Passive office in a hot dry climate

Contents 1. Introduction 1.1. Climate and Context 1.2. Site Plan 2. Literature Review 3. Improved Design 3.1. South Block 3.1.1. Windcatcher 3.1.2. Chilled Ceiling 3.1.3. Solar Chimney 3.1.4. Trombe Wall 3.1.5. Sun Shading 3.2. Site 4. Energy Characteristic 5. Ventilation Characteristic 6. Conclusions 7. Recommendations for public buildings 8. Appendices 9. References 10. List of figures

03 03 03 04 06 06 07 07 07 07 07 09 10 11 12 13 14 16 17

exit from the two possible outlets, south-east and southwest corner. The wind blows over a large water body and is sufficiently cooled, requiring no further cooling for the building. Other suggestions were to plan the building underground to take advantage of constant temperature of the ground, plant trees around for shading as well as evaporative cooling. Use of shaded courtyards, narrow opening in the south and west, maximizing views towards the north etc.

Introduction 1.1 Climate and Context Cairo, Egypt, located in the hot arid zone of the northern African continent, is the capital of the country with a rich and diverse history. The city is an oasis in a vast expanse of sandy desert stretching in all directions. In a previous study the climate of the place was studied in detail with the architectural interventions by the people of the place to make their lives comfortable and beat the hot summer sun.

1.2 Site Plan To recapitulate the proposal, the site consists of 3 office blocks, each further constructed from two base geometries. The base configuration has been predefined for the study, specified in figure 02.

The city is located at 30°N latitude and according to Köppen climate classification [1], belongs to the hot desert climate (BWh) with the annual precipitation less than 50% of the threshold. The altitude of the place is also low, signified by the h in the classification, which is 23m above M.S.L. The key points from the previous study was that the site has prevalent winds from the north for more than 30% of the time, mostly during summer months, and at a speed of average 3m/s. The hottest months are from May to October with the highest reaching in July and August.

The maximum solar heat gain is from the south-west quadrant when the sun has reached its afternoon low position and the temperature has reached the peak.

Image 01 shows the sunpath overlaid with temperature at that time.

Figure 2: Proportion of the base geometry

The blocks are placed around a central triangular courtyard, depressed by one level. The configuration ensures shading and light breezes in the area, further, a wind catcher along with shading umbrellas assist in this regard. Green patch of grass surrounds the blocks, and avenues of palm trees are located on western side.

These trees help shade the building and prevent excessive heat gain. Also, a recreational area exists on the western side, filled with shading trees and umbrellas.

Above the courtyard is network of shaded pathways which connect all three blocks together, and a central lift goes down to the basement parking. Two units, of each block, face each other, and have a small courtyard in the center. This has been done to ensure that open spaces are not exposed to direct sun. The back sides of these blocks have bare surfaces to prevent heat gain from windows. The detailed design is explained in the following pages.

Figure 1: Sunpath of Cairo overlaid with temperature

The study suggested to avoid orienting the building in that direction and take necessary precaution, like shading, to prevent heat gain from south-west. The sun during those times varies from 80° altitude to 10° (measured from the horizon).

Further the study showed that the prevalent winds can be channelled and directed into the site, for outdoor thermal comfort of the people, by placing the blocks around the central courtyard. The wind is then drawn into the site and

(Refer to group report for the architectural drawings of the proposed site plan.)

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Figure 3: Proposed site plan

natural ventilation in the building due to chimney effect [4]. Solar rays pass the glass and are absorbed by absorbing wall surface to warm the air inside chimney.

Because of chimney effect, the air is warmed and contracted less which makes it move upward. This upward movement makes a drive force causing the air below to replace the solar chimney’s air [6]. Khedari et al [5] found that with solar chimney, room temperature reaches ambient temperature due to the natural ventilation created by solar chimney. It was concluded that solar chimneys reduce the daily consumption of electricity in HVAC system.

Literature Review There is a growing awareness regarding the need to reduce energy consumption and to improve indoor environment quality [2]. Consequently, various strategies and measures have been discovered and improved over the years to reduce the impact of buildings on the environment. To maintain thermal comfort, the employed mechanism can be divided broadly into two categories: active and passive mechanism.

Passive design responds to local climate and site conditions in order to maximise the comfort and health of building users while minimising energy use. Passive cooling refers to any technologies or design features adopted to reduce the temperature of buildings without the need for power consumption [3].

In hot climates, it is a common practice to have thick walls to prevent heat gain and high variation in diurnal range of temperatures. This serves as an advantage since the very same thermal mass can be modified and driven as a solar chimney. The magic material is glass, which heats up the air inside. A special type of solar chimney called a trombe wall, uses this concept. It can function well for both cold and hot climate depending upon how air is allowed to flow.

Amongst the many strategies the significant ones which have been used in this design are the following- a. Solar chimney, b. Evaporative cooling, c. Trombe wall, d. Wind driven controlled ventilation, e. Insulated walls, f. Thermal massing, g. Low-e double glazing, h. Mesh covered glazing (shaded), i. Green roofing, j. Natural daylight, k.

Orientation, l. High solar reflecting surface, m. Chilled ceiling.

Thermal mass is an essential component of a passive solar design to store heat [18]. By converting solar energy into its own molecular motion, a massive material allows indoor air to remain cooler during solar gain; later, when outdoor temperatures drop, the mass returns some of its

Solar chimney is a thermosyphon solar inactive system which improves the indoor air quality by enhancing 4

energy to the space through radiation and convection [18]. This

coefficient of the window, since then conduction and/or convective heat transfer medium is reduced.

J Mathur et el [7] concluded that there is a potential of inducing ventilation corresponding to 55–150 m3/h airflow rate for 300– 700W/m2 solar radiation incident on the vertical surface. Further it increases with increase in the gap between absorber and glass cover. Other studies have also shown the relation with stack height, inlet and outlet vent dimension.

Rubin [16] determined that the overall thermal conductance for a double-glazing window with clear glass will have an approximate value of 3 W/m2K and if a solar control film of plastic (polyester film) adheres on one of the glasses this value is reduced to 2 W/m2K. Álvarez et al. [17] concluded that the glass with a solar control film increases its temperature, but reduces the energy passing through it by 30% towards the interior of the cavity. In their experimental setup the indoor temperature was at 24°C while on the outside it was 32°C. We can safely assume that using of low-e double glazing will significantly reduce thermal gain. Other mechanisms such shading, deep-set windows, narrow opening etc will reduces the impact by preventing direct access to sun.

Another important strategy applied on the site is evaporative cooling. which is a common process in nature and its applications for cooling the air are being used since the ancient years [8]. Evaporative cooling is a process of heat and mass transfer based on the transformation of sensible heat into latent one. The nonsaturated air reduces its temperature, providing the sensible heat that transforms into latent heat to evaporate the water [9].

The Harappan Civilization, and the people following them in the Vedic age used to have a courtyard with trees inside to assist in cooling. The use of green cover for cooling for quite possibly known to them. A Japanese experiment confirmed this when it was observed that the surface temperature of the roof slab decreased from 60°C to 30°C during the day, by which a 50% reduction in heat flux into the room could be expected [19]. There have been other experiments to show the effect of different species of plants on the heat gain of the building.

Wind as a free driving force is one of the important renewable energy [10]. One of the natural ventilation devices, neglected in current building industry, is the windcatcher or wind tower system [11]. Windcatcher is an architectural feature mounted on the roof of a building which looks like a tower and brings in the fresh air from outside [12]. This technology captures the external wind and induces it into the building. It cools the inner part indirectly by removing the stored heat inside the building structure [11].

The layout of the design shall be like this; in the first part the individual block which is the most crucial, has been thoroughly redesigned based on the group findings.

Following which the principles have been applied to other blocks with specific tailoring. In the later part, energy and ventilation strategies have been tested for reference.

Some architectural drawings are presented in appendices for a clearer understanding of the design.

Kolokotroni et al. showed that windcatcher efficiency is altered by changing outdoor wind speed, changing temperature difference and changing the location and number of openings, like windows [13]. In a different experiment, it was observed that windcatchers are functional even in low speed wind locations [14].

Measuring temperature, relative humidity and airflow velocity, the research team found out even in a calm weather, windcatcher can bring thermal comfort for dwellings by inducing certain volume of air circulation [14].

Using the wind velocity in the indoor space, and knowing the temperature conditions, the heat loss due to ventilation can be calculated. Further, based on Fanger PMV model the percentage of dissatisfied occupants can be calculated. This method provides designers with an easy tool to find the effectiveness of the design.

Most of the heat gains or losses in a building are through the roofs and walls, mostly on walls with large windows or glazing which in some cases covers the whole facade.

Windows are responsible for a disproportionate amount of unwanted heat gain and heat loss between buildings and the environment [15]. It is a common knowledge that having multiple glazing reduces the solar heat gain 5

Improved Design 3.1 South Block The traditional architecture of Egypt spans for over a hundred years and has some awe-inspiring structures and buildings. They have also shown present generation some of the most efficient passive means of keeping the building cool. It will be a folly not to adopt the contextual style and methods in order to make the design efficient.

After all, context gives character and character gives identity.

The façade has been inspired by the great Fatimid mosque of al-Hākim bi Amr Allāh, in the old city of Qahera. The proposed design has a gallery of arches on the southern side of the building. They are carved in the thick thermal mass of 600mm. The primary aim of this brick layer is to stop solar heat gain and preventing high diurnal range of temperatures in the interior. The stored heat can be used to warm the place at nights, when the temperatures are low.

Figure 4: Wall construction

The building footprint has an area of 705m² and a total built-up area of 1441m². The gross office area being 1010m².

The key feature of the design is the use of solar chimney and wind catchers for ventilation, skylight and high windows for light, chilled ceiling for cooling and good thermal properties of the material to prevent high heat gain. PV panels are installed on the roof for generating electricity.

A layer of insulated wall follows next, which is the main wall type for this project. This insulated wall is essentially a sandwiched panel of brickwork, having been insulated on either side with rigid insulation. A finishing plaster coat is applied for architectural purposes as well as preventing the insulation form coming in contact with moisture.

Figure 5: South elevation

Figure 6: North elevation

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3.1.1 Windcatcher

Thus, the two systems work simultaneously to ventilate the indoor space. The eastern chimney work well in the morning time when the sun due east, while the other side works even better because it faces the hot afternoon sun.

To drive the wind into the building, the two towers have wind scoops and the main linear block has a curved roof on top. The curvature and the incline of the roof, force the wind into the building through the openings in the extended wall. A central duct goes all the way to the ground floor, which is also ventilated naturally. Water from the local lake is pumped through a network of pipes in the ceiling as well as some of it sprayed in the tower for cooling the wind.

Figure 8: Section of solar chimney and windtower

3.1.4 Trombe Wall On the ground floor, the south wall is made thick with thermal massing and a glass curtain wall is installed on the outside. The system is heated up and the high temperature of the air between causes it to rise and escape from the top. The system is highly efficient due to its south facing nature.

Figure 7: Section of windcatcher

3.1.2 Chilled Ceiling The presence of nearby water body serves as a great advantage. Water from the Al-Fostat lake is used to circulate in pipes along the ceiling for cooling the mass.

The water is also used for evaporative cooling in the towers as well as on site.

3.1.3 Solar Chimney The two towers have been divided into two parts by the virtue of a thick brick thermal wall. On one side is the wind tower diverting winds into the building, while in the other external side is a glass curtain wall. Solar radiation heats the air space between the glass and the wall, causing the air to move upward because of buoyancy. Presence of vents near the ceiling of adjoining rooms cause the air to move out, and the fresh ones are channelled into the rooms by the windcatcher through the vents near the floor.

Figure 9: Section of trombe wall

3.1.5 Sun Shading All external glazing have been shaded by a metal perforated mesh, with designs inspired from Egyptian 7

mashrabiya. The high window ensures adequate light without overheating. The window without the screen is adequately protected form the sun due to overhangs for most part of the year. During the solstices, since the hot sun is lower in the sky compared to the summer months, a shading device is needed. The mashrabiya protects during those times. The shading mask (without the mesh) is shown in figure xx. It is observed that there is a small time of the year when further shading is required. Thus, the design caters to all year-round conditions.

Figure 11: Arched opening with high window behind the mesh

Figure 12: The skylight and high window effectively light the interior office space

Figure 10: Shadow mask of the southern typical window

Figure 13: Ground floor plan

Figure 14: First floor plan

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3.2 Site

completely open and naturally ventilated, taking benefit of the uninterrupted lake view and cool breeze.

The next part of design includes catering the design needs of each individual block, which have different orientations. For the east block, the direction of the windcatchers on the tower has been reversed to face the north. The prevalent winds blow from north, and so even the wind scope has a steeper slope to drive in more air.

The south tower functions the same as the original, taking advantage of solar radiation from mid-day onwards to heat up the air space. This is the only solar chimney in the block, since all others will not have a good orientation.

The thermal mass behind the trombe wall is removed to give an uninterrupted natural light.

Figure 15: East block faces SW and NE while West block faces NW and SE

Figure 16: Modified strategies

The fenestrations of the NW and NE faรงade have increased area with larger openings in the arched thermal wall. While the openings on SW wall are covered with metal mesh. The number of PV panels from the main block is reduced since the output from this direction will be lower. Moreover, the solar chimney on installed on the north tower will not function since there will be no direct solar radiation falling on it. In this case the north wall is

For the west block, a similar change is brought about, which is increased fenestration area of the lake facing faรงade, removal of northern solar chimney and trombe wall, reduced number of PV panels. A major deviation in the design of this block is that all fenestrations are now open to natural light. Since, except for the SW, all facades are sun protected due to the nature of building orientation.

Figure 17: East block modifications

Figure 18: West block modifications

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The building has further scope in reduction of this energy by making use of on site renewable system, like the PV panels on roof. The PV panels have been put over a roof area of 135m². This corresponds to about 29m² of actual PV panels. The annual electricity production by these panels can be calculated on Revit GBS. This gives us an annual production of 93,859 kWh.

Energy Characteristic The building is defined as an office space, running from 9 to 5, with net simulated area of 900m². The building is designed to be free running, but for energy simulation it is assumed to be on HVAC so that the equivalent calculation can be done.

A quick calculation reveals the following energy demand pattern (suggested by Green Building Studio ©)

Figure 20: PV energy production

On a closer examination we observe that the annual electricity demand is 111,104 kWh (Figure 19), while the production is 93,859 kWh which is about 84.5%. Thus, a major chunk of energy demand can be met by the PV panels itself, and the payback period is also a small-time frame of 10 years.

Figure 19: Energy intensity

Further reductions are still possible by using triple glazing, covering the windows even more, and designing deeper overhangs. A compromise has to be reached between this reduction and decreased natural lighting in the building. Moreover, the passive measures undertaken on site have not been numerically studied, which could further result in lesser energy demand.

Energy in kWh Month

Cooling

Lighting

Other

Total

January

859

2696

6557

10112

February

941

2439

5568

8948

March

1696

2777

5645

10118

April

2084

2663

4970

9717

May

2571

2775

5056

10402

June

3113

2665

5108

10886

July

3155

2696

5143

10994

August

3528

2853

5464

11845

September

2985

2508

4886

10379

October

2761

2775

5074

10610

November

1441

2584

5070

9095

December 883 2620 Table 1: Annual energy demand

6292

9795

In short, the building has potential to freely run using passive measures and independently produce its own energy on site for any active measures.

14000

Energy in kWh

12000 10000 8000 6000 4000 2000 0

Cooling

Lighting

Figure 21: Monthly energy demand

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Miscellaneous

A simplified section of C2 was simulated to observe the air flow pattern in the building. Figure xx shows the air speed distribution when the site inlet speed is 2m/s. At ground. The shape of the wind scoop helps channelling and speeding air into the vent. The results are tabulated in table 2.

Ventilation Characteristic The building uses multiple simultaneous ventilation techniques as outlined in section 3.1 (1,3,4). Each part of the block has a highlight measure which aids in ventilating the indoors. There are two main circuit established, C1 and C2. C1 in the tower while C2 in the long open office.

C1 is solar chimney and windtower back to back, with one side acting as inlet and the other outlet. The advantage of this system is that both the passive measure work simultaneously to create a breezy cool indoor space. In order avoid high solar radiation, the tower is the region with least fenestrations, and hence the ventilation rate can be controlled effectively without issues of infiltration.

(See appendices for CFD simulation of C1 circuit.)

Room

Average Velocity m/s

Uniformity Index

PPD

1 2 3

0.39 0.77 0.22

93% 92% 88%

5.90% 11.30% 5.00%

Table 2: PPD for circuit C2

For an average Cairo temperature of 27° and humidity of 50%, no more than 12% of occupants are dissatisfied when the place is naturally ventilated. This shows the immense potential in this system. Moreover, the dissatisfaction is due to high velocity which can be controlled by vent area.

C2 works in the long office zone, again with the aid of a type of solar chimney (trombe wall). The central service shaft, like in C1, functions as the inlet duct and distributes air on either side. From the south façade air is driven out via the trombe wall, while on the north side it is by the windows.

Figure 22: Air distribution in C2 circuit

Figure 23: Ventilation system at play in the design

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3. Double skin façade on certain blocks facing the sun, which could act like a solar chimney to drive stale air out.

Conclusions A building can be designed to run freely and all it takes is a better understanding of the site, context and technology. This was the main observation and gist of the design exercise. Climate of a place can be harnessed to make use of, instead of shunning it and making a sealed conditioned box.

The benefits of designing a climatic building is the reduced energy consumption and better indoor quality.

Other researches have shown that people working in a free running building are comfortable over a wider range of temperatures. They in fact, prefer the rhythmic nature of climate and seasons.

In any case, with little intervention and using passive methodologies we can establish good recommended space quality. In the case of the current design, it was only after detailed study of the local climate were we able to identify the factors which we could harness and others which we needed to avoid. For instance, the sun is usually high in the Cairo sky, with temperatures ranging from 27°C to 35°C. Although this is not comfortable for people, it does not necessarily mean that the building has to run against them. The ideal situation is to use this resource to run the building. Passive it the need of the hour.

Figure 25: Double skin facade as a means to drive air out

4. Ground-coupled heat exchangers to pre-cool air, this means that the windtower diverts the wind into the ground from where it is cooled and brought into the rooms.

5. Use of wind turbine to produce energy on site.

This can be further worked upon by having structures which divert and concentrate winds on the turbines. The on-site potential for a 15’ wind turbine is calculated to be 934kW. (Green Building Studio ©).

6. The use of subterranean spaces has got a huge advantage in these hot climates. Ancient sites of underground cities like Cappadocia, have shown the benefit of building below. The temperature of the ground is more stable than air, and with depth the seasonal fluctuations are lesser. Buildings underground are much cooler (in warm climates) reducing the need for further cooling. This saves significant energy in HVAC. The main central courtyard has been designed with this idea in mind.

From conception to design evolution, the idea was to develop a building which does not require conventional HVAC. The strategies and its significance have been discussed in section 3. Other methods which could have been applied for further efficiency are: 1. Covered terraces, and use of vegetation over it.

The benefits are two-fold, first it blocks direct solar radiation from the sun and secondly the plants transpire, producing evaporative cooling.

With passive technologies it becomes more and more sustainable. The only shortcoming is that the efficiency cannot be validated by using conventional CAD programs. For instance, Revit cannot evaluate the effectiveness of the solar chimney or the ground based heat exchanger. It however can suggest possible means of reduction energy. This calls for an informed decision by the architects and engineers to take proper measures.

Figure 24: Trellis shading possibility on the terrace

2. Façade mounted PV panels to introduce shading as well as generate energy.

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Figure 27 shows a comparison of heat gain in the earlier case and later with a shade above the roof. The decrease is 10 times. Thus, it is a good idea to have shades for the building also, and not just over fenestrations. Overhangs/pergolas will shade the structure and prevent from high gains.

Recommendations for public buildings Having done this design exercise, certain key understanding can be applied to a wide range of building typology to strive for sustainability. The following section lists the possible design ideas which can be implemented in general to all public buildings.

1. Buildings should be oriented to catch the predominant wind and use it for natural ventilation. In case of Cairo, this is due north.

2. If this is not possible then a mix-mode ventilation mechanism should be adopted, which uses both active as well as passive means of cooling.

3. Roof profile should be such that wind creates a differential pressure and it is driven into the building. It essentially takes place due to venturi effect.

Figure 28: Solar heat gain comparison Figure 26: Pressure difference inside and outside drives air and ventilates the space

5. Greening terraces, patios and any other public spaces. Plants have multiple advantages, they prevent heat island effect, cool the surrounding, control direct radiation and also create soothing effect.

The plants used as part of this design are palms which are native to the place. Trees of the family Arecaceae are especially suitable for the dry climate.

6. Walls of high thermal mass are absolutely essential for the extreme temperatures of Cairo. They store heat and keep the building cool during the day while releasing the heat in the night to warm it. A standard 225mm thick brick wall has an average 30kJ/K of thermal mass, while the design has proposed a 600mm thick wall of adobe bricks having a thermal mass of 82kJ/K. Public buildings should be made of mud bricks of suitable dimension to have good thermal mass. The table below lists the penetration depth of material needed for various time period. For equal time interval the depth of earth bricks is much lower than concrete.

4. Use of solar shades even on blank faรงade and roof, apart from using proper insulation. This ensures minimal heat gain from solar radiation.

In the present case the windscoop acts like a secondary skin protecting the skylight/primary roof from direct solar gain.

Figure 29: Time lag for different material (values in meter)

Figure 27: Double roof for added thermal protection

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Appendices A 3D perspective of the south block is shown in figures 30 and 31, explaining the different parts and strategies employed.

Figure 30: North view of the designed block

Figure 31: South perspective of the designed block

Figure 32: Final site plan with the three modified buildings

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Figure 33: Solar energy production capacity of the roof area

Figure 34: Airflow in the wind tower, graphs of sections cut at inlet and outlet vents

Figure 35: Airflow in the tower block, plans cut at inlet and outlet vent (first floor)

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References [1]. M. C. Peel1, B. L. Finlayson, and T. A. McMahon. Updated world map of the Köppen-Geiger climate classification.

[2]. Sunwoo Lee, Sang Hoon Park, Myong Souk Yeo, Kwang Woo Kim. An experimental study on airflow in the cavity of a ventilated roof.

[3]. Hanan M. Taleb. Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in U.A.E. buildings.

[4]. K. Pantavou, G. Theocharatos, A. Mavrakis, M. Santamouris, Evaluatingthermal comfort conditions and health responses during an extremely hotsummer in Athens, Build. Environ. 46 (2011) 339–344.

[5]. Khedari, B. Boonsri, J. Hirunlabh, Ventilation impact of a solar chimney on indoor temperature fluctuation and air change in a school building, Energy Building (June) (2000) 89–93.

[6]. Somaye Asadia, Maryam Fakharib, Rima Fayazb, Akram Mahdaviparsa. The effect of solar chimney layout on ventilation rate in buildings.

[7]. Jyotirmay Mathur, N.K. Bansal, Sanjay Mathur, Meenakshi Jain, Anupma. Experimental investigations on solar chimney for room ventilation.

[8]. Velasco Gómez E, Rey Martínez F C., Tejero González A. The phenomenon of evaporative cooling from a humid surface as an alternative method for air-conditioning, International Journal of Energy and Environment 2010.

[9]. Amer O, Boukhanouf R, Ibrahim H G. A Review of Evaporative Cooling Technologies, International Journal of Environmental Science and Development 2015.

[10]. Junyent-Ferre Gomis-Bellmunt O, Sumper A, Sala M, Mata M. Modeling and control of the doubly fed induction generator wind turbine. Simulation Modelling Practice and Theory [11]. Omidreza Saadatian, Lim Chin Haw, K. Sopian, M.Y. Sulaiman. Review of windcatcher technologies [12]. Bahadori MM. Passive cooling systems in Iranian architecture. Scientific American Journal 1978 [13]. Kolokotroni M, Ayimomitis A, Ge YT. The suitability of wind driven natural ventilation towers for modern offices in the UK: a case study. World Renewable Energy Congress; 2002.

[14]. Yaghoubi MA, Sabzevari A, Golneshan AA. Wind towers: measurement and performance. Solar Energy 1991 [15]. J. Xamána Y. Olazo-Gómeza Y. Cháveza J.F. HinojosabI. Hernández-PérezaI. Hernández-Lópezc I. Zavala-Guilléna Computational fluid dynamics for thermal evaluation of a room with a double-glazing window with a solar control film.

[16]. M. Rubin. Calculating heat transfer through windows Energy Research, Vol 6 (1982) [17]. G. Álvarez, J. Flores, C. Cortina. Heat transfer through a douvent glass with chemically deposited solar control coating ISES Solar World Congress II [18]. H.S. Carslaw, J.C. Jaeger. Conduction of Heat in Solids (second ed.), Clarendon Press, Oxford UK (1959) [19]. S. Onmura, M. Matsumoto, S. Hokoi. Study on evaporative cooling effect of roof lawn gardens (2000) [20]. Figure 25: http://www.esru.strath.ac.uk/EnvEng/Web_sites/05-6/Hotel_exemplar/ventilation.html [21]. Figure 29: Exterior climate thermal comfort heat air exchange energy daylight, Heinrich Manz

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List of figures Figure 1: Sunpath of Cairo overlaid with temperature ....................................................................................................... 03 Figure 2: Proportion of the base geometry ........................................................................................................................ 03 Figure 3: Proposed site plan .............................................................................................................................................. 04 Figure 4: Wall construction ................................................................................................................................................ 06 Figure 5: South elevation................................................................................................................................................... 06 Figure 6: North elevation ................................................................................................................................................... 06 Figure 7: Section of windcatcher ....................................................................................................................................... 07 Figure 8: Section of solar chimney and windtower ............................................................................................................ 07 Figure 9: Section of trombe wall ........................................................................................................................................ 07 Figure 10: Shadow mask of the southern typical window .................................................................................................. 08 Figure 11: Arched opening with high window behind the mesh ......................................................................................... 08 Figure 12: The skylight and high window effectively light the interior office space ............................................................ 08 Figure 13: Ground floor plan .............................................................................................................................................. 08 Figure 14: First floor plan................................................................................................................................................... 08 Figure 15: East block faces SW and NE while West block faces NW and SE ................................................................... 09 Figure 16: Modified strategies ........................................................................................................................................... 09 Figure 17: East block modifications ................................................................................................................................... 09 Figure 18: West block modifications .................................................................................................................................. 09 Figure 19: Energy intensity ................................................................................................................................................ 10 Figure 20: PV energy production ....................................................................................................................................... 10 Figure 21: Monthly energy demand ................................................................................................................................... 10 Figure 22: Air distribution in C2 circuit ............................................................................................................................... 11 Figure 23: Ventilation system at play in the design............................................................................................................ 11 Figure 24: Trellis shading possibility on the terrace ........................................................................................................... 12 Figure 25: Double skin facade as a means to drive air out ................................................................................................ 12 Figure 26: Pressure difference inside and outside drives air and ventilates the space ...................................................... 13 Figure 27: Double roof for added thermal protection ......................................................................................................... 13 Figure 28: Solar heat gain comparison .............................................................................................................................. 13 Figure 29: Time lag for different material (values in meter) ............................................................................................... 13 Figure 30: North view of the designed block ...................................................................................................................... 14 Figure 31: South perspective of the designed block .......................................................................................................... 14 Figure 32: Final site plan with the three modified buildings ............................................................................................... 14 Figure 33: Solar energy production capacity of the roof area ............................................................................................ 15 Figure 34: Airflow in the wind tower, graphs of sections cut at inlet and outlet vents ........................................................ 15 Figure 35: Airflow in the tower block, plans cut at inlet and outlet vent (first floor)............................................................. 15

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