effect of courtyard height and proportions on energy ... · effect of courtyard height and...

Effect of Courtyard Height and

Proportions on Energy Performance of

Multi-Storey Air-Conditioned Desert

Buildings.

Khaled El-Deeb, PhD Ahmed Sherif, PhD Abbas El-Zafarany, PhD

[Alexandria University, Egypt.] [The Ameican University in Cairo] [Cairo University, Egypt]

[email protected] [email protected] [email protected]

ABSTR ACT

Courtyard buildings have been always recommended as a passive architectural technique in desert

environments in order to maintain indoor thermal comfort. Nowadays, an increasing number of

buildings are air-conditioned. The importance of using passive techniques, then, becomes to reduce

energy consumption. A previous study, however, showed that in desert environments, the energy

performance of two-storey residential courtyard buildings proved less efficient than other solid forms,

even when attached to neighbouring buildings from three sides in a compact urban fabric. Their

performance was relatively better in mild desert climates than in extreme hot ones. The study was

limited to a single family house with “thin” depth of zones surrounding the courtyard.

In multi-storey courtyard buildings, the courtyard results in more height and self-shading on the facades

overlooking the courtyard. This will have a direct effect on the energy consumed for cooling and

heating, as well as on that consumed by artificial lighting

This study questions the effect of courtyard height proportions and thickness of the built area

surrounding it on the energy consumption in multi-storey air-conditioned courtyard buildings and tracks

that effect under different desert climates. Courtyard buildings of 1-10storey-height were modelled using

the DesignBuilder software and simulated using EnergyPlus simulation engine for the desert climates of

Khargah, Cairo, Alexandria and for the temperate climate of Berlin for comparison. All cases were

compared to the corresponding solid building forms of the same built area.

Air-conditioned courtyard houses has not shown a significant improvement in energy savings in desert

environments, buildings with bigger depth surrounding the courtyard had a much better performance

than thinner buildings, giving small energy savings with building depth exceeding 12m

Keywords: multi-storey courtyard, air-conditioned, desert buildings, energy performance simulation.

INTRODUCTION

Courtyard buildings have been always recommended as a passive architectural technique in desert

environments in order to maintain indoor thermal comfort. Nowadays, an increasing number of buildings

are air-conditioned. The importance of using passive techniques, then, becomes to reduce energy

consumption. A previous study, however, showed that in desert environments, the energy performance

of two-storey residential courtyard buildings proved less efficient than other solid forms, even when

attached to neighbouring buildings from three sides in a compact urban fabric [1]. Their performance

was relatively better in mild desert climates than in extreme hot ones. The study was limited to a single

30th INTERNATIONAL PLEA CONFERENCE16-18 December 2014, CEPT University, Ahmedabad

1

family house with “thin” depth of zones surrounding the courtyard. Neither the effect of change in

building depth (BD) surrounding the courtyard was not studied, nor the effect of courtyard height

proportions (HP), while both are still questionable.

Review of recent literature demonstrated that the performance of a courtyard as a passive cooling

strategy was discussed in numerous publications. The effect of a naturally ventilated courtyard on

thermal performance was studied in hot arid, tropical and warm humid tropical climates [2, 3, 4]. Results

showed that a courtyard building with controlled natural ventilation, of specified opening time improved

thermal performance. However in hot arid climate, the thermal performance resulting from continuous

day and night natural ventilation was worse than keeping the building closed without natural ventilation

[2].

The shading effect of different courtyard forms [5] and that of courtyard proportions [6] were

studied. It was found that in Rome, courtyards with deep proportions were recommended over shallow

ones. However, in both studies the tested buildings were solid with no windows, and thus both the effect

of transmitted solar radiation and the energy needed for artificial lighting were not considered.

The passive effect of courtyard with plants and water pool on energy consumed for heating and

cooling was studied [7]. It was found that passive features alone could not maintain comfort during hot

summer times in Tehran, and that similar effects could be obtained through envelope components such

as insulation and double glazing. However, the energy needed for artificial lighting that compensates for

the effect of shading was not accounted for.

A study of energy performance of courtyard buildings in different climatic conditions showed that

better performance was achieved in hot-dry and hot-humid climates rather than in cold and temperate

ones [8]. The study was limited to zones overlooking the courtyard and ignored the influence of the

external perimeter walls and zones. The impact of integrating deep courtyards in mid-rise housing

buildings in Dubai was evaluated, showing that a six-storey courtyard building achieved up to 6.9%

savings [9]. The addressed heights ranged from 4 to 10 stories high, while two-storey low-rise residential

buildings that are common in some countries like Saudi Arabia were not considered.

Some studies addressed the effect of orientation on thermal performance for non-air-conditioned

buildings in a hot-humid tropical climate [10] and the implications of orientation on thermal energy

efficiency of passive buildings in mild temperate climate [11].

Literature showed that the combined effect of building depth surrounding the courtyard and the

courtyard’s height proportions on energy consumed in heating, cooling and lighting of air-conditioned

buildings in the desert needs more investigation.

OBJECTIVES

This research aims at exploring the effect of courtyard on energy consumption of heating, cooling

and lighting in air-conditioned multi-storey residential desert buildings based on two parameters: height

proportions, and the depth of built area surrounding the courtyard.

METHODOLOGY

Six courtyard buildings with fixed courtyard plan dimensions (12X12m) were tested for energy

performance in the following cases of thickness of built area surrounding the courtyard: 4, 6, 8, 10, 12,

20m. Values of thicknesses 14, 16, 18m were interpolated.Each case was tested in building heights of

1,2,4,6,8 and 10 floors. These represented courtyard section length-to-height proportions of 1:0.25,

1:0.5, 1:1, 1:1.5, 1:2, and 1:2.5 respectively. Then, for each of the six main cases, a solid square building

of the same built area and height (but with no courtyard) was tested for comparison.

30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad

2

The energy use intensity (EUI) of each of the courtyard BD cases was compared in different HPs in

order to detect how the building’s height affects the overall energy consumption per square meter. This

overall value in each courtyard building case was compared to its corresponding solid square case to

detect which form was more efficient in energy consumption.

Figure 1: Tested courtyard height and building depth proportions and solid square buildings.

All courtyard and solid building cases were modelled using Design Builder software and simulated

using EnergyPlus. Even at small building thickness, it was assumed the thickness is divided into two

zones one facing the courtyard and the other on the external perimeter.

Table 1: Simulation parameters of tested Buildings

Simulations were performed for four cities: Alexandria, Cairo, and Khargah located in Egypt, and

classified as hot arid according to koeppen-Geiger classification [12]. For comparison; Berlin, a

temperate city with warm summer was simulated. Despite being classified as desert, the first three cities

represent three different cases: Alexandria is a Mediterranean coastal city, Cairo is inland 220 km south

of Alex., Khargah lies in the sahara 600km south of Alex. Figure 2 shows the difference in climate.

Khargah is the highest in temperature, and out of comfort level for nearly all the year. Cairo is less in

temperature than Khargah, yet higher than Alexandria. Berlin is the lowest.

4m 6m 8m 10m 12m 20m

2

COURTYARD and SOLID SQUARE

Building Cases.

Height Proportions (HP)

1:2.5 1:2 1:1.5 1:1 1:0.5 1:0.25

Building Depth (BD)

Form Square

Courtyard Dimensions 12X12m

WWR 20% fixed for all forms

Occupancy 0.13 person/m2

Schedule Residential Type

Cooling 23 Type: Fluorescent Suspended

Heating 21

Type Split

SIMULATION PARAMETERS

BUILDING

Daylightin

g control

LIGHTING

CONSTRUCTION

External walls

HVAC

Illuminance:

300 lux

Dimming:

On/off

20cm concrete block + 2cm cement plaster each side

10cm concrete block + 2cm cement plaster each side

Insulated with 10 cm polystyrene foam

20cm concrete + 10cm flooring + 2cm plaster

Double-glazed clear

Sensor Height:

0.8m

Internal walls

Roof

Internal slab

Windows


3

Figure 2: Mean daily maximum and minimum temperatures in tested cities for each month.

RESULTS AND DISCUSSION

Performance simulations showed a clear difference across the tested cities.

Height proportions:

In desert climates, results showed that EUI for all forms increased by increasing height in all cities.

For example, In Khargah city, dominated by cooling loads, a courtyard building with BD 8m in different

cases of floor HPs showed that the ground floor was always of the least consumption, then the second

floor consumed more cooling energy, and starting from the third one the cooling energy at each floor

were nearly constant, then it increased again at the top floor, Figure 3. This indicated that the ground

floor was significantly lower in consumption due to the heat sink to the ground, while the top floor was

higher but with a small difference than the preceding floor despite being subjected to the solar radiation

due to the thermal insulation of the roof by 10cm. Thus in low-rise cases, the positive effect of heat sink

on minimizing the overall EUI was significant. This effect became less as height increased.

As the tested buildings are fully air-conditioned with no natural ventilation, they were not directly

affected by air temperature inside the courtyard. These results differed from what is expected in naturally

ventilated courtyard buildings where height promotes natural convection, and stack ventilation. The

decreased direct solar radiation at bottom floors increased lighting energy consumption, and its radiant

fraction; and so, minimized the expected savings in cooling loads resulting from self-shading.

Figure 3: EUI per floor in courtyard buildings, with total height 1,2,4,6 and 8 Floors in Khargah

city representing courtyard height ratios 1:0.25 to 1:2.

-5

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Khargah Cairo Alexandria Berlin

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1 2 3 4 5 6 7 8 9 10 11 12

MAX MINMean Daily Maximum Mean Daily Minimum

Mea

n D

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s o

C

Lighting Heating Cooling

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4m 6m 8m 10m 12m 14m 16m 18m 20m 4m 6m 8m 10m 12m 14m 16m 18m 20m 4m 6m 8m 10m 12m 14m 16m 18m 20m 4m 6m 8m 10m 12m 14m 16m 18m 20m

10 10 10 10

KHARGAH CAIRO ALEX BERLIN

COURT

Sum of BUILDING LIGHTING (Kwhr/M2) Sum of BUILDING HEATING (Kwhr/M2) Sum of BUILDING COOLING (Kwhr/M2)

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1 2 4 6 8

ON

10 cm

COURT 1:1 - 8m

KHARGAH

Sum of FLOOR LIGHTING (Kwhr/M2) Sum of FLOOR HEATING (Kwhr/M2) Sum of FLOOR COOLING (Kwhr/M2)

1: 0.25 1: 0.5 1: 1.0 1: 1.5 1: 2.0Courtyard Height

Proportions

Floor Number

KHARGAH


4

The reflectance of wall paint was assumed to be 50% as the color of the accumulated dust of the desert

usually overrides the color of light paints.

In Berlin, dominated by heating loads, the contrary occurred. The heat sink lead the ground floor to

consume more heating, making the building of 1 or 2 floors consume more than a the 4-storey one, then

a gradual increase occurred as height increased, Figure 4.

Figure 4: EUI in Kwhr/m2 for courtyard building with BD 8m, in case of different building heights

in the four cities.

In Cairo and Alexandria the same pattern occurred as in Khargah, however, consumption values

differed according to climate. Figure 4 shows that increasing HPs lead to an increase in the overall

energy consumption in all tested desert cities.

Depth of Building Surrounding the Courtyard:

Forms with BD alternatives 4m-20m surrounding the courtyard were tested. Changing BD while

fixing courtyard dimensions means that the exposed surface area-to-built volume ratio (S:V) was also

changed. This ratio was also changed by changing HP at each BD.

Results showed that in both extreme hot and cold climates of Khargah and Berlin, the BD was a

determinant factor, Figures 5,6. In Khargah, as BD increased, total energy consumption decreased, in

spite of the increase in lighting energy that was overcome by greater savings in cooling loads. On the

other hand, in Berlin, the increase in BD lead to a large decrease in heating loads due to both the

increased internal area protected from external conditions, as well as the increased lighting energy and

its emitted thermal loads that help decrease heating loads, while increase cooling loads in summer. The

result was a decrease in the overall consumption.

Figure 5: Energy use intensity in Kwhr/m2 for courtyard height proportion 1:2.5 (building height 10 floors), in case of different building depths in tested cities.

0

50

100

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200

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350

1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10

ALEX CAIRO KHARGAH BERLIN

8m

COURT

Sum of BUILDING LIGHTING (Kwhr/M2) Sum of BUILDING HEATING (Kwhr/M2)

Sum of BUILDING COOLING (Kwhr/M2)

0

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1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


8m

COURT



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1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


8m

COURT



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1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


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COURT



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1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


8m

COURT




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COURT


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1: 0

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BERLINKHARGAH CAIRO ALEX

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COURT



Courtyard Height

Proportions

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CAIRO ALEX

Building

Depth


5

In all cities, BD 4m was of the highest EUI followed by BD 6m, as their S:V ratio were much

higher than the other BDs, thus they were more liable to be affected by the outdoor climate. The S:V

ratio for BDs 4 and 6m at HP 1:1 for example were 58%, 42% respectively, while BDs 8 to 20m ranged

from 18-33% only.

In Alexandria, the climate is moderate and close to comfort levels for long annual periods. Cooling

loads were not as high as the extreme environment of Khargah because the difference in temperature

between indoor and outdoor is relatively small. For that, the effect of BD was the lowest of the four

cities. Forms of different BDs other than 4m were of close EUI values. Lighting consumption increased

uptill BD 8m then became nearly constant. Savings occured in lighting at low HPs, up to 1:1 (4 floors)

and small BDs. The courtyard building with BD 8m was the lowest in consumption at all tested building

heights. EUI of BD 6m was nearly similar to the rest of BDs starting from HP 1:0.5 (2 floors). The BD

4m case was of the highest consumption until HP 1:1.5 (6 floors), then became of similar values to BD

10-20m cases.

Figure 6: Energy use intensity in Kwhr/m2 for courtyard buildings of different building depths and

height proportions.

In Cairo, whose climate showed higher temperatures than Alexandria and lower than Kharga,

results showed some similarity to either cities. As in Khargah, BD was inversely proportional to

consumption, however, the differences in consumption between BD cases were much smaller than the

corresponding values in Khargah, while larger than those in Alexandria. At BDs 10-20m, a slight

decrease in cooling loads occured while lighting loads were nearly the same.

120

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Sum of 1 Sum of 2 Sum of 4 Sum of 6 Sum of 8 Sum of 10

ALEX - COURT 1:1 - 4m ALEX - COURT 1:1 - 6m




ALEX - COURT 1:1 - 20m

CITY FORM

Val...

Sum ... Sum ... Sum ... Sum ... Sum ... Sum o...

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BERLIN - COURT 1:1 - 4m BERLIN - COURT 1:1 - 6m




BERLIN - COURT 1:1 - 20m

CITY FORM

Val...


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CAIRO - COURT 1:1 - 4m CAIRO - COURT 1:1 - 6m




CAIRO - COURT 1:1 - 20m

CITY FORM

Val...


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KHARGAH - COURT 1:1 - 4m KHARGAH - COURT 1:1 - 6m




KHARGAH - COURT 1:1 - 20m

CITY FORM

Val...


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ALEX - COURT 1:1 - 4m ALEX - COURT 1:1 - 6m ALEX - COURT 1:1 - 8m



CITY FORM

Val...


Depth 4m

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16m

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CITY FORM

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CITY FORM

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10m

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CITY FORM

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CITY FORM

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CITY FORM

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Depth 4m

10m

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20mDEPTH

ALEX

CAIROKHARGAH

BERLIN

1:0.25 1:0.5 1:1 1:1.5 1:2 1:2.5 1:0.25 1:0.5 1:1 1:1.5 1:2 1:2.5

1:0.25 1:0.5 1:1 1:1.5 1:2 1:2.5 1:0.25 1:0.5 1:1 1:1.5 1:2 1:2.5

Kwhr/m2

Courtyard Height

Proportions

Kwhr/m2

Courtyard Height

Proportions


6

Courtyard or Solid Building:

In order to evaluate whether the performance of multi-storey courtyard buildings achieve savings in

comparison with solid ones without courtyard, each of the tested building forms was compared to a solid

square form with the same built area and no courtyard, Figure 7.

In Khargah, results showed that courtyard buildings did not achieve savings in any case of HPs for

BD 4-14m, moreover, it lead to a significant increase in consumption. Only at BD 16m, minor savings

occurred in case of HP 1:0.25 and 1:0.5 only. Also, minor savings were achieved in BD 18m at HPs upto

1:1. The only case where saving were achieved at all heights was in the BD 20m, especially at up to 1:1

height ratio, while up to 1:2, savings were very small.

In Berlin, courtyard buildings did not show any improvement compared to the solid square until

BD 16m, at which saving were achieved in nearly all floors. Savings increased as BD increased. In most

cases it caused a high increase in consumption that reached 40% in some cases.

In Cairo, minor savings were achieved at and some cases of BDs 8m and 16m. At BDs 18-20m,

savings upto 6-8% were achieved at low HPs. The courtyard building consumed more energy than its

corresponding solid building not exceeding 5% in most of the other cases except for BD 4m at low HPs.

In Alexandria, courtyard building achieved energy savings compared to their corresponding solid

ones in the majority of cases. In the cases that did not achieve savings, the increase in consumption was

was less than 4% except for BD 4m at low HPs. This indicated that Courtyard building is more liable to

be used in the moderate climate of Alexandria than in other tested cities.

Figure 7: Percentage of change in energy consumption of courtyard buildings compared to its corresponding solid square.

-20%

-10%

0%

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40%

1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10

COURT COURT COURT COURT COURT COURT COURT COURT COURT

4m 6m 8m 10m 12m 14m 16m 18m 20m

ALEX

Total

Total

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-10%

0%

10%

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30%

40%

1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


4m 6m 8m 10m 12m 14m 16m 18m 20m

KHARGAH

Total

Total

-20%

-10%

0%

10%

20%

30%

40%

1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


4m 6m 8m 10m 12m 14m 16m 18m 20m

BERLIN

Total

Total

-20%

-10%

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1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


4m 6m 8m 10m 12m 14m 16m 18m 20m

CAIRO

Total

Total

ALEX

CAIRO

KHARGAH

BERLIN

-20%

-10%

0%

10%

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30%

40%

1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


4m 6m 8m 10m 12m 14m 16m 18m 20m

BERLIN

Total

Total

-20%

-10%

0%

10%

20%

30%

40%

1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10 1 2 4 6 8 10


4m 6m 8m 10m 12m 14m 16m 18m 20m

BERLIN

Total

Total

1: 0

.25

1: 0

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1: 1

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1: 1

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1: 2

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1: 2

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1: 0

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1: 2

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1: 1

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1: 1

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1: 2

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1: 2

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1: 0

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1: 0

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1: 1

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1: 2

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1: 2

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1: 0

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1: 1

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1: 2

.0

1: 2

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1: 0

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1: 0

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1: 1

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1: 1

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1: 2

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1: 2

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1: 0

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1: 0

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1: 1

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1: 2

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1: 0

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1: 0

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1: 2

.5

Courtyard Building

Courtyard

Proportions

Building Depth


7

CONCLUSION

Height proportions had a lower effect than building depth which was a key factor in the cities with

extreme cold and hot climates, Khargah and Berlin. EUI values decreased significantly by the increase in

depth due to the decrease of exposed surface area with respect to the indoor air-conditioned volume.

This BD effect was less in Cairo and nearly insignificant in Alexandria where temperature differences

between indoor and outdoor is small, thus decreasing heat transfer by conduction.

For a fixed depth, a courtyard with lower height proportions consumed less energy in desert cities

due to the effect of the heat sink to the ground which became of less impact as height increased, leading

to an increase in EUI accompanied by the increase in artificial lighting and its consequent cooling loads.

This nearly cancelled the self-shading effect of the courtyard. The opposite effect occurred in Berlin.

Compared to the corresponding solid square, the courtyard building achieved significant savings in

the moderate climate of Alexandria especially in case of medium height proportions (1:1) at small BD

and in low height at large BD. In khargah and Cairo, that are more hot cities, significant saving were

only achieved at large BD (18m-20m) and low height proportions (1:0.25 to 1:1) while a significant

increase in consumption occured especially at small BD and higher height proportions in most cases.

Further research is required to quantify the effect of courtyard house with more proportions.

ACKNOWLEDGEMENTS

This research is financially supported by King Abdullah University of Science and Technology

(KAUST) as part of the Integrated Desert Building Technologies Project IDBT (Award no.UK-C0015).

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