Introduction

The accelerating impacts of climate change, rapid urbanization, and growing energy insecurity have converged to create a global imperative for sustainable thermal comfort strategies, especially in regions characterized by extreme climatic conditions1,2,3. Countries located in arid and semi-arid zones are particularly vulnerable, as they experience severe summer temperatures, increasing frequency of heatwaves, and limited access to reliable energy infrastructure. Iraq, situated in the heart of the Middle East, exemplifies these challenges4. The need for efficient and energy-efficient cooling techniques has increased to a critical level as summer temperatures in the southern and central regions routinely surpass 50 °C and urban populations become more crowded in buildings with inadequate insulation5. The reliance on conventional vapor-compression air conditioning systems offers only short-term relief while exacerbating the energy crisis in Iraq6,7. These systems account for 60–70% of overall electricity use in residential and commercial buildings during the summer months8,9,10. The reliance on electricity-intensive cooling systems leads to frequent blackouts, grid overload, increased carbon emissions, and higher operational costs. The electricity system in Iraq is predominantly reliant on fossil fuel-based power generation, with extensive dependence on private diesel generators as auxiliary sources11. This energy paradigm leads to considerable environmental degradation, incurs major economic expenses, and intensifies disparities in access to thermal comfort among groups of people12,13. In light of these complex issues, passive and low-energy cooling methods have received more attention. Among these, evaporative cooling is a cost-effective, environmentally friendly, and technically applicable solution for arid and hot areas14,15,16,17. Direct evaporative cooling (DEC) systems operate by utilizing the enthalpy of vaporization to reduce air temperature through water evaporation, without dependence on refrigerants or mechanical compression cycles14,15,18,19,20. These systems have several benefits as inexpensive startup costs, ease of use, less maintenance, and low electricity consumption, only fans and pumps needed21. Consequently, implementing DEC technology can offer a cost-efficient and sustainable approach to improving thermal comfort in residential and public buildings in hot and arid climates22. However, the effectiveness of DEC is highly dependent on design conditions, and on local climatic variables, particularly ambient dry-bulb temperature and relative humidity, which influence the wet-bulb depression and thus cooling potential. Despite the long-standing historical use of evaporative cooling in Iraq, modern quantitative studies assessing its viability across the country’s diverse climatic zones are scarce. Previous studies have frequently concentrated on the integration of DEC systems with vapor-compression cycles for hybrid configurations or the optimization of operational timing in remote areas23,24. Even though there are increasing worries about water scarcity in arid areas like Iraq, DEC systems is still a practical and sustainable approach when combined with the right water management practices. Recent research has demonstrated that DEC systems can function effectively with alternative water sources, such as rainwater harvesting, condensate recovery, and treated greywater, greatly lowering the need for freshwater resources25,26. A number of water conservation techniques can be incorporated to improve sustainability and address issues with water consumption in DEC systems. The potential of using alternative water sources, like treated wastewater or greywater, for cooling applications without sacrificing system performance has been highlighted by recent studies27. Evaporative cooling combined with hybrid systems or indirect evaporative cooling (IEC) techniques can further reduce freshwater dependency while maintaining acceptable thermal comfort levels in arid regions like Iraq, where water scarcity is a problem28. However, these studies frequently lack a broader regional analysis of evaporative cooling performance using modern thermal comfort indices, and do not sufficiently evaluate the standalone potential of DEC in naturally ventilated or free-running buildings. The absence of such assessments leaves a critical knowledge gap for architects and engineers, seeking sustainable climate-specific cooling strategies for Iraq. Thermal comfort is defined as a state of mind in which an individual expresses satisfaction with the thermal environment that is a cornerstone of building performance and occupant well-being29,30,31. It plays a central role in energy demand, health outcomes, and productivity, especially in regions where indoor conditions are closely coupled with outdoor thermal extremes. Numerous models have been created to quantify thermal comfort, including empirical indices, adaptive models, and physiological simulations. The predicted mean vote (PMV), created by Fanger, continues to be extensively employed for assessing steady-state comfort levels in mechanically conditioned indoor environments32,33. These models estimate an average thermal sensation on a seven-point scale from cold (− 3) to hot (+ 3) by taking into account a set of personal (clothing insulation and metabolic rate) and environmental (air temperature, humidity, air speed, and mean radiant temperature) parameters32,34. Although PMV indices are traditionally utilized in mechanically regulated indoor settings, their application has been broadened to evaluate the comparative efficacy of passive cooling solutions, contingent upon the establishment of suitable assumptions for interior thermal conditions and occupant behaviour35,36,37,38. Conversely, outdoor thermal comfort is more effectively evaluated using dynamic indices like the heat stress index (HSI), which amalgamate environmental extremes with human physiological reactions39,40. The Köppen–Geiger climate classification system categorizes global climates based on long-term temperature and precipitation patterns41,42. It divides regions into arid, semi-arid, temperate, and tropical climate zones, influencing human thermal comfort. This helps researchers and designers correlate climatic characteristics with comfort indices, identify constraints, determine seasonal comfort potentials, and develop climate-responsive building systems43,44. Thus, the climate characteristics would be more essential to determine appropriate strategies for dealing with factors impacting the thermal comfort. The climate characteristics method is used in various fields like agriculture, urban planning, and environmental management to analyse climatic conditions45. This method can provide a clear understanding of temperature, precipitation, humidity, wind patterns, and seasonal changes in specific regions46,47,48. It is also used for identifying the long-term climate trends49. Middle East in general, Iraq specifically has more warm days relatively to other places. Iraq has one of the hottest climates around the world, actually it regarded in recent years one of the hottest places on earth i.e. reaches 53 °C in July50, which add a stress on the building air conditioning. More stress on the buildings air conditioning has been added due to decreased vegetation cover during the last four decades because of wars that Iraq went through and climatic change that effect world. This research presents a novel, climate-based evaluation of evaporative cooling system as a viable low-energy thermal comfort strategy of building across three representative Iraqi cities (i.e. Baghdad, Basrah, and Mosul) which represent distinct climatic zones under the Köppen–Geiger classification. To achieve this, multiple tools and datasets such as energyplus weather (EPW) and transient system simulation tool (TRNSYS) are used. The PMV and HSI models are also employed to evaluate the thermal comfort potential of air processed by evaporative cooling under variable summer conditions in Iraq. The analysis covers a five-month summer period (May–September), during which cooling demand is highest in Iraq. This study aims to provide practical insights into the application and limitations of direct evaporative cooling in real-world Iraqi circumstances, beyond technical modeling.

Research methodology and model description

Research methodology

This study employed a systematic four-stage framework to evaluate the climatic viability and thermal comfort performance of DEC systems in several Iraqi cities. The assessment encompassed the peak summer duration from 1st May to 30th September, when cooling demand in Iraq was at its zenith. The methodology combineded climate classification, building performance modelling, and thermal comfort analysis for a thorough evaluation. In Step 1, representative climate types were determined utilizing the Köppen–Geiger classification together with the relevant EPW files. A case study for a structure situated in three cities (Baghdad, Basrah, and Mosul) was picked due to their climatic variability, encompassing hot and arid climates. In Step 2, building-scale simulations were performed utilizing TRNSYS. The thermal comfort conditions in a building were modelled under two scenarios: using only mechanical ventilation to handle the cooling load, and the other employing DEC system. The key performance indicators, focusing on air temperature reduction and indoor relative humidity, were used to evaluate the system effectiveness. Step 3 involved the application of recognized thermal comfort models to assess occupant satisfaction levels. Comfort indices such as the PMV and HSI were calculated using hourly climate-adjusted outputs from the simulation environment. These indices provided a quantitative basis for comparing comfort outcomes across different cities and timeframes. Finally, in Step 4, results from the simulation and comfort models were synthesized to evaluate correlations between climatic variables (e.g., temperature, humidity), cooling system effectiveness, and resulting comfort levels. The analysis facilitated the identification of climatic conditions under which evaporative cooling achieved optimal performance. This integrated approach, supported by EPW climate data, TRNSYS building modelling, and the CBE (Thermal Comfort Tool), enabled a robust evaluation of evaporative cooling as a low-energy thermal comfort strategy suitable for climatic context in Iraq. It was worthwhile to mention that the CBE is an online application developed by the University of California, Berkeley, assisting researchers, engineers, architects, and facility managers in evaluating thermal comfort conditions in accordance with ASHRAE Standard 5551.

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Overall methodological framework of the study, illustrating the workflow for evaluating direct evaporative cooling performance and thermal comfort in Baghdad, Basrah, and Mosul.

Characterisation of Iraqi climate

The effectiveness of passive and low-energy cooling systems such as DEC depended critically on local climatic conditions. In this work, the Köppen–Geiger climate classification was adapted from a traditional climatological tool into a performance-oriented framework for evaluating the feasibility of evaporative cooling in Iraq. This novel adaptation did not only consider temperature and precipitation patterns, but also the psychrometric suitability of each climate zone, particularly focusing on wet-bulb depression as a key indicator of DEC potential52,53.

Two dominant climate types were identified across Iraq: the BWh (hot desert) zone, covering central and southern regions such as Baghdad and Basrah, and the BSh (hot semi-arid) zone, present in northern areas like Mosul (Fig. 2). These zones differed in their dry-bulb temperatures, relative humidity levels, and seasonal cooling demands. While BWh regions experience extremely hot, dry summers ideal for DEC performance, BSh zones offered moderate humidity and cooler summer peaks, providing useful contrast for comparative analysis54.

To reinforce the climate zoning, this study incorporated hourly meteorological data from EnergyPlus Weather (EPW) files to evaluate dry- and wet-bulb temperatures, relative humidity, and wet-bulb depression across the cooling season (May to September). This allowed a finer-resolution evaluation of evaporative cooling potential beyond categorical climate types55.

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Köppen–Geiger climate classification map of Iraq showing the studied cities used as reference locations for this study (updated from53.

The selected cities also reflected Iraq’s demographic and energy landscape: Baghdad, as the capital and largest urban centre; Basrah, the hottest and most humid major city with intensive industrial activity; and Mosul, representing northern semi-arid conditions with large urban populations. This combination supported a geographically diverse and climatically grounded assessment of DEC feasibility and performance56. The summary of climate characteristics for three cities examined in this study was induced in the Table 1.

Table 1 Summary of key climatic parameters (e.g., longitude, average yearly temperature, elevation above sea level…etc.) for the three studied Iraqi cities (Baghdad, Basrah, and Mosul)57.
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A case study of building performance evaluation

To translate the climate-based analysis of evaporative cooling feasibility into real-world applicability, a building-scale simulation was conducted as a case study to evaluate the indoor thermal performance of a DEC system in a typical Iraqi residential setting. The aim of this component was to assess the operational behaviour of DEC in providing thermal comfort under actual building conditions within the selected climate zones, focusing specifically on Baghdad, Basrah and Mosul as representative locations due to its high cooling demand and extreme summer temperatures.

Building description

The case study was based on a simplified single-zone residential building model, representative of common urban dwellings in Iraq. The building had a total floor area of \(100\text{m}^2\), a ceiling height of \(3\text{m}\). Thermal transmittance values were assumed as \(1.6\text{W}/\text{m}^2.\text{K}\) for walls and \(1.8\text{W}/\text{m}^2.\text{K}\) for the roof. Windows occupied approximately \(15\text{\%}\) of the wall surface area and were modelled as single-glazed panes with a U-value of \(5.7\text{W}/\text{m}^2.\text{K}\). Infiltration was set at \(0.5\) air changes per hour (\(\text{A}\text{C}\text{H}\)), and internal loads included occupancy (5 persons), lighting, and typical appliance heat gains (approximately \(3.5\text{W}/\text{m}^2\)). These parameters allowed for dynamic simulation of indoor air conditions, cooling system behaviour, and comfort indices across the summer cooling season. The building’s peak cooling demand load was estimated based on climatic extremes during the summer period in three cities to be \(10\text{k}\text{W}\). The building envelope thermal properties were identified to reflect typical residential construction practices in Iraq, rather than optimized or code-compliant designs, in order to isolate the climatic influence on evaporative cooling performance.

System configuration and simulation setup

A DEC system represented in Fig. 3, was modelled using TRNSYS (Transient System Simulation Tool), configured to simulate hourly performance during the cooling season (May 1st to September 30th). Natural ventilation was not explicitly modelled, and all airflow was mechanically controlled to ensure consistent and comparable operating conditions across the simulated scenarios. The evaporative cooler was modelled using Type 506, assuming an effectiveness of 85%, and an airflow rate of \(1500\;m^2/h\), providing approximately \(5\text{A}\text{C}\text{H}\) to the indoor zone. The system operated daily from 1st May to 30th September, aligned with peak thermal discomfort periods. Fan energy consumption was set at \(200 W\), and the system assumes continuous water availability for media saturation. All TRNSYS simulations were performed using standard library components with fixed operational parameters applied consistently across the three cities to ensure comparability of thermal comfort outcomes. The building and cooling system were simulated using TRNSYS components as followed:

  • Type 9 for EPW weather file input,

  • Type 56 for zone thermal dynamics,

  • Type 65/25 for result visualization and data logging,

  • Type 77 for psychrometric property analysis.

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Illustrates the evaporative cooling process applied to the supply air; return or exhaust airflow is implicitly accounted for in the building simulation and not shown for clarity.

Significance of the case study

The case study operationalised climatic feasibility analysis by simulating how evaporative cooling performs within a typical residential building enveloped under realistic conditions. By simulating a representative residential building under actual weather and occupancy conditions, it examined how DEC technologies interacted with building thermal mass, envelope properties, and internal gains within the unique climatic context of Iraq. The results went beyond simple temperature lowering, clarifying how system parameters and external climate conditions affect PMV and other measures of indoor thermal comfort. Moreover, the findings highlighted potential trade-offs, particularly regarding indoor humidity, that must be addressed in practical applications. This case study delivered actionable insights to advance climate-responsive design, offering valuable guidance for architects, engineers, and policymakers aiming to adopt sustainable cooling strategies. It reinforced the broader aim of this research to advance context-driven solutions for thermal comfort in energy-constrained, heat-intensive environments like Iraq.

Thermal comfort index

Thermal comfort satisfaction was influenced by various factors, including temperature, air velocity, mean radiant temperature, humidity, clothing, metabolic rate, and psychological state. ASHRAE Standard 55-2010 introduced a model to assess thermal comfort58,59. Key indoor parameters (air temperature, relative humidity, and thermal comfort indices) were recorded on an hourly basis. PMV was calculated using standard assumptions: metabolic rate is \(1.1\text{m}\text{e}\text{t}\), clothing insulation of \(0.5\text{C}\text{l}\text{o}\), air velocity of \(0.2\text{m}/\text{s}\), and mean radiant temperature assumed equal to air temperature. This model highlights the subjective nature of thermal sensation, emphasizing that thermal comfort is fundamentally a psychological state. Consequently, an individual’s perception of comfort within a particular environment may fluctuate over time due to psychological factors and adaptive behavioural responses60. These adaptive behaviours elucidated the disparities between PMV forecasts and empirical observations in naturally ventilated or free-running buildings. Although the PMV model has recognized limitations in predicting subjective thermal sensation in naturally ventilated and evaporatively cooled buildings, it remains widely used as a comparative comfort indicator. Field studies based on subjective surveys have shown that PMV can capture general comfort trends in evaporatively cooled environments when interpreted alongside climatic context and system characteristics61,62. In this study, PMV is therefore employed to support relative performance comparison rather than absolute prediction of occupants’ thermal sensation.

Results and discussion

Climate suitability for evaporative cooling

Figure 4 showed that the period from May to September represents the peak of summer in Iraq, characterized by extreme heat and varying levels of humidity across main three cities investigated. Figure 4a, for instance, showed that Baghdad, located in central Iraq, experiences some of the most extreme summer temperatures in the country, often exceeding 45 °C and occasionally reaching 50 °C. For instance, in July and August, average daily maximum temperatures in Baghdad ranged from 44 to 46 °C, with nighttime temperatures rarely dropping below 28 °C. The city experienced high sun radiation and protracted heatwaves due to its inland desert climate and low levels of cloud cover. Basrah, situated in the south near the Persian Gulf, also faces extreme heat, with temperatures frequently surpassing 48 °C. In July, the average maximum temperature in Basrah reaches 50 °C, with nighttime temperatures averaging 33 °C (Fig. 4b). However, its coastal location moderated nighttime temperatures slightly compared to Baghdad, though the combination of heat and humidity creates a more oppressive environment. Mosul, in the north, experiences less oppressive summer temperatures, typically ranging from 35 to 45 °C. For example, in July and Augest, Mosul’s average maximum temperature was around 45 °C, with nighttime temperatures averaging 24 °C (Fig. 4c). Its higher elevation and proximity to the Tigris river contributed to this moderation, though it still endures significant heat stress during peak summer months.

Relative humidity during this period varies dramatically among the three cities. Baghdad, with its arid desert climate, maintains low humidity levels, often averaging around 15–30%. In July, the average relative humidity in Baghdad is 20% during the day and approximately 35% at night. This diminishes the apparent heat intensity; yet, the absence of moisture worsens drought conditions and elevates evaporation rates, so further depleting water supplies. Basrah, however, has elevated humidity levels, frequently surpassing 60%, because to its nearness to the Persian Gulf. The average relative humidity in Basrah in August is 65% during the day and can reach 80% at night. The stifling environment created by the heat and humidity raises the risk of heat-related disorders. Although not as humid as Basrah, Mosul has moderate humidity, with an average of 30–40%. In June, Mosul’s average relative humidity was 35% during the day and 50% at night. The presence of the Tigris river and its northern location contributed to this balance, though humidity can spike during occasional rainfall events.

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Outdoor air conditions for Baghdad, Basrah, and Mosul from 1st May to 30th September, showing relative humidity and dry bulb temperature plotted on a psychrometric chart.

Heat stress index overview of three cities

The Heat Stress Index (HSI), a composite metric based on temperature and relative humidity, quantifies apparent temperature and serves as a key indicator for evaluating the health and thermal comfort impacts of summer heat exposure. Figure 5 shows the HSI analysis in three major Iraqi cities (Baghdad, Basrah, and Mosul) during the peak summer months from 1st May to 30th September. These cities, despite being located within the same country, exhibit significant differences in heat stress due to their distinct geographical and climatic conditions. For instance, the HSI analysis confirms Basrah as Iraq’s most vulnerable city, with extreme heat-humidity combinations exceeding safe thresholds for 78% of summer hours. Understanding these variations is essential for addressing public health risks, urban planning, and air conditioning strategies in a region increasingly vulnerable to extreme heat. The HSI revealed in Fig. 5, is calculated using outdoor climatic conditions and is employed to characterize summer heat stress severity and cooling demand, rather than indoor thermal comfort.

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Comparative analysis of the heat stress index in Baghdad, Basrah, and Mosul from 1st May to 30th September, highlighting seasonal variations in thermal stress.

HSI provides essential insights into public health vulnerability and climate-responsive cooling design in hot and arid regions. Long-term exposure to high HSI levels has been associated with increased risks of heat exhaustion, dehydration, cardiovascular stress, and reduced outdoor and indoor work productivity. Accordingly, Basrah emerges as the most vulnerable city, with extreme heat–humidity combinations exceeding tolerable thresholds for approximately 78% of summer hours, indicating a persistent thermal stress environment that poses serious public health concerns. These conditions necessitate cooling strategies that extend beyond conventional ventilation, emphasizing the need for enhanced air movement, adaptive operating schedules, or hybrid cooling systems incorporating evaporative and auxiliary dehumidification mechanisms. Conversely, Mosul’s comparatively lower HSI values suggest a reduced health risk profile and support the feasibility of direct evaporative cooling as a standalone, low-energy solution. Baghdad represents an intermediate case, where evaporative cooling remains effective but requires climate-adaptive control to balance temperature reduction and humidity increase. Integrating HSI-based assessments into cooling system design therefore enables more resilient, health-conscious, and climate-responsive building strategies in extreme environments.

Outdoor air speed patterns of three cities

Outdoor air speed, or wind speed, is a critical factor influencing thermal comfort, air quality, and the dispersion of pollutants, particularly during the hot summer months in Iraq. Thus, it is reported as a climatic indicator of thermal stress and environmental conditions, rather than as a direct input affecting the mechanically controlled indoor airflow rate. This analysis examines the patterns of outdoor air speed in three major Iraqi cities (i.e. Baghdad, Basrah, and Mosul) from May to September (Fig. 6). These cities, while geographically distinct, experience varying wind speeds due to their topographical and climatic differences.

For instance, Fig. 6a shows that Baghdad experiences relatively low wind speeds during the summer months, averaging between 5 and 10 km/h. The city’s inland desert location and lack of significant topographical features contribute to these calm conditions. The low wind speeds can reduce the potential for evaporative cooling, exacerbating the already extreme heat. For example, in July, when temperatures often exceed 45 °C, the lack of wind (averaging 6 km/h) makes the heat feel more oppressive, increasing the risk of heat-related illnesses. Low wind speeds also hinder the dispersion of pollutants, leading to poor air quality, particularly in urban areas with high traffic and industrial activity.

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Comparison of outdoor air velocity in Baghdad, Basrah, and Mosul from 1st May to 30th September, illustrating daily and seasonal variations.

Contribution of mechanical ventilation to the thermal comfort

For a period of five months (1st May to 30th September), the conditioned room was supplied with ambient air without any processing (i.e., utilizing only mechanical ventilation) at a constant rate of 5 ACH, consistent with the evaporative cooling scenario. In the Fig. 7, the conditions of mechanical ventilation for each single hour from 1st May to 30th September of three cities (i.e. Baghdad, Basrah and, Mosul) were dropped (plotted) on the psychrometric chart with natural conditions. It can be seen that a significant number of dot points, particularly summer hours, are out of the comfortable region. It can be seen in Fig. 7a of the Baghdad city that during the summer season (i.e. 1st May to 30th September), it is only 23% of summer hours that is located in the comfort zone. On the other side, Basrah city has the worst conditions among three cities investigated. Around 6% of the summer hours was located in the comfort zone. Mosul city has a better thermal comfort compared to others where the thermal comfort hours presented 31% of summer hours.

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Hourly mechanical ventilation conditions from 1st May to 30th September for Baghdad, Basrah, and Mosul, plotted on a psychrometric chart to illustrate variations in temperature and humidity in comfortable region.

Indoor thermal response of the building integrated with evaporative cooling

Figure 8 illustrated building indoor conditions particularly temperature and humidity content of air processed through the evaporative cooling for each hour from 1st May to 30th September of three cities: Baghdad, Basrah and, Mosul. The highest temperatures recorded in Baghdad and Basrah reach approximately 30 °C, while the lowest temperatures in these cities fall below 15 °C (Fig. 8a,b). In contrast, the highest temperature observed in Mosul after evaporative cooling was around 27 °C, with the lowest temperature recorded at 12 °C (Fig. 8c). The humidity levels in all three cities exhibits significant fluctuations. For instance, the humidity content in Baghdad and Basrah exceeds 0.018 kg/kg, whereas in Mosul, it did not surpass 0.016 kg/kg. It was noteworthy that the recommended humidity level for thermal comfort should not exceed 0.016 kg/kg59.

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Temperature and humidity conditions after the direct evaporative cooling stage for Baghdad, Basrah, and Mosul from 1st May to 30th September, illustrating the impact of DEC on indoor air properties.

Maintaining humidity levels below 0.016 kg/kg is essential for ensuring occupant comfort, especially in arid and semi-arid regions where evaporative cooling is widely used. When humidity levels surpass this threshold, the air can retain excessive moisture, resulting in discomfort and potential health concerns. In the context of the observed data, the humidity levels in Baghdad and Basra, which exceed 0.018 kg/kg, suggest that evaporative cooling alone may be insufficient to achieve optimal comfort conditions in these cities. In contrast, Mosul’s humidity levels, which remain below 0.016 kg/kg, align more closely with the recommended standards, indicating that evaporative cooling is better suited for this region.

Insights from PMV analysis for evaporative cooling

The indoor thermal comfort evaluation of building located in Baghdad, Basrah, and Mosul, can be effectively conducted using the PMV method, a widely recognized thermal comfort index. In Fig. 9, it can be found out that Baghdad and Basrah, which experience hot and arid climates, the PMV values can significantly reduce air temperature responding to increase in humidity levels due to the evaporative cooling. As shown in Fig. 9, the PMV values in Baghdad during the five-month study period range between \(+1.25\) and \(-1.25\). However, the thermal comfort zone, where optimal comfort is achieved, is defined by a narrower PMV range of \(-0.5\) to \(+0.5\). While the ranges of PMV values of Basrah and Mosul cities are (\(+1.5\) to \(-1.25\)) and (\(+1\) to \(-1.75\)) respectively. It is noted that high humidity levels in Baghdad and Basrah cities can diminish the effectiveness of evaporative cooling, as the air becomes overly saturated, reducing evaporative potential and increasing the PMV value.

These findings underscore the importance of considering local climatic conditions when designing and implementing evaporative cooling systems. While evaporative cooling can significantly reduce air temperature, its effectiveness in achieving thermal comfort is highly dependent on maintaining humidity levels within acceptable limits. In Baghdad and Basra, where high humidity levels diminish the system efficiency, supplementary strategies such as hybrid cooling systems or dehumidification may be necessary to achieve optimal comfort. This analysis reinforces the value of the PMV method as a robust tool for assessing thermal comfort and guiding the development of climate-appropriate cooling solutions.

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PMV values and thermal comfort zones after the direct evaporative cooling stage for Baghdad, Basrah, and Mosul from 1st May to 30th September, illustrating the effectiveness of DEC in achieving occupant comfort.

A key limitation of direct evaporative cooling lies in the trade-off between dry-bulb temperature reduction and the increase in the air humidity. While evaporative cooling substantially reduces indoor air temperature, excessive humidity can diminish thermal comfort by restricting the evaporative heat loss of occupant bodies. This effect is evident in Baghdad and Basrah, where humidity ratios occasionally exceed recommended comfort limits, leading to elevated PMV values despite significant temperature reductions. However, lower level of humidity in Mosul city allows temperature reductions to translate more effectively into improved comfort. These results indicate that the performance of evaporative cooling is strongly climate-dependent and highlight the importance of adaptive operation, adequate ventilation, or hybrid cooling strategies in humid hot and arid claimants.

Thermal comfort comparison between mechanical ventilation and evaporative cooling

A comparison of the thermal comfort percentages for the three cities under study using air processed with mechanical ventilation and those attained with an evaporative cooling system was shown in Fig. 10. The results revealed that Mosul attains the highest percentage of thermal comfort hours at 25% under mechanical ventilation of air conditions, while Basrah recorded the lowest at approximately 5%. However, a significant improvement in thermal comfort hours was observed in all three cities when evaporative cooling was applied to the ambient air. Notably, Basrah, which exhibited the poorest thermal comfort conditions using mechanical ventilation, experiences a substantial increase, reaching 60% when evaporative cooling was utilized. Likewise, the conditions in Baghdad exhibited the most significant overall rise in thermal comfort percentage, somewhat exceeding that of Basrah. In Mosul, where ambient summer temperatures are comparatively lower, direct evaporative cooling can occasionally reduce indoor air temperatures below the optimal thermal comfort range during certain periods, resulting in a smaller net improvement in comfort hours compared to hotter cities.

Fig. 10
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Comparison of the percentage of hours achieving thermal comfort in Baghdad, Basrah, and Mosul under mechanical ventilation versus direct evaporative cooling conditions.

Conclusions

The study offered an extensive examination of thermal comfort conditions in Baghdad, Basrah, and Mosul, highlighting the essential function of evaporative cooling in alleviating severe summer temperatures. It was also shown that DEC could be crucial in creating sustainable cooling plans in areas with limited energy resources, which has applications for building designers, legislators, and urban planners. The approach used here provides a framework for assessing comparable cooling interventions in other hot and dry environments by fusing thermal comfort indices with simulation-based analysis. Using both the Köppen climate classification and EnergyPlus weather files, the climatic features of these cities were examined. Many components of the TRNSYS software library were utilized to simulate the outdoor air conditions subjected to evaporative cooling in the principal cities of Iraq: Baghdad, Basrah, and Mosul. The findings indicated that the implementation of evaporative cooling systems significantly enhanced thermal comfort in all three cities. In Basrah, characterized by the lowest thermal comfort under ambient conditions (merely 5% of summer hours within the comfort zone), the implementation of evaporative cooling elevates the proportion of thermal comfort hours to 60%. Likewise, Baghdad showed a notable enhancement in thermal comfort, marginally exceeding Basrah, whereas Mosul, with 25% of summer hours within the comfort zone under mechanical ventilation, undergoes a relatively lesser improvement as evaporative cooling lowers temperatures to levels that intermittently fall outside the ideal comfort range. Basrah was the most vulnerable city in Iraq, with extreme heat-humidity combinations exceeding acceptable criteria for 78% of summer. Mechanical ventilation conditions were the poorest, with only 5% of summer hours within the comfort zone. The PMV results in Baghdad over the five-month study period fluctuated between + 1.25 and − 1.25. The thermal comfort zone, where maximal comfort was attained, was delineated by a more restricted PMV range of − 0.5 to + 0.5. The PMV value ranged for Basrah and Mosul are (+ 1.5 to -− .25) and (+ 1 to − 1.75), respectively. Comparing evaporative cooling to mechanical ventilation situations, the number of thermally acceptable hours during peak summer conditions in Baghdad, Basrah, and Mosul increased significantly by 41.28%, 54.48%, and 30.55%, respectively. This study underscored the efficacy of evaporative cooling in improving thermal comfort during excessive heat, while also stressing the necessity for region-specific strategies to tackle the issues associated with elevated humidity levels. Aligning cooling solutions with local climatic conditions could promote energy efficiency, mitigate health hazards, and improve the quality of life in areas susceptible to excessive heat. By adding field measurements, investigating hybrid cooling strategies, and evaluating long-term performance under anticipated climate change scenarios, future research could build on this work. The study’s overall findings highlight the significance of climate-responsive design and sustainable cooling technologies for enhancing occupant comfort, lowering energy consumption, and minimizing environmental effects in harsh climates. For controlled comparison across diversity climates, this study has been limited to a single zone with fixed thermal comfort parameters. Accordingly, the occupant-adaptive behaviour and complex building geometries were excluded. Future research, therefore, could extend this work through multi-zone modelling, adaptive comfort frameworks, field validation, and the evaluation of hybrid or seasonally adaptive cooling strategies.