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Numerical study of effects of Shavadoon connections (a vernacular architectural pattern) on improvement of natural ventilation
Tunnelling and Underground Space Technology 82 (2018) 170–181
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Numerical study of effects of Shavadoon connections (a vernacular architectural pattern) on improvement of natural ventilation
T
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Hadi Samsam-Khayani, Mohammd Reza Tavakoli , Shabnam Mohammadshahi, Mahdi Nili-Ahmadabadi Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Shavadoon (Shavadan) Natural (free) ventilation Numerical solution Tal Darizeh
Architects and engineers working in different climatic conditions have come up with many new ideas to adapt with nature. In so doing, they have managed to construct environmentally friendly buildings that can provide the required cooling/heating without using nonrenewable energies. Shavadoon is one such building. Constructed at a depth of 5–12 m below ground level, this structure takes advantage of the high thermal capacity of soil to provide thermal comfort conditions, thus helping the inhabitants of the building to escape the exhausting heat during summer. Tals (structural elements used in Shavadoons) act as communication bridges for connecting neighboring Shavadoons. As a first step in this study, two separate Shavadoons were simulated. Then, the effect of Tals and the effect of communication methods on ventilation velocity were studied. The results showed that adding a Tal could reduce the existing vortices around the stairway, thus increasing the inlet flow rate by 57%. Adding a second Tal and connecting the two Shavadoons via two Tals, while not affecting the overall flow rate, created an even flow rate distribution through the Tals. Tal length also influenced the flow rate: increasing the length of the Tals caused the flow rate through them to decrease.
1. Introduction Building energy is the highest energy user amongst all sectors (Chenari et al., 2016) and heating, ventilation and air conditioning (HVAC) system consumes about 60–70 percent of the total energy consumption of a building (Bayoumi, 2017). Several work have been conducted and reached that underground buildings can reduce the total energy consuming in comparison with aboveground buildings (Barker, 1986; Mumin, 2001; Van Dronkelaar et al., 2014) and ease land problems and use, as well (El-Hamid and Khair-El-Din, 1991; Admiraal, 2006). On the other hand, different methods are used in different regions of Iran for controlling environmental conditions in a building. In the regions to the north of Khuzestan Plain, particularly in the Dezful region, which have hard (conglomerate) beds, it is possible to build parts of the building under ground level so as to strike a balance between creating a proper interaction with the environment and providing the required thermal comfort conditions for the building inhabitants. Shavadoon is a cool underground space constructed in the traditional buildings of this area. The very hard ground makes excavation into the ground (sometimes to a maximum depth of 10 m below ground level) possible without any need for bracing walls and
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ceilings. This excavated space can provide the means for the inhabitants to rest during the day, to store their foodstuff, and to meet their general needs in terms of cooling. Capable of maintaining a constant temperature throughout the day, Shavadoon provides a temporary summer residence for the inhabitants of traditional houses in the area. During a hot summer day with a temperature of circa 50 °C, Shavadoon can provide a comfort limit temperature of circa 25 °C. The following are among the few studies conducted in this field. Introducing the Shavadoon for the first time, Bina (2008) studied empirically a number of Shavadoons and measured their internal temperatures. He showed that, even during the hottest summer day, the temperature inside a Shavadoon was less than the minimum outdoor temperature. The other result obtained in this study was that Shavadoon temperature variations were slight throughout the 24 h. Moradi and Eskandari (2012) compared the results obtained from the numerical solution with the empirical results to study the cooling/heating performance of a Shavadoon in different months of the year. Nasrollahei et al. (2013) investigated the cooling operation of a Shavadoon. Their results showed that the temperatures inside a Shavadoon during the 24 h were within the thermal comfort temperature range. Hazbei et al. (2015) studied a Shavadoon and its bed chamber
Corresponding author. E-mail address: [email protected] (M.R. Tavakoli).
https://doi.org/10.1016/j.tust.2018.08.045 Received 26 September 2017; Received in revised form 14 June 2018; Accepted 18 August 2018 0886-7798/ © 2018 Elsevier Ltd. All rights reserved.
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(shabestan). They also simulated a local Shavadoon during the summer and winter months and showed that the cooling and heating requirements of the inhabitants could be properly met without additional expenses through proper use of natural laws such as free convection. Their results were in good agreement (within a 10% margin) with the empirical results. Mohammadshahi et al. (2016) conducted a numerical simulation of the flow rates and heat transfer within a sample Shavadoon. They subsequently studied the effects of such parameters as Darizeh cross section and position as well as the inlet shape on the Shavadoon temperature. Their results showed that adding a gate to the Darizeh was effective in reducing the inlet flow rate to the Shavadoon. Mukhtar et al. (2018) analyzed the thermal performance of a naturallyventilated underground shelter in a hot and humid country such as Malaysia. They found that the room temperature of the shelter was significantly lower than the outdoor temperature during the hottest month and vice-versa during the coldest month. As a first step in the present study, the two Shavadoons introduced in (The Filbandzadeh House Shavadoon) and (The Ghasri House Shavadoon) were simulated and their respective mean temperatures as well as inlet flow rates obtained. Then, the effects of Tals and Shavadoon communication were studied. Ultimately, the relevant effects of Tal position, number of Tals, and Tal length were examined.
Fig. 3. The stairway.
(circa 1.5 m across) (Fig. 2) located in the yard, a Shavadoon ends in its main component, the sahn (Fig. 5) which has a square plan. The stairway connects the yard to the sahn (Fig. 3). The slope of this stairway is, in most cases, greater than that of a modern stairway. After every 12–18 steps, a foot rest is provided. The space provided by the foot rest can be used to provide accommodation in cases where the number of users exceeds the Shavadoon capacity. A cylindrical duct with an approximate diameter of 1 m, called Darizeh, is included in the
2. Structure of a Shavadoon Fig. 1 shows a Shavadoon and its different components, and Figs. 2–8 show views different Shavadoon structural components including the entrance, the stairway, the foot rest, the sahn, the kat, the Darizeh, and the Tal. Generally starting at a relatively wide entrance
Fig. 4. The foot rest. Fig. 1. A Shavadoon and its components.
Fig. 2. The entrance.
Fig. 5. The sahn. 171
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kat or the sahn ceiling to provide light and ventilation (Fig. 7). Kats (Fig. 6) are chambers connected to the sahn which are connected to the neighboring Shavadoons via tunnels called “Tal” (Fig. 8). In addition to
providing access, these tunnels could stimulate air ventilation, and in fact establish an underground communication network for a group of houses the inhabitants of which were close family members or friendly neighbors. The Tals of Shavadoons built near the river would open to suitable places along the river bank, thus providing the inhabitants of the Shavadoon with cool river air. In places with no access to a river, the Tals would be connected to Qantas (underground water system) to provide the Shavadoon inhabitants with the cool air that existed around these valuable hydraulic structures. Fig. 9 shows a schematic of the Shavadoon communication system. Sometimes, the Tals would be fitted with metal grids to censure the privacy of the inhabitants. Tals were also used as communication bridges between adjacent Shavadoons during summer days when hot weather made open air traffic less frequent. Tals were also used as spaces for exchanging foodstuff and supplying other daily needs. 3. City of Dezful Located in southwestern Iran to the north of Khuzestan Province, Dezful (like the other cities in the region) has a hot and humid climate. The mean local summer temperature in the area varies between 16 and 53 °C, and the maximum temperature fluctuation in the 24 h is approximately 35 °C. Table 1 lists the regional temperatures in different months of the year (NOAA, 2012). Protection against the exhausting temperatures during hot summer days and great temperature fluctuations in the region have always been the main concerns of the architects who endeavored to provide thermal as well as living comfort conditions for the people of this area.
Fig. 6. The kat.
4. Shavadoon temperature Fig. 10 compares the outdoor and Shavadoon temperatures during summer based on the results obtained in (Bina, 2008). As can be observed, the ambient temperature during the hottest days can amount to 45 °C which is far from that required to provide standard living and thermal comfort conditions; whereas the temperature inside the Shavadoon is 25 °C which is well within the thermal comfort range (Ponni and Baskar, 2015; Bayoumi, 2018) (human thermal comfort is 20 and 23 °C in the cold and warm season, respectively (Moradi and Eskandari, 2012)). Therefore, no nonrenewable energy is required for cooling the Shavadoon to provide thermal comfort conditions therein. Shavadoon cooling is not only affected by the earth’s crust temperature (which provides the required cooling in the summer) but also by ventilating the air inside Shavadoon. The earth’s shell comprises two parts: an upper layer which contains the ground surface and a layer beneath that. The upper layer is rapidly cooled and heated following the extreme weather variations/fluctuations during the 24 h as well as during different seasons. The second layer, where the basement floors are constructed, lies between 1 and 20 m below the ground level. Eq. (1) expresses the temperature variations of the earth crust at different depths in the course of a year (Kusuda and Achenbach, 1965).
Fig. 7. The Darizeh.
T (z , t ) = Tmean−Tamp e−z
π /365α
2π ⎛ z × cos ⎛⎜ t −t0− 365 2 ⎝ ⎝ ⎜
365 ⎞ ⎞ ⎟ πα ⎠ ⎠ ⎟
(1)
where T (z, t) is the undisturbed ground temperature at time t (day) and depth z (m), Tmean is the mean surface temperature (average air temperature) which is the ground temperature at an infinite depth, Tamp is
Fig. 8. The Tal.
Fig. 9. Underground communication between Shavadoons.
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Table 1 Climatic data for Dezful (NOAA, 2012). Month
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
Record high (°C) Average high (°C) Daily mean (°C) Average low (°C) Record low (°C)
28 17.2 10.8 5.3 −9
29 19.6 13.2 6.8 −4
36 24.1 17.3 10 −2
40.5 30 22.8 14.7 3
46.5 37.5 29.9 20.5 10
50 43.7 35.1 23.8 16
53.6 46 37 26.2 19
52 44.9 35.8 25.5 16.5
48 41.7 32 21.1 10
43 34.8 25.6 16.2 6
35 26.2 17.9 10.8 1
29 19.3 12.5 6.8 −2
53.6 32.08 24.16 15.64 −9
Maximum outdoor tem. (°C)
distribution and temperature variations in the area). However, these fluctuations are greatly reduced at greater depths. At depths between 10 and 12 m, these temperature fluctuations almost disappear, resulting in a relatively constant temperature equal to the mean annual temperature in the region. Due to the fact that seasonal temperature variations are transferred from the ground surface to the ground depth after a delay of several months, we can practically store the cold of the winter for the purpose of providing the coolness required for maintaining thermal comfort conditions throughout the summer (Givoni, 1993). As already mentioned, air ventilation can also contribute to increased coolness inside the Shavadoon. Due to the upward movement of the hotter air during the day, the upper cooler air layers cannot reach the ground surface. During the night in the absence of radiation energy from the sun, however, the cooler heavier air layers at higher altitudes finds an opportunity to move towards the ground surface. Upon entering the Shavadoon, this cool air can be stored for several hours and used by the Shavadoon inhabitants. For this reason, the inlet and openings of a Shavadoon must be designed in such a way that they can provide fast ventilation during the night. During the day, however, the stored air must not be ventilated so that the hot air can be prevented from entering the Shavadoon. To this end, gates are used to block the exit of air during daytime (Mohammadshahi et al., 2016).
Minimum outdoor tem. (°C)
JUNE
JULY
28.5
26.24
45.5 25.5
27
24.84
25.25
46
45.5
Indoor tem. (°C)
AUGUST
Fig. 10. Comparison of ambient temperature with that inside a Shavadoon (Bina, 2008).
the amplitude of surface temperature (The maximum surface temperature will be Tmean + Tamp and the minimum value will be Tmean − Tamp), α is the thermal diffusivity of the soil (m2/day) and t0 is the day of the year with the minimum surface temperature (day). Considering the values given in (Ghobadian, 2012) and using the physical properties of soil given in Table 2 (Ghobadian, 2012), the local temperatures in Table 1 (NOAA, 2012), and Eq. (1) (Kusuda and Achenbach, 1965), we plotted the annual temperature variation characteristic at different depths (from the ground level) (Fig. 11). As can be observed, there are dramatic temperature fluctuations at the ground level as well as shallow depths (due to the specific temperature
5. Computational models In this work, the thermal properties of air are assumed to be constant and the governing (continuity, momentum, and energy) equations for steady flow can be written in (2)–(4):
Table 2 Soil properties (Ghobadian, 2012). Density Thermal Conductivity Thermal diffusivity Specific heat capacity
(kg/m3) (W/m K) (m2/day) (H/kg K)
2730 5. 55 0. 1996 880
Continuity:
Momentum:
Energy:
ui
∂ (ρuj ) = 0 ∂x j ∂τij ∂p ∂ + (ui uj ) = ρgi− ∂x j ∂x i ∂x j ∂T ∂ 2T =α ∂x i ∂x i ∂x j
(2)
(3)
(4)
Assuming that the density fluctuations are negligible, the equations for incompressible turbulent flow can be averaged and substituting the averged quantities into the equations results in the Reynolds Average Navier-Stokes given below (Bejan, 2004):
∂uj ∂x j
ρuj
ui
=0
∂Rij ∂p ∂ ⎛ ∂ui ⎞ ∂ui + =− ⎜μ ⎟ + ∂x i ∂x j ⎝ ∂x j ⎠ ∂x j ∂x j
∂T ∂u′i T ′ ∂ 2T + =α ∂x i ∂x i ∂x i ∂x j
(5)
(6)
(7)
This averaging procedure introduces additional unknown terms (Rij) called Reynolds stresses which act like additional stresses and contain products of the fluctuating quantities based on eddy viscosity models. In fact, the RANS model is closed in K-epsilon model here and as it is able to capture the general flow features in indoor environment (Ng
Fig. 11. Temperature distribution at different depths and hours of the day (Moradi and Eskandari, 2012). 173
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Fig. 12. View of Shavadoon Design 1 and its boundary conditions.
method. The high resolution method (used for independently solving the mass and momentum equations) was implemented to calculate the advection terms and the higher-order convective scheme was used for discretizing the equations (Ng et al., 2006, 2007; Liu et al., 2017). SIMPLEC was used for pressure and velocity coupling and the equations were solved statically. The Gauss-Seidel iteration and the algebraic multi-grid methods were used for discretizing and accelerating convergence respectively. A 10−6 convergence radius/limit was considered for the governing equations. To conduct realistic simulations, we used the inlet boundary condition at the beginning of the solution domain instead of the boundary condition at the Shavadoon inlet. Using such boundary conditions would cause air to enter the Shavadoon based on the flow characteristics and actual conditions instead of creating a forced air flow into the Shavadoon. For simplicity, the stairway was assumed to be an inclined surface. Above the inlet and outlet to the Shavadoon, a rectangular range was considered to maintain a closer approximation between the actual and the simulated models. Table 3 lists the physical characteristics of the two studied Shavadoons. The Darizeh diameter, the total sahn and kat cross sectional area, and the inlet cross sectional area in Shavadoon Design 2 were assumed to be 1.5 times, 1.8 times, and 1.08 times those in Shavadoon Design respectively. In addition, the cross sectional area of the stairway end connected to the sahn in Design 1 was 1.12 of that in Design 2.
et al., 2007; Ng and Ng, 2007) at reasonable accuracy (Nasrollahei et al., 2013; Hazbei et al., 2015; Mohammadshahi et al., 2016). The boundary conditions implemented in this investigation are shown in Fig. 12 and are as follows: Inlet: As mentioned in the previous section, air ventilation inside the Shavadoon occurs at night. Accordingly, a wind velocity of 1.8 m/s and an average temperature of 29.5 °C were assumed at inlet in the simulations in accordance with the regional meteorological data (Nasrollahei et al., 2013). Shavadoon’s walls: The Shavadoon wall temperature was assumed to be equal to the average annual regional temperature (23 °C) (Mohammadshahi et al., 2016). Outlet: A constant pressure is defined at the outlet. Walls: For all solid walls, the no-slip condition is used. 6. Numerical solution The Shavadoons introduced in (The Filbandzadeh House Shavadoon) and (The Ghasri House Shavadoon) were initially studied in the present study. Figs. 13 and 14 show the schematics of these Shavadoons. The CFD analysis was performed using ANSYS CFX to solve the Reynolds Average Navier-Stokes equations which describe the conservation of mass, momentum and energy via a finite volume
7. Results 7.1. Numerical analysis of Shavadoon performance As already mentioned, a good Shavadoon must be able to provide rapid ventilation during the night without allowing any ventilation during the day. For this reason, while Shavadoon doors and openings would be traditionally opened during the night to provide for Table 3 Structural features of Shavadoon Designs 1 and 2.
Fig. 13. Plan of Shavadoon Design 1.
Feature
Design 2
Design 1
Darizeh Diameter (m) Total Cross Sectional Area (sahn + kats) (m2) Inlet Area (m2) End of Stairway (Leading to Sahn) Cross Sectional Area (m2)
0.75 68.2 3.7 4.9
0.5 37.5 3.4 5.5
Table 4 Five different fluid meshes for Design 1.
Fig. 14. Plan of Shavadoon Design 2. 174
Mesh Size
Very coarse
Coarse
Medium
Fine
Very Fine
No. of Elements * 103 Shavadoon average temperature (°C)
100 27.6
200 27
400 26.5
800 26.4
1200 26.37
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Fig. 15. Shavadoon meshing used in the study. Table 5 Comparison of calculated temperature with the literature values.
Temperature °C Error %
Experimental
Numerical
Bina (2008)
Mohammadshahi et al. (2016)
Hazbei et al. (2015)
Moradi and Eskandari (2012)
Present work
26.2 –
27.5 4.8
29.04 10
29.8 13.7
26.37 0.65
Table 6 Comparison of calculated entrance velocity with the literature values.
wind speed around the entrance door [m/s]
Nasrollahei et al. (2013)
Present work
Error %
0.7
0.74
5.7
Fig. 17. Temperature contour at the height of 1 m above the floor in Shavadoon Design 1.
temperature error of less than 1% according to Table 5. In addition, the rectangular region at the top of the Shavadoon was used in our study to model the atmospheric condition and applying the input boundary condition to this boundary, allows the flow to enter without coercion and the existence of central yard (rectangular region) and its structure reduces the wind speed around the entrance door to Shavadoon, so that it can reduce the wind speed in outdoors from 1.8 to 0.7 m/s (Table 6). Subsequently, Shavadoon Design 2 (Fig. 14) was simulated, as shown in Fig. 16. The same mesh element size as Design 1 was selected for modeling Design 2. The inlet flow rates for Designs 1 and 2 were ultimately calculated as 0.21 kg/s and 0.31 kg/s respectively. The velocity and temperature contours at a height of 1 m, obtained for Shavadoon Designs 1 and 2, are shown in Figs. 17–20. As can be observed, very low-velocity air circulation occurs in the kats adjacent to the sahn in Design 1, thus providing a more suitable space for resting. The uniform temperature in the sahn in Design 2 is the result of better circulation, as can be observed in the velocity contour corresponding to this design.
Fig. 16. A perspective view of Shavadoon Design 2.
ventilation as well as take in fresh air, they had to be kept closed during the day. Shavadoon Design 1 (Fig. 13), with dimensions corresponding to those of the actual Shavadoon, was simulated first (Fig. 12). The sensitivity of the numerical solution to the selected mesh size was duly checked by calculating the temperature inside the Shavadoon. Five different mesh sizes are considered to investigate the influence of mesh size (Table 4). These meshes are indicated as very coarse, coarse, medium, fine, and very fine, respectively. As shown in that Table, reducing the mesh element number below 1,200,000 would not produce a perceptible change in the average calculated temperature. Therefore, the number of mesh elements was set to 1,200,000. Fig. 15 shows a schematic of the studied mesh. By using this mesh, we calculated the average temperature as 26.37 °C which was very close to that the recorded in the experimental results obtained in (Bina, 2008) and had a 175
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Fig. 18. Velocity contour at the height of 1 m above the floor in Shavadoon Design 1. Fig. 20. Velocity contour at the height of 1 m above the floor in Shavadoon Design 2.
a greater flow velocity is induced in the kat opposite the entrance in Design 1 as a result of adding the Tal. Fig. 23 shows the stream lines in the plane of symmetry of Shavadoon Design 1 before the connection. Fig. 24 shows the stream lines of the same design after the first connection. As can be observed, the inlet flow is increased by 57% and we can conclude that the ventilation velocity/rate in both the Shavadoons is increased, thus providing better comfort conditions during the day.
7.2.2. Case 2: Effect of Tal position In this case, the position of the Tal was changed from the adjacent kat in Design 2 to the wall adjacent to the sahn, as shown in Fig. 25, and the relevant flow rates were calculated (Table 9). The results showed that, as in the previous case, a 0.13 kg/s flow was established from Shavadoon 1 to Shavadoon 2. In fact, changing the position of the Tal led to a 48% increase in the inlet flow rate to Shavadoon 1 as compared with its singular state. In other words, changing the position of the Tal in the design 2 would reduce the inlet flow rate to Shavadoon 1 by 9% as compared to Case 1. Fig. 26 show the velocity contour obtained at a height of 1 m from the Shavadoon floors. The greater flow velocity in Design 2 is due to the addition of the Tal. The flow velocity through the Tal was less than that obtained for Connection 1. In other words, due to the existence of the Tal adjacent to the Darizeh in Connection 1, air suction occurred at a greater velocity. Fig. 27 shows the stream lines through Shavadoon Design 1 on the stairway plane of symmetry where a more uniform flow can be observed.
Fig. 19. Temperature contour at the height of 1 m above the floor in Shavadoon Design 2.
The inlet flow rate in Design 2 is greater due to its larger Darizeh diameter and larger inlet cross sectional area, as shown in Table 3. 7.2. Connecting the two Shavadoons
7.2.3. Case 3: Effect of number of Tals In this section, both the Tals in Cases 1 and 2 were added to the Shavadoons to produce the geometry shown in Fig. 28. The resulting flow rates obtained in this case are listed in Table 10. Comparison of Tables 9 and 10 revealed no significant changes in the flow rate. For this reason, the transferred flow rates from the Tals were calculated separately. The flow rates through Tals A and B were thus calculated as 0.07 kg/s and 0.06 kg/s respectively. The velocity contour at a distance of 1 m from the floor and the stream lines on Shavadoon 2 stairway are shown in Figs. 29 and 30 respectively. Although connecting the Shavadoons via the Tals did not affect the total flow rate, it established a more uniform flow through the stairway in Shavadoon 1 and reduced the existing vortices.
In this section, the effect of the existence of Tals and the shape of that will be discussed and written in the following sections as showed in Table 7. 7.2.1. Case 1: Effect of the Tals As shown in Fig. 21 in this case, a Tal was designed at the end of the kat facing the entrance in Design 1 to connect this kat to the kat adjacent to the Shavadoon in Design 2 which has a Darizeh in its ceiling. The necessary flow rates were then obtained (Table 8). The results showed that adding this Tal led to a 0.15 kg/s air circulation from the Shavadoon 1 towards Shavadoon 2. Fig. 22 shows the velocity contour at a height of 1 m from the floor of the Shavadoons. As can be observed, 176
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Table 7 Comparison of Shape of connection in this study. Name
Section
Design 1
7.1
Design 2
7.1
Case 1 (Connection 1)
7.2.1
Case 2 (Connection 2)
7.2.2
Case 3 (Connection 3)
7.2.3
Case 4 (Connection 4)
7.2.4
Shape of connection
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Fig. 21. The first connection (Connection 1) between the Shavadoons. Table 8 Inlet flow rate through the stairway and outlet flow through the Darizeh after establishing Connection 1. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.21 0.33
0.36 0.18
Fig. 24. Stream lines on the plane of symmetry in Design 1 after establishing Connection 1.
Fig. 25. Connection 2 between the two studied Shavadoons. Table 9 Inlet flow to the stairway and outlet flow from the Darizeh after establishing Connection 2.
Fig. 22. Velocity contour at the height of 1 m from the floor, obtained after establishing Connection 1 between the Shavadoons.
Fig. 23. Stream lines on the plane of symmetry in Design 1 in the singular case.
Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.23 0.31
0.36 0.18
Fig. 26. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 2.
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Fig. 29. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 3.
Fig. 27. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1 after establishing Connection 2.
Fig. 28. Connection 3 between the studied Shavadoons. Table 10 Inlet flow rate through the stairway and outlet flow rate through the Darizeh after establishing Connection 3. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.23 0.31
0.36 0.18
Fig. 30. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1 after establishing Connection 3.
7.2.4. Case 4: Total effect of Tal positions In this section, both the Tals were added, as shown in Fig. 31. The calculated flow rates in this case are listed in Table 11. Comparison of Tables 10 and 11 showed no significant change in the respective flow rates, with the flow rates transferred through Tals A and B being calculated as 0.11 kg/s and 0.03 kg/s respectively. The flow rate through Tal C was less than that through Tal B due to the greater length of the former. Figs. 32 and 33 show the velocity contours at 1 m above the floor and the stream lines on the plane of symmetry in Design 1 respectively.
7.3. Effect of Darizeh diameter Fig. 31. Connection 4 between the studied Shavadoons.
In this section, the effect on flow rate of the Darizeh diameter in the design 2 was studied. As shown in Fig. 21, the Darizeh diameter in Design 2 was changed from 0.75 m to 0.5 m. The relevant flow rates were then calculated (Table 12). Comparison of Tables 12 and 8 revealed that the inlet flow rate through Shavadoon Design 1 and the outlet flow rate through the Darizeh of design 2 were reduced by 24 and 44 percent respectively. In other words, upon considering equal Darizeh
dimensions for the two Shavadoons under the same condition, the total flow rate decreased. Fig. 34 shows the velocity contour obtained at a height of 1 m from the Shavadoon floors. As can be observed, the flow velocity through the Shavadoons is reduced. In other words, reducing the Darizeh of design 2 diameter led to a slower velocity distribution
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Table 11 Inlet flow rate through the stairway and outlet flow rate through the Darizeh after establishing Connection 4. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.23 0.32
0.37 0.18
Fig. 34. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 1, obtained for equal Darizeh diameters.
Fig. 32. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 4.
Fig. 35. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1, obtained for equal Darizeh diameters.
due to the greater cross sectional area of the Shavadoon. Fig. 35 shows the stream lines on the plane of symmetry of Shavadoon Design 1. As can be observed, the vortices are reduced due to the decreased inlet flow rate. 8. Conclusion Shavadoon is a vernacular architectural pattern which provides cool underground spaces with favorable comfort conditions in buildings located in hot and humid climates. Through utilization of such natural energy resources as the earth’s energy and air ventilation, a Shavadoon can provide favorable living conditions. During the night, air is allowed to circulate into the Shavadoon and be stored within for a few hours, thus providing coolness for the inhabitants during hot days. Therefore, a Shavadoon must be designed for rapid ventilation during the night. In this study, the Shavadoons introduced in (The Filbandzadeh House Shavadoon) and (The Ghasri House Shavadoon) were simulated. Comparison of the numerical and the empirical results showed that the physics of the flow had been correctly simulated. At the next step, the Shavadoons were connected and the established connections duly studied. The simulation results showed that connecting the Shavadoons via Tals could increase the flow rate by 57%. Displacing the Tals reduced this flow rate by 9%. Then, the Shavadoons were connected via two
Fig. 33. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1 after establishing Connection 4.
Table 12 Inlet flow rate through the stairway and outlet flow rate through the Darizeh upon establishing Connection 1 and reducing Darizeh diameter in Design 2. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.16 0.25
0.20 0.21
180
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Tals and duly simulated. The results showed that adding the second Tal did not affect the total flow rate, although it led to a more uniform velocity and flow distribution through the Tals. In the simulations, the Darizeh diameter in one Shavadoon was 1.5 times that in the other, establishing an air current/suction towards the Shavadoon with the greater Darizeh. To eliminate this effect, equal Darizeh diameters were assumed in the subsequent simulations. This led to an inlet flow rate reduction of 24% as compared to the case of unequal Darizeh diameters. In all, we can conclude that Shavadoons are well capable of providing comfort conditions during hot seasons without any extra cooling/heating expenses or using nonrenewable energies. In addition, connecting Shavadoons via underground ducts (Tals) to provide means of communication, particularly during exhausting summer days, can not only supply the daily requirements of inhabitants, but also provide for faster ventilation, thus prolonging the comfort condition hours during the day.
conservation in hot arid areas. Archit. Plann. 3, 3–18. Ghobadian, V., 2012. Climatological Investigation of Iranian Historical Buildings. University of Tehran. Givoni, B., 1993. Empirical model of building with a passive evaporative cool tower. Sol. Energy 33, 425–434. Hazbei, M., Nematollahi, O., Behnia, M., Adib, Z., 2015. Reduction of energy consumption using passive architecture in hot and humid climates. Tunn. Undergr. Space Technol. 47, 16–27. Kusuda, T., Achenbach, P.R., 1965. Earth temperature and thermal diffusivity at selected stations in the United States. ASHRAE Trans. 71, 61–74. Liu, K.S., Sheu, T.W.H., Hwang, Y.H., Ng, K.C., 2017. High-order particle method for solving incompressible Navier-Stokes equations within a mixed Lagrangian-Eulerian framework. Comput. Methods Appl. Mech. Eng. 325, 77–101. Mohammadshahi, Sh., Nili-Ahmadabadi, M., Nematollahi, O., 2016. Improvement of ventilation and heat transfer in Shavadoon via numerical simulation: a traditional HVAC system. Renew. Energy 96, 295–304. Moradi, H., Eskandari, H., 2012. An experimental and numerical investigation of Shovadan heating and cooling operation. Renew. Energy 48, 364–368. Mukhtar, A., Ng, K.C., Yusoff, M.Z., 2018. Passive thermal performance prediction and multi-objective optimization of naturally-ventilated underground shelter in Malaysia. Renew. Energy 123, 342–352. Mumin, A., 2001. Suitability of sunken courtyards in the desert climate of Kuwait. Energy Build. 33, 103–111. Nasrollahei, N., Mahdavinejad, M., Hadiyanpour, M., 2013. Studying the thermal and cryogenic performance of Shevadun in native (Local) buildings of Dezful based on modeling and environmental measuring. Am. J. Energy Res. 1, 45–53. Ng, K.C., Ng, E.Y.K., 2007. Development and validation of a CFD code with application to three-dimensional indoor airflow. Comput. Fluid Dyn. 15, 462. Ng, K.C., Yusoff, M.Z., Yin, E., Ng, K., 2006. Multi-grid solution of Euler equations using high resolution NVD differencing scheme for unstructured meshes. Prog. Comput. Fluid Dyn. 6, 389–401. Ng, K.C., Ng, E.Y.K., Yusoff, M.Z., Lim, T.K., 2007. Applications of high-resolution schemes based on normalized variable formulation for 3D indoor airflow simulation. Int. J. Num. Methods Eng. 73, 948–981. Ng, K.C., Yusoff, M.Z., Ng, E.Y.K., 2007. Higher-order bounded differencing schemes for compressible and incompressible flow. Int. J. Num. Methods Fluids 53, 57–80. NOAA, 2012. Dezful Climate Normals 1961–1990. National Oceanic and Atmospheric Administration. Ponni, M., Baskar, R., 2015. A study on indoor temperature and comfort temperature. Int. J. Eng. Sci. Invent. 4, 7–14. The Filbandzadeh House Shavadoon (drawings), The Iranian Cultural Heritage Organization, Khuzestan Province. The Ghasri House Shavadoon (drawings), The Iranian Cultural Heritage Organization, Khuzestan Province. Van Dronkelaar, C., Cóstola, D., Mangkuto, R.A., Hensen, J.L.M., 2014. Heating and cooling energy demand in underground buildings: potential for saving in various climates and functions. Energy Build. 71, 129–136.
Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.tust.2018.08.045. References Admiraal, J., 2006. A bottom-up approach to the planning of underground space. Tunn. Undergr. Space Technol. 21, 464–465. Barker, M., 1986. Using the earth to save energy: four underground buildings. Tunn. Undergr. Space Technol. 1, 59–65. Bayoumi, M., 2017. Energy saving method for improving thermal comfort and air quality in warm humid climates using isothermal high velocity ventilation. Renew. Energy 114, 502–512. Bayoumi, M., 2018. Improving natural ventilation conditions on semi-outdoor and indoor levels in warm-humid climates. Buildings 8, 75. Bejan, A., 2004. Convection Heat Transfer. John Wiley, USA. Bina, M., 2008. An climatological investigation of Shavadoon. J. Fine Art (Honarhaye Ziba) 33, 37–46. Chenari, B., Dias Carrilho, J., Gameiro Da Silva, M., 2016. Towards sustainable, energyefficient and healthy ventilation strategies in buildings: a review. Renew. Sustain. Energy Rev. 59, 1426–1447. El-Hamid, A., Khair-El-Din, M., 1991. Earth sheltered housing: an approach to energy
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Numerical study of effects of Shavadoon connections (a vernacular architectural pattern) on improvement of natural ventilation
T
⁎
Hadi Samsam-Khayani, Mohammd Reza Tavakoli , Shabnam Mohammadshahi, Mahdi Nili-Ahmadabadi Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Shavadoon (Shavadan) Natural (free) ventilation Numerical solution Tal Darizeh
Architects and engineers working in different climatic conditions have come up with many new ideas to adapt with nature. In so doing, they have managed to construct environmentally friendly buildings that can provide the required cooling/heating without using nonrenewable energies. Shavadoon is one such building. Constructed at a depth of 5–12 m below ground level, this structure takes advantage of the high thermal capacity of soil to provide thermal comfort conditions, thus helping the inhabitants of the building to escape the exhausting heat during summer. Tals (structural elements used in Shavadoons) act as communication bridges for connecting neighboring Shavadoons. As a first step in this study, two separate Shavadoons were simulated. Then, the effect of Tals and the effect of communication methods on ventilation velocity were studied. The results showed that adding a Tal could reduce the existing vortices around the stairway, thus increasing the inlet flow rate by 57%. Adding a second Tal and connecting the two Shavadoons via two Tals, while not affecting the overall flow rate, created an even flow rate distribution through the Tals. Tal length also influenced the flow rate: increasing the length of the Tals caused the flow rate through them to decrease.
1. Introduction Building energy is the highest energy user amongst all sectors (Chenari et al., 2016) and heating, ventilation and air conditioning (HVAC) system consumes about 60–70 percent of the total energy consumption of a building (Bayoumi, 2017). Several work have been conducted and reached that underground buildings can reduce the total energy consuming in comparison with aboveground buildings (Barker, 1986; Mumin, 2001; Van Dronkelaar et al., 2014) and ease land problems and use, as well (El-Hamid and Khair-El-Din, 1991; Admiraal, 2006). On the other hand, different methods are used in different regions of Iran for controlling environmental conditions in a building. In the regions to the north of Khuzestan Plain, particularly in the Dezful region, which have hard (conglomerate) beds, it is possible to build parts of the building under ground level so as to strike a balance between creating a proper interaction with the environment and providing the required thermal comfort conditions for the building inhabitants. Shavadoon is a cool underground space constructed in the traditional buildings of this area. The very hard ground makes excavation into the ground (sometimes to a maximum depth of 10 m below ground level) possible without any need for bracing walls and
⁎
ceilings. This excavated space can provide the means for the inhabitants to rest during the day, to store their foodstuff, and to meet their general needs in terms of cooling. Capable of maintaining a constant temperature throughout the day, Shavadoon provides a temporary summer residence for the inhabitants of traditional houses in the area. During a hot summer day with a temperature of circa 50 °C, Shavadoon can provide a comfort limit temperature of circa 25 °C. The following are among the few studies conducted in this field. Introducing the Shavadoon for the first time, Bina (2008) studied empirically a number of Shavadoons and measured their internal temperatures. He showed that, even during the hottest summer day, the temperature inside a Shavadoon was less than the minimum outdoor temperature. The other result obtained in this study was that Shavadoon temperature variations were slight throughout the 24 h. Moradi and Eskandari (2012) compared the results obtained from the numerical solution with the empirical results to study the cooling/heating performance of a Shavadoon in different months of the year. Nasrollahei et al. (2013) investigated the cooling operation of a Shavadoon. Their results showed that the temperatures inside a Shavadoon during the 24 h were within the thermal comfort temperature range. Hazbei et al. (2015) studied a Shavadoon and its bed chamber
Corresponding author. E-mail address: [email protected] (M.R. Tavakoli).
https://doi.org/10.1016/j.tust.2018.08.045 Received 26 September 2017; Received in revised form 14 June 2018; Accepted 18 August 2018 0886-7798/ © 2018 Elsevier Ltd. All rights reserved.
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(shabestan). They also simulated a local Shavadoon during the summer and winter months and showed that the cooling and heating requirements of the inhabitants could be properly met without additional expenses through proper use of natural laws such as free convection. Their results were in good agreement (within a 10% margin) with the empirical results. Mohammadshahi et al. (2016) conducted a numerical simulation of the flow rates and heat transfer within a sample Shavadoon. They subsequently studied the effects of such parameters as Darizeh cross section and position as well as the inlet shape on the Shavadoon temperature. Their results showed that adding a gate to the Darizeh was effective in reducing the inlet flow rate to the Shavadoon. Mukhtar et al. (2018) analyzed the thermal performance of a naturallyventilated underground shelter in a hot and humid country such as Malaysia. They found that the room temperature of the shelter was significantly lower than the outdoor temperature during the hottest month and vice-versa during the coldest month. As a first step in the present study, the two Shavadoons introduced in (The Filbandzadeh House Shavadoon) and (The Ghasri House Shavadoon) were simulated and their respective mean temperatures as well as inlet flow rates obtained. Then, the effects of Tals and Shavadoon communication were studied. Ultimately, the relevant effects of Tal position, number of Tals, and Tal length were examined.
Fig. 3. The stairway.
(circa 1.5 m across) (Fig. 2) located in the yard, a Shavadoon ends in its main component, the sahn (Fig. 5) which has a square plan. The stairway connects the yard to the sahn (Fig. 3). The slope of this stairway is, in most cases, greater than that of a modern stairway. After every 12–18 steps, a foot rest is provided. The space provided by the foot rest can be used to provide accommodation in cases where the number of users exceeds the Shavadoon capacity. A cylindrical duct with an approximate diameter of 1 m, called Darizeh, is included in the
2. Structure of a Shavadoon Fig. 1 shows a Shavadoon and its different components, and Figs. 2–8 show views different Shavadoon structural components including the entrance, the stairway, the foot rest, the sahn, the kat, the Darizeh, and the Tal. Generally starting at a relatively wide entrance
Fig. 4. The foot rest. Fig. 1. A Shavadoon and its components.
Fig. 2. The entrance.
Fig. 5. The sahn. 171
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kat or the sahn ceiling to provide light and ventilation (Fig. 7). Kats (Fig. 6) are chambers connected to the sahn which are connected to the neighboring Shavadoons via tunnels called “Tal” (Fig. 8). In addition to
providing access, these tunnels could stimulate air ventilation, and in fact establish an underground communication network for a group of houses the inhabitants of which were close family members or friendly neighbors. The Tals of Shavadoons built near the river would open to suitable places along the river bank, thus providing the inhabitants of the Shavadoon with cool river air. In places with no access to a river, the Tals would be connected to Qantas (underground water system) to provide the Shavadoon inhabitants with the cool air that existed around these valuable hydraulic structures. Fig. 9 shows a schematic of the Shavadoon communication system. Sometimes, the Tals would be fitted with metal grids to censure the privacy of the inhabitants. Tals were also used as communication bridges between adjacent Shavadoons during summer days when hot weather made open air traffic less frequent. Tals were also used as spaces for exchanging foodstuff and supplying other daily needs. 3. City of Dezful Located in southwestern Iran to the north of Khuzestan Province, Dezful (like the other cities in the region) has a hot and humid climate. The mean local summer temperature in the area varies between 16 and 53 °C, and the maximum temperature fluctuation in the 24 h is approximately 35 °C. Table 1 lists the regional temperatures in different months of the year (NOAA, 2012). Protection against the exhausting temperatures during hot summer days and great temperature fluctuations in the region have always been the main concerns of the architects who endeavored to provide thermal as well as living comfort conditions for the people of this area.
Fig. 6. The kat.
4. Shavadoon temperature Fig. 10 compares the outdoor and Shavadoon temperatures during summer based on the results obtained in (Bina, 2008). As can be observed, the ambient temperature during the hottest days can amount to 45 °C which is far from that required to provide standard living and thermal comfort conditions; whereas the temperature inside the Shavadoon is 25 °C which is well within the thermal comfort range (Ponni and Baskar, 2015; Bayoumi, 2018) (human thermal comfort is 20 and 23 °C in the cold and warm season, respectively (Moradi and Eskandari, 2012)). Therefore, no nonrenewable energy is required for cooling the Shavadoon to provide thermal comfort conditions therein. Shavadoon cooling is not only affected by the earth’s crust temperature (which provides the required cooling in the summer) but also by ventilating the air inside Shavadoon. The earth’s shell comprises two parts: an upper layer which contains the ground surface and a layer beneath that. The upper layer is rapidly cooled and heated following the extreme weather variations/fluctuations during the 24 h as well as during different seasons. The second layer, where the basement floors are constructed, lies between 1 and 20 m below the ground level. Eq. (1) expresses the temperature variations of the earth crust at different depths in the course of a year (Kusuda and Achenbach, 1965).
Fig. 7. The Darizeh.
T (z , t ) = Tmean−Tamp e−z
π /365α
2π ⎛ z × cos ⎛⎜ t −t0− 365 2 ⎝ ⎝ ⎜
365 ⎞ ⎞ ⎟ πα ⎠ ⎠ ⎟
(1)
where T (z, t) is the undisturbed ground temperature at time t (day) and depth z (m), Tmean is the mean surface temperature (average air temperature) which is the ground temperature at an infinite depth, Tamp is
Fig. 8. The Tal.
Fig. 9. Underground communication between Shavadoons.
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Table 1 Climatic data for Dezful (NOAA, 2012). Month
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
Record high (°C) Average high (°C) Daily mean (°C) Average low (°C) Record low (°C)
28 17.2 10.8 5.3 −9
29 19.6 13.2 6.8 −4
36 24.1 17.3 10 −2
40.5 30 22.8 14.7 3
46.5 37.5 29.9 20.5 10
50 43.7 35.1 23.8 16
53.6 46 37 26.2 19
52 44.9 35.8 25.5 16.5
48 41.7 32 21.1 10
43 34.8 25.6 16.2 6
35 26.2 17.9 10.8 1
29 19.3 12.5 6.8 −2
53.6 32.08 24.16 15.64 −9
Maximum outdoor tem. (°C)
distribution and temperature variations in the area). However, these fluctuations are greatly reduced at greater depths. At depths between 10 and 12 m, these temperature fluctuations almost disappear, resulting in a relatively constant temperature equal to the mean annual temperature in the region. Due to the fact that seasonal temperature variations are transferred from the ground surface to the ground depth after a delay of several months, we can practically store the cold of the winter for the purpose of providing the coolness required for maintaining thermal comfort conditions throughout the summer (Givoni, 1993). As already mentioned, air ventilation can also contribute to increased coolness inside the Shavadoon. Due to the upward movement of the hotter air during the day, the upper cooler air layers cannot reach the ground surface. During the night in the absence of radiation energy from the sun, however, the cooler heavier air layers at higher altitudes finds an opportunity to move towards the ground surface. Upon entering the Shavadoon, this cool air can be stored for several hours and used by the Shavadoon inhabitants. For this reason, the inlet and openings of a Shavadoon must be designed in such a way that they can provide fast ventilation during the night. During the day, however, the stored air must not be ventilated so that the hot air can be prevented from entering the Shavadoon. To this end, gates are used to block the exit of air during daytime (Mohammadshahi et al., 2016).
Minimum outdoor tem. (°C)
JUNE
JULY
28.5
26.24
45.5 25.5
27
24.84
25.25
46
45.5
Indoor tem. (°C)
AUGUST
Fig. 10. Comparison of ambient temperature with that inside a Shavadoon (Bina, 2008).
the amplitude of surface temperature (The maximum surface temperature will be Tmean + Tamp and the minimum value will be Tmean − Tamp), α is the thermal diffusivity of the soil (m2/day) and t0 is the day of the year with the minimum surface temperature (day). Considering the values given in (Ghobadian, 2012) and using the physical properties of soil given in Table 2 (Ghobadian, 2012), the local temperatures in Table 1 (NOAA, 2012), and Eq. (1) (Kusuda and Achenbach, 1965), we plotted the annual temperature variation characteristic at different depths (from the ground level) (Fig. 11). As can be observed, there are dramatic temperature fluctuations at the ground level as well as shallow depths (due to the specific temperature
5. Computational models In this work, the thermal properties of air are assumed to be constant and the governing (continuity, momentum, and energy) equations for steady flow can be written in (2)–(4):
Table 2 Soil properties (Ghobadian, 2012). Density Thermal Conductivity Thermal diffusivity Specific heat capacity
(kg/m3) (W/m K) (m2/day) (H/kg K)
2730 5. 55 0. 1996 880
Continuity:
Momentum:
Energy:
ui
∂ (ρuj ) = 0 ∂x j ∂τij ∂p ∂ + (ui uj ) = ρgi− ∂x j ∂x i ∂x j ∂T ∂ 2T =α ∂x i ∂x i ∂x j
(2)
(3)
(4)
Assuming that the density fluctuations are negligible, the equations for incompressible turbulent flow can be averaged and substituting the averged quantities into the equations results in the Reynolds Average Navier-Stokes given below (Bejan, 2004):
∂uj ∂x j
ρuj
ui
=0
∂Rij ∂p ∂ ⎛ ∂ui ⎞ ∂ui + =− ⎜μ ⎟ + ∂x i ∂x j ⎝ ∂x j ⎠ ∂x j ∂x j
∂T ∂u′i T ′ ∂ 2T + =α ∂x i ∂x i ∂x i ∂x j
(5)
(6)
(7)
This averaging procedure introduces additional unknown terms (Rij) called Reynolds stresses which act like additional stresses and contain products of the fluctuating quantities based on eddy viscosity models. In fact, the RANS model is closed in K-epsilon model here and as it is able to capture the general flow features in indoor environment (Ng
Fig. 11. Temperature distribution at different depths and hours of the day (Moradi and Eskandari, 2012). 173
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Fig. 12. View of Shavadoon Design 1 and its boundary conditions.
method. The high resolution method (used for independently solving the mass and momentum equations) was implemented to calculate the advection terms and the higher-order convective scheme was used for discretizing the equations (Ng et al., 2006, 2007; Liu et al., 2017). SIMPLEC was used for pressure and velocity coupling and the equations were solved statically. The Gauss-Seidel iteration and the algebraic multi-grid methods were used for discretizing and accelerating convergence respectively. A 10−6 convergence radius/limit was considered for the governing equations. To conduct realistic simulations, we used the inlet boundary condition at the beginning of the solution domain instead of the boundary condition at the Shavadoon inlet. Using such boundary conditions would cause air to enter the Shavadoon based on the flow characteristics and actual conditions instead of creating a forced air flow into the Shavadoon. For simplicity, the stairway was assumed to be an inclined surface. Above the inlet and outlet to the Shavadoon, a rectangular range was considered to maintain a closer approximation between the actual and the simulated models. Table 3 lists the physical characteristics of the two studied Shavadoons. The Darizeh diameter, the total sahn and kat cross sectional area, and the inlet cross sectional area in Shavadoon Design 2 were assumed to be 1.5 times, 1.8 times, and 1.08 times those in Shavadoon Design respectively. In addition, the cross sectional area of the stairway end connected to the sahn in Design 1 was 1.12 of that in Design 2.
et al., 2007; Ng and Ng, 2007) at reasonable accuracy (Nasrollahei et al., 2013; Hazbei et al., 2015; Mohammadshahi et al., 2016). The boundary conditions implemented in this investigation are shown in Fig. 12 and are as follows: Inlet: As mentioned in the previous section, air ventilation inside the Shavadoon occurs at night. Accordingly, a wind velocity of 1.8 m/s and an average temperature of 29.5 °C were assumed at inlet in the simulations in accordance with the regional meteorological data (Nasrollahei et al., 2013). Shavadoon’s walls: The Shavadoon wall temperature was assumed to be equal to the average annual regional temperature (23 °C) (Mohammadshahi et al., 2016). Outlet: A constant pressure is defined at the outlet. Walls: For all solid walls, the no-slip condition is used. 6. Numerical solution The Shavadoons introduced in (The Filbandzadeh House Shavadoon) and (The Ghasri House Shavadoon) were initially studied in the present study. Figs. 13 and 14 show the schematics of these Shavadoons. The CFD analysis was performed using ANSYS CFX to solve the Reynolds Average Navier-Stokes equations which describe the conservation of mass, momentum and energy via a finite volume
7. Results 7.1. Numerical analysis of Shavadoon performance As already mentioned, a good Shavadoon must be able to provide rapid ventilation during the night without allowing any ventilation during the day. For this reason, while Shavadoon doors and openings would be traditionally opened during the night to provide for Table 3 Structural features of Shavadoon Designs 1 and 2.
Fig. 13. Plan of Shavadoon Design 1.
Feature
Design 2
Design 1
Darizeh Diameter (m) Total Cross Sectional Area (sahn + kats) (m2) Inlet Area (m2) End of Stairway (Leading to Sahn) Cross Sectional Area (m2)
0.75 68.2 3.7 4.9
0.5 37.5 3.4 5.5
Table 4 Five different fluid meshes for Design 1.
Fig. 14. Plan of Shavadoon Design 2. 174
Mesh Size
Very coarse
Coarse
Medium
Fine
Very Fine
No. of Elements * 103 Shavadoon average temperature (°C)
100 27.6
200 27
400 26.5
800 26.4
1200 26.37
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Fig. 15. Shavadoon meshing used in the study. Table 5 Comparison of calculated temperature with the literature values.
Temperature °C Error %
Experimental
Numerical
Bina (2008)
Mohammadshahi et al. (2016)
Hazbei et al. (2015)
Moradi and Eskandari (2012)
Present work
26.2 –
27.5 4.8
29.04 10
29.8 13.7
26.37 0.65
Table 6 Comparison of calculated entrance velocity with the literature values.
wind speed around the entrance door [m/s]
Nasrollahei et al. (2013)
Present work
Error %
0.7
0.74
5.7
Fig. 17. Temperature contour at the height of 1 m above the floor in Shavadoon Design 1.
temperature error of less than 1% according to Table 5. In addition, the rectangular region at the top of the Shavadoon was used in our study to model the atmospheric condition and applying the input boundary condition to this boundary, allows the flow to enter without coercion and the existence of central yard (rectangular region) and its structure reduces the wind speed around the entrance door to Shavadoon, so that it can reduce the wind speed in outdoors from 1.8 to 0.7 m/s (Table 6). Subsequently, Shavadoon Design 2 (Fig. 14) was simulated, as shown in Fig. 16. The same mesh element size as Design 1 was selected for modeling Design 2. The inlet flow rates for Designs 1 and 2 were ultimately calculated as 0.21 kg/s and 0.31 kg/s respectively. The velocity and temperature contours at a height of 1 m, obtained for Shavadoon Designs 1 and 2, are shown in Figs. 17–20. As can be observed, very low-velocity air circulation occurs in the kats adjacent to the sahn in Design 1, thus providing a more suitable space for resting. The uniform temperature in the sahn in Design 2 is the result of better circulation, as can be observed in the velocity contour corresponding to this design.
Fig. 16. A perspective view of Shavadoon Design 2.
ventilation as well as take in fresh air, they had to be kept closed during the day. Shavadoon Design 1 (Fig. 13), with dimensions corresponding to those of the actual Shavadoon, was simulated first (Fig. 12). The sensitivity of the numerical solution to the selected mesh size was duly checked by calculating the temperature inside the Shavadoon. Five different mesh sizes are considered to investigate the influence of mesh size (Table 4). These meshes are indicated as very coarse, coarse, medium, fine, and very fine, respectively. As shown in that Table, reducing the mesh element number below 1,200,000 would not produce a perceptible change in the average calculated temperature. Therefore, the number of mesh elements was set to 1,200,000. Fig. 15 shows a schematic of the studied mesh. By using this mesh, we calculated the average temperature as 26.37 °C which was very close to that the recorded in the experimental results obtained in (Bina, 2008) and had a 175
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Fig. 18. Velocity contour at the height of 1 m above the floor in Shavadoon Design 1. Fig. 20. Velocity contour at the height of 1 m above the floor in Shavadoon Design 2.
a greater flow velocity is induced in the kat opposite the entrance in Design 1 as a result of adding the Tal. Fig. 23 shows the stream lines in the plane of symmetry of Shavadoon Design 1 before the connection. Fig. 24 shows the stream lines of the same design after the first connection. As can be observed, the inlet flow is increased by 57% and we can conclude that the ventilation velocity/rate in both the Shavadoons is increased, thus providing better comfort conditions during the day.
7.2.2. Case 2: Effect of Tal position In this case, the position of the Tal was changed from the adjacent kat in Design 2 to the wall adjacent to the sahn, as shown in Fig. 25, and the relevant flow rates were calculated (Table 9). The results showed that, as in the previous case, a 0.13 kg/s flow was established from Shavadoon 1 to Shavadoon 2. In fact, changing the position of the Tal led to a 48% increase in the inlet flow rate to Shavadoon 1 as compared with its singular state. In other words, changing the position of the Tal in the design 2 would reduce the inlet flow rate to Shavadoon 1 by 9% as compared to Case 1. Fig. 26 show the velocity contour obtained at a height of 1 m from the Shavadoon floors. The greater flow velocity in Design 2 is due to the addition of the Tal. The flow velocity through the Tal was less than that obtained for Connection 1. In other words, due to the existence of the Tal adjacent to the Darizeh in Connection 1, air suction occurred at a greater velocity. Fig. 27 shows the stream lines through Shavadoon Design 1 on the stairway plane of symmetry where a more uniform flow can be observed.
Fig. 19. Temperature contour at the height of 1 m above the floor in Shavadoon Design 2.
The inlet flow rate in Design 2 is greater due to its larger Darizeh diameter and larger inlet cross sectional area, as shown in Table 3. 7.2. Connecting the two Shavadoons
7.2.3. Case 3: Effect of number of Tals In this section, both the Tals in Cases 1 and 2 were added to the Shavadoons to produce the geometry shown in Fig. 28. The resulting flow rates obtained in this case are listed in Table 10. Comparison of Tables 9 and 10 revealed no significant changes in the flow rate. For this reason, the transferred flow rates from the Tals were calculated separately. The flow rates through Tals A and B were thus calculated as 0.07 kg/s and 0.06 kg/s respectively. The velocity contour at a distance of 1 m from the floor and the stream lines on Shavadoon 2 stairway are shown in Figs. 29 and 30 respectively. Although connecting the Shavadoons via the Tals did not affect the total flow rate, it established a more uniform flow through the stairway in Shavadoon 1 and reduced the existing vortices.
In this section, the effect of the existence of Tals and the shape of that will be discussed and written in the following sections as showed in Table 7. 7.2.1. Case 1: Effect of the Tals As shown in Fig. 21 in this case, a Tal was designed at the end of the kat facing the entrance in Design 1 to connect this kat to the kat adjacent to the Shavadoon in Design 2 which has a Darizeh in its ceiling. The necessary flow rates were then obtained (Table 8). The results showed that adding this Tal led to a 0.15 kg/s air circulation from the Shavadoon 1 towards Shavadoon 2. Fig. 22 shows the velocity contour at a height of 1 m from the floor of the Shavadoons. As can be observed, 176
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Table 7 Comparison of Shape of connection in this study. Name
Section
Design 1
7.1
Design 2
7.1
Case 1 (Connection 1)
7.2.1
Case 2 (Connection 2)
7.2.2
Case 3 (Connection 3)
7.2.3
Case 4 (Connection 4)
7.2.4
Shape of connection
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Fig. 21. The first connection (Connection 1) between the Shavadoons. Table 8 Inlet flow rate through the stairway and outlet flow through the Darizeh after establishing Connection 1. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.21 0.33
0.36 0.18
Fig. 24. Stream lines on the plane of symmetry in Design 1 after establishing Connection 1.
Fig. 25. Connection 2 between the two studied Shavadoons. Table 9 Inlet flow to the stairway and outlet flow from the Darizeh after establishing Connection 2.
Fig. 22. Velocity contour at the height of 1 m from the floor, obtained after establishing Connection 1 between the Shavadoons.
Fig. 23. Stream lines on the plane of symmetry in Design 1 in the singular case.
Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.23 0.31
0.36 0.18
Fig. 26. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 2.
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Fig. 29. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 3.
Fig. 27. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1 after establishing Connection 2.
Fig. 28. Connection 3 between the studied Shavadoons. Table 10 Inlet flow rate through the stairway and outlet flow rate through the Darizeh after establishing Connection 3. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.23 0.31
0.36 0.18
Fig. 30. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1 after establishing Connection 3.
7.2.4. Case 4: Total effect of Tal positions In this section, both the Tals were added, as shown in Fig. 31. The calculated flow rates in this case are listed in Table 11. Comparison of Tables 10 and 11 showed no significant change in the respective flow rates, with the flow rates transferred through Tals A and B being calculated as 0.11 kg/s and 0.03 kg/s respectively. The flow rate through Tal C was less than that through Tal B due to the greater length of the former. Figs. 32 and 33 show the velocity contours at 1 m above the floor and the stream lines on the plane of symmetry in Design 1 respectively.
7.3. Effect of Darizeh diameter Fig. 31. Connection 4 between the studied Shavadoons.
In this section, the effect on flow rate of the Darizeh diameter in the design 2 was studied. As shown in Fig. 21, the Darizeh diameter in Design 2 was changed from 0.75 m to 0.5 m. The relevant flow rates were then calculated (Table 12). Comparison of Tables 12 and 8 revealed that the inlet flow rate through Shavadoon Design 1 and the outlet flow rate through the Darizeh of design 2 were reduced by 24 and 44 percent respectively. In other words, upon considering equal Darizeh
dimensions for the two Shavadoons under the same condition, the total flow rate decreased. Fig. 34 shows the velocity contour obtained at a height of 1 m from the Shavadoon floors. As can be observed, the flow velocity through the Shavadoons is reduced. In other words, reducing the Darizeh of design 2 diameter led to a slower velocity distribution
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Table 11 Inlet flow rate through the stairway and outlet flow rate through the Darizeh after establishing Connection 4. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.23 0.32
0.37 0.18
Fig. 34. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 1, obtained for equal Darizeh diameters.
Fig. 32. Velocity contour at the height of 1 m from the Shavadoon floor after establishing Connection 4.
Fig. 35. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1, obtained for equal Darizeh diameters.
due to the greater cross sectional area of the Shavadoon. Fig. 35 shows the stream lines on the plane of symmetry of Shavadoon Design 1. As can be observed, the vortices are reduced due to the decreased inlet flow rate. 8. Conclusion Shavadoon is a vernacular architectural pattern which provides cool underground spaces with favorable comfort conditions in buildings located in hot and humid climates. Through utilization of such natural energy resources as the earth’s energy and air ventilation, a Shavadoon can provide favorable living conditions. During the night, air is allowed to circulate into the Shavadoon and be stored within for a few hours, thus providing coolness for the inhabitants during hot days. Therefore, a Shavadoon must be designed for rapid ventilation during the night. In this study, the Shavadoons introduced in (The Filbandzadeh House Shavadoon) and (The Ghasri House Shavadoon) were simulated. Comparison of the numerical and the empirical results showed that the physics of the flow had been correctly simulated. At the next step, the Shavadoons were connected and the established connections duly studied. The simulation results showed that connecting the Shavadoons via Tals could increase the flow rate by 57%. Displacing the Tals reduced this flow rate by 9%. Then, the Shavadoons were connected via two
Fig. 33. Stream lines on the plane of symmetry of the stairway in Shavadoon Design 1 after establishing Connection 4.
Table 12 Inlet flow rate through the stairway and outlet flow rate through the Darizeh upon establishing Connection 1 and reducing Darizeh diameter in Design 2. Geometry
Inflow (kg/s)
Outflow (kg/s)
Design 2 Design 1
0.16 0.25
0.20 0.21
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Tals and duly simulated. The results showed that adding the second Tal did not affect the total flow rate, although it led to a more uniform velocity and flow distribution through the Tals. In the simulations, the Darizeh diameter in one Shavadoon was 1.5 times that in the other, establishing an air current/suction towards the Shavadoon with the greater Darizeh. To eliminate this effect, equal Darizeh diameters were assumed in the subsequent simulations. This led to an inlet flow rate reduction of 24% as compared to the case of unequal Darizeh diameters. In all, we can conclude that Shavadoons are well capable of providing comfort conditions during hot seasons without any extra cooling/heating expenses or using nonrenewable energies. In addition, connecting Shavadoons via underground ducts (Tals) to provide means of communication, particularly during exhausting summer days, can not only supply the daily requirements of inhabitants, but also provide for faster ventilation, thus prolonging the comfort condition hours during the day.
conservation in hot arid areas. Archit. Plann. 3, 3–18. Ghobadian, V., 2012. Climatological Investigation of Iranian Historical Buildings. University of Tehran. Givoni, B., 1993. Empirical model of building with a passive evaporative cool tower. Sol. Energy 33, 425–434. Hazbei, M., Nematollahi, O., Behnia, M., Adib, Z., 2015. Reduction of energy consumption using passive architecture in hot and humid climates. Tunn. Undergr. Space Technol. 47, 16–27. Kusuda, T., Achenbach, P.R., 1965. Earth temperature and thermal diffusivity at selected stations in the United States. ASHRAE Trans. 71, 61–74. Liu, K.S., Sheu, T.W.H., Hwang, Y.H., Ng, K.C., 2017. High-order particle method for solving incompressible Navier-Stokes equations within a mixed Lagrangian-Eulerian framework. Comput. Methods Appl. Mech. Eng. 325, 77–101. Mohammadshahi, Sh., Nili-Ahmadabadi, M., Nematollahi, O., 2016. Improvement of ventilation and heat transfer in Shavadoon via numerical simulation: a traditional HVAC system. Renew. Energy 96, 295–304. Moradi, H., Eskandari, H., 2012. An experimental and numerical investigation of Shovadan heating and cooling operation. Renew. Energy 48, 364–368. Mukhtar, A., Ng, K.C., Yusoff, M.Z., 2018. Passive thermal performance prediction and multi-objective optimization of naturally-ventilated underground shelter in Malaysia. Renew. Energy 123, 342–352. Mumin, A., 2001. Suitability of sunken courtyards in the desert climate of Kuwait. Energy Build. 33, 103–111. Nasrollahei, N., Mahdavinejad, M., Hadiyanpour, M., 2013. Studying the thermal and cryogenic performance of Shevadun in native (Local) buildings of Dezful based on modeling and environmental measuring. Am. J. Energy Res. 1, 45–53. Ng, K.C., Ng, E.Y.K., 2007. Development and validation of a CFD code with application to three-dimensional indoor airflow. Comput. Fluid Dyn. 15, 462. Ng, K.C., Yusoff, M.Z., Yin, E., Ng, K., 2006. Multi-grid solution of Euler equations using high resolution NVD differencing scheme for unstructured meshes. Prog. Comput. Fluid Dyn. 6, 389–401. Ng, K.C., Ng, E.Y.K., Yusoff, M.Z., Lim, T.K., 2007. Applications of high-resolution schemes based on normalized variable formulation for 3D indoor airflow simulation. Int. J. Num. Methods Eng. 73, 948–981. Ng, K.C., Yusoff, M.Z., Ng, E.Y.K., 2007. Higher-order bounded differencing schemes for compressible and incompressible flow. Int. J. Num. Methods Fluids 53, 57–80. NOAA, 2012. Dezful Climate Normals 1961–1990. National Oceanic and Atmospheric Administration. Ponni, M., Baskar, R., 2015. A study on indoor temperature and comfort temperature. Int. J. Eng. Sci. Invent. 4, 7–14. The Filbandzadeh House Shavadoon (drawings), The Iranian Cultural Heritage Organization, Khuzestan Province. The Ghasri House Shavadoon (drawings), The Iranian Cultural Heritage Organization, Khuzestan Province. Van Dronkelaar, C., Cóstola, D., Mangkuto, R.A., Hensen, J.L.M., 2014. Heating and cooling energy demand in underground buildings: potential for saving in various climates and functions. Energy Build. 71, 129–136.
Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.tust.2018.08.045. References Admiraal, J., 2006. A bottom-up approach to the planning of underground space. Tunn. Undergr. Space Technol. 21, 464–465. Barker, M., 1986. Using the earth to save energy: four underground buildings. Tunn. Undergr. Space Technol. 1, 59–65. Bayoumi, M., 2017. Energy saving method for improving thermal comfort and air quality in warm humid climates using isothermal high velocity ventilation. Renew. Energy 114, 502–512. Bayoumi, M., 2018. Improving natural ventilation conditions on semi-outdoor and indoor levels in warm-humid climates. Buildings 8, 75. Bejan, A., 2004. Convection Heat Transfer. John Wiley, USA. Bina, M., 2008. An climatological investigation of Shavadoon. J. Fine Art (Honarhaye Ziba) 33, 37–46. Chenari, B., Dias Carrilho, J., Gameiro Da Silva, M., 2016. Towards sustainable, energyefficient and healthy ventilation strategies in buildings: a review. Renew. Sustain. Energy Rev. 59, 1426–1447. El-Hamid, A., Khair-El-Din, M., 1991. Earth sheltered housing: an approach to energy
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