the plants and improved the overall microclimate despite the lower ventilation rate. Quantitative results confirmed the differences observed in the qualitative analysis. WDNV achieved the highest ventilation capacity, with an average ACH of 5.35 h⁻¹, approximately three times higher than SCNV (1.75 h⁻¹) and nearly 89 times greater than the control greenhouse (0.06 h⁻¹). Similarly, WDNV exhibited the highest sensible heat removal rate, reaching 11.55 kW compared with 3.33 kW for SCNV and 0.41 kW for the control condition. However, higher ventilation capacity did not translate into superior crop-zone thermal conditions. The average canopy temperature in the control greenhouse reached 39.68°C. WDNV reduced this value to 38.94°C, whereas SCNV achieved the lowest canopy temperature of 36.98°C. Likewise, SCNV produced the highest temperature reduction effectiveness (TRE = 0.54), compared with only 0.14 for WDNV. These findings demonstrate that airflow organization and heat-removal pathways can be more important than airflow quantity alone when evaluating greenhouse ventilation performance. Temperature distribution results further highlighted the superiority of SCNV. The Temperature Uniformity Index increased from 0.52 in the control greenhouse to 0.75 under WDNV and reached 0.91 under SCNV. This substantial improvement indicates a more homogeneous thermal environment and a reduced likelihood of localized hot spots that could negatively affect crop growth and productivity.
Seasonal analysis revealed that SCNV performance was strongly influenced by solar radiation availability. ACH increased from 1.48 h⁻¹ in October to 1.93 h⁻¹ in April, while SHRR increased from 2.85 kW to 3.62 kW during the same period. The solar collector exhibited an average thermal efficiency of 6.63%, ranging between 5.80% and 7.43%. Although this efficiency was relatively modest, it was sufficient to maintain continuous buoyancy-driven ventilation without external energy consumption. Overall, the results clearly indicate that greenhouse ventilation effectiveness cannot be evaluated solely by air exchange rate. The organization of airflow, thermal stratification characteristics, and conditions within the crop growth zone play equally important roles in determining greenhouse microclimate quality.
This study comparatively evaluated wind-driven natural ventilation (WDNV) and solar chimney-assisted natural ventilation (SCNV) in a greenhouse located in the hot-arid climate of Ahvaz during transitional seasons. The results demonstrated that although WDNV provided substantially higher ventilation capacity (ACH = 5.35 h⁻¹) than SCNV (ACH = 1.75 h⁻¹), a higher air exchange rate did not necessarily result in a superior greenhouse microclimate. The solar chimney system generated a more stable and organized airflow pattern, reduced recirculation and stagnation zones, and promoted controlled thermal stratification. Consequently, SCNV achieved superior crop-zone conditions, reducing canopy temperature to 36.98°C while improving temperature reduction effectiveness (0.54) and temperature uniformity (0.91). These improvements were achieved using only solar-induced buoyancy forces, with an average collector thermal efficiency of 6.63% and no external energy requirement. The findings highlight the importance of evaluating greenhouse ventilation systems using multiple indicators that account for airflow organization, thermal distribution, and crop-zone conditions rather than relying solely on ventilation capacity. Under hot-arid climatic conditions, SCNV appears to be a promising sustainable and low-energy alternative for greenhouse climate control. Future research should focus on optimizing solar chimney geometry, reducing airflow resistance within the chimney channel, and investigating system performance under different wind conditions. The integration of thermal curtains or secondary ceiling systems may further enhance thermal stratification and improve crop-zone cooling. Additionally, incorporating humidity transport, CO₂ distribution, plant physiological responses, and economic assessments would facilitate the practical application of solar chimney technology in commercial greenhouse production.
This research was financially supported by Shahid Chamran University of Ahvaz, Iran, through a research grant awarded to the authors. The authors gratefully acknowledge the financial support provided by Shahid Chamran University of Ahvaz for conducting this study.
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
During the preparation of this manuscript, the authors used ChatGPT for English language editing, grammar improvement, and translation refinement. After using this tool, the authors carefully reviewed, revised, and edited all content as necessary and take full responsibility for the content of the publication.
The data supporting the findings of this study are available from the corresponding author upon reasonable request.
The authors gratefully acknowledge Shahid Chamran University of Ahvaz for its financial support and research grant, which made this study possible. The authors also appreciate the administrative and research support provided by the university throughout the course of this work.
The authors avoided data fabrication, falsification, and plagiarism, and any form of misconduct.
