Architectural & Urban design department, German University in Cairo, Egypt
Responding to the local climate and site conditions has always been a vital strategy, especially when it is accompanied by minimizing energy consumptions. Over the last decades, the dependence on mechanical equipment has rapidly increased in Egyptian residential buildings. Locally, simple passive strategies, as shading, orientation, thermal mass, daylighting and natural ventilation are rarely considered in the architectural design process. However, residential buildings are the major electric energy consumers in the building sector. Therefore, this research investigates the potential of the re-
Keywords: passive design, sustainability, energy efficiency
Today, environmental and energy problems pose as the number one global problem. Significantly, climate change due to the increasing temperatures caused great concern all over the world. Therefore, man has no choice but to diminish energy consumption rates. As population and energy concerns increase, the demand for low energy practices is urgently needed. In order to recommend low energy architectural practices, passive design has been proposed as a solution (Omer, 2008). Passive design is an approach to building design that utilizes architectural design to minimize energy consumption and to improve thermal comfort. In other words, passive architectural design is to consider all the surrounding environment of the building in the architectural design process, which results that the building responds to all the needs and potentials of its local climate and can dramatically reduce primary energy consumption. The optimum target of passive architectural design is to eliminate requirements for active mechanical systems and to sustain thermal comfort for occupants (Cheung, Fuller, & Luther, 2005) (Mikler, Albert Bicol, Breisnes, & Labrie, 2008).
During the last 60 years in Egypt, architects and designers neglected traditional knowledge of local suitable techniques due to the westernization. In other words, passive design strategies such as shading, orientation, thermal mass, natural lighting and ventilation are no longer considered in the architectural design process (Abdel-
In 2014, residential buildings in Egypt was the major consumer of energy recording 52% of the total produced electrical energy of the country as shown in Figure 1 (EEHC, 2015). Furthermore, electricity consumption for residential buildings is expected to reach 35% growth yearly in the future, based on the 10% yearly increase from 1998 to 2008. Moreover, energy consumption of several residential buildings was examined and it revealed that cooling energy is the major required load in the building, achieving 67% of the total energy consumption of the unit.
Additionally, Egypt is characterized by the massive utilization of prototypical design in governmental housing projects, which doesn't take into consideration the climatic factors, coupled with poor quality in the construction industry (Mourtada, 2009) (Georgy & Soliman, 2007).
1.1 Research Problem
The problem addressed by the research can be based on the following: first, high energy consumption rates are recorded for cooling due to the massive expansions in using mechanical air conditions. Besides, climate change caused high summer temperatures, which reflected on the cooling energy. Second, the governmental residential projects are characterized by the massive utilization of prototypes in most of the cases, which doesn't consider the local climate, orientation or any specific consideration for each location. Consequently, this prototyping results in a massive increase in the energy consumption levels. Therefore, passive cooling strategies that are durable and low technology can dramatically be an approach for controlling the energy consumption and saving cooling energy.
1.2 Research Aim
The research investigates the potential of re-
2. Literature Review
Passive cooling is considered as the highest efficient energy conservation method and it has the lowest economic impact in comparison with mechanical systems. Most studies in hot climates have revealed that most of the energy efficient spaces are those which use passive techniques for cooling. Thus, passive cooling systems and strategies have achieved significant interest by designers and architects recently (Santamouris, 2007).
Moreover, the passive cooling of buildings is broadly categorized under three sections as shown in Figure 2 (Geetha & Velraj, 2012). The first stage focuses on designing a building that reduces and minimizes the energy needs by various factors, such as neighborhood planning, building layout and orientation. Generally, a building should be designed to be compatible to the climate of its region and its microclimate. Reducing the internal gains of the building is vital for improving the effect of passive cooling techniques. Site design and planning aspects are considered a key factor for reducing internal gains, as designing a site is influenced by many factors, for example; economic considerations, zoning regulation and adjacent developments. Controlling the solar radiation is the initial step towards heat gain protection (Yannas, 1990). Second, the following stage is concerned about modifying and modulating the gained heat, through the building envelope with all its components as windows, walls, roofs and shading elements. Managing a building thermally was mentioned previously to be an effective stage to reach energy reductions. The building envelope is the tool in achieving the heat modulation strategy, as it absorbs heat during the day and regulates the magnitude of indoor temperature, reduces peak cooling load and transfers a part of the absorbed heat to the night hours. Generally, it is responsible for minimizing heat loss in winter and heat gain in summer. At last, using the modulation and solar protection strategy in many cases may not achieve the full targeted thermal efficiency level. Therefore, the third stage concentrates on getting rid of the heat that enters the space using the upper atmosphere and the ambient sky by the natural processes of heat transfer. Dissipation of the excess heat depends on two main conditions: the availability of an appropriate environmental heat sink, and the establishment of an appropriate thermal coupling between the building and the sink combined with a sufficient temperature difference for this transfer of heat.
In other comparative climates as the hot humid climates, the application of passive measures and strategies for example, glazing, shading, insulation, and natural ventilation was highly effective in reducing the cooling load of buildings achieving 43% reductions (Omer, 2008). Therefore, applying of suitable passive strategies to Cairo's climate is expected to be highly effective and result a reduction in the energy consumption of the tested buildings.
3. Cairo's Case
3.1 Cairo's Climate
Köppen's climate classification sorted Egypt as a hot arid climate region. The allocated symbol for the climate of Egypt is BWh; where (B) refers to hot dry, while (W) specify that precipitation < ½ water consumption and letter (h) indicates that the average annual temperature exceeds 18°C as shown in Figure 3. Hot arid climates are specified by exceptionally hot dry summer, dry winters, and continuous sunshine for the whole year, and maximum temperatures of 45°C. (Henderson-
3.2 Local Case Study
The reference project for the experimental phase of this research was selected to be in the 5th settlement of New Cairo city as shown in Figure 5. The criteria for selecting this reference project is as follow:
As shown in Figure 7, the masterplan of the selected reference project consisting three zones of land plots ranging around 300 m2, the plots have different orientations in all the orientation axes. The four main axes had the higher percentages than the secondary axes, while land plots facing East axis orientation achieved the highest percentage across all the axes by 24.6%, and the lowest percentage was achieved by the South-
4.1 Parametric Simulation Structure
The research objectives shape and determine the suitable methodology that is necessary to achieve the experimental stage of the research. Moreover, the methodology of the study will be constructed in several stages. In other words, the study was conducted on a residential building in Cairo in a stepped parametric analysis. The study investigated the effect of several suitable passive cooling strategies selected referring to the climatic analysis of the location. Each strategy was investigated in a sequential process as shown in Figure 8. The evaluation of the whole process is through the achieved reduction in the cooling load. Additionally, a comparison between the base case and the final improved proposal in the terms of required cooling load will be conducted to show the effectivity of the applied strategies.
4.2 Reference Case Performance
Practically, a complete urban cell was modelled in Design-
Moreover, the simulation was conducted in the base case to determine the default cooling load and indoor air temperature to be used for the evaluation of the different studied strategies in the further stages of the research as shown in Chart 1 & Chart 2 respectively. Since that the last floor gets the highest solar radiation, it was used as a reference space for the air temperature examination. On one hand, it was found that Bedroom 1 in Unit B (BB1) has the highest indoor air temperature. On the other hand, the initial annual cooling load of the building is around 51,000 kWh.
4.3 Applied Strategies
In this part of the research all the determined strategies in the previous methodology of the research will be examined and its effect by itself will be determined and explained. Moreover, the heat control stage was neglected from the application stage, as the masterplan was already planned and executed.
The roof of the building is the most exposed building element to the direct solar gain. In contrast, the current roof construction is not insulated. The upgrading in the U-
The wall area of the building is the greatest among all the building enveloped components, therefore the wall type could have a great impact on the energy consumption of the building by the transfer of heat through it. In this part of the study, four wall types were investigated as alternatives for the exterior wall of the building as shown in Table 2. Finally, alternatives were compared with the base case wall which was a single red brick wall.
Glazing is responsible for nearly 30 % of energy loads of a building, and it has a large impact on the thermal comfort because of its effect on the indoor air temperature (Lechner, 2014). Therefore, single glazing in the windows was substituted with three other alternatives of glazing to investigate the effect of glazing on the required cooling load as in Table 3.
Many studies positively supported the impact and importance of shading elements on the heat gains in hot arid climates. After testing the shading configurations to achieve the optimum balance between adequate daylight inside most of the spaces and thermal performance, the simulation results and successful configurations were inputted to Design-
After the positive effect that was found by window shading in overcoming solar radiation, a shading surface will be utilized to overcome solar radiation affecting the building's roof. Not only improving the thermal performance, but also shading the roof gives the opportunity of utilizing the roof as a used outdoor space. However, insulation was utilized in the new alternative roof in the study, but on one hand, shading the roof could give more improvement. On the other hand, the simulation could conclude the higher effective strategy on the roof, the shading technique or the roof insulation. Thus, shading was introduced to the Design-
Night ventilation was reported to be an efficient cooling strategy in hot arid climates (AREE, 2011). It works by utilizing temperature differences in improving ventilation. In other words, cool night air is presented to the building replacing the indoor hot air. In consequence, a reduction in the mean radiant temperature of the space can be achieved, while by day, hot air is prevented from entering the building by changing window operation. (Geros, Santamouris, Karatasou, Tsangrassoulis, & Papanikolaou, 2005)
Therefore, night ventilation was investigated during summer in the study, and window operation schedule was created in design builder. Moreover, windows glass panels are closed from 8:00 to 20:00 in front the air flow, while keeping daylight entering. During the winter, heat resulting from occupants, light and electrical equipment's was used to improve internal spaces temperatures, besides closing the windows to sustain this heat. Moreover, sufficient ventilation rates were considered during the whole day.
Wind catchers is one of the oldest passive dissipation techniques used in residential buildings of high dense cities to drive fresh cool air inside the building directing it to living spaces, and louvers could be added to protect the interior of the building and volume control dampers are used to control the flow (Li & Mak, 2007).
Moreover, a cross-
Furthermore, wind catchers were modeled in Design Builder as shown in Figure 14, and zones were created as cavity zones, the exterior opening was created as a window operating using the same night schedule applied previously as all the windows. In addition, the wind catcher strategy was applied on all the living spaces, even the spaces that have windows directed to the north, as they enhance the chance of assembling air, as they are higher than surrounding buildings.
5. Simulation Results
5.1 Effectivity of the Applied Strategies
In this part of the research the outcome of each strategy will be explained through its effect in reducing the cooling load of the building and analyzing its effect on the different units or levels of the building.
In the heat modulation stage, EPS roof insulation with thickness 5 cm was applied to the building, which improved the U-
While in the heat dissipation stage, night ventilation was utilized by assigning a window schedule that closes windows during midday peak external temperatures and operates during the night to cool the indoor environment. Internal temperatures were reduced and consequently the energy consumption decreased by 6.34%. During winter, the internal heat gains were sustained by closing windows, however appropriate ventilation rates were supplied. Cross ventilation was introduced after the new schedule of the windows, and cross ventilation was implemented by keeping doors open during opening windows to create an inner flow of air. Particularly, cross ventilation improved the energy efficiency by 3.44%. Improving ventilation in order to improve cooling was a target. Therefore, another ventilation strategy was introduced to improve the previous strategies by enhancing the flow of the cool air coming from the North direction through wind catchers. Moreover, the strategy improved the total energy performance by 4.073%.
Additionally, all the possible reductions of different applied passive strategies and remarks for improving performance were illustrated in Table 4. At the end, we can conclude that residential development in climatic conditions of Cairo is a great opportunity to adopt energy efficient practices to form energy efficient and sustainable communities.
5.2 Total Reduction
In general, the results of the simulation carried out in this research revealed the great potential of utilizing energy efficient practices in Cairo. In addition, these energy efficient practices were proposed in this study through passive strategies and techniques, which massively improved the energy efficiency of the studied residential building. Moreover, the total energy consumption for cooling of the building decreased by 54.8% as shown in Chart 3. To conclude, the achieved energy savings provide an example of the possible energy reductions that could be accomplished in the future built environments. Chart 4. presents a comparison of the initial buildings internal temperatures and the final modified version proposed for summer months of Bedroom 1 of B unit (BB1), which shows that highest recorded internal temperatures was improved and deviated towards thermal comfort ranges.
Referring to the objective of the research, the aim was to define passive cooling strategies concerning about their characteristics, classifications and typologies. Consequently, the literature review of this study included a list of basic principles in passive cooling building design and different techniques. Furthermore, different applications of passive strategies were studied in diverse climatic conditions through multiple international experiences. Moreover, investigating the efficiency and potential of applying passive cooling strategies in the local climate of Cairo shaped the research methodology. Therefore, out of numerous passive design strategies and techniques that were discussed in the theoretical framework, selection of the suitable and appropriate strategies and techniques with the climatic conditions of Cairo to be applied. The study was carried out through different stages revealing several findings as the following; first, the research revealed that passive cooling strategies could have high potential in reducing the energy consumption levels of residential buildings in Cairo, reaching a 54.8% cooling load reduction of the building. Second, effects of different strategies were revealed and discussed to support users and stakeholders with a guideline for applying these strategies. Finally, the recommendations and a discussion on why passive strategies are abandoned nowadays will be discoursed in the following section in brief.
Passive design features showed to be highly effective in achieving energy efficiency in buildings. Thus, it would be expected that these strategies are widely used and practiced in Cairo's urban development, but in the real time it is rarely utilized in Egypt. Therefore, a question could be proposed "why isn't passive design applied widely?" Based on the different experience, few reasons will be proposed and different involved roles will be pointed out to identify the barriers.
First reason that could have affected the application of passive strategies or energy efficient practices is the non-
Another reason is formed by the building owner, as they could play a key role in overcoming the energy crisis, but in reality, owners are interested in maximum profits through low construction standards and costs coupled with maximum utilization of the land plot. Therefore, awareness should be widely used to develop their knowledge about the importance of adopting these strategies and the economic benefits for them. As a conclusion, further studies could be conducted and the research introduces these recommendations:
At last, it is important to closely examine and implement passive design strategies, as they could be modified to be adapted to today's buildings. Passive strategies were developed by many generations of architects and builders; therefore, we should not abandon using these strategies.
AREE., 2011. Aqaba Residence Energy Efficiency, the Center for the Study of the Built Environment (CSBE) October.
Atwa, M., 2016. Architectural design with environmental solutions as a scope for sustainability. Master thesis, Al-
Brown, M., 1990. The thermal mass of buildings in reducing energy consumption. Solar Energy Eng, 112, pp.273-
Cheung, C.K., Fuller, R.J. and Luther, M.B., 2005. Energy-
CIAO, C. I., 2015. Climate Consultant Software Database 6.0. California, USA.
Egyptian Electricity Holding Company, 2015. Annual Report. Online.
El Araby, M., 2002. Urban growth and environmental degradation: The case of Cairo, Egypt. Cities, 19(6), pp.389-
Emmerich, S.J., Dols, W.S. and Axley, J.W., 2001. Natural ventilation review and plan for design and analysis tools. US Department of Commerce, Technology Administration, National Institute of Standards and Technology.
Geetha, N.B. and Velraj, R., 2012. Passive cooling methods for energy efficient buildings with and without thermal energy storage-
Georgy, R.Y. and Soliman, A.T., 2007. Energy Efficiency and Renewable Energy: Egypt National Study. Plan Bleu, march.
Geros, V., Santamouris, M., Karatasou, S., Tsangrassoulis, A. and Papanikolaou, N., 2005. On the cooling potential of night ventilation techniques in the urban environment. Energy and Buildings, 37(3), pp.243-
Lechner, N., 2014. Heating, cooling, lighting: Sustainable design methods for architects. John wiley & sons.
Li, L. and Mak, C.M., 2007. The assessment of the performance of a windcatcher system using computational fluid dynamics. Building and environment, 42(3), pp.1135-
Maile, T., Fischer, M. and Bazjanac, V., 2007. Building energy performance simulation tools-
Manio?lu, G. and Y?lmaz, Z., 2006. Economic evaluation of the building envelope and operation period of heating system in terms of thermal comfort. Energy and Buildings, 38(3), pp.266-
Mikler, V., Bicol, A., Breisnes, B. and Labrie, M., 2008. Passive Design Toolkit: Best Practices. City of Vancouver.
Mourtada A., 2009. National consultation on Egypt's policies for energy efficiency in buildings in Egypt: energy efficiency codes in the policy mix. JCEE. MEDENEC.Cairo
Omer, A.M., 2008. Energy, environment and sustainable development. Renewable and sustainable energy reviews, 12(9), pp.2265-
Omer, A.M., 2008. Renewable building energy systems and passive human comfort solutions. Renewable and sustainable energy reviews, 12(6), pp.1562-
Santamouris, M., 2007. Advances in passive cooling. Earthscan.
Yannas, S., 1990. Solar control techniques. In Proc. Workshop on passive cooling, Aranovich E, Oliveria Fernandes E, Steemers TC (eds.), Ispra, Italy, April, pp. 75-
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