Roof geometry as a factor of thermal behavior: simulation based study of using vaults and domes in the Middle East zone

Roof geometry as a factor of thermal behavior: simulation based study of using vaults and domes... Abstract Vaults and domes were used as a roofing system and have been developed through time to mitigate the increasing structural, functional and climatic challenges. The evolutions in simulation programs open new research works and projects that study old domed/vaulted buildings practice and also what new constructed buildings designs should be. The significant climatic challenge of the selected region is hot temperature, so the thermal performance of building envelope specially the roofs is an important theme to be discussed. In this research, 14 roof cases between vaults, domes and double domes in five different arch-bases are proposed and thermally examined in three different cities represent three climatic conditions through the Middle East zone which are Cairo, Riyadh and Istanbul. The study depends on Autodesk Simulation CFD that could calculate the solar heating influence with consideration of natural distribution of heat flux and heat transfer. From comparing total heat flux, heat flux per proposed surface area unit and heat flux per horizontal surface area unit of all examined cases, the study finds that the pointed double domes roof is an effective one according to Cairo and Riyadh climatic conditions, while under Istanbul climatic conditions cases of half-circular/pointed domes and vaults have convergent results. 1 INTRODUCTION Architects and researchers attempt to create applicable and comfortable buildings and indoor spaces in order to reach the objectives of sustainable design; decrease the environmental loads and increase the occupants comfort. Each part of building needs well-versed studies to reach proper characteristic and feathers and to obviously identify its behavior. The sustainable building is designed to achieve the highest performance, over the complete building life cycle through minimizing natural resource consumption, emissions and harmful impacts on site ecosystems and maximizing the quality of the indoor environment [1]. Many strategies for building formation are used to sustain environmental and indoor climate performance. The building form design to mitigate extreme climatic conditions through several design guidelines from summer direct sun and provide adequate and comfort ventilation [2, 3]. It is recommended to use a massive domed structure which is a successful strategy. Besides its thermal benefits, the radiant heat is minimized while radiant cooling is maximized. Domes also allow vertical air movement for better ventilation cycle. Moreover, the building envelope plays an effective role regarding the sun heat protection and hence providing comfort spaces. The study of building envelope shows that the rooftop is the most part that gains sun heat and affects the indoor spaces thermal comfort [4]. This study argues that the vaulted and domed roofs thermal performance is much better than the flat one, so different cases at different sites are examined to achieve the proper proposal for each site. 2 HISTORY OF VAULT/DOME ROOFING From the prehistoric age, vaults and domes were used as a roofing system and have developed to mitigate the increasing structural, functional and climatic challenges in many different climates. The early uses of the dome were found in the tombs of Mycenae, Greece during the Bronze Age. The next development of vault/domed roofing done during the Romans period that was the first fully recognition the architectural potentialities of the dome. The Roman development in dome construction culminated in the Pantheon. Then, the Byzantine builders discover the proper handling of the pendentive which was finally achieved in Hagia Sophia at Constantinople [5]. The next step in developing arches-based roofs is during the Islamic age. Under Byzantine influence the early Muslims adopted the use of the dome [6], in order to the hot-arid climate of the Islamic empire the Islamic builders significantly form this type of roofing not only for mosques but also for houses (Figure 1). Figure 1. View largeDownload slide Qasr Amra; one of the oldest vault/dome roofing examples, Jordan, 743 A.D. Figure 1. View largeDownload slide Qasr Amra; one of the oldest vault/dome roofing examples, Jordan, 743 A.D. From this brief, the arches-based roofs were used for multi purposes: first, structure reasons that allow covering wide spans relative to the flat roof specially in the memorial buildings; second, the possibility of covering spaces with stone and brick in steed of wooden roofs for the climates that have shortage in forests; third, the climatic benefits of vault/dome roofing found in desert and semi-desert regions. 3 REVIEW OF THE CLIMATIC STUDY OF VAULTS AND DOMES Many studies deals with the efficiency of using vaults and domes as a rooftop in term of dimensions such as the structure stability of different arches ratios [7, 8], the materials efficiency of this kind of construction, the economic and added value of using curved roof in steed of the flat one and the climatic effect of this kind of roofing which is the main concern of this article. As the temperature value is the significant coefficient of the building studies in hot-arid climate, this kind of research needs more studies to reach the best thermal performance of the new designed curved roofing as well as the old buildings [9]. According to the previous studies in this area, it is identified that the spaces with curved roofs have lower indoor temperature and lower heat gain compared with the spaces with flat roofs [10, 11]. The cause is that such roofs dissipate more solar radiation than flat roofs do by convention and thermal radiation at night due to the larger convection heat-transfer surface area [12], especially with surface thermal treatments [13]. This implies that vault/dome roofs are suitable for hot dry regions, which explain why curved roofs have been widely adopted by builders in hot-dry areas in the past. Despite the vaults and domes had been examined in many research projects, the arches-based curved roofing and the adoption between domes and vaults need a separate research, not to prove the efficiency of curved roofing in hot-arid climate but to provide the best proposal of different curved roofing types with different climatic conditions according to a digital simulation study that takes form ratio parameters in consideration. 4 METHODOLOGY 4.1 Model design A modular unit is proposed to fit different study cases. It consists of three basic models; one is square to fit the dome's structure, the second case is rectangular with double space area to fit the vault's structure and the third one uses two domes in steed of the vault. Each of the three basic cases is roofing with five different arches to construct dome/vault in addition to a flat roof under the same conditions (Figures 2 and 3). Figure 2. View largeDownload slide The conceptual design of study models plans. Figure 2. View largeDownload slide The conceptual design of study models plans. Figure 3. View largeDownload slide The roofing proportions of dome/vault study models. Figure 3. View largeDownload slide The roofing proportions of dome/vault study models. The matrix of cases types has two axes; the horizontal axis is the rooftop type between three types; single dome, vault and double domes, the vertical axis is the type of arch between four types according to the angle of construction 90°, 120° and 180° in addition to pointed arch and the flat roof (Table 1). The proposed models are built in brick on a sandy soil with the theory of arches to minimize the economical budget (Table 2). Table 1. Cases matrix description. Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Table 1. Cases matrix description. Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Table 2. Material properties of the model. Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 aSurface albedo under cloud-free summer conditions Table 2. Material properties of the model. Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 aSurface albedo under cloud-free summer conditions 4.2 Climatic condition of the selected sites The study selects three different sites with three different climatic conditions in the Middle East zone that historically used this kind of environmental techniques to mitigate its climate (Figure 4). The Middle East has permanently been a dry place. The key climate of the Middle East is dry and hot, even though winter is mild with a little rain. To the north of the desert are the great steppes. According to Köppen–Geiger classification, [12] this climate could be classified into sub-regions according to the following factors: The annual precipitation: this factor classifies the climate to desert, semi-desert and steppe. Temperature: this factor classifies the climate too hot and warm. Figure 4. View largeDownload slide World climate classifications and the selected zone [13]. Figure 4. View largeDownload slide World climate classifications and the selected zone [13]. The sites selected from the certified locations according to Energy Plus weather files in order to have direct access to different simulation software, also selected to represent three different major zones (Figure 5). The sites are: Cairo: Egypt’s capital that represent hot and semi-desert climate, and historically it has great contribution in the domes and vaults architecture. Riyadh: capital of Kingdom Saudi Arabia represent the hot and desert climate, that has little experiences in this kind of roofing in order to the nature of urban desert settlements. Istanbul: the historical capital of Turkey represents the warm and steppe zone, it has many monuments and vernacular buildings in domes and vaults. Figure 5. View largeDownload slide Average temperature and total precipitation of the selected sites [14]. Figure 5. View largeDownload slide Average temperature and total precipitation of the selected sites [14]. 5 SIMULATION PROCESS The simulation research strategy recreated some aspects of the physical environment in one of a variety mode, from a highly abstract computer simulation to full-scale real life mock-up. Simulation is increasingly used as an alternative to lengthy and costly physical experiments [15]. The logical argumentation research strategy uses a sequence of logical steps within a closed system. The research examines the thermal performance of roofs due to the solar heating under average hot day conditions of the selected three sites. The study kept all conditions that affect the simulation process constant. The thermal digital simulation requires detailed data of air temperature distribution and the selected locations in longitude and latitude. The study uses heat flux on the outer skin in order to compare results. Simulation process conditions: Sites: Cairo [N 30 7–E 31 23]. Riyadh [N 24 42–E 46 40]. Istanbul [N 41 0–E 28 58]. Orientation: the domes units are centralized while the vaults and double domes orient its long axis to the north–south direction, the same process can be regenerated for the other orientations, and the unit acts as a stand-alone model. Solar heating conditions: August is the hottest month as weather recorders, data of solar heating/radiation is calculated automatically by entering longitude/latitude and the time. Computational fluid dynamics programs mainly depend on airflow and provide comprehensive predictions of indoor air quality and thermal comfort, such as the distributions of temperature, relative humidity, air velocity and contaminant concentrations. For this research, the study needs to examine the thermal behaviors of different roofing types. The study adopts Autodesk Simulation CFD that could calculate the solar heating influence with consideration of fluid flow, naturally distribution of heat flux and heat transfer. Autodesk Simulation CFD support calculation of internal incompressible flow, particularly for turbulent and compressible flows with complex geometry, also support radiative heat transfer through transparent media and simulates the effects of shadowing on other objects [16], it will be acceptable in thermal environment simulations and solar heating. 6 RESULTS AND DISCUSSION The output of the simulation process has a lot of data that represent the physical practice of models under certain conditions. There are three important factors that directly affected thermal performance of roofing geometry. These factors are the total heat flux for the roof whole area, the heat flux per horizontal surface area unit, and finally, heat flux per proposed surface area unit. The latter two factors are calculated in watt/m2 which is a direct factor of solar influence on the roof shape creating shades and self-shaded areas. 6.1 Single dome on 3.6×3.6 m2 space The clear thermal differences between flat and domed roofs in terms of the heat flux (Table 3 and Figure 6), and hence the flat roof—as predicted—is the worst case in thermal performance. The heat flux density per horizontal surface area unit results of dome roofing cases are ranged from 21.0 W/m2 as maximum and 14.2 W/m2 as minimum; for the 90° Dome in Riyadh and 120° Dome in Istanbul relatively. Table 3. Heat flux digital simulation results for cases 1:5. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Table 3. Heat flux digital simulation results for cases 1:5. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Figure 6. View largeDownload slide Heat flux for cases 1–5 in the three different sites. Figure 6. View largeDownload slide Heat flux for cases 1–5 in the three different sites. 6.2 Vault on 3.6×7.2 m2 space The vault is affected by arches dimension. The wide arches allow sun rays to be perpendicular on a line and create more shadows on the other curvature of vaults. The orientation of sun during daytime on north-south vault let different parts to get heat loss. The study also shows a clear difference on self-shaded areas for 90° and 180° arches vaults; it is concluded that the wider angle the more self-shaded areas. Clear thermal differences between flat and vault roofs in terms of the heat flux are presented (see Table 4). The highest total heat flux density for vault roof toping cases 7:10 (Table 4) is calculated for 90° vault in Riyadh as 43.7 W/m2, while the lower total heat flux density is calculated for 180° vault in Istanbul 26.6 W/m2. Table 4. Heat flux digital simulation results for cases 6:10. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 Table 4. Heat flux digital simulation results for cases 6:10. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 6.3 Double dome on 3.6×7.2 m2 space The multi-domes rooftop creates both shade and shadow, so the cases 11, 12, 13 and 14 have efficient performance especially on Cairo and Riyadh (Table 5), while Istanbul has warm climate that no need for over construction according to building economics. Table 5. Heat flux digital simulation results for cases 11:14. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 Table 5. Heat flux digital simulation results for cases 11:14. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 The effect of climate on the models varies from site to another, as domes and vaults create a drop on temperatures and heat flux in the cases of hot regions [Cairo and Riyadh], while the drop is more slight in the warm climate [Istanbul]. In the case of Istanbul the 90° and 120° arches seem to work as one case also 180° and pointed arches have limited differences. In this research, nine cases are examined as a rooftop for a rectangular space between vault/dome roofing and different arches dimensions in addition to the flat roof. Figure 7 shows the heat flux per unit area for these cases and show that the double pointed dome is the best thermal performance in cases. Figure 7. View largeDownload slide Heat flux for cases 6–14 in the three different sites. Figure 7. View largeDownload slide Heat flux for cases 6–14 in the three different sites. 7 CONCLUSION This paper represents a simulation study for different rooftop types based on the arches. Historically vaults and domes are used in Middle East region to mitigate its hot and arid climates that provide a sun protection surface better than the flat roofing. The study selects three different sites Cairo, Riyadh and Istanbul as different climatic conditions in the selected zone and examined a range of proposals between domes, vaults and double domes also examine different arches dimension in each case. It is identified that the wider angle of dome and more circular decrease the heat flux and surface temperature, the study found that the half-circular vault is more effective than the pointed one, while the pointed dome is better than half-circular one. According to Cairo and Riyadh climatic conditions, a pointed double domes solution is an effective one, while under Istanbul climatic conditions cases of half-circular/pointed domes/vaults have convergent results. Based on work done in this research, the study recommends using pointed domes on desert and semi-desert climates in Riyadh and Cairo. The pointed dome achieves the less heat flux per unit area, because the large self-shaded area and dissipate more heat than other cases do by convention and thermal radiation due to the enlarged curved surface. While the warm and steppe zone in Istanbul; the slight curved vault/dome create a suitable thermal performance according to the condition of climate. For architects and construction sector the study recommends using simulation studies in the early stage design to find the best solution according to the different climatic conditions, the best thermal performance affects the energy consumption and hence the environmental and sustainable aspects. REFERENCES 1 ASHRAE . ASHRAE Green Guide . The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. , 2006 . 2 Brown GZ , Dekay M . Sun, Wind and Light Architectural Design Strategies , 2nd edn . John Wiley & sons Inc , 2001 . 3 Radhi H , Sharples S , Taleb H , et al. . Will cool roofs improve the thermal performance of our built environment? A study assessing roof systems in Bahrain . Energy Build 2017 ; 135 : 324 – 37 . Google Scholar CrossRef Search ADS 4 Gangulya A , Chowdhury D , Neogi S . Performance of building roofs on energy efficiency—a review . Energy Procedia 2016 ; 90 : 200 – 8 . Google Scholar CrossRef Search ADS 5 Karydis N . Limiting the Use of Centering in Vaulted Construction. s.l.: Center of ancient studies, University of Pennsylvania, 2012 . 6 Arce I . Umayyad arches, vaults & domes: merging and re-creation. Contributions to early Islamic Construction History. 2nd International Congress on Construction History . Cambridge University Press , 2006 : 195 – 220 . 7 Huberman N , Pearlmutter D , Meir IA . Optimizing structural roof form for life cycle energy efficiency . Energy Build 2015 ; 104 : 336 – 49 . Google Scholar CrossRef Search ADS 8 Lin Y , Yang W . Solar energy model and thermal performance of an electrochromic dome-covered house . Energy Sustainable Dev 2017 ; 39 : 82 – 90 . Google Scholar CrossRef Search ADS 9 Yaghoubi M , et al. . Thermal study of domed roofs in a traditional bazaar (the case of old Ganj-Alikhan bazaar in Kerman, Iran) . Energy Sustainable Dev 2017 ; 39 : 67 – 81 . Google Scholar CrossRef Search ADS 10 Hadavand M , Yaghoubi M . Thermal behavior of curved roof buildings exposed to solar radiation and wind flow for various orientations . Appl Energy 2008 ; 85 : 663 – 79 . Google Scholar CrossRef Search ADS 11 Tang R , Meir IA , Wu T . Thermal performance of non air-conditioned building with vaulted roofs in comparison with flat roofs . Build Environ 2006 ; 41 : 268 – 76 . Google Scholar CrossRef Search ADS 12 Pearlmutter D . Roof geometry as a determinant of thermal behavior: a comparative study of vaulted and flat roof surfaces in a hot-arid zone . Archit Sci Rev 1993 ; 36 : 75 – 86 . Google Scholar CrossRef Search ADS 13 Faghiha AK , Bahadorib MN . Thermal performance evaluation of domed roofs . Energy Build 2011 ; 43 : 1254 – 63 . Google Scholar CrossRef Search ADS 14 Chen H . Köppen Climate Classification. [Online] January 2013. http://hanschen.org/koppen/#maps. 15 Kottek M , Grieser J , Beck C , et al. . World Maps of KÖPPEN-GEIGER Climate Classification. [Online] 2006. http://koeppen-geiger.vu-wien.ac.at/present.htm. 16 Groat L , Wang D . Architectural Research Methods . John Wiley & sons, Inc , 2002 . © The Author(s) 2018. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Low-Carbon Technologies Oxford University Press

Roof geometry as a factor of thermal behavior: simulation based study of using vaults and domes in the Middle East zone

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Abstract

Abstract Vaults and domes were used as a roofing system and have been developed through time to mitigate the increasing structural, functional and climatic challenges. The evolutions in simulation programs open new research works and projects that study old domed/vaulted buildings practice and also what new constructed buildings designs should be. The significant climatic challenge of the selected region is hot temperature, so the thermal performance of building envelope specially the roofs is an important theme to be discussed. In this research, 14 roof cases between vaults, domes and double domes in five different arch-bases are proposed and thermally examined in three different cities represent three climatic conditions through the Middle East zone which are Cairo, Riyadh and Istanbul. The study depends on Autodesk Simulation CFD that could calculate the solar heating influence with consideration of natural distribution of heat flux and heat transfer. From comparing total heat flux, heat flux per proposed surface area unit and heat flux per horizontal surface area unit of all examined cases, the study finds that the pointed double domes roof is an effective one according to Cairo and Riyadh climatic conditions, while under Istanbul climatic conditions cases of half-circular/pointed domes and vaults have convergent results. 1 INTRODUCTION Architects and researchers attempt to create applicable and comfortable buildings and indoor spaces in order to reach the objectives of sustainable design; decrease the environmental loads and increase the occupants comfort. Each part of building needs well-versed studies to reach proper characteristic and feathers and to obviously identify its behavior. The sustainable building is designed to achieve the highest performance, over the complete building life cycle through minimizing natural resource consumption, emissions and harmful impacts on site ecosystems and maximizing the quality of the indoor environment [1]. Many strategies for building formation are used to sustain environmental and indoor climate performance. The building form design to mitigate extreme climatic conditions through several design guidelines from summer direct sun and provide adequate and comfort ventilation [2, 3]. It is recommended to use a massive domed structure which is a successful strategy. Besides its thermal benefits, the radiant heat is minimized while radiant cooling is maximized. Domes also allow vertical air movement for better ventilation cycle. Moreover, the building envelope plays an effective role regarding the sun heat protection and hence providing comfort spaces. The study of building envelope shows that the rooftop is the most part that gains sun heat and affects the indoor spaces thermal comfort [4]. This study argues that the vaulted and domed roofs thermal performance is much better than the flat one, so different cases at different sites are examined to achieve the proper proposal for each site. 2 HISTORY OF VAULT/DOME ROOFING From the prehistoric age, vaults and domes were used as a roofing system and have developed to mitigate the increasing structural, functional and climatic challenges in many different climates. The early uses of the dome were found in the tombs of Mycenae, Greece during the Bronze Age. The next development of vault/domed roofing done during the Romans period that was the first fully recognition the architectural potentialities of the dome. The Roman development in dome construction culminated in the Pantheon. Then, the Byzantine builders discover the proper handling of the pendentive which was finally achieved in Hagia Sophia at Constantinople [5]. The next step in developing arches-based roofs is during the Islamic age. Under Byzantine influence the early Muslims adopted the use of the dome [6], in order to the hot-arid climate of the Islamic empire the Islamic builders significantly form this type of roofing not only for mosques but also for houses (Figure 1). Figure 1. View largeDownload slide Qasr Amra; one of the oldest vault/dome roofing examples, Jordan, 743 A.D. Figure 1. View largeDownload slide Qasr Amra; one of the oldest vault/dome roofing examples, Jordan, 743 A.D. From this brief, the arches-based roofs were used for multi purposes: first, structure reasons that allow covering wide spans relative to the flat roof specially in the memorial buildings; second, the possibility of covering spaces with stone and brick in steed of wooden roofs for the climates that have shortage in forests; third, the climatic benefits of vault/dome roofing found in desert and semi-desert regions. 3 REVIEW OF THE CLIMATIC STUDY OF VAULTS AND DOMES Many studies deals with the efficiency of using vaults and domes as a rooftop in term of dimensions such as the structure stability of different arches ratios [7, 8], the materials efficiency of this kind of construction, the economic and added value of using curved roof in steed of the flat one and the climatic effect of this kind of roofing which is the main concern of this article. As the temperature value is the significant coefficient of the building studies in hot-arid climate, this kind of research needs more studies to reach the best thermal performance of the new designed curved roofing as well as the old buildings [9]. According to the previous studies in this area, it is identified that the spaces with curved roofs have lower indoor temperature and lower heat gain compared with the spaces with flat roofs [10, 11]. The cause is that such roofs dissipate more solar radiation than flat roofs do by convention and thermal radiation at night due to the larger convection heat-transfer surface area [12], especially with surface thermal treatments [13]. This implies that vault/dome roofs are suitable for hot dry regions, which explain why curved roofs have been widely adopted by builders in hot-dry areas in the past. Despite the vaults and domes had been examined in many research projects, the arches-based curved roofing and the adoption between domes and vaults need a separate research, not to prove the efficiency of curved roofing in hot-arid climate but to provide the best proposal of different curved roofing types with different climatic conditions according to a digital simulation study that takes form ratio parameters in consideration. 4 METHODOLOGY 4.1 Model design A modular unit is proposed to fit different study cases. It consists of three basic models; one is square to fit the dome's structure, the second case is rectangular with double space area to fit the vault's structure and the third one uses two domes in steed of the vault. Each of the three basic cases is roofing with five different arches to construct dome/vault in addition to a flat roof under the same conditions (Figures 2 and 3). Figure 2. View largeDownload slide The conceptual design of study models plans. Figure 2. View largeDownload slide The conceptual design of study models plans. Figure 3. View largeDownload slide The roofing proportions of dome/vault study models. Figure 3. View largeDownload slide The roofing proportions of dome/vault study models. The matrix of cases types has two axes; the horizontal axis is the rooftop type between three types; single dome, vault and double domes, the vertical axis is the type of arch between four types according to the angle of construction 90°, 120° and 180° in addition to pointed arch and the flat roof (Table 1). The proposed models are built in brick on a sandy soil with the theory of arches to minimize the economical budget (Table 2). Table 1. Cases matrix description. Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Table 1. Cases matrix description. Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Dome roofing Vault roofing Double domes Flat roof Case 1 Case 6 90° Arch Case 2 Case 7 Case 11 120° Arch Case 3 Case 8 Case 12 180° Arch Case 4 Case 9 Case 13 Pointed arch Case 5 Case 10 Case 14 Table 2. Material properties of the model. Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 aSurface albedo under cloud-free summer conditions Table 2. Material properties of the model. Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 Density Specific heat Emissivity Conductivity Surface albedoa kg/m3 J/kg K W/m K Brick 1920 835 0.94 0.72 0.3 Soil (sandy) 1600 800 0.76 0.3 0.4 aSurface albedo under cloud-free summer conditions 4.2 Climatic condition of the selected sites The study selects three different sites with three different climatic conditions in the Middle East zone that historically used this kind of environmental techniques to mitigate its climate (Figure 4). The Middle East has permanently been a dry place. The key climate of the Middle East is dry and hot, even though winter is mild with a little rain. To the north of the desert are the great steppes. According to Köppen–Geiger classification, [12] this climate could be classified into sub-regions according to the following factors: The annual precipitation: this factor classifies the climate to desert, semi-desert and steppe. Temperature: this factor classifies the climate too hot and warm. Figure 4. View largeDownload slide World climate classifications and the selected zone [13]. Figure 4. View largeDownload slide World climate classifications and the selected zone [13]. The sites selected from the certified locations according to Energy Plus weather files in order to have direct access to different simulation software, also selected to represent three different major zones (Figure 5). The sites are: Cairo: Egypt’s capital that represent hot and semi-desert climate, and historically it has great contribution in the domes and vaults architecture. Riyadh: capital of Kingdom Saudi Arabia represent the hot and desert climate, that has little experiences in this kind of roofing in order to the nature of urban desert settlements. Istanbul: the historical capital of Turkey represents the warm and steppe zone, it has many monuments and vernacular buildings in domes and vaults. Figure 5. View largeDownload slide Average temperature and total precipitation of the selected sites [14]. Figure 5. View largeDownload slide Average temperature and total precipitation of the selected sites [14]. 5 SIMULATION PROCESS The simulation research strategy recreated some aspects of the physical environment in one of a variety mode, from a highly abstract computer simulation to full-scale real life mock-up. Simulation is increasingly used as an alternative to lengthy and costly physical experiments [15]. The logical argumentation research strategy uses a sequence of logical steps within a closed system. The research examines the thermal performance of roofs due to the solar heating under average hot day conditions of the selected three sites. The study kept all conditions that affect the simulation process constant. The thermal digital simulation requires detailed data of air temperature distribution and the selected locations in longitude and latitude. The study uses heat flux on the outer skin in order to compare results. Simulation process conditions: Sites: Cairo [N 30 7–E 31 23]. Riyadh [N 24 42–E 46 40]. Istanbul [N 41 0–E 28 58]. Orientation: the domes units are centralized while the vaults and double domes orient its long axis to the north–south direction, the same process can be regenerated for the other orientations, and the unit acts as a stand-alone model. Solar heating conditions: August is the hottest month as weather recorders, data of solar heating/radiation is calculated automatically by entering longitude/latitude and the time. Computational fluid dynamics programs mainly depend on airflow and provide comprehensive predictions of indoor air quality and thermal comfort, such as the distributions of temperature, relative humidity, air velocity and contaminant concentrations. For this research, the study needs to examine the thermal behaviors of different roofing types. The study adopts Autodesk Simulation CFD that could calculate the solar heating influence with consideration of fluid flow, naturally distribution of heat flux and heat transfer. Autodesk Simulation CFD support calculation of internal incompressible flow, particularly for turbulent and compressible flows with complex geometry, also support radiative heat transfer through transparent media and simulates the effects of shadowing on other objects [16], it will be acceptable in thermal environment simulations and solar heating. 6 RESULTS AND DISCUSSION The output of the simulation process has a lot of data that represent the physical practice of models under certain conditions. There are three important factors that directly affected thermal performance of roofing geometry. These factors are the total heat flux for the roof whole area, the heat flux per horizontal surface area unit, and finally, heat flux per proposed surface area unit. The latter two factors are calculated in watt/m2 which is a direct factor of solar influence on the roof shape creating shades and self-shaded areas. 6.1 Single dome on 3.6×3.6 m2 space The clear thermal differences between flat and domed roofs in terms of the heat flux (Table 3 and Figure 6), and hence the flat roof—as predicted—is the worst case in thermal performance. The heat flux density per horizontal surface area unit results of dome roofing cases are ranged from 21.0 W/m2 as maximum and 14.2 W/m2 as minimum; for the 90° Dome in Riyadh and 120° Dome in Istanbul relatively. Table 3. Heat flux digital simulation results for cases 1:5. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Table 3. Heat flux digital simulation results for cases 1:5. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 1 Flat rooftop 7.78 Cairo 445.0 57.2 34.3 Riyadh 484.9 62.3 37.4 Istanbul 342.4 44.0 26.4 Case 2 Dome on 90° arch 9.2 Cairo 215.4 23.4 16.6 Riyadh 271.6 29.5 21.0 Istanbul 200.4 21.7 15.5 Case 3 Dome on 120° arch 10.77 Cairo 193.8 18.0 15.0 Riyadh 208.3 19.3 16.1 Istanbul 183.7 17.0 14.2 Case 4 Dome on 180° arch 15.45 Cairo 230.2 14.9 17.8 Riyadh 265.7 17.2 20.5 Istanbul 202.4 13.1 15.6 Case 5 Dome on pointed arch 17.17 Cairo 235.2 13.7 18.1 Riyadh 262.7 15.3 20.3 Istanbul 214.6 12.5 16.6 Figure 6. View largeDownload slide Heat flux for cases 1–5 in the three different sites. Figure 6. View largeDownload slide Heat flux for cases 1–5 in the three different sites. 6.2 Vault on 3.6×7.2 m2 space The vault is affected by arches dimension. The wide arches allow sun rays to be perpendicular on a line and create more shadows on the other curvature of vaults. The orientation of sun during daytime on north-south vault let different parts to get heat loss. The study also shows a clear difference on self-shaded areas for 90° and 180° arches vaults; it is concluded that the wider angle the more self-shaded areas. Clear thermal differences between flat and vault roofs in terms of the heat flux are presented (see Table 4). The highest total heat flux density for vault roof toping cases 7:10 (Table 4) is calculated for 90° vault in Riyadh as 43.7 W/m2, while the lower total heat flux density is calculated for 180° vault in Istanbul 26.6 W/m2. Table 4. Heat flux digital simulation results for cases 6:10. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 Table 4. Heat flux digital simulation results for cases 6:10. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Heat flux density/proposal surface area unit m2 W W/m2 W/m2 Case 6 Flat rooftop 23.0 Cairo 1372 59.7 52.9 Riyadh 1421 61.8 54.8 Istanbul 1077 46.8 41.6 Case 7 Vault on 90° arch 25.1 Cairo 1032 41.1 39.8 Riyadh 1132 45.1 43.7 Istanbul 825.3 32.9 31.8 Case 8 Vault on 120° arch 28.0 Cairo 940.6 33.6 36.3 Riyadh 953.1 34.0 36.8 Istanbul 718.3 25.7 27.7 Case 9 Vault on 180° arch 36.1 Cairo 1035 28.7 39.9 Riyadh 1091 30.2 42.1 Istanbul 689.4 19.1 26.6 Case 10 Vault on pointed arch 36.6 Cairo 1166 31.9 45.0 Riyadh 1208 33.0 46.6 Istanbul 715.2 19.5 27.6 6.3 Double dome on 3.6×7.2 m2 space The multi-domes rooftop creates both shade and shadow, so the cases 11, 12, 13 and 14 have efficient performance especially on Cairo and Riyadh (Table 5), while Istanbul has warm climate that no need for over construction according to building economics. Table 5. Heat flux digital simulation results for cases 11:14. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 Table 5. Heat flux digital simulation results for cases 11:14. Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 Case no. Description Total surface area Site Total heat flux Heat flux density/horizontal surface area unit Total heat flux density/proposed surface area unit m2 W W/m2 W/m2 Case 11 Double dome on 90° arch 18.4 Cairo 653.2 35.5 25.2 Riyadh 682.6 37.1 26.3 Istanbul 443.4 24.1 17.1 Case 12 Double dome on 120° arch 21.5 Cairo 649.3 30.2 25.1 Riyadh 707.4 32.9 27.3 Istanbul 440.8 20.5 17.0 Case 13 Double dome on 180° arch 30.5 Cairo 838.8 27.5 32.4 Riyadh 957.7 31.4 36.9 Istanbul 539.9 17.7 20.8 Case 14 Double dome on pointed arch 34.3 Cairo 864.4 25.2 33.3 Riyadh 1032 30.1 39.8 Istanbul 555.7 16.2 21.4 The effect of climate on the models varies from site to another, as domes and vaults create a drop on temperatures and heat flux in the cases of hot regions [Cairo and Riyadh], while the drop is more slight in the warm climate [Istanbul]. In the case of Istanbul the 90° and 120° arches seem to work as one case also 180° and pointed arches have limited differences. In this research, nine cases are examined as a rooftop for a rectangular space between vault/dome roofing and different arches dimensions in addition to the flat roof. Figure 7 shows the heat flux per unit area for these cases and show that the double pointed dome is the best thermal performance in cases. Figure 7. View largeDownload slide Heat flux for cases 6–14 in the three different sites. Figure 7. View largeDownload slide Heat flux for cases 6–14 in the three different sites. 7 CONCLUSION This paper represents a simulation study for different rooftop types based on the arches. Historically vaults and domes are used in Middle East region to mitigate its hot and arid climates that provide a sun protection surface better than the flat roofing. The study selects three different sites Cairo, Riyadh and Istanbul as different climatic conditions in the selected zone and examined a range of proposals between domes, vaults and double domes also examine different arches dimension in each case. It is identified that the wider angle of dome and more circular decrease the heat flux and surface temperature, the study found that the half-circular vault is more effective than the pointed one, while the pointed dome is better than half-circular one. According to Cairo and Riyadh climatic conditions, a pointed double domes solution is an effective one, while under Istanbul climatic conditions cases of half-circular/pointed domes/vaults have convergent results. Based on work done in this research, the study recommends using pointed domes on desert and semi-desert climates in Riyadh and Cairo. The pointed dome achieves the less heat flux per unit area, because the large self-shaded area and dissipate more heat than other cases do by convention and thermal radiation due to the enlarged curved surface. While the warm and steppe zone in Istanbul; the slight curved vault/dome create a suitable thermal performance according to the condition of climate. For architects and construction sector the study recommends using simulation studies in the early stage design to find the best solution according to the different climatic conditions, the best thermal performance affects the energy consumption and hence the environmental and sustainable aspects. REFERENCES 1 ASHRAE . ASHRAE Green Guide . The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. , 2006 . 2 Brown GZ , Dekay M . Sun, Wind and Light Architectural Design Strategies , 2nd edn . John Wiley & sons Inc , 2001 . 3 Radhi H , Sharples S , Taleb H , et al. . 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Solar energy model and thermal performance of an electrochromic dome-covered house . Energy Sustainable Dev 2017 ; 39 : 82 – 90 . Google Scholar CrossRef Search ADS 9 Yaghoubi M , et al. . Thermal study of domed roofs in a traditional bazaar (the case of old Ganj-Alikhan bazaar in Kerman, Iran) . Energy Sustainable Dev 2017 ; 39 : 67 – 81 . Google Scholar CrossRef Search ADS 10 Hadavand M , Yaghoubi M . Thermal behavior of curved roof buildings exposed to solar radiation and wind flow for various orientations . Appl Energy 2008 ; 85 : 663 – 79 . Google Scholar CrossRef Search ADS 11 Tang R , Meir IA , Wu T . Thermal performance of non air-conditioned building with vaulted roofs in comparison with flat roofs . Build Environ 2006 ; 41 : 268 – 76 . Google Scholar CrossRef Search ADS 12 Pearlmutter D . Roof geometry as a determinant of thermal behavior: a comparative study of vaulted and flat roof surfaces in a hot-arid zone . Archit Sci Rev 1993 ; 36 : 75 – 86 . Google Scholar CrossRef Search ADS 13 Faghiha AK , Bahadorib MN . Thermal performance evaluation of domed roofs . Energy Build 2011 ; 43 : 1254 – 63 . Google Scholar CrossRef Search ADS 14 Chen H . Köppen Climate Classification. [Online] January 2013. http://hanschen.org/koppen/#maps. 15 Kottek M , Grieser J , Beck C , et al. . World Maps of KÖPPEN-GEIGER Climate Classification. [Online] 2006. http://koeppen-geiger.vu-wien.ac.at/present.htm. 16 Groat L , Wang D . Architectural Research Methods . John Wiley & sons, Inc , 2002 . © The Author(s) 2018. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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International Journal of Low-Carbon TechnologiesOxford University Press

Published: Sep 1, 2018

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