Scholarly article on topic 'Thermal Comfort through the Microclimates of the Courtyard. A Critical Review of the Middle-eastern Courtyard House as a Climatic Response'

Thermal Comfort through the Microclimates of the Courtyard. A Critical Review of the Middle-eastern Courtyard House as a Climatic Response Academic research paper on "Agriculture, forestry, and fisheries"

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{"Traditional prototype" / "Courtyard house" / "Thermal comfort" / "Passive cooling" / "Natural ventilation"}

Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Haval A. Abdulkareem

Abstract The last few decades have seen a dramatic increase in using the mechanical means of air-cooling in the Middle East to provide thermal comfort that has caused high rates of energy consumption. This has drawn the attention of specialists who see the reuse of traditional prototype as a highly efficient strategy to confront this issue in contemporary architecture. An in-depth investigation is undertaken regarding this approach by this paper concentrating on thermal comfort through the microclimates of the courtyard to reveal its limitations and possibilities to make a fruitful contribution to contemporary architecture.

Academic research paper on topic "Thermal Comfort through the Microclimates of the Courtyard. A Critical Review of the Middle-eastern Courtyard House as a Climatic Response"

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ScienceDirect

Procedia - Social and Behavioral Sciences 216 (2016) 662 - 674

Urban Planning and Architecture Design for Sustainable Development, UPADSD 14-16 October

Thermal comfort through the microclimates of the courtyard. A critical review of the middle-eastern courtyard

house as a climatic response

Haval A. Abdulkareem*

Architectural Engineering Department, University of Duhok, Duhok, Iraq

Abstract

The last few decades have seen a dramatic increase in using the mechanical means of air-cooling in the Middle East to provide thermal comfort that has caused high rates of energy consumption. This has drawn the attention of specialists who see the reuse of traditional prototype as a highly efficient strategy to confront this issue in contemporary architecture. An in-depth investigation is undertaken regarding this approach by this paper concentrating on thermal comfort through the microclimates of the courtyard to reveal its limitations and possibilities to make a fruitful contribution to contemporary architecture. © 2016Publishedby ElsevierLtd. Thisisan openaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of IEREK, International experts for Research Enrichment and Knowledge Exchange Keywords: Traditional prototype; Courtyard house; Thermal comfort; Passive cooling; Natural ventilation

1. Introduction

Twentieth century architecture of the Middle East is considered a prim consumer of energy, most of which is utilised for the provision of thermal comfort for occupants to enable them to survive the severe climatic conditions for which this region is renowned [1]. This is highly indicative of the lack of climatic rationale in architecture design

* Corresponding author. Tel.: +9647504572189. E-mail address: haval.abdulkareem@uod.ac

1877-0428 © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of IEREK, International experts for Research Enrichment and Knowledge Exchange doi:10.1016/j.sbspro.2015.12.054

in the region, an issue which has drawn the researchers' attention. In this context, traditional models are believed most researchers to offer key lessons about the best solutions to confront these concerns in contemporary applications [2-4]. As such, a number of authors believe the courtyard house of a highly suitable prototype that offers a comfortable internal environment in this climatic region [5-8]. Fathy [7] claimed that at night, this architectural system accomplishes a significant reduction in air temperature (10-20 C°). Moreover, Scudo [9] stated that this strategy did and still performs as a free cooling system and thus it should be incorporated in contemporary architecture. But is this true? Other researches have shown how unsuitable the courtyard is in terms of thermal comfort [10,11]. In a study of non-shaded patios, Etzion [10] found that, "In summer, most of the time the courtyard is warmer than the ambient air temperature near the house, day and night. In a few cases the temperature differences between the ambient air and the air inside the courtyard were as high as 7 °C." Apart from that, Dunham [12] pointed out that a comfortable internal environment can only be achieved by small courtyards. Furthermore, Al-Hemiddi & Megren Al-Saud [13] concluded that a remarkable cooling effect is attained when a courtyard includes a fountain and is covered during the day by a tent.

If this architectural system climatically accomplishes the inhabitants' needs, then there are a number of questions that must be addressed. Firstly, why is this space uninhabited most of the day except early in the morning? Secondly, what is the purpose of covering this space with a sheet during the day? Moreover, if the patio performs well environmentally in a temperate climate, does this mean that it can offer the same quality in a region that is characterized with extremely high temperatures most of the year? Furthermore, why have people resorted to air conditioning systems over the last decades rather than relying on traditional cooling strategies? Finally, what possibilities can the reemployment of the courtyard offer in a modern context as it has been used under different climatic and cultural factors?

Perhaps a lack of complete understanding of the patio's environmental role is because morphological and interventionist aspects are addressed alone. Based on the literature review, to undertake an in-depth investigation, both morphological and interventionist factors as well as behavioural aspects must be considered in this article as integral parts of an overarching strategy of climate adaptation. As a result, its limitations and the need for optimisation can be clearly revealed in order to make a fruitful contribution to contemporary architecture. In addition, the cultural context should also be addressed to discover the socio-cultural forces behind this strategy and their impact on its performance.

2. Forces behind the formation of the courtyard house

In-depth insight into the procedures or forces that decisively affect building morphology is necessary to understand the prevailing housing typologies in the Middle East, particularly the courtyard house. In spite of endeavours undertaken by a number of authors to more theoretically and deeply investigate the drivers that have shaped the courtyard house, most have identified Islam as the main determinant behind the built form [14-18].

In this context, a sense of privacy is believed to be the major factor behind the formation of the built environment, which can be seen when referring to the words of God Almighty in the Holy Quran [19]. After the revelation of those verses, builders began to accurately organise and orient rooms in a formula that provides vocal and visual comfort. Apparently, creating closed spaces for inhabitants to be entirely detached and isolated was not required to attain visual and vocal comfort inside their houses since that would give rise to psychological problems. Thereby, the process was made in parallel with the accomplishment of the logical connection with environmental components. Consequently, the introverted design was employed in configuring their shelters as El-Shorbagy [20] stated. Hence, the courtyard became the main space for daily life activities as it provides a limited visual axis between the inside and the outside [20]. The reality that the building form is informed by many factors is ignored by many arguments which place robust emphasis on just the single concept of achieving religious needs. Owing to the idea that the introverted focus through courtyards is an efficient strategy that makes a house proficiently adapted to social requirements, including religious values and thermal conditions, it is argued that this formula was adopted by people who followed Islam [15].

Nevertheless, relating the emergence and proliferation of the courtyard to Islamic architecture indicates a lack of rigour. According to Rapoport [21], "Courtyard houses, and separation of domains in general, are used in cultures which are both crowded and hierarchy." Rapoport [22] also stated that this tactic has been utilized throughout the

history of architecture and is found as a common design element in various places around the world, including civilizations such as the Indus Valley (5,000 B.P.), Qatal Hüyük (10,000 B.P.), ancient Greece and Rome, and Mesopotamia. According to Roaf [23], the ancient Mesopotamian urban fabric was strongly based on buildings with courtyards, a design approach that was introduced in the Uruk period. In addition, it was considered a typical model and a formula for designing both palaces and houses of worship, especially Babylonian temples and late Assyrian temples. The most notable examples of the use of courtyards in Mesopotamian architecture are the palace at Mari (Tell Hariri), the Kassite palace at Dur-Kurigalzu, the palace of Sargon at Dur-Sharrukin, and the most spectacular, Nebuchadnezzar, or what is called the Southern Citadel in Babylon [23].

If this design strategy was motivated by Islamic societies at the time due to socio-cultural reasons, mainly privacy, so the question addressed here is why it has been applied by other communities worldwide. Why was it largely used in the Middle East before the emergence of Islam, as in the case of Mesopotamian architecture? To neutrally address the above questions, a substitute method, which also takes into account the other parameters around the built environment, of looking at the courtyard house in relation to the mentioned theories is required. As pointed out by Ragette [8], "The creation of shelter is our response to the environment and the context of our existence, which consists of a complex set of components." In this context, the climatic point of view should be taken into consideration. Oliver [24] rightly stated, "Dwellings are built to serve a variety of functions, but one of the most important is to create living conditions that are acceptable to their occupiers, particularly in relation to the prevailing climates." Accordingly, traditional architecture, including the courtyard house, was the result of unfavourable prevailing climatic conditions that forced builders in this region to use climatic rationale and intuitively create convenient solutions to provide living thermal requirements [25]. This means that the factor of climate was foremost behind the idea of courtyard house.

Nonetheless, the impact of cultural norms, including Islamic Sharia cannot be denied. As Rapoport [21] pointed out; in general, settlements and the form of dwellings have been affected by the requirements of harem and purdah, which are demanded by Islamic culture. There is a clear effect of privacy and gender separation in the resultant built form with respect to the height of buildings, the distribution of rooms, and the position of the main doors and external windows.

3. The courtyard house from a climatic point of view

3.1 The mechanism of the courtyard

After determining the impact of socio-cultural restrictions and the notable role of climate on the formation of the courtyard house, understanding the climatic processes that take place in this central open space is the key point to analysing and evaluating its environmental performance and limitations. An abundance of literature about this topic refers to a single study that was conducted by Dunham (1960). Before describing the climatic processes, it should be noted that the study region is located between the latitudes 10° and 35° north, which means the solar angle is high for most of the summer. In addition, the diurnal temperature variation is very pronounced in hot-dry climates, particularly in this region. During the summer, the air temperature significantly decreases from day to night, equal to about 15 to 20°C [26]. This considerable range is the result of factors that include slight cloud cover, a significant amount of heat exchange between sun, space, and earth, and receiving large amount of heat from the sun over the day that is exchanged into the atmosphere overnight [12]. In this context, Dunham, [12] described the mechanism of the courtyard in two regular cycles, namely over the day and night. Nonetheless, it should be noted that the courtyard experiences three different scenarios over the day, namely over the morning, noon, and afternoon. Thus, its mechanism is precisely described in four different cycles as follows:

By nightfall, courtyard surfaces, which are made of materials with high capacity for storing heat, including its floor, surrounding walls, and the earth beneath, are much hotter than the sky since during the day they soak up and store considerable quantities of heat, making these surfaces main heat sources in the courtyard. Accordingly, heat exchange between the courtyard house envelope and its environment commonly occurs through two modes, namely convective heat transfer and radiant heat exchange. Regarding convection, because sky cooled air has very high density, it sinks down and accumulates inside the courtyard, especially close to the ground [12]. Thereby, courtyard

Figure 1Thermal performance of a traditional courtyard house during the night in Baghdad (adapted from Al-Azzawi [30]) Note: the measurements are effective temperatures that were recorded in a Baghdadi courtyard house in August 1972 [30]

surfaces, which are at temperatures higher than the incoming air, come in contact with the accumulated air and, as a result, convective heat transfer begins to play a fundamental role. This means that the large stores of heat in those surfaces are lost to the adjacent air, and a cooler environment is created (Fig. 1). This process is known as thermosyphonic convection, which relies heavily on the difference in temperature between the received air from the sky and the courtyard [27]. In the meantime, indoor air temperatures have almost reached their peak in the rooms that adjoin the open space, while the courtyard is getting colder. Again, due to this thermal variation between the indoor environment and the outdoor space, convective heat exchange occurs, and air currents are created. Hence, through the lower parts of the openings that overlook the courtyard, cool air is pulled into the surrounding rooms whereas the warmer indoor air is drawn up and discharged through the upper outlets [28]. As a result, thermal discomfort is significantly mitigated. The collected heat within the floor of the courtyard can also be removed during the night in the form of long-wave radiant release, owing to the exposure of the floor surface to the clear sky [6]; consequently, the night time temperature drops in this central space. Nevertheless, it should be pointed out that, "Clouds tend to disrupt nocturnal cooling by emitting infrared radiation downward where it is absorbed by the surface, thus partially compensating for surface radiative loss, slowing nocturnal cooling" [29]. This process is also affected by the dimensions of the courtyard, particularly by its height and width. A narrower and deeper courtyard means that its view to the sky is limited, resulting in smaller discharge of long wave radiant heat, while a wider courtyard means that the courtyard has more exposure to the sky, leading to significant loss of long wave radiant heat [11]. This means that when the horizontal surface becomes more visible to the sky as in the case of the roof, this process takes place more easily and effectively because of the lack of barriers such as high walls around the courtyard that absorb a remarkable part of the radiation [27]. In short, after sunset, it is clear that the temperatures in the courtyard house are alleviated by heat transfer to the ambient air as well as the sky through convection and radiation.

The second cycle occurs early in the morning (Fig. 2) and can be described as the period in which the microclimate is almost stable, whereby the air temperature in the courtyard is either the same as that inside or comparatively higher. Furthermore, the temperature of the courtyard house envelope is at its lowest. This is due to the fact that during this period, the solar elevation angle (the angle between the horizon and the sun) is low so the impact of solar radiation is negligible and the central open space is almost shaded [28]. In addition, during the previous night, the building mass has been cooled to some extent. This means that the convective air current does not have that a large role between indoor and outdoor temperatures since the variation in air pressure between those spaces is at their minimum value.

As soon as the sun rises, the outer layers of the courtyard begin receiving sun rays; as a result, the sunlit parts of

walls and floors receive heat because the solar radiation progressively becomes intense and strong [31]. By noon, the third cycle takes place (Fig. 3). The courtyard floor is completely covered by direct sunlight, and the air temperature there increases remarkably. The important role of the thermal mass of the structure in the thermal behaviour of the courtyard [32] lies in its lowering of the ambient air temperature through convective heat exchange, so the heat is lost to the neighbouring surfaces. Nevertheless, it should be pointed out that this cannot be steadily and sufficiently effective. This is owing to the fact that the cooling capacity of the floor and walls is relatively high early in the morning, but is lower later on; hence, the courtyard's components gradually change from heat absorption to emission. In the meantime, the penetration of hot air from outside to inside is slowed down by the thick adobe walls due to their capacity of insulation [33]; consequently, the variation in air temperature and thus air pressure between the courtyard and the adjoining spaces is clearly sensed. Accordingly, the central open space begins performing as a chimney in which hot air flows up due to its lighter density and cooler air is drawn into the courtyard from those rooms through the windows [34]. Further comfort is possibly provided by these convective air currents.

Figure 4 Thermal performance of a traditional courtyard house in the late afternoon in Baghdad (adapted from Al-Azzawi [30]) Note: the measurements are effective temperatures that were recorded in a Baghdadi courtyard house in August 1972 [30]

Lastly, the fourth cycle occurs late in the afternoon (Fig. 4). During this period, the surrounding rooms have lost almost all of their coolness [34], so feeling thermally comfortable requires other skills and much effort. During this cycle, living in neither the courtyard nor the adjoining rooms is desirable, and inhabitants resort to other environmental strategies such as evaporative cooling.

3.2 The adaptive behaviour of a family during a 24-hour daily cycle

Apart from theoretical analysis, in order to investigate the validity of the above description of the courtyard's mechanism, it is necessary to examine the daily activities of a family during the 24-hour daily cycle in the indigenous courtyard dwellings to determine whether or not the residents shift in accordance to the above climatic theories. In this context, a study was conducted by Al-Azzawi [35] on the subject 'daily impact of climate on the pattern of urban family life', and reported that people shift horizontally and vertically (Fig. 5) during a summer day as follows:

First, the ground floor and particularly the courtyard can be considered the first destination for inhabitants to start their day, which usually begins with breakfast. Hence, around 06:00 am (at daybreak), they leave the roof terrace, or the "Satih", which is used for night sleeping, and head down to the courtyard to avoid the early sunlight. Once they descend, the mattresses, blankets, and sheets are protected and kept away from the intense solar radiation throughout the day. For this purpose, a specific room, usually located on the top floor, called "Baytoona" or "Bayt al-Firash" is utilised. In case there is not enough area to have this kind of room, or there is not enough space inside the Baytoona to house all sleeping furnishings, steel-framed beds are used on the roof terrace to carry the bedding and the mattresses which are protected from sunlight by reed-mats and old blankets.

Second, in the forenoon, the occupants begin their migration from the sunlit part of the courtyard to the shaded part in a horizontal movement to keep away from scorching heat of direct sunlight. In the meantime, one or two female members of the family wash the floor of the courtyard as well as the floor of the summer sitting room, or "talar" and then spray water over those floors. It should be noted that the process of sprinkling water over the floors is repeated at intervals throughout the day. Owing to a flooring type that can be easily penetrated by water, some of the sprinkled water is absorbed and stored by the floors for a while. As a result, this action plays a remarkable role in alleviating the thermal discomfort by reducing the air temperature and increasing the relative humidity to some extent. Evaporative cooling takes place so that the temperature of the floors is decreased; thus, the relatively warmer air that is close to the floor surfaces loses some heat through heat exchange. In addition, the amount of water vapour in the prevailing dry air is also increased. This strategy is rigorously examined in a later section.

Third, around noon, horizontal migration again occurs. The courtyard becomes absolutely uninhabitable because its floor is fully covered by direct sunlight, which is quite intense. Therefore, the summer sitting room which overlooks the courtyard becomes the next destination for the occupants at noon, which usually begins with a lunch.

Fourth, once they have eaten lunch, the inhabitants start migration from the summer sitting space at the ground floor to the sitting room at the basement, or "sardab" in a vertical movement, whereby the occupants spend their afternoon in a relatively cooler environment. It should be pointed out that, of course, a sardab is not provided in all traditional dwellings. In the absence of this habitable room in the basement, the residents stay in "talar" until the sunset. Before leaving the basement in the late afternoon, the women again start washing the roof terrace and then spray water over its floor so that the heat stored over the day can be mitigated.

Finally, after spending their afternoon in the basement living room, vertical movement again takes place. The inhabitants go up to the courtyard for dinner. It should be noted that during dinner time or shortly after the rooftop becomes fairly dry after being washed and sprinkled with water, one or two female members of the family bring out the mattresses and other sleeping materials from their stockroom to the rooftop. They then distribute the bedding on "takhts", which are beds usually made of steel, so that its temperature can be lowered by the cold and clear sky through outgoing radiation. Later in the evening, once dinner is finished, tea is drunk, and the pots and other cooking equipment are washed, the rooftop is the last destination for inhabitants during the 24-hour daily cycle. They go up to the rooftop around 09:00 pm for the evening and then go to sleep. However, the dwellers may move to the rooftop to have dinner after sunset if ground floor is thermally uncomfortable, particularly on very hot days. The next day, the same movement cycle takes place again.

[In some cases] during the day, particularly from late morning to late afternoon, the courtyard is sometimes covered over at roof terrace level with a canvas or a plain white sheet in order to produce more shade. This helps to reduce the surface temperature of the floor and walls of the courtyard and consequently lowers the temperature of the air [30].

After examining the pattern of family life during a 24-hour daily cycle in a traditional courtyard dwelling, a number of facts can be clearly understood. Firstly, it is clear that the courtyard faces more than one scenario during the day. It is fairly habitable early in the morning, and this is exactly what is stated in the theoretical analysis. However, there is a slight contradiction regarding the role of thermal mass. This is owing to inhabitants' movement to the summer living space before lunch time and their descent to the basement afterwards, which probably means that once the courtyard is covered by solar radiation, the thermal mass cannot efficiently benefit the residents in terms of providing thermal comfort. Furthermore, preferring to stay on the roof terrace during the night rather than spending the night in the courtyard is probably evidence supporting the statement, "Long-wave radiant loss (day and

night) is smaller from a patio than from an exposed outdoor horizontal surface, owing to the partial blockage of the sky, and long-wave radiation absorption, by the walls," by Givoni [27]. Finally, and most importantly, if this indigenous housing prototype were well suited to the prevailing hostile environment and the courtyard was a source of thermal comfort as it is claimed in most of the papers on this topic, then questions arise as to why the inhabitants do not stay in this space during the day except early in the morning and why it is entirely covered with a sheet from late morning to late afternoon. Perhaps one can safely argue that the level of thermal comfort that is provided in the courtyard house is not just a foregone conclusion of the courtyard design, but it is also largely due to the adaptive behaviour of the inhabitants.

3.3 Factors that affect the thermal performance of the courtyard 3.3.1 The courtyard's geometry

The courtyard's geometry plays a crucial role in its thermal behaviour. Blocking solar radiation is one of the fundamentals in attaining satisfactory thermal comfort during the summer, and this is highly affected by the geometry of the courtyard, namely the proportion of its height to length and width. Direct exposure of the floor and walls are minimised by maximising the height (Fig. 6). In this context, Dunham [12] rightly argued that, "Only a small courtyard can be protected from the Sun." This is because more shade is provided, thus reducing thermal impact. This can be done by extending the courtyard's height through adding more floors, which increase the designated limit of cutting off solar radiation, therefore allowing less sunlight to reach the surfaces [30]. This means that a single-storey dwelling cannot act as efficiently as a two-storey dwelling in terms of providing shading area. It can be argued that this may adversely affect the thermal performance of the courtyard, particularly at night. This is because a smaller courtyard means a smaller "sky view factor (S.V.F)" (Fig. 6). This means less heat is lost to the sky via long-wave radiation [11]. In this context, based on her work in the city of Yazd in Iran, Roaf [36] believes that for most of the day except the afternoon, larger courtyards are cooler than smaller ones, especially in the morning. However, this causes an increase in surface to volume ratio, which means greater quantities of heat are collected. In addition, according to the analysis of the family life pattern, it seems that protecting this open space from sun is a priority rather than making it more exposed to the sky as the rooftop is already a substitute to the courtyard for use at night. Therefore, Dunham [12] suggested that if there is a need for a large dwelling, instead of creating one large courtyard, it is environmentally better to have two or more small ones. This is due to the fact that direct sunlight covers more floor area in a larger courtyard than in two courtyards and thus the shaded area in a larger courtyard is smaller than that is provided in two courtyards.

icft SUMMER.

Figure 6 A comparison between single-story and two-story courtyard houses in terms of their exposure to the direct sunlight and the S.V.F.

(adapted from Ragette [8])

3.3.2 Additional means of producing air currents

The significance of equipping courtyards with system for producing air movement within the courtyard as natural convection lies in the following. Firstly, heat is mitigated by the existence of fast winds in the case that the temperature is below 33°C, whereby the temperature of the skin is reduced through convective heat loss [27]. Secondly, part of the absorbed heat in the courtyard is removed by wind. However, it should be pointed out that the air movement in this open space is usually low compared to the movement of ambient air, so the wind cannot significantly carry away solar heat so most of it is collected by the floor and walls [27]. Therefore, additional means of promoting air currents such as wind catchers have been used in this region to increase air movement.

Wind catcher

Introducing ambient air into the courtyard directly or indirectly either through the talar, the summer living room on the ground floor, or through the sardab, the living room in the basement, can be done using one or more vertical air shafts, which are called wind catchers or badgirs. A wind catcher is basically a tower used in hot regions, particularly the Middle East, for bringing air into the inside of a space. Even though the early history of this element is still under debate, there was, of course, a climatic rationale behind it. A badgir consists of an air passage surrounded by thick walls made of materials with high thermal mass such as mud bricks and fired bricks. Usually, this air passage is divided into a number of smaller passages by partition walls so that the tower can introduce relatively cool air and discharge hot air at the same time. In addition, this increases the thermal mass of the tower since the materials respond to the ambient heat after seven to 10 hours. The highest part of the badger is raised above the rooftop level; this part consists of a number of vents in which the wind is captured and hot air is drawn out, while the lower part is located in the talar or sardab with an outlet [5].

This wind tower is believed by Ghaemmaghami & Mahmoudi [37] to perform the role of an air conditioner, whereas its role is identified by others as a ventilator [7, 37]. Generally, temperature differences and the wind conditions are believed to be the main parameters in the mechanism of the wind scoop. However, whether the air is pulled down via a wind tower and discharged in courtyard during the day or vice versa during the night, effective air currents play an important role in providing thermal comfort for the residents and can be created through this integration. However, it should be pointed out that there are a number of factors such as the height of the badgir, its morphology, its orientation, the construction materials, and its integration with other elements affect the thermal performance of wind catchers.

The role of the introduced air currents

According to Givoni [27], the sensation of heat is mitigated by greater air movement when the temperature is below 33°C, so that the temperature of the skin is mitigated through convective heat loss. However, he claims, in case that the temperature exceeds 37°C, the sensation of heat is increased by increasing the air movement [27]. In this context, it should be pointed out that in places like Baghdad, where the maximum mean temperature exceeds 43°C most of the summer [30], it can be argued that the air brought in through the above described mean may be not cool enough or could be warm air (above 37 C), and may cause thermal discomfort. This can be critically evaluated by understanding the body's mechanism regarding heat loss. The body can lose heat in a moderate climate through radiant and convective heat transfer. Once the ambient temperature starts rising, the role of these processes declines and will be stopped altogether if the ambient temperature reaches the temperature of the skin. Then:

The only way the body can lose heat is by evaporation, hence the importance of a draught. The drier the draught of air, the more effective it will be in evaporating sweat from the skin, thus cooling the body and giving a sense of well-being. It does not matter if the draught is slightly warmer than the ambient air: it will evaporate sweat and cool the body just the same [39].

3.3.3 Means of evaporative cooling

Another important factor is equipping the courtyard with system for producing evaporative cooling. It is believed that the use of water, whether using water bodies such as basins, fountains, and jars, or the operational procedures of sprinkling water on the floors by the residents, is of supreme significance in fostering the evaporative cooling that contributes to further thermal comfort in the courtyard house, particularly in the hot-arid regions of the Middle East [5, 7, 30, 39]. According to Givoni [27], "The patio's air temperature near the ground level can be lowered by enhancing evaporative cooling of the air within the space. To enhance evaporative cooling, the "confined" still air within the patio should be in contact with water with as large a surface area as practical." When the air moves over the water, its level of moisture is increased. The absorption of water is increased if the air is drier and warmer because it moves to the same level as the water in terms of temperature and vapour pressure. When water is exposed to dry air, it loses its characteristic as a liquid and conversion to a gas begins. The temperature of air is mitigated until it reaches the temperature of the water. It should be pointed out that once the wet-bulb and dry-bulb temperatures are equalised, the process halts [40]. In this context, it should be noted that the water layer in contact with air in most of the water basins in courtyards is not sufficiently large. Thus, if the surface is not well-protected from solar radiation, a remarkable reduction in the air temperature of the courtyard will not take place. This is because the ambient air temperature and the water temperature will be similar since water gains heat from sunrays. Herein lies the paramount importance of shading the courtyard as well as the role of the operational procedures of sprinkling water, which results in an increase in the surface area of water in contact with air.

3.3.4 The location of windows

The location of windows also plays a certain role in the environmental behaviour of the courtyard. As mentioned earlier, the position of windows has been largely subject to social rules, which led to avoiding external openings and relying on the inward looking windows for visual privacy. This affects the process of natural ventilation in the courtyard house and thus the overall thermal performance of the house. This is due to the fact that during the night, when cool air moves downward into the courtyard and then into surrounding spaces through the windows, openings in the wall that faces the street are needed in order to discharge hot air to promote natural ventilation. To overcome this, alternative solutions have been used throughout the Middle East. For example, in Baghdad and some other places, small openings that overlook alleys at a high level on the ground floor have been created. Larger openings covered by timber lattice screens, or "mashrabiya", have been used at the first floor to provide better air movement and cross-ventilation, particularly at night [30]. In Diyarbakir and some other places, according to Bekleyen & Dalkilif [41], in order to encourage the process of natural ventilation, windows were created around the courtyard at lower (to introduce the air into the rooms adjacent) and upper levels (to allow hot air to go out). However, it should be pointed out that this tactic might not perform effectively as it fosters air circulation around the windows only without reaching the end of rooms. However, the windows are built not only to provide an escape for hot air, but also to introduce air and light, particularly on the first floor. In addition, they are sometimes associated with means of evaporative cooling (Fig. 7). In this context, 'A porous water jar is placed behind the window so that air temperature will decrease as it is moistened when it passes over the jar on its way indoors' [42].

3.3.5 Vegetation

Another significant contributor in providing thermal comfort is vegetation. The important role of plants and greenery in optimising the microclimate and supplying further thermal comfort in the courtyard house has been highlighted by many authors [6, 43, 44]. Plants are climatically beneficial in a courtyard in various ways. Firstly, a certain reduction in solar gains is achieved by the use of plants as they provide shade [6]. Secondly, it is believed that the air temperature can be lowered by the use of plants since a considerable amount of solar radiation is absorbed by plants' leaves during the process of photosynthesis; however, this process converts a little of the absorbed radiation into chemical energy. This is because, 'Quantitatively, the plants' efficiency in transforming energy is very low (1-2%) and therefore the thermal effect of photosynthesis (i.e., in lowering the heating effect of the absorbed radiation) can be practically discounted' [27]. However, most importantly, the majority of the absorbed

Hot air escaping from high claustre work opening

Shutters control air movement

Evaporative cooling as breeze passes over surface of porous water pot

Sun Shade

Porous Water Pot

Figure 7 Section illustrates integrating window with porous water [45]

radiant energy is consumed via 'evaporation of water from the leaves'. As a result, plants are cooled, which mitigates the ambient air temperature, and the water content in the air is increased as well [27]. Although plants can play a significant role in supplying comfortable conditions and improving the microclimate of the courtyard house, unfortunately, owing to the prevailing severe climate and lack of water in most places, shrubs and other plants cannot be grown easily [28].

4. Conclusion

The climatic response of the middle-eastern traditional prototype is precisely investigated throughout this study concentrating on a courtyard house. Possibility of being a housing typology that fairly adapted to certain climatic zones has enhanced various researchers, including the author, to deeply understand the performance of this traditional prototype to provide an integrated insight about the possibilities that can be profitably applied in contemporary architecture. In order to achieve that, the study sheds light on the interaction of multi aspects, including socio-cultural drivers, design treatments (morphological and interventionist aspects) as well as the adaptive behaviour of dwellers.

In order to critically evaluate the performance of any urban form, the climatic specification of the place should be identified. In a certain context of the hot climate, apparently, among all the evolution that had been done in equipping the courtyard with additional systems for providing satisfactory indoor comfort, it has been unable to perfectly do its environmental task resulting in being uninhabited most of the summer day. This is due to the limitations of those additional systems which are investigated in details throughout this paper; however, this does not deny their positive role in enhancing natural cooling. As this study shows, therefore, different activities were being practiced, including operational procedures and the daily migration, by the inhabitants in order to live thermally comfortable. This strongly supports the fundamental role of the adaptive behaviour in the overall environmental performance of a courtyard house.

Is this traditional typology therefore a state of unsuitable response to the prevailing climate? At the time with unavailability of mechanical alternatives, it had been a best available option to be inhabited within the hostile environment. Once the mechanical systems were introduced to the Middle East, the transition from passive design strategies to active ones widely happened. However, entirely relying on air conditioning systems gives rise to high rates of energy consumption and greenhouse gas emissions. Meanwhile, improper reemployment of vernacular strategies may cause extreme consumption of energy for air conditioning which will be installed later. To overcome

these concerns, therefore, reviving indigenous technologies should be based upon a good understanding and further improvement of their performance with the avoidance of a superficial, largely formalistic approach to the revival of vernacular architecture. To provide further thermal comfort, in addition, they have to be integrated with active design strategies that are based on renewable energy in a hybrid system so that environmentally friendly architecture can be produced.

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