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Comprehensive Analysis of Thermal Performance and Indoor Air Quality in Traditional Hejazi Houses in Jeddah – Saudi Arabia

Project Overview

Project Type:

Thermal Performance and Indoor Air Quality Analysis of Traditional Residential Buildings

Project Location:

Jeddah, Hejaz Region, Saudi Arabia

Year of Completion:

2023

Overall Objective:

To conduct a scientific evaluation of the efficacy of natural ventilation, indoor air quality, and thermal performance inherent in vernacular architecture within a hot-humid climatic zone.

Climate:

Hot and humid, characterized by consistently high temperatures for most of the year and significant relative humidity.

Simulation Parameters:

Client:

University of Pennsylvania

Simulation and Energy Optimization Specialist:

Dr. Amirhossein Janzadeh

Project Introduction

This research project was conceived with the explicit aim of performing a rigorous, in-depth investigation into the thermal dynamics, indoor air quality profiles, and natural ventilation patterns intrinsic to the traditional domestic architecture of the Hejaz region.
The vernacular building tradition of Jeddah is fundamentally rooted in climatic logic, employing an intelligent, passive design strategy that masterfully harnesses natural air currents for spatial cooling and comfort.
Within a climatic context where reliance on energy-intensive mechanical cooling systems is exceptionally pronounced, a scientifically grounded analysis of passive design performance holds significant potential to inform and advance sustainable architectural practice. Consequently, a representative, physically extant traditional house was selected as a case study. Its complete system of airflow patterns, temperature stratification, and ventilation effectiveness was subjected to comprehensive numerical simulation.

Research Key Objectives

The research aims for this project were established within a multi-layered, interconnected framework:

To analyze the spatial distribution of airflow velocity and direction within the building’s interior volumes.
To examine the patterns of temperature distribution across various rooms and functional zones.
To evaluate the Age of Air metric as a primary indicator of indoor air quality, healthfulness, and freshness.
To conduct a comparative assessment of natural ventilation performance under characteristic summer and winter conditions.
To investigate the functional role of the central staircase as a vertical ventilation shaft.
To analyze the influence of indoor-outdoor temperature differentials on the operative logic governing the use of openings.
To estimate the aggregate annual volume of fresh air intake facilitated by the passive design.

Research Methodology and Tools

To ensure the accuracy and reliability of the findings, a hybrid methodological approach was employed, integrating Computational Fluid Dynamics(CFD) micro-scale analysis with macro-scale building energy performance simulation using DesignBuilder software. A precise three-dimensional digital model of the building was constructed based on its actual dimensions and situated within the specific climatic context of Jeddah. Authentic annual meteorological data; encompassing dry-bulb temperature, wind speed and direction, and solar radiation, were rigorously integrated into the simulation environment.

Analysis Time Scenarios;

The investigation was conducted across four critical diurnal periods representing peak seasonal conditions:

Summer Design Day: July 24 –10:00 AM
Summer Design Day: July 24 – 5:00 PM
Winter Design Day: December 24 – 10:00 AM
Winter Design Day: December 24 – 5:00 PM

The analysis focused intensively on a western-facing room on both the second and third floors. Results were visualized through horizontal plan slices at occupant level and through vertical building sections that captured the full height of the staircase.

Annual Natural Ventilation Simulation;

The final phase of the study involved a holistic annual simulation to quantify the total volumetric intake of fresh air into the building over a complete yearly cycle. This advanced analysis accounted for dynamic seasonal shifts in temperature, prevailing wind patterns, and the adaptive use of openings, thereby providing a comprehensive and realistic assessment of the building’s long-term environmental performance. This component was essential for evaluating the inherent climatic sustainability and resilience of the traditional design.

Comparative Analysis of Simulation Results

1) Detailed Results – Western Room, Second Floor:

Summer – 10:00 AM;

Average Airflow Velocity: 0.47 meters per second
Average Space Temperature: 30.5 °C
Age of Air: 18.85 seconds
Interpretation: Demonstrates highly effective natural ventilation, resulting in a plentiful supply of fresh air and excellent indoor air quality.

Summer – 5:00 PM;

Average Airflow Velocity: 0.07 meters per second
Average Space Temperature: 35.12 °C
Interpretation: Reveals a significant degradation in ventilation efficacy, directly attributable to the elevated outdoor temperature and the consequent reduction in the driving thermal gradient.

Winter – 10:00 AM;

Average Airflow Velocity: 0.24 meters per second
Average Space Temperature: 15.32 °C
Age of Air: 29.86 seconds
Interpretation: Confirms that natural ventilation remains functionally efficient in maintaining conditions within the thermal comfort zone.

Winter – 5:00 PM;

Average Airflow Velocity: 0.33 meters per second
Average Space Temperature: 12.83 °C
Age of Air: 24.89 seconds
Interpretation: Indicates robust air exchange rates and optimal passive cooling performance during the evening period.

2) Western Room, Second Third Floor;

At the third-floor level, a general increase in the age of air accompanied by a noticeable reduction in airflow velocity was recorded. This pattern highlights the direct impact of vertical elevation, spatial geometry, and the positioning of openings on the operational efficiency of natural ventilation. In a broader comparative reading, the second floor exhibited a more balanced performance in relation to both thermal comfort and indoor air quality.

Summer – 10:00 AM;

Average Airflow Velocity: 0.07 meters per second
Average Space Temperature: 37.4 °C
Age of Air: 179.21 seconds
Interpretation: Indicates limited natural ventilation capacity; elevated indoor temperatures have diminished ventilation performance and increased air age, although a measurable airflow current is still present within the space.

Summer – 5:00 PM;

Average Airflow Velocity: 0.045 meters per second
Average Space Temperature: 34.28 °C
Age of Air: 336.36 seconds
Interpretation: Reveals a substantial decline in airflow intensity, primarily resulting from the reduced indoor–outdoor thermal differential; natural ventilation operates at very low efficiency, and indoor air becomes comparatively stagnant and aged.

Winter – 10:00 AM;

Average Airflow Velocity: 0.16 meters per second
Average Space Temperature: 19.35 °C
Age of Air: 96.65 seconds
Interpretation: Demonstrates effective natural ventilation performance while maintaining winter morning thermal comfort; indoor air remains relatively fresh and adequately renewed.

Winter – 5:00 PM;

Average Airflow Velocity: 0.9 meters per second
Average Space Temperature: 23.57 °C
Age of Air: 394.05 seconds
Interpretation: Although airflow velocity is notably high, the elevated age of air suggests indoor air accumulation and a relative reduction in the rate of fresh air replacement.

3) Staircase Analysis as a Ventilation Shaft;

The staircase functions as a vertical air-transfer shaft, playing a critical role in facilitating airflow movement between floors. Findings indicate that during warmer daytime hours, the temperature differential between interior and exterior environments intensifies vertical air suction and stack-driven flow, whereas this driving force diminishes under colder conditions. This behavior reflects one of the fundamental environmental principles embedded in vernacular architectural design strategies across warm-climate regions.

Summer – 10:00 AM;

Average Airflow Velocity: 0.11 meters per second
Average Space Temperature: 18.09 °C
Age of Air: 25.3 seconds
Interpretation: Demonstrates that the stair shaft efficiently channels natural ventilation; airflow remains moderate and continuous, while thermal conditions stay within a relatively comfortable range.

Summer – 5:00 PM;

Average Airflow Velocity: 0.34 meters per second
Average Space Temperature: 34.35 °C
Age of Air: 120.5 seconds
Interpretation: Indicates an increase in airflow velocity; however, elevated ambient temperatures and external thermal gradients reduce the overall effectiveness and perceived quality of ventilation.

Winter – 10:00 AM;

Average Airflow Velocity: 0.6 meters per second
Average Space Temperature: 22.61 °C
Age of Air: 35.7 seconds
Interpretation: Confirms strong ventilation performance within the stair shaft, supporting effective fresh air distribution while maintaining desirable thermal comfort conditions.

Winter – 5:00 PM;

Average Airflow Velocity: 0.84 meters per second
Average Space Temperature: 26.67 °C
Age of Air: 42.3 seconds
Interpretation: Reflects robust and clearly perceptible airflow; natural ventilation operates efficiently, ensuring consistent fresh air circulation throughout the vertical shaft.

Important Technical Notes;

The operational logic for natural ventilation was modeled to activate only when the indoor temperature exceeded the outdoor temperature, reflecting realistic occupant behavior.
All mechanical cooling and heating systems were deactivated(Off) in the simulation model to isolate and study the performance of the passive design in isolation.
Comprehensive data visualization included charts detailing the maximum, minimum, and average values for each measured parameter.
The Age of Air index was established as the principal, scientifically rigorous metric for assessing the healthfulness and refresh rate of the indoor air.

Project Achievements

Empirical Validation: Provided quantitative proof of the inherent energy efficiency and environmental performance of traditional Hejazi architecture.
Data-Driven Design Toolkit: Generated a robust set of performance data that can directly inform sustainable design strategies for new construction and rehabilitation.
Transferable Design Principles: Identified key passive design principles that are directly applicable and adaptable to contemporary architectural projects in similar climates.
Pathway to Reduced Mechanical Dependency: Demonstrated a viable model for significantly reducing reliance on conventional HVAC systems, lowering both energy consumption and carbon footprint.
Enhanced Occupant Well-being: Validated design approaches that intrinsically improve indoor environmental quality, contributing directly to occupant health, comfort, and productivity.

Conclusion

The findings of this comprehensive study compellingly demonstrate that the traditional Hejazi houses of Jeddah represent a highly successful and refined paradigm of climate-responsive, passive sustainable architecture. Through the sophisticated integration of natural ventilation, thoughtfully conceived spatial geometry, and strategically deployed openings, these structures achieved effective internal temperature regulation and superior indoor air quality without any dependence on mechanical energy inputs.
These evidence-based insights offer a valuable and inspiring repository of knowledge for contemporary architects and designers, providing a foundational reference for developing innovative, context-sensitive, and truly passive design solutions tailored for hot and humid regions worldwide.

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