Climate Change scenarios effects on residential ...

Building Simulation Cairo 2013 - Towards Sustainable & Green Built Environment, Cairo, June 23 rd - 24

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Topic name: Climate Change and Architecture

Climate Change scenarios effects on residential buildings shading strategies in Egypt Mohamed M. Mahdy1,2,*, Marialena Nikolopoulou1and Mohammad Fahmy2 1

Centre for Architecture and Sustainable Environment, Kent School of Architecture, University of Kent, UK. 2 Department of Architecture, Military Technical Collage, Cairo, Egypt. * Corresponding author. [email protected],

Abstract: As a vital method for mitigating the solar radiation effect on buildings, shading is considered of paramount importance, especially in Egypt as a hot arid climate country, with very high solar radiation intensity most of the year. Hence, the importance of studying shading strategies against future climate change emerged. After IPCC recent reports and conference in Doha 2012, the climate change physical concept is getting more scientific understanding as "most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations". Therefore, current practice of construction industry in Egypt needs to consider passive architectural design for residential buildings, which consume about 20% of the energy consumed in the built environment, and emit about 4% of CO2. So, this paper investigates the effect of climate change on shading, which is one of the most effective passive design techniques, as well as on the energy consumption to support both policy and decision makers taking steps forward towards energy efficiency obligations. To attain that, an HVAC case study building is dynamically simulated in three dominant Egyptian climatic zones, using current climate conditions in addition to three other morphed climate change scenarios (2020, 2050 and 2080). A comparison is then held in the four different periods with and without the Egyptian Residential Energy Code (EREC) recommended shading parameters. The results show a minor effect for the future climate change on the efficiency of the current shading strategies that are approved and recommended by EREC, which confirms the effectiveness of using the existing shading specifications in future climatic conditions. Keywords: Passive Architecture, Shading techniques, Energy Consumption, climate change.

1. Introduction 1.1. Background The sun is having a strong and direct impact on human life, as it is the origin for all kinds of energy sources on Earth [1]. But it's like a coin, the first face is the positive which is to take advantage of the solar energy used for different purposes, and the second face is negative represented in the overheating in some regions of the world. The solar radiation that reaches the Earth is estimated by about 50% of its original strength [1, 2], as shown in Fig. 1, and it consists of the outcome of direct solar radiation, reflected radiation from the surface of the earth and clouds and the rays absorbed by the atmosphere [1]. The building envelope can be considered the selective pathway for a building to work

Figure 1: Rates of solar energy that is reflected and absorbed by the Earth.[2]

with the climate, responding to heating, cooling, ventilating, and natural lighting needs [3]. As the building envelope controls the flow of heat between outdoor and indoor environments [4], a good envelope design can show optimization between natural lighting and thermal performance through passive solar techniques [5, 6]. Among envelope elements, openings provide

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Building Simulao n Cairo 2013 - Towards Sustainable & Green Built Environment, Cairo, June 23 - 24

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Topic name: Climate Change & Architecture

physical access to the building, create views to the outside, admit daylight or solar energy for heating, and supply natural ventilation [4]. It is also considered the main source of heat penetrating inside the building, as shown in Fig. 2 (penetrating varies by the type of glass and by its specifications as transparency and purity grade) [1, 7, 8].

solar altitude is generally so low that to be effective, horizontal layouts would have to be excessively long [10]. In these cases, a good solution could be the use of vertical fins [1]. Among the most important factors in determining the behaviour of the occupant is the thermal and daylighting requirements [15]. Hence, the shading systems have to provide thermal and visual comfort both reliably and economically in summer and in winter, Fig. 3 and 4 [10, 15].

Fig. 2:The difference in the rate of heat permeability through various building envelope components[1, 9]

Therefore, the most effective way to reduce the solar load on fenestration is to intercept direct sun radiation before it reaches the glass [8, 10] to control the indoor temperature, improve thermal comfort and reduce cooling loads [11-13] as fully shaded openings during hot weather can reduce solar heat gain by as much as 80% [4, 10, 11]. A considerable amount of literature has been published on shading devices, a previous study on a high-rise residential building in Taiwan [11] indicated that envelope shading is the best strategy to decrease cooling energy consumption, which achieved savings of 11.3% on electricity consumption. Another study [14] showed that power consumption readings from direct air conditioning indicate an average savings of 25% if external shading is properly installed. In the northern hemisphere, due to solar incidence angles, horizontal louvers can considerably reduce solar heat gain on south, southeast and southwest exposures, during late spring, summer, and early fall. On east and west exposures, during the entire year, the

Figure 3: User requirements for sun-shading systems.[15]

Figure 4: Day lighting and thermal requirements for sun-shading systems.[15]

1.2. Main purpose In previous eras, architects were designing based on the premise of unchanging climate, which means that, the building that provides thermal comfort at the beginning of its establishment is supposed to continue the same level of performance in the future until the end of its useful life. This assumption is no longer valid. It is becoming increasingly difficult to ignore

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the element of global climate change, as evidenced by the reports of the International Panel on Climate Change [16]. The hours of sunshine and the proportion of direct radiation to diffused radiation are projected to increase in the future, while the modeling studies demonstrate a steady increase in cooling capacity and associated energy consumption required [17]. Therefore, the need to minimize overheating will become an increasing factor in design, and the ability to maintain acceptable internal thermal comfort will determine whether to demolish or refurbish the existing buildings. For that reason, it is even more critical for the designers to simulate the performance of buildings under future climatic conditions, to provide an indication of the future thermal behavior of the building and its ability to provide acceptable conditions, perhaps with some modifications during their service life [17]. The main objective of the present study is to evaluate the effectiveness of the current EREC recommended shading parameters under the future climate change conditions. The authors have conducted earlier experiments on the effect of climate change on different components of the building envelope and published results in [18, 19] for the study of external wall specifications. This work extends our earlier experiments by studying the shading as one of the main elements that affect the inner thermal comfort. In order to achieve our objective, a computerized simulation tool (DesignBuilder) is used to carry out investigations on the effect of shading devices on three different parameters: Monthly Energy Consumption (kWh), Indoor Air Temperature (°C) and Solar Gain from exterior windows (kWh). A typical residential building with mechanical air conditioning (HVAC) installed, was used for the simulations. The thermal performance simulations taking place in the summer period, in three main Egyptian climatic zones defined in the

Egyptian Residential Energy Code (EREC) [20]. These include Cairo and Delta, the North coast, and the Southern climatic zone. These simulations ran under the current climate conditions, and under different climate change scenarios of three periods: 2020, 2050 and 2080. 2. Simulation Methodology To carry out the simulations, a model of a typical residential building in Cairo was employed, which is then tested in the three different climatic zones, while keeping the same orientation of the building in each one of the climatic zones. The following points define the building envelope configurations of the case study: 2.1. General specifications 2.1.1. The Model Definition The building consists of six floors, where each has four residential flats with an approximate area of 80 m2. The average number of occupants per flat is four. The building floor plan is shown in Fig.5.

Figure 5: Typical plan for the Modeled flat.

2.1.2. External Wall Specifications The specifications for wall constructions used are presented in Table 1. The thermal properties for the construction materials were obtained from EREC [20], and the

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Egyptian Specifications for Insulation Work Items [21].

Thermal

Appropriate materials were used for the construction in the different three climatic zones evaluated in the simulations, according to the authors research [19], which recommended the use of the double wall of half red-brick with 5 cm of internal expanded polystyrene thermal insulation layer (Dins) wall as the optimum external wall in Aswan, and the use of the double wall of half red-brick with 5 cm air gap in between (Dair) wall for Alexandria and Cairo, as shown in Fig.6. These are the optimum specifications shown to achieve indoor thermal comfort, minimize the energy consumption, while attaining the maximum financial benefits on a 40-year period, which would make them a more appealing option for occupants, justifying their higher initial cost.

These three climatic zones are: (1) Cairo and Delta zone (Cairo governorate), (2) North coast zone (Alexandria governorate) and (3) the Southern zone (Aswan governorate). About 50% of the construction projects carried out in Egypt are located in Cairo and Alexandria governorates [22]. While Aswan governorate is considered a very different zone in terms of the climatic aspects compared to the other zones.

Table 1: External Walls main characteristics. External Walls

ABBRV.

Thick. (cm)

U-Value (W/m2K)

Double wall of half redbrick with 5 cm air gap in between.

Dair

29

1.463

Double wall of half redbrick with additional internal 5 cm of expanded polystyrene thermal insulation layer.

Figure 7: Egypt's climatic zones map[20].

2.1.4. Weather Data Files Dins

29

0.503

Figure 6: Wall sections used.

2.1.3. Climatic Zones The paper will focus on the main three (of the eight) Egyptian climatic zones (shown in Fig. 7 defined in the Egyptian Residential Energy Code (EREC) [20].

Four different weather data files: 2002, 2020, 2050 and 2080 were used in the simulations. The current weather data file (2002) was downloaded from the official site of the U.S Department of Energy [23]. The Climate Change World Weather File Generator (CCWorldWeatherGen) [24] was used to generate the future weather data files for 2020, 2050 and 2080, and they cover the periods 2010-2039, 2040-2069 and 2070-2099 respectively [25]. CCWorldWeatherGen [24], is a Microsoft Excel based tool, generating climate change weather data files, which can be used in BPS programs by transforming current Energy Plus Weather files (EPW) into climate change EPW files that are compatible with the majority of BPS programs [26].

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2.1.5. Building Performance Simulation Software (BPS): Modelling and simulations were carried out using the dynamic thermal simulations tool, DesignBuilder [27] in its third version (V3). 2.1.6. Activities and HVAC Systems A fixed activity template, which defines the schedule for energy consumption based on the lifestyle in Egypt (holidays, working hours) was used in simulations to obtain the total energy consumption in kWh from house appliances, lighting and the HVAC systems. The HVAC specifications include the split air-conditioning units that are generally used for domestic purposes in Egypt. The HVAC systems were the only focus in this experiments, as according to our previous study [18] natural ventilation was not sufficient to achieve thermal comfort in the summer period; under the same experimental conditions in Cairo. 2.2. Shading parameters The EREC recommendations (Annex A-3) [20] were taken as a guideline and followed literally in the preparation of the shading devices concerned in this study.

Figure 8: Solar analysis of the model used in Alexandria.

Figure 10: Solar analysis of the model used in Aswan.

The different external shading treatments for the building model in each climatic zone (Alexandria, Cairo and Aswan) are shown in Figures 8, 9 and 10 respectively. 2.2.1. Window, Wall Ratio (WWR) WWR is the ratio between the areas of the openings in an external façade to the total area of this façade [20], The openings appropriate ratios are chosen to achieve lighting levels that ensure a healthy life, visual and psychological comfort to the occupants, and lights up the inner space and its contents properly to fit the nature of the activity within the space and help to perform it efficiently [1, 28], however at the same time achieve privacy in addition to meeting the requirements of EREC [20] in terms of Solar Heat Gain Coefficient (SHGC) and Shaded Glass Ratio (SGR), according to the climatic zone of the building and the direction of the openings, to prevent the penetration of excess quantities of heat which would increase the thermal loads on the inner space. The first step was to calculate the proportion of the fenestration area to the total façade area. Table 2 shows the WWR for the different elevations of the typical residential building used. Table 2: WWR for different façades.

Figure 9: Solar analysis of the model used in Cairo .

Elevation

Openings (m2)

Elevation (m2)

WWR (%)

North East South

69.6 39.6 69.6

445 328 445

15.6 12 15.6

West

39.6

328

12

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Table 3: Solar specifications for the simulated building. Alexandria

Cairo

Aswan

East

South

West

East

South

West

East

South

West

SHGC

0.55

0.71

0.55

0.45

0.64

0.45

0.34

0.52

0.34

Verify SHGC

No

Yes

No

No

No

No

No

No

No

SGR

65%

-

65%

70%

60%

70%

75%

60%

75%

Vertical

-

Vertical

Vertical

Horz.

Vertical

Vertical

Horz.

Vertical

PF

0.80

-

1

0.80

0.40

1

1

0.40

1

Dimensions

1m

-

1.3m

1m

0.5m

1.3m

1.3m

0.5m

1.3m

Sun-breaker

2.2.2. Solar Heat Gain Coefficient (SHGC) SHGC is the ratio between the sum of penetrated solar radiation through glass, and the heat emitted from the glass by convection and radiation, to the incident total solar radiation on the glass surface [20]. Specifying the value of Solar Heat Gain Coefficient (SHGS) for the openings was the second step (using Table B1/ Annex B) [20], according to the type of glass and frame used, and whether fixed or movable. Single clear (6.4 mm) glass with a moving aluminum frame was used in the simulated building, which leads to SHGC of 0.71. 2.2.3. The maximum allowable SHGC Using Tables 3-2, 3-4 and 3-16 mentioned in EREC [20], and according to the building orientation and WWR, the maximum allowable SHGC values were obtained for each façade, then listed in Table 3. 2.2.4. Verifying SHGC compatibility with EREC requirements Verifying that value of SHGC does not exceed the maximum allowed in EREC, otherwise the openings are not compatible with the requirements of the code; in this case EREC recommends one of the following three methods: Reduce the size of the openings, so that it achieves allowable SHGC. Improve the properties of used glass or change the frame. Use shading for the openings partially or fully, using one of the external shading means.

The results of this comparison mentioned in Table 3. As our objective was to evaluate the effect of the external shading, the third choice was used in all simulations. 2.2.5. Shaded Glass Ratio (SGR) SGR is the ratio between the shaded glass areas to the total area of the opening during the period from 9:00 am to 5:00 pm on 21st of September [20]. The SGR coefficient can be determined with help of Table 2B/ Annex B [20], and Tables 3-2, 3-4 and 3-16 for the horizontal, vertical and combined sun-breakers in the three aforementioned climatic zones. The SGR factor calculation is subject to the façade orientation and to the sun-breaker Prominence Factor (PF) as shown in Fig. 11 and 12, where: PF= W/ (A+B) Where; A is the opening width or height, W is the sun-breaker depth and B is the distance between opening and the sunbreaker. Using this equation, the sunbreakers dimensions can be determined, as mentioned in Table 3.

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Figure 11:Vertical Sun-breakers.

Figure 12:Horizontal Sun-breakers.

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Table 4: Average Monthly Energy Consumption (kWh) (with and without using shading devices) 2002

2020

2050

2080

without shading

with the without with the without shading difference shading shading difference shading

with the without shading difference shading

with the shading difference

May

433.06

428.81

4.25

482.23 477.79

4.44

539.33

534.62

4.71

654.43

649.42

5.01

June

574.98

570.72

4.26

628.83 624.77

4.06

708.02

703.80

4.22

843.09

838.67

4.42

July

656.17

651.33

4.84

755.92 750.99

4.93

888.33

883.33

4.99

1060.84 1055.31

5.53

August 705.44

698.78

6.66

835.22 828.30

6.91

958.53

951.46

7.08

1146.21 1138.96

7.25

521.83

509.00

12.83

608.29 595.69

12.60

689.41

676.67

12.74

871.61

12.80

Sept.

858.81

Table 5: Average Monthly Indoor Air Temperature (°C) (with and without using shading devices) 2002

2020

2050

2080

without shading




May

25.83

25.77

0.05

26.17

26.12

0.05

26.47

26.43

0.04

27.00

26.96

0.04

June

26.79

26.75

0.03

27.01

26.98

0.03

27.33

27.30

0.03

27.85

27.82

0.03

July

27.15

27.11

0.04

27.49

27.45

0.03

27.90

27.87

0.03

28.52

28.48

0.03

August 27.22

27.17

0.05

27.62

27.56

0.05

27.99

27.94

0.05

28.74

28.68

0.05

26.72

26.62

0.10

27.08

26.98

0.10

27.37

27.27

0.10

27.97

27.88

0.10

Sept.

Table 6: Shading effect on solar gains from exterior windows. (kWh) 2002

2020

2050

2080

without shading




May

172.04

158.97

13.06

165.19 152.43

12.76

165.56

152.80

12.76

165.64

152.88

12.76

June

169.77

156.76

13.01

162.25 150.03

12.22

161.40

149.15

12.25

161.40

149.15

12.25

July

167.14

153.84

13.30

157.34 144.94

12.41

156.23

143.71

12.51

156.32

143.82

12.50

August 164.10

146.40

17.71

155.81 138.71

17.10

154.15

137.12

17.03

154.83

137.77

17.06

174.01

137.93

36.09

169.29 134.09

35.20

167.64

132.95

34.68

167.66

132.97

34.69

Sept.

Figure 13: Shading devices effect in reducing exterior window's solar gains

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3. Results and Discussion The results show the effect of using shading devices on three different outcomes: Monthly Energy Consumption (kWh), Indoor Air Temperature (°C) and Solar Gains from exterior windows (kWh). These measures were taken during the summer period for the three climatic zones, under different weather scenarios. The results are almost with the same indications, so the results for the Cairo and Delta climatic zone (as the intermediate zone), were discussed and its results were displayed as a representative for the two other zones, as follows: 3.1. Monthly Energy Consumption Energy consumption was calculated for each flat per month during the summer period, with and without the external shaded devices obtained from EREC, Table 4. As noticed, the effect of using EREC recommended shading devices is almost identical during the different four weather periods that was simulated in this research. For example during July the differences for the various climatic scenarios were 4.84, 4.93, 4.99 and 5.53 kWh respectively. 3.2. Indoor Air Temperature The indoor air temperatures were investigated during the hot period in Egypt for the different climatic zones, through the aforementioned weather periods, by calculating the difference in the internal temperatures while using the external not used. shading devices, and in case The stability of the effect of using sun breakers (Table 5) has been observed, during the various climatic scenarios used in the simulations, and as an example, in the month of July, the shading effect on reducing the indoor air temperature while using the HVAC systems, for the different four weather periods were mentioned as 0.04, 0.03, 0.03 and 0.03 °C consecutively. 3.3. Solar Gains from exterior windows For further verification, the solar gains from exterior windows were extracted as one of

the simulation results, to find out the amount of solar radiation that have been blocked by the use of different sun breakers recommended by EREC. Table 6 shows the solar gains from exterior windows in the different months that have been simulated, using different weather data files. Comparing the effect of using shading devices namely (the difference) over the different climate change scenarios, illustrate the firmness of the effect of using the recommended sun breakers over the various parameters of the experiments, as the average blocked solar radiation values over July are 13.30 kWh for the current weather conditions, 12.41 kWh for 2020 weather data file, 12.51 kWh for 2050 climate change scenario and 12.50 kWh for the predicted weather in 2080. This is almost constant, despite the projected climate change. Complementary to the above, Fig. 13 illustrates graphically the effect of sun breakers for all the weather periods, to illustrate the differences between what obscured by sun breakers at present, and the stability of its effect under the impact of various climate change scenarios in the future. 4. Conclusion Passive architecture techniques have a noticeable impact on improving the thermal performance of residential buildings, particularly in hot arid zones like Egypt. In this paper, the constancy of the impact of shading devices recommended by EREC were discussed, on buildings in three different climatic zones in Egypt, under the influence of present and future climatic conditions (three sets of future weather data files). The analysis of three of the main parameters of the simulation results (monthly energy consumption, indoor air temperature and solar gains from exterior windows) suggest that, the effect of solar shading devices approved by EREC is almost constant under the influence of climate change scenarios, its efficiency and effectiveness will be ongoing as they are in

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the future, where the solar radiation's incidence angles (which affects the prominence factor of the shading devices) does not seem to be affected by the future climate change. However, this passive adaptation to climate change on the building scale might be more effective if comprehensive applications of passive techniques took place rather than only shading windows, or wall construction as we discussed partially before. This comprehensive orientation will be our future research objective. References [1] Shafaq El-Wakeel, M.S., Climate and Tropical Architecture. 1989, Cairo: Alem Al Kutob. 324. [2] Daniel B. Botkin, E.A.K., Environmental Science, Earth as a Living Planet. 2011. [3] USDoE, U.S.D.o.E.-. Energy Efficiency and Renewable Energy: Building Envelope. 2004 [cited; Available from: www.eere.energy.gov. [4] Okba, E.M., Building Envelope Design as a Passive Cooling Technique in Passive and Low Energy Cooling for the Built Environment. 2005: Santorini, Greece [5] Makram, A.A.S., Sustainable Architecture as an Approach for Hospitals Design in Architecture. 2008, Alexandria university: Alexandria. p. 253. [6] Azizah Kassim, H.B., Energy Efficiency Opportunities for Government Hospitals. 2003, report prepared under the Malaysian, Danish environmental cooperation program. [7] Datta, G., Louver Shading Devices on Thermal Perfomance of Building by Trnsys Simulation. Renewable Energy, 2001. 23: p. 497 507. [8] Offiong, A. and A.U. Ukpoho, External Window Shading Treatment Effects on Internal Environmental Temperature of Buildings. Renewable Energy, 2004. 29(14): p. 2153-2165.

[9] Khudari, H.A.W., The Impact of Form on Energy Savings - a Study of Hospital Buildings in Egypt, in Architecture. 2001, Cairo University: Cairo. [10] Palmero-Marrero, A.I. and A.C. Oliveira, Effect of Louver Shading Devices on Building Energy Requirements. Applied Energy, 2010. 87(6): p. 2040-2049. [11] Al-Tamimi, N.A.F., Sharifah Fairuz Syed, The Potential of Shading Devices for Temperature Reduction in HighRise Residential Buildings in the Tropics. Procedia Engineering, 2011. 21: p. 273-282. [12] Vincenzo Corrado, V.S., Andrea Vosilla, Performance Analysis of External Shading Devices, in Plea2004 - The 21th Conference on Passive and Low Energy Architecture. 2004: Eindhoven, The Netherlands. [13] Radhi, H., A. Eltrapolsi, and S. Sharples, Will Energy Regulations in the Gulf States Make Buildings More Comfortable - a Scoping Study of Residential Buildings. Applied Energy, 2009. 86(12): p. 2531-2539. [14] Yang, K.H. and R.L. Hwang, Energy Conservation of Buildings in Taiwan. Pattern Recognition, 1995. 28(10): p. 1483-1491. [15] Kuhn, T.E., C. Bühler, and W.J. Platzer, Evaluation of Overheating Protection with Sun-Shading Systems. Solar Energy, 2001. 69, Supplement 6(0): p. 59-74. [16] IPCC, I.P.o.C.C.-. Fourth Assessment Report of the Ipcc. 2007: Cambridge. [17] Levermore, G.J., Courtney, R., Watkins, R., Cheung, H., Parkinson, J.B., Laycock, P., Natarajan, S., Nikolopoulou, M., McGilligan, C., Muneer, T., Tham, Y., Underwood, C.P., Edge, J.S., Du, H., Sharples, S., Kang, J., Barclay, M. and Sanderson, M., Deriving and Using Future Weather Data for Building Design from Uk Climate Change Projections an Overview of the Copse Project.

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2012, Manchester University: Manchester, UK. [18] Mohamed Mahdy, M.N., From Construction to Operation: Achieving Indoor Thermal Comfort via Altering External Walls Specifications in Egypt in International Conference on Green Buildings Technologies and Materials (GBTM). 2012: China. [19] Mohamed Mahdy, M.N., The Cost of Achieving Thermal Comfort Via Altering External Walls Specifications in Egypt; from Construction to Operation through Different Climate Change Scenarios, in Building Simulation 2013: France. [20] Centre, H.a.B.N.R., Egyptian Code for Improving the Efficiency of Energy Use in Buildings, Part 1: Residential Buildings (306/1). in ECP 305-2005 U.a.U.D.-E. Ministry of Housing, Editor. 2008: Cairo - Egypt. [21] Centre, H.a.B.N.R., The Egyptian Specifications for Thermal Insulation Work Items, in 176/1998, U.a.U.D.-E. Ministry of Housing, Editor. 2007: Cairo - Egypt. [22] Joe Huang, L.B., and others, The Development of Residential and Commercial Building Energy Standards for Egypt, in Energy conservation in buildings workshop 2003. [23] USDoE, U.S.D.o.E.-. Weather Data. 2012 [cited; Available from: http://apps1.eere.energy.gov/buildings/ energyplus/weatherdata_about.cfm. [24] Group, S.E.R. Climate Change World Weather File Generator. 2012 [cited; Available from: http://www.serg.soton.ac.uk/ccworldwe athergen/. [25] H Du, C.U.a.J.E., Generating Design Reference Years from the Ukcp09 Projections and Their Application to Future Air-Conditioning Loads. Building Services Engineering Research and Technology, 2012. 33(1): p. 63-79.

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