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study of Iran)

Vernacular architecture is known as an ideal source of sustainable design because it aims to achieve thermal comfort temperature via passive low energy strategies (Wahid, 2012). The ways to achieve a comfortable temperature can differ from place to place depending on the culture and climate. Tehran, the capital of Iran, has been selected as a case study for this research. According to Roaf (1997), Iran has buildings from antiquity and a rich diversity of types due to its geographic location and climate diversity. It is thus one of the most architecturally fascinating regions. To achieve comfortable passive ventilation and thermal conditions in the historical architecture of the arid regions of Persia, the flow of air, or water and air was used (Castle, 2012). Naciri (2007) suggests that the techniques are discovered and applied slowly to modern forms of today. Soleymanpour, Parsaee, and Banaei (2015) have conducted research into the vernacular techniques used in Iran and have presented a sample graph that summarises its application (Table 3. 1 to Table 3. 4).

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Table 3. 1: Analysing climate comfort vernacular houses of Yazd city, a hot and dry city of Iran

Table 3. 2: Analysing climate comfort vernacular houses of Bushehr city, a hot and humid city of Iran

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Table 3. 3: Analysing climate comfort vernacular houses of Rasht city, a temperate and humid city of Iran

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As mentioned, Soleymanpour et al. (2015) outline the vernacular architecture of different climates of Iran. Whilst there are no vernacular buildings specifically listed for semi-arid climates, the mixture of cold and arid climates would give an idea as to what needs to be considered for a semi-arid climate. The information in the above tables show that in most climates of Iran, the courtyards are part of the vernacular design strategy, especially in hot and cold climates. Moreover, the building is generally orientated to the south so that windows can benefit from the south sun in cold climates (the cool season is also the dominant season in the Tehran case study, which is explained in chapter 8 and 9). Nevertheless, Pourvahidi and Ozdeniz (2013) state that there is a slight difference in the vernacular architecture of hot and dry climates and the climate zone classified as hot and dry with cold winters (semi-arid climate). Although the vernacular design is similar, the main difference “is the provision of more open spaces... [In hot dry climate as oppose to hot dry with cold winters, a] Central courtyard is very suitable for summer to keep the coolness and humidity of night and give refreshment during the summer days. It is also suitable for winter to protect the rooms from winter winds” (Pourvahidi & Ozdeniz, 2013, p. 13).

Moreover, the materials ideally need to have a high thermal capacity, both in dry and cold climates, and wind catchers are experienced as useful in dry hot climates (Pourvahidi & Ozdeniz, 2013; Soleymanpour et al., 2015) (this is particularly the case for warm seasons in the case study of Tehran).

The features of the courtyard and wind tower, which are the iconic features of Iran’s vernacular architecture are explained in more detail:

 Badgir or wind catchers: These are chimney like structures above roof level

designed to catch the fresh, less dusty air, or used as means to extract exhaust air (Figure 3. 8). They are one of the masterpieces of Iran’s architecture, and reflect the understanding of predecessors in working with climate design and in providing an example of clean energy (A'zami, 2005) which provides natural ventilation and cooling (L. Li & Mak, 2007).

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Figure 3. 8: Baghe Dowlatabad windcatcher (Neoh, 2015)

According to Roaf (1997) these structures date back to 2000 BC in the Middle-East and the central plateau of the city of Yazd in Iran. However, Maleki (2011) claims that the first historical evidence of their use date back to 4000 BC, and were found by a Japanese expedition to a house in the north east of Iran at the site of Teppeh Chackmaq. Regardless of date, it is apparent that these structures were born in Iran in the Middle-East and are perfectly suited the climate conditions. The greatest Badgirs are allocated in Yazd, and date between 1868 and 1900, with the most elaborate example being Baghe Dowlatabad (Roaf, 1997) shown in Figure 3. 8 and Figure 3. 9.

Figure 3. 9: Below the dome of Baghe Dowlatabad (Najafi, 2015)

Badgirs work by mainly taking fresh air into the building and exhausting hot, polluted air (Moghaddam et al., 2011). In large towers, the temperature difference between the top and bottom of the shaft can be 2°C (Roaf, 1997). In some situations, it has been

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seen that the cool air in the basement, guided by the wind tower, can have a temperature difference of 9°C when the outside air is 32°C (Maleki, 2011).

There are also different types of wind catcher; for example, wind towers differ in height, placement, and the number of openings at the top. Wind catchers have an inlet and sometimes an outlet, which is a division of the wind tower shaft. Sometimes the outlets are placed somewhere other than a division in the wind tower; such as the outlet vents on the dome (Figure 3. 9) or skylights (Bahadori, 1978).

The sucess of windcatchers is due to the effect of wind and bouyancy, which helps to maintain natural ventilation through the living spaces (Moghaddam et al., 2011). There are two scenarios, namely; when there is wind, and when there is no wind. Moghaddam et al. (2011) explain these as follows:

 Scenario 1- Wind assisted ventilation in wind catchers: When the wind hits the internal blades of the wind catcher, since the density of the air is thick, it creates positive pressure and descends into the room. However, the other hole (or holes) of the wind catcher, which are on the leeward side, have a negative pressure and act as a sucking machine releasing the hot and exhausted air from the building to outside.

 Scenario 2- Buoyancy assisted ventilation in wind catchers: The wind catcher functions even when there is no wind, whether day or night. In the day, the sun hits the wind catcher on the southern façade causing the air to heat and rise acting as a solar chimney. Also, the hot air inside the room rises up to escape through the vent (Norton, 1997). This creates a suction effect which helps to draw the cool air inside the room from the porch, or as Naciri (2007) claims, the cool air can be sucked in from the northern section of the wind catcher and enable comfort through evaporation and air motion (Maleki, 2011). However, if the outside air is warmer than inside, the cool air stays inside the room keeping the occupants more comfortable (Norton, 1997).

Nevertheless, when there is no wind at night, the cold night air moves down, gets warmed up again, and goes up to be released. Although, this air circulation continues until the temperature of the outside and inside walls become equal, it is usually daylight before that is achieved. Roaf (1997) summarises that the wind catcher’s purpose is to cool down the building

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structure at night and to help cool down the occupants through natural ventilation during the day.

Moghaddam et al. (2011) claim that the principles of wind catchers can be adopted in new buildings in order to create thermally comfortable environment. It will be explained in section 3.2.2.3 that the contemporary use of wind catcher technique in high rise buildings is wing walls as it is a technique to capture wind in high rise buildings. Also thermal flue is the contemporary version of a solar chimney used in high rise buildings also mentioned in section 3.2.2.4. Last but not least, wind catchers are also used in conjunction with courtyards, which are another beneficial strategy in providing a thermally comfortable temperature.

 Courtyards: are one of the typical traditional architecture features of Iran with all the

other building spaces surrounding their open rectangular space. They have both an environmental and social function, and act as a source of fresh air, light and heat (Cho & Mohammadzadeh, 2013). Figure 3. 10 illustrates an example of a courtyard in Kashan, one of the cities of Iran.

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Courtyards have been used in different places (Norton, 1997) because they are energy efficient in all climates, but particularly in those that are hot-dry and hot-humid (Aldawoud & Clark, 2008). Furthermore, they play several roles and provide several advantages. One of their most important characteristics is that they act as a reservoir of cool air and are an excellent thermal regulator (Cho & Mohammadzadeh, 2013; Heidari, 2010b). In order to maximise their efficiency, courtyards should be sufficiently deep compared to the height of the walls so that they can stay shaded for most of the day (Norton, 1997). Donham (1960) believes that this allows more ‘heat dissipation’ from surrounding indoor rooms and ensures less thermal impact from the sun. Heidari (2010b, p. 20) adds that courtyards, especially those central placed that are surrounded by the building on all four sides, “introduce the outdoor into the heart of the building core and maximise the thermal interaction between them”.

In terms of their summer night functionality, the cold air sinks into the centre courtyard and the fabric of the building is cooled down, hence the rooms’ temperatures surrounding the inner court drop substantially (Naciri, 2007; Sozer et al., 2011). This night cooling technique, along with the courtyard being shaded for most of the day, helps the walls and floors to hold the coolness throughout the hot day and provides comfort to occupants. Norton (1997) states that it is important that the house has no, or limited, external openings on the outer façade so that the cool air can stay in the base of the yard, enabling the courtyard to functions as a reservoir of coolness.

The most important factor of the courtyard design is the height of the surrounding walls, which affect the air velocity in the central yard. Olgyay (1992) also states that it is important that the courtyard is also the optimum shape, namely rectangular, to maintain a more successful climate response. Heidari (2010b, p. 25) concludes that the, “air flow pattern in courtyard[s] are the function of their depth to width ratio”. He also states that the smaller the size of courtyard, the better it is in warm seasons to achieve shade during the day and minimise the thermal impact.

Courtyards also have the role of connecting rooms as well as serving as a gathering area for families. These common spaces are likewise the source of daylight (Sozer et al., 2011). Khodabakhsh and Mofidi (2001) state that, in traditional countries of the Middle-East, the attitude towards daylight and views are very different from western cultures. They believe that the people of this region do not openly invite sunlight due to the risk of overheating. Moreover, privacy is part of the culture (Naciri, 2007) and

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so buildings opening up to light from their inner courtyards present an acceptable solution culturally as well as environmentally. As the openings concentrate on the inside, courtyards provide views and often offer garden and fountain sights for the rooms surrounding them (Saatci, 1997).

Water features in courtyards, provide a significant advantage for managing temperature (Castle, 2012). In summer, they help with cooling by producing an evaporative cooling effect to decrease temperature and increase comfort level (Castle, 2012). Oliver (1997) also indicates that traditional houses that have pools or fountains in the yard help significantly in reducing the heat. This is achieved via cross ventilation over the water, which impacts on the surrounding rooms and spaces, functioning as an additional cooling system.

Figure 3. 11: Boroujerdi-ha house using a courtyard, wind catchers and roof vents (a) 3d view, (b) elevation view, (c) the roof (Gharleghi & Sadeghy, 2012)

Boroujerdi-ha mansion in Kerman is an example that uses a few of the techniques described, such as domes, water, courtyards and wind catchers, to ventilate and cool inside spaces (Figure 3. 11). Wind passes through the courtyard and over the water, which helps the air to cool down. It then enters the building, gets warmed up and is pushed up by the fresh cool air entering the space. Gharleghi and Sadeghy (2012) explain that the hot air rises up to the high ceiling of the dome in the central part of the house, which is built intentionally high to guide unwanted hot air above the living level area, and exhaust air through openings at the top of the dome. They add that Boroujerdi-ha house also has three wind catchers, which catch cooler air from above, channel it down into the rooms, and cool it via evaporation and convection.

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Depending on the climate, exhaustion is achieved either by the courtyard, for the rooms not connected to the dome, or via the vents on the dome in the main gathering room of the house.

Never the less, it is important for the courtyards to be narrow enough to maintain shaded area during summer and wide enough to receive solar radiation during cool season to help with heating loads (Donham, 1960; Givoni, 1976). In such case there is seasonal movement in living spaces for occupants between warm season and cool season in order to respond to climate conditions (Memarian & Sadoughi, 2011). This means that with the house enclosed from outside and opening to the courtyard, the sunny side of the courtyard houses which is the north is used during cool season and the shaded side which is the south is used during warm season (Soflaei, Shokouhian, & Mofidi, 2015). Most of courtyard houses in desert climate are along the north-south direction or northeast–southwest, or northwest–southeast, to maximise the use of summer and winter living (Ghobadian, 2006, cited in Soflaei, Shokouhian, & Mofidi Shemirani, 2016). Never the less, Soflaei et al. (2016) believes that in desert climates “The south–north or west–east direction without a rotation angle can be considered the appropriate orientation for courtyards. However, the local geographic and environmental conditions, as well as the latitudinal location, cannot be neglected.”

Other techniques also used in arid countries around the world are as follows:

1. Mashrabiyya: grills over the window openings providing shade and permitting air circulation, often in hot, humid climates (Earls, 1997).

2. Pierced walls: Cross ventilation between large windows facing inner courtyards and small, eye-level windows facing outside; these are usually used in India (Ganapathi, 1997).

3. Vents or coral slabs: vents allowing air to enter at the top, pass through the cavity wall, and enter the room at floor level (Zandi, 1997).

4. Double skin roof: ventilated space between the outer roof and inner ceiling that prevents thermal gain; these are used in Bojnordiha house in Iran (Castle, 2012). 5. Air funnel: the entrance lobby acts as a wind tunnel cooling the rooms in contact with

it and directing air to the courtyard, which acts like the lungs of the house (Ganapathi, 1997).

6. Water (Ghanat and water features): Ghanats are vertical shafts in the ground, often used to supply water and to help with cooling the air when it passes above. Roaf (1997) claims that many traditional buildings have these tunnels in order to provide comfort.

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7. Use of domes: domes are usually situated above a main square room in the house with small air vents to draw hot air out of the space. They are often seen in the houses of Yazd in Iran (Naciri, 2007).

8. Kasbah: tall walls with very small windows built closely to each other, and mostly in North Africa, to protect occupants from extremely sunny days (Figure 3. 12). The plan of a Kasbah usually combines a major atrium inside, typically referred to as courtyard, which is an important asset in climate control within these houses (Naciri, 2007).

Figure 3. 12: Kasbah (Naciri, 2007)

9. Covered streets: this method draws in the cool air, stored in the shaded streets between dwellings, to the courtyards via convection (Figure 3. 13). It helps the exteriors of north African houses to stay cool during the day (Naciri, 2007).

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10.Passive downdraft evaporative cooling: this technique is mostly seen in India where a fine mist of water is released at the top of three large intakes located above the atrium or courtyard. The mist helps to cool down the air, which then descends slowly and helps occupants to achieve thermal comfort. An example of this is Torrent Research Centre in Ahmadabad, which achieves 72% of its human comfort through this technique, with 6 to 9 ac/h on different floors in summer (Wahid, 2012).

All of these traditional systems have been effective when there is a need to provide natural ventilation or to control any discomfort temperature. Soleymanpour et al. (2015) claims that the climate comfort of buildings today have decreased because of their dependence on new technologies. This is not a good solution for all climates and therefore suggests a lack of human-oriented design. Consequently, research is needed into how to incorporate as well as translate old strategies into modern tall buildings considering the seasonal variations of semi- arid climates.