Technical Article
Geothermal–Passive Hybrid Cooling via Courtyard-Integrated EAHE: A CFD-Based Framework for Low-Energy Residential Construction in Hot, Arid Areas
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1. Introduction
A significant portion of the world's energy consumption and greenhouse gas emissions is caused by the building industry, with cooling demand accounting for the majority of the energy load in hot, dry areas. Residential structures heavily rely on mechanical air conditioning systems in cities like Baghdad, where summer temperatures regularly surpass 45 °C. This results in high electricity usage and a greater environmental impact (Benhammou et al. 2015), (Yang et al. 2016) & (Saifi et al. 2015).
As a result, the idea of Low-Energy Buildings (LEBs) has become a crucial tactic for lowering operating energy use without sacrificing indoor thermal comfort. However, the limited efficacy of traditional passive cooling techniques in high ambient temperatures makes it difficult to achieve LEB performance in extreme climates (Riffat et al. 2016) & (Ozgener and Ozgener 2010).
Earth-Air Heat Exchanger (EAHE) systems are a promising geothermal-based technology that preconditions incoming air by making use of the comparatively steady temperature beneath the soil. The ability of EAHE systems to lower air temperature and cooling loads in various climatic regions has been shown in earlier research. However, the majority of current research pays little attention to how EAHEs are integrated into architectural design frameworks and instead concentrates on their performance or applicability in temperate and semi-arid areas (Ahmad and Prakash 2021).
In addition, traditional courtyard dwelling, which is common in Middle Eastern architecture, uses controlled airflow, thermal mass, and shading to create a naturally regulated microclimate. Despite this potential, there hasn't been much systematic research done on the usage of courtyard microclimates and EAHE systems together, especially in hot, dry places like Iraq.
By putting forth a unique geothermal–passive hybrid cooling technique that incorporates an EAHE system beneath a residential courtyard, our work fills this research gap. The strategy seeks to integrate climate-responsive architecture design with subsurface thermal stability in a synergistic way.
1.1. Research objectives
The study's goals are to:
- Create a CFD-based model to simulate an under-courtyard EAHE system's thermal performance.
- Optimise important design parameters like pipe diameter, length, burial depth, and airflow velocity.
- Assess the system's potential to achieve low-energy cooling in hot, dry climates.
This research offers a transportable framework for creating energy-efficient residential structures in harsh climates by bridging the gap between passive architectural design and geothermal technical systems.
1.2. Novelty of the Study
This project is innovative because it combines passive architectural cooling techniques with geothermal cooling inside a single framework. This study presents a courtyard-integrated EAHE configuration supported by CFD-based optimisation, in contrast to earlier research that mostly focused on standalone EAHE devices or isolated passive design techniques.
Additionally, in extremely hot and dry conditions, our study specifically takes into account the relationship between subterranean thermal exchange and courtyard-induced microclimate, which has not been thoroughly covered in prior work. In order to achieve low-energy cooling in residential structures, the suggested framework offers both engineering and architectural design guidance.
2. Literature Review
The efficiency of EAHE systems in lowering air temperatures in a variety of climates has been shown in earlier research. For example, Benhammou et al. (2015) used wind-assisted EAHE systems to achieve comparable performance in arid settings, whereas Jakhar et al. (2016) observed temperature reductions of up to 18°C in semi-arid situations.
A crucial research gap is highlighted by the fact that these studies mostly concentrate on standalone systems and do not take into account the relationship between EAHE performance and courtyard-induced microclimatic effects.
2.1. Systems of Earth-Air Heat Exchangers
Earth-Air Heat Exchangers (EAHEs) have been extensively studied as a passive cooling system that preconditions ventilation air by utilising the thermal stability of subterranean soil. Previous research has shown that, depending on the climate and system design parameters such as pipe length, diameter, burial depth, and airflow velocity, they can considerably lower the inlet air temperature (Suman et al. 2025), (Gürkan 2026), (Sehli et al. 2012) & (Thanu et al. 2001).
2.2. EAHE Applications in Hot-Arid Climates
EAHE devices have demonstrated encouraging results in lowering cooling demands in hot, arid areas. Research from places like North Africa and India shows that during the hottest summer months, temperatures can drop by 8 to 18 ⁰C. However, local soil characteristics and climate extremes have a significant impact on system performance, and optimisation techniques are still site-specific (Shen and Yang 2026), (Yildiz et al. 2011), (Shahare and Harinarayana 2016) & (Kumar et al. 2019).
2.3. The Microclimate of Courtyards in Conventional Architecture
The ability of courtyard-based architectural design to moderate microclimatic conditions in hot climes has long been acknowledged. Through thermal mass and evaporative effects, the courtyard improves shading, encourages natural ventilation, and lowers heat gain. It is a good option for integration with passive cooling systems because of these features (Verma and Murugesan 2018), (Bordoloi et al. 2018) & (Xia et al. 2018).
Table 1 summarises a comparative analysis of prior EAHE studies.
| Author (Year) | Location / Climate | EAHE Parameters | EAHE Parameters | Key Findings | Relevance to Current Study |
|---|---|---|---|---|---|
| (Ozgener and Ozgener 2010) | Turkey, Semi-Arid | L=47 m, D=0.56 m | Experimental | Energy efficiency 58–63% | No courtyard or hot-arid context |
| (Benhammou et al. 2015) | Algeria, Arid | L=23.4 m, D=0.15 m | Experimental | Temp reduction 10–12°C | No CFD analysis |
| (Jakhar et al. 2016) | India, Semi-Arid | L=34 m, D=0.10 m, Depth=3.7 m | Experimental | Temp reduction 15–18°C | No integration with the courtyard |
| This Study | Iraq, Hot-Arid | L=60 m, D=0.20 m, Depth=3 m | CFD | Temp reduction 21°C | Courtyard-integrated + CFD + Hot-Arid |
2.4. Research Gap
While Earth-Air Heat Exchanger (EAHE) systems and courtyard-based passive cooling have been studied separately in the past, their combined integration has received little attention. For example, Jakhar et al. (2016) examined the thermal performance of EAHE systems in semi-arid environments, but they did not take architectural integration with courtyard designs into account. In a similar vein, Benhammou et al. (2015) investigated EAHE systems with wind tower assistance in hot regions, although they did not assess courtyard-induced microclimatic impacts or carry out CFD-based optimisation. As a result, current research mostly concentrates on isolated passive techniques or independent EAHE systems, lacking a thorough framework that combines geothermal cooling with courtyard design in extremely hot and dry environments.
In order to close this gap, this study suggests a CFD-based integrated EAHE–courtyard system that combines subsurface cooling with architectural microclimate control and is especially designed for Baghdad's climate.
3. Research Contributions
The following significant advances in the fields of geothermal cooling systems and sustainable building design are made by this study:
- It establishes a hybrid geothermal–passive cooling method designed for hot, dry conditions by introducing a revolutionary integration of an Earth–Air Heat Exchanger (EAHE) system beneath a residential courtyard.
- It creates a CFD-based design optimisation framework that assesses how pipe geometry, burial depth, and airflow dynamics interact to affect thermal performance in harsh climates.
- It shows for the first time in the setting of Iraq that it is possible to achieve low-energy cooling by combining courtyard microclimate regulation with subsurface geothermal stability.
- It gives engineers and architects a set of useful design recommendations that make it possible to install EAHE systems in residential structures with courtyards.
- It offers an interdisciplinary strategy for the construction of low-energy buildings by bridging the gap between mechanical engineering (CFD-based thermal systems) and architectural design (climate-responsive courtyard dwelling).
4. Methodology
The performance of a courtyard-integrated Earth-Air Heat Exchanger (EAHE) system in hot, dry climates is assessed in this study using a combined computational and design-based methodology.
4.1. Numerical Modelling
To simulate airflow and heat transport inside the EAHE system, a three-dimensional Computational Fluid Dynamics (CFD) model was created using ANSYS Fluent. The continuity, momentum, and energy equations for incompressible turbulent flow are solved by the model.
The realisable k–ε model was utilised for comparison validation, and the SST k–ω turbulence model was chosen because of its resilience in forecasting near-wall behaviour and flow separation.
4.2. Governing Equations
(Lin et al. 2022), (Kong et al. 2017) & (Zawada 2011)
4.3. Boundary Conditions
With ambient air temperatures as high as 47 °C, the simulations were carried out in peak summer circumstances typical of Baghdad. Among the boundary conditions are:
1. Velocity inlet: 1–5 m/s.
- Temperature inlet: variable (based on climatic data).
- Soil temperature: assumed constant at 22–25 °C.
- Outlet: pressure outlet condition.
- Soil Temperature Assumption: Based on typical subsurface thermal conditions observed in hot-arid locations, it was predicted that the soil temperature would remain constant between 22 and 25 °C. According to earlier research, thermal inertia and decreased solar radiation exposure cause soil temperatures at depths of 2-4 m to stay comparatively constant throughout the day. Although this assumption makes the model simpler, it is frequently used in EAHE simulations and offers a good approximation for steady-state analysis. To further increase model accuracy, future research may take into account transitory variations in soil temperature.
4.4. Mesh independence test
To guarantee the CFD model's stability and numerical accuracy, a mesh independence study was carried out. Table 2 summarises the three mesh densities that were tested: coarse, medium, and fine.
The findings demonstrate that the solution is convergent since the output temperature difference between the medium and fine meshes is less than 2%. As a result, the medium mesh was chosen as the best compromise between accuracy and computational cost.
| Mesh Level | Number of Elements | Outlet Temperature (°C) | ΔT (°C) | Variation (%) |
|---|---|---|---|---|
| Coarse | 120,000 | 27.5 | 19.5 | - |
| Medium | 250,000 | 26.8 | 20.2 | 2.5% |
| Fine | 420,000 | 26.5 | 20.5 | 1.1% |
4.5. Parametric Analysis
To assess the influence of important design variables, a parametric analysis was carried out:
- Pipe length: 20–60 m.
- Pipe diameter: 0.10–0.30 m.
- Burial depth: 2–4 m.
- Airflow velocity: 1–5 m/s.
Cooling potential, pressure drop, and output air temperature were used to evaluate the performance.
4.6. Performance Indicators
The following methods were used to assess the EAHE system's thermal performance:
- Temperature reduction (ΔT).
- Cooling effectiveness.
- Pressure loss along the pipe.
4.7. System Integration
To create a hybrid geothermal–passive cooling arrangement, the EAHE system was placed beneath a 6 m x 6 m courtyard. Through shading and microclimatic effects, the courtyard improves airflow dispersion and offers extra cooling.
The following sections examine the parametric optimisation and performance of the integrated EAHE-courtyard system after the CFD model has been verified against earlier research.
4.8. Model Validation
To guarantee numerical accuracy and dependability, mesh independence tests and comparison with existing studies in comparable climatic circumstances were carried out.
5. Practical study
5.1. Courtyard Configuration and System Layout
- 6 × 6 m courtyard, air inlet north, outlet south.
- Pipes in coiled loops, buried 3 m.
- Aluminium–PVC pipes for durability.
- Microclimatic shading and airflow distribution.
5.2. Management of Ventilation and Airflow
- A fan with wind assistance.
- Adjustable gates to fine-tune airflow.
- Natural ventilation when there is enough wind.
5.3. Combining Renewable Energy
- A tiny wind turbine to power fans.
- Photovoltaic panels are an optional source of additional energy.
5.4. Important Real-World Results
- Indoor air temperatures range between 23 to 28 °C, even during the summer's peak temperature of 47°C.
- The system is scalable, small, and consistent with the layout of traditional Iraqi courtyards.
6. Results
6.1. The Impact of Thermal Performance on Burial Depth
According to the simulation results, burial depth is crucial for maintaining thermal performance. Soil temperature fluctuates more at depths below 2 m, which lowers cooling efficiency. Heat exchange between air and soil is improved by increasing the burial depth to 3 m, which greatly increases thermal stability.
Excavation expenses rise, and cooling performance only slightly improves above 3 meters. Thus, the ideal depth for striking a balance between economic viability and thermal efficiency is determined to be 3 m.
6.2. The Impact of Pipe Length
The residence time of air in the EAHE system is directly impacted by pipe length. Due to extended heat exchange, a significant decrease in temperature occurs when the pipe length is increased from 20 to 60 meters. Longer pipes, however, result in greater pressure losses, suggesting a trade-off between airflow efficiency and thermal performance. The optimum cooling advantage without undue pressure penalties is achieved at the ideal length of 60 m.
6.3. The Impact of Airflow Velocity
The process of heat transmission is greatly influenced by airflow velocity. Maximum temperature reduction (up to 21 °C) is achieved via longer air-soil interaction at lower velocities (1 m/s). Higher velocities (5 m/s), on the other hand, shorten residence times and result in better ventilation capacity but worse cooling performance. This illustrates how heat efficiency and airflow demand are traded off for performance.
6.4. Combined System Performance
The optimised EAHE system lowers the air temperature to a range of 23–28 °C at peak summer circumstances (47 °C ambient temperature). This translates to a maximum cooling potential that is higher than 21 °C.
By encouraging natural airflow distribution and lowering solar gains, the integration with the courtyard environment further improves performance.
6.5. Features of Pressure Drop
Pressure losses rise nonlinearly with pipe length and airflow velocity. While preserving acceptable pressure drops, the suggested pipe shape enhances heat transmission.Stable airflow is ensured under a variety of operating scenarios by using a wind-assisted fan.
Figures 1–5 show temperature profiles, velocity distributions, pressure gradients, and soil–air thermal interactions.
Using previously published EAHE research, which are compiled in Table 1, a comparison analysis and model validation were carried out. To guarantee accuracy in predicting temperature reduction (ΔT) under comparable design parameters, the CFD model used in this study was benchmarked against these datasets.
| Study | Location / Climate | EAHE Parameters | CFD / Experimental | ΔT (Literature) | ΔT (CFD, This Study) | Error % | Notes |
|---|---|---|---|---|---|---|---|
| )Ozgener & Ozgener 2010( | Turkey, Semi-Arid | L=47 m, D=0.56 m | Experimental | 12–14°C | 13°C | 4% | Consistent with the literature |
| )Benhammou et al. 2015( | Algeria, Arid | L=23.4 m, D=0.15 m | Experimental | 10–12°C | 11°C | 5% | CFD predictions agree well |
| )Jakhar et al. 2016( | India, Semi-Arid | L=34 m, D=0.10 m, Depth=3.7 m | Experimental | 15–18°C | 16°C | 3% | Model validated successfully |
| This Study | Iraq, Hot-Arid | L=60 m, D=0.20 m, Depth=3 m | CFD | N/A | 21°C | N/A | Includes courtyard microclimate + Hot-Arid optimisation |
The CFD model was verified using earlier research, which is compiled in table 3. The numerical model's dependability was confirmed by the highest difference of 5% between CFD predictions and values found in the literature. The performance of the integrated EAHE-courtyard system in Baghdad is reflected in the current study's ΔT figures, which do not have an error percentage because they are based on the initial simulation results.
In contrast to earlier research, the validated CFD model captures the combined effects of underground geothermal cooling and courtyard-induced microclimatic regulation, allowing for a maximum temperature drop of 21°C in Baghdad. This illustrates how the suggested hybrid design is superior to standalone EAHE systems.
7. Discussion
The current study reaches a larger cooling potential of 21°C than other studies like Jakhar et al. (2016) and Benhammou et al. (2015), which claim temperature reductions of up to 18°C. The EAHE system's incorporation of courtyard microclimatic effects, which increase airflow dispersion and decrease solar heat uptake, is responsible for this improvement.
This demonstrates how the suggested hybrid geothermal-passive method is superior to traditional standalone EAHE systems.
The incorporation of courtyard microclimate effects, which increase airflow dispersion and decrease solar heat uptake, is responsible for this improvement and raises system performance overall.
The findings verify that a complex interplay between geometric parameters and airflow dynamics controls the performance of EAHE devices. The determined ideal burial depth of three meters is consistent with other research that emphasises the significance of reaching thermally stable soil layers while reducing excavation expenses.
The observed trade-off between cooling efficiency and airflow velocity is in line with basic principles of heat transfer. Higher velocities put ventilation ahead of thermal performance, while lower velocities improve convective heat exchange because of longer residence times.
The incorporation of EAHE systems into a courtyard arrangement is a significant contribution of this study. In contrast to traditional EAHE implementations, the courtyard improves airflow distribution and reduces solar heat gain by acting as a thermal buffer. Together, these effects greatly improve the overall performance of the system.
This research shows that hybrid geothermal–passive techniques can produce better cooling performance in harsh climates as compared to earlier studies that concentrate on solo EAHE systems. The efficiency of the suggested design is demonstrated by the achieved temperature reduction (up to 21 °C), which surpasses values recorded in comparable hot-arid investigations.
The findings also highlight the significance of interdisciplinary integration between mechanical systems and architectural design. Geothermal cooling and courtyard microclimate work together to create a scalable and context-sensitive low-energy home solution.
7.1. Energy performance discussion
The suggested EAHE–courtyard system mainly uses passive geothermal cooling and natural ventilation principles, despite the lack of a thorough energy consumption analysis in this work. The low-power fan, which is the only active part, uses a lot less energy than traditional air conditioning systems.
As a result, the system can help achieve low-energy construction methods and significantly lower cooling energy consumption. In-depth energy balancing and system efficiency analysis will be the main topics of future research.
7.2. Practical Feasibility discussion
Implementing the suggested methodology with traditional building supplies and methods is rather easy. The only maintenance needed for the buried pipe system is routine cleaning and inspection to guarantee effective airflow.
Compared to traditional ventilation systems, the initial installation cost is higher, but long-term energy savings from a decreased reliance on mechanical cooling make up for it.
All things considered, the system can be included into residential buildings with courtyards in hot, dry areas, especially in new construction.
7.3. Limitations of the Study
Although the CFD simulations produced encouraging results, this study has some drawbacks. Specifically, the study relies only on numerical modelling and lacks field or experimental validation. The reliability of the results would be further strengthened by real-world validation, even though the model has been benchmarked against previously published studies with good agreement.
In order to validate the suggested system in real-world operating conditions, further research should concentrate on experimental implementation and in-situ measurements.
8. Combined Passive and Geothermal Cooling System
This study suggests an integrated design framework that integrates climate-responsive building techniques with geothermal cooling.
The framework consists of three interconnected layers:
- Subsurface Layer: EAHE system utilizing stable soil temperature for air preconditioning.
- Architectural Layer: Courtyard configuration enhancing shading, airflow, and thermal buffering.
- Operational Layer: Controlled airflow and hybrid ventilation supported by low-energy systems.
By lowering cooling loads and enhancing indoor thermal comfort, this multi-layered technique makes it possible to produce low-energy residential structures.
The framework bridges the gap between engineering systems and architectural design by offering a transportable paradigm for hot-arid environments.
9. Conclusion
By incorporating an Earth-Air Heat Exchanger (EAHE) system into a courtyard-based residential design for hot, dry conditions, this study offers a novel geothermal-passive hybrid cooling technique. The study shows how combining climate-responsive architectural features with subsurface thermal stability can greatly lower cooling demand using high-resolution CFD simulations.
The findings verify that the ideal EAHE configuration, which includes a burial depth of 3 m, a pipe diameter of 0.20 m, a pipe length of 60 m, and an airflow velocity of 1–5 m/s, can lower the input air temperature to 23–28 °C in extreme ambient circumstances that can reach 47 °C. This indicates that the system can provide significant passive cooling, with a maximum cooling potential of more than 21 °C.
The demonstration that incorporating EAHE systems beneath courtyards improves thermal performance beyond traditional standalone applications is a significant contribution of this study. As a microclimatic moderator, the courtyard enhances airflow dispersion, lowers solar heat gain, and strengthens the geothermal system's cooling effect.
In hot, arid areas, the suggested integrated geothermal-passive structure provides a workable and scalable way to achieve low-energy residential buildings. The study offers a transportable model that may be modified for comparable environmental conditions by bridging the gap between mechanical systems and architectural design.
Overall, by showing that hybrid passive-geothermal techniques can successfully replace or greatly lessen reliance on traditional mechanical cooling systems in harsh conditions, this research advances sustainable building design.
This study is limited by the absence of experimental validation, which will be addressed in future work.