sustainability
Article
Impact of Green Roof and Orientation on the Energy
Performance of Buildings: A Case Study from
Saudi Arabia
Hassan Saeed Khan and Muhammad Asif *
Architectural Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261,
Saudi Arabia; [email protected]
* Correspondence: [email protected]; Tel.: +966-860-7906
Academic Editor: Tomonobu Senjyu
Received: 30 January 2017; Accepted: 13 April 2017; Published: 18 April 2017
Abstract: Saudi Arabia is one of the largest countries in the Middle East region in terms of population,
geographic area and scale of economy. It has a fast growing energy sector with over 76% of the
total electricity being consumed in the building sector. Domestic buildings account for 51% of
total electricity consumption. Predominantly due to hot climatic conditions, most of the energy
consumption in buildings is attributed to the heating, ventilation and air conditioning (HVAC) loads.
In terms of supply mix, the country entirely relies on oil and gas to meet its energy requirements.
The high growth in energy demand is imposing stringent energy, environmental and economic
challenges for Saudi Arabia. The present work aims to explore prospects of energy saving in
buildings through the application of green roof technology. With the help of ECOTECT modelling,
the work examines the effectiveness of green roof on considering modern faculty homes built in the
King Fahd University of Petroleum and Minerals situated in the hot-humid climatic conditions of
the Easter Province of the country. The same building has also been investigated for the hot-dry
climate of Riyadh, the capital city. The work also examines the impact of orientations on the energy
performance of buildings.
Keywords: buildings; sustainability; green roof; energy modeling; energy efficiency; monthly load
discomfort analysis
1. Introduction
The global concerns on energy and environmental challenges are becoming ever more important.
Growing demand for energy, depletion of natural resources and global warming are leading problems
in this respect [1,2]. Global warming and climate change are leading to wide-ranging challenges
including sea level rise, seasonal disorder and natural catastrophes [3,4]. The building sector has an
important role in the international energy and environmental scenarios as it consumes almost 40%
of energy and results in over a third of greenhouse gas (GHG) emissions [5]. The building sector
is experiencing a rapid growth in countries across the world due to factors like population growth,
infrastructure development, modernization and urbanization. To tackle the facing of energy and
environmental problems, the world is aiming to promote sustainable development as is reflected
by the recent global agreement on climate change, COP21 [6]. The building sector has a crucial
contribution to make towards improving sustainability standards and addressing the energy and
environmental challenges. In the backdrop of the global drive for sustainability, buildings are facing
significant improvement in their energy efficiency standards especially in the developed countries.
Efforts are being made both on the policy and technological fronts. While buildings performance
Sustainability 2017, 9, 640; doi:10.3390/su9040640
www.mdpi.com/journal/sustainability
Sustainability 2017, 9, 640
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regulations and standards are being made stringent through robust policy frameworks, technological
advancements are improvising effective solutions to help the cause.
Saudi Arabia is one of the largest countries in the Middle East in terms of geographic area,
economy and infrastructural development. Owing to factors like increasing population, modernization
and economic development, the energy demand in the country is rapidly surging. Estimates suggest
that between 2000 and 2014, the primary energy demand increased by over 100%. Buildings account
for almost 80% of the total electricity consumption in the country. The residential buildings alone
consume almost 50% of the total national power generation [1]. Owing to its rich oil and gas reserves,
it has traditionally cherished heavily-subsidized energy tariffs. The situation however is fast changing.
As of the recently announced strategic policy framework, Vision 2030, there are targets to remove
200 billion Saudi Riyals of energy subsidies by 2020 [7,8]. The situation is bound to bring a paradigm
shift in the energy consumption patterns. The role of energy conservation strategies and energy
efficiency measures is set to become critical. Green roofs can be applied as an energy saving options in
Saudi Arabia.
Green roofs are a passive strategy that can be a useful solution in different climates to reduce
energy consumption in buildings. It offers energy saving and reduction in GHG emissions while
enhancing the aesthetic qualities and architectural presentation of buildings [9]. It is being used as
an energy saving measure in countries around the world [10,11]. Although it can reduce the energy
demand in different climatic conditions, its performance mainly depends on climatic conditions,
building function, insulation of the building envelope and the type of green roof [12]. Green roofs
not only protect the roof from solar radiations and extensive heat fluctuations, but also maintain the
indoor temperature by working as insulation. In summer, it reduces the indoor air temperature of the
building by providing shading, insulation and evapotranspiration against the solar radiation, while
in winter, it works as a wind shield to reduce the heating loads, but the winter effect is less than the
summer effect.
The present work aims to investigate the prospects of the green roof, a passive energy saving
option, in hot climates by focusing on the climatic conditions of Saudi Arabia. Its main objectives are
as follows:
•
•
•
To examine the effectiveness of the green roof in hot climates in terms of energy saving.
To determine the impact of building materials in improving energy performance of buildings.
To study the influence of the orientation on the energy performance of buildings.
The above parameters have been investigated for modern residential villas situated in the city
of Dhahran. It is also important to mention that we are considering the same building in the Riyadh
climate, as well. Basically, Saudi Arabia has three main population bases, Dhahran/Dammam, Riyadh
and Jeddah. The twin cities of Dhahran and Dammam are situated on the east coast of the country,
while Jeddah is on the west coast. Both of these locations have quite similar climates, hot and humid.
The study has therefore chosen one of these locations, Dhahran, as the representative of the hot and
humid climate. Riyadh, on the other hand, has a predominant hot and dry climate. ECOTECT software
has been used to model the energy performance of these villas with wide ranging features.
2. Project Brief
The King Fahd University of Petroleum and Minerals situated in the city of Dhahran in Saudi Arabia
is one of the largest universities in the Middle East region. Owing to its on-campus huge infrastructure
consisting of academic and administration blocks, faculty and student residential buildings, community
centers, schools, workshops and warehouses, it presents an urban scale environment. Already having
over 1000 residential units for faculty and staff, it has constructed 200 new villas for faculty. Most of
these new villas are positioned north-south while some are oriented northeast-southwest. A small
proportion of villas also face northwest, as shown in Figure 1.
and some other composite materials. Windows are double glazed with aluminum frame. The HVAC
system used in these residential buildings is a constant-volume DX unit, while two separate units are
installed on the rooftop, one for each floor. The capacity of the HAVC system at the ground floor is
11.9 tons, and the supply of air flow is approximately 11.3 ACH. The capacity of the HVAC system on
the first floor is 9.4 tons, and the supply airflow is 9.4 ACH. The lighting power density at the ground
Sustainability 2017, 9, 640
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floor and first floor is respectively 21 W/m2 and 13 W/m2.
Sustainability 2017, 9, 640
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provided with two attached baths and one shared toilet, as shown in Figure 2b. The window-wall
ratio (WWR) is almost 10%. The structural members on the external facade are concrete masonry
units (CMU), hollow blocks, while the roof is constructed with reinforced cement concrete (RCC) slab
and some other composite materials. Windows are double glazed with aluminum frame. The HVAC
system used in these residential buildings is a constant-volume DX unit, while two separate units are
installed on the rooftop, one for each floor. The capacity of the HAVC system at the ground floor is
11.9 tons, and the supply of air flow is approximately 11.3 ACH. The capacity of the HVAC system on
the first floor is 9.4 tons, and the supply airflow is 9.4 ACH. The lighting power density at the ground
floor and first floor is respectively 21 W/m2 and 13 W/m2.
Figure 1. Compound
Compound consisting of 200 new villas inside KFUPM.
Each villa consists of two stories with almost 450 m2 of built-up area. The clearance height of each
story is 3 m. Main facilities provided on the ground floor are guest room, kitchen, dining, family dining,
laundry, toilets, store and service area, as shown in Figure 2a, while on first floor, four bedrooms are
provided with two attached baths and one shared toilet, as shown in Figure 2b. The window-wall
ratio (WWR) is almost 10%. The structural members on the external facade are concrete masonry
units (CMU), hollow blocks, while the roof is constructed with reinforced cement concrete (RCC) slab
and some other composite materials. Windows are double glazed with aluminum frame. The HVAC
system used in these residential buildings is a constant-volume DX unit, while two separate units are
installed on the rooftop, one for each floor. The capacity of the HAVC system at the ground floor is
11.9 tons, and the supply of air flow is approximately 11.3 ACH. The capacity of the HVAC system on
the first floor is 9.4 tons, and the supply airflow is 9.4 ACH. The lighting power density at the ground
Figure 1. Compound
of 2002new
floor and first floor is respectively
21 W/m2 consisting
and 13 W/m
. villas inside KFUPM.
(a)
(a)
Figure 2. Cont.
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(b)
Figure 2. (a) Ground Floor plan of KFUPM faculty housing; (b) first Floor plan of KFUPM faculty housing.
Figure 2. (a) Ground Floor plan of KFUPM faculty housing; (b) first Floor plan of KFUPM faculty housing.
3. Literature Review on the Green Roof
3. Literature Review on the Green Roof
Green roofs are one of the passive strategies used to reduce the heat transfer and improve the
thermal
comfort
of aofbuilding
or space
by application
of reduce
vegetation
thetransfer
roof. It not
only
reducesthe
Green
roofs
are one
the passive
strategies
used to
theon
heat
and
improve
direct and
radiation
incidences
on the roofof
[13],
but also improves
the life
of thereduces
roof
thermalthe
comfort
of adiffuse
building
or space
by application
vegetation
on the roof.
It span
not only
by
modifying
the
temperature
fluctuations
experienced
by
its
different
layers,
as
it
reduces
thethe
the direct and diffuse radiation incidences on the roof [13], but also improves the life span of
thermal
stresses
and
heat
aging
of
roof
components
[14].
Green
roofs
are
basically
composite
roof by modifying the temperature fluctuations experienced by its different layers, as it reduces the
structures in which plants are provided above a soil layer. Below the soil layer, a filter is provided to
thermal stresses and heat aging of roof components [14]. Green roofs are basically composite structures
stop the soil from washing. Rain water storage, which is plastic profile elements, substituting
in which plants are provided above a soil layer. Below the soil layer, a filter is provided to stop
draining gravel, is provided to store water for plants for the dry season. It also takes surplus water
the soiltofrom
washing.
water
storage,
which
is plastic the
profile
elements,
substituting
draining
the roof
gutter. Rain
A root
barrier
is provided
underneath
drainage
layer to
protect the watergravel, proofing
is provided
to
store
water
for
plants
for
the
dry
season.
It
also
takes
surplus
water
to the
membrane [15]. Alternatively, offsite prefabricated growing medium in the form of blocks
roof gutter.
A root
barrier
provided
underneath
drainage
layer
to can
protect
the water-proofing
can also
be used
withisplants
already
sprouted. the
In this
case, the
block
be easily
removed for
maintenance
purposes [16].
Thereprefabricated
are three types
of green
roofs, extensive,
semi-intensive
and
membrane
[15]. Alternatively,
offsite
growing
medium
in the form
of blocks can
also
intensive
green
roofs.
The
intensive
green
roof
is
relatively
heavy
weight
construction,
provided
on
be used with plants already sprouted. In this case, the block can be easily removed for maintenance
thick
growing
(soil),
and of
it requires
moreextensive,
maintenance
because of theand
types
of plantsgreen
used, roofs.
as
purposes
[16].
There media
are three
types
green roofs,
semi-intensive
intensive
it
creates
a
garden-like
environment
[17].
On
the
other
hand,
the
extensive
roof
is
light
weight
The intensive green roof is relatively heavy weight construction, provided on thick growing media
construction, which requires less maintenance and little human intervention because of less variety
(soil), and it requires more maintenance because of the types of plants used, as it creates a garden-like
of plant types.
environment [17]. On the other hand, the extensive roof is light weight construction, which requires
Studies show that the green roof is more effective in a hotter and drier climate as urban heat
less maintenance
human
intervention
ofroofs
less variety
plant types.
temperatureand
can little
be reduced
more
effectively because
[18]. Green
are moreofeffective
at reducing the heat
Studies
show
green roof
more 70–90%
effective
hotter
climate
as urban
heat
gain than
heatthat
loss,the
as according
to is
a study,
of in
theaheat
gainand
wasdrier
reduced
in summer,
while
temperature
can
be reduced
more [19].
effectively
[18].
Green
roofs
areon
more
effectivebuilding
at reducing
the heat
10–30%
of heat
loss in winter
From one
of the
studies
made
a residential
in Cairo,
it
was
found
that
the
cost
saving
of
the
green
roof
as
compared
to
the
conventional
roof
is
between
15
gain than heat loss, as according to a study, 70–90% of the heat gain was reduced in summer, while
32% [20].
From
another
it is concluded
17% of thebuilding
HVAC energy
10–30%and
of heat
loss in
winter
[19].study,
Frommade
one in
of Jordan,
the studies
made on athat
residential
in Cairo,
demand
canthe
be reduced
by using
the
greenroof
roofas
[21].
In another
done in a Mediterranean
it was found
that
cost saving
of the
green
compared
toresearch
the conventional
roof is between
a 6–49%
in energy
demand
was noticed
because of the
green
[22].HVAC
Green roofs
15 and climate,
32% [20].
Fromreduction
another study,
made
in Jordan,
it is concluded
that
17%roof
of the
energy
can also reduce storm water management by 40%, as according to a research undertaken in
demand can be reduced by using the green roof [21]. In another research done in a Mediterranean
Singapore, the green roof can reduce the peak flow by 65% and retain overall runoff by 11.6% for a
climate,maximum
a 6–49% 1-mm/min
reduction rainfall
in energy
demand was noticed because of the green roof [22]. Green roofs
intensity [23]. A surface temperature difference between the green roof
can alsoand
reduce
storm waterroof
management
byan40%,
as according
to aInresearch
undertaken
the conventional
was noted as
average
of 20 °C [14].
a research
conductedin
onSingapore,
porous
the green
roof
can
reduce
the
peak
flow
by
65%
and
retain
overall
runoff
by
11.6%
for
a
maximum
tiles in Guangzhou China, it is noted that the thermal performance of the roof is influenced
by
1-mm/min
rainfall
intensity
A tiles.
surface
difference
between
the
roof up
andtothe
moisture
content
in the [23].
porous
Thetemperature
surface temperature
of the
roof can
begreen
decreased
11.3 °C roof
if porous
contain
a sufficient
of [14].
waterIn
[24].
In the caseconducted
of the greenon
roof,
there is
conventional
wastiles
noted
as an
average amount
of 20 ◦ C
a research
porous
tiles
in Guangzhou China, it is noted that the thermal performance of the roof is influenced by moisture
content in the porous tiles. The surface temperature of the roof can be decreased up to 11.3 ◦ C if porous
Sustainability 2017, 9, 640
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tiles contain a sufficient amount of water [24]. In the case of the green roof, there is not only a soil layer
containing moisture content, but also plants provide shading above the whole roof surface.
There are many factors affecting green roof design, like thermal conductivity, specifics heat, density,
thermal absorptance, solar absorptance, height of plants, leaf area index, etc. A 150 mm–1200 mm soil
depth is required for the intensive green roof to support large plants, while growing media required
for the extensive roof can be 50–150-mm thick [19]. Moreover, the typical weight of the intensive green
roof is almost 290 kg/m2 –968 kg/m2 , while for the extensive green roof, it is from 20 to 169 kg/m2 [25].
The purpose of the thick soil layer is to create thermal mass, which not only increases the time lag,
but also reduces thermal transmittance. Furthermore, soil depth, organic matter and water balance in
the soil layer affect the soil thermal performance [26]. According to a study, a 10 cm-thick soil layer is
enough to control the heat penetration [19]. Another research work done in Singapore reveals that the
thermal resistance of roof can be increased by 0.4 KW for every 10-cm increase in the thickness of the
substrate layer with clay [27]. Water content the in soil layer also changes the thermal properties of it,
as more water content can increase the thermal conductivity of the layer [28]. Organic matter in soil
also maintains good soil structure [29]. Required benefits from plants can be achieved by providing
proper irrigation [30].
The vegetation layer not only creates good aesthetics, but is also good for the environment [31].
A change in the physical characteristics of plants changes the impact on the environment. In a harsh
climate, only limited species of plants can survive. Plants’ survivability in a hot climate also depends
on the availability of irrigation [32]. In a research work, after studying twelve different species (forbs,
sedum and grasses) commonly used for extensive green roofs, in three different combinations of plants
and three different water regimes (wet, moderate and dry), it is concluded that under dry conditions,
a diverse plant mix has greater survivability than a monoculture [33]. Moreover, sedums have better
drought tolerance than forbs and grasses. According to another study, the survival of plants depends
on plant water use, leaf succulence and substrate properties. Plants with high water holding capacity
and high succulence leaves survive longer [32]. Moreover, the mean thermal conductivity value for
leaves varies from 0.268 to 0.58 W/m2 K [17].
4. Climatic Analysis of Saudi Arabia and the Application of the Green Roof
Mostly, Saudi Arabia has a desert climate with extreme heat during the day and an abrupt
temperature drop during the night and low average annual rainfall, except in the province of Asir,
along the western coast, where an average of 300 millimeters of rainfall occurs from October to March.
The average summer temperature in Saudi Arabia is 45 ◦ C and can go up to 54 ◦ C [34]. The average
temperature during spring and autumn is 29 ◦ C, while in winter, it rarely drops to 0 ◦ C. Now, from the
literature review, it is clear that green roofs reduce the cooling load more significantly than heating
loads [19]. This is because of the plant foliage, which absorbs most of the solar radiation and makes
foliage hotter than the surrounding temperature. Additionally, the heat transfer to the roof system is
reduced as the substrate layer gets further cooled because of evapotranspiration. Hence, the green roof
can be very effective in the Saudi climate, which mostly has hot weather. Moreover, it can not only be
applied in new buildings, but also old buildings on the existing roof structure with only the addition of
green roof layers, and hence, it can be really helpful in reducing the Saudi buildings’ energy demand.
4.1. Dhahran Climate
Dhahran has a hot desert climate. The area within 40 km of this station is covered by oceans and
seas (77%), lakes and rivers (14%), shrublands (6%) and built-up areas (3%) [35]. Normally, summer
duration is from 15 May to 28 September, and the average daily high temperature is above 38 ◦ C.
The hottest day of the year, typically falling in July, has an average high temperature of over 43 ◦ C
and average low temperature of around 30 ◦ C. On the other hand, in winter, the average daily high
temperature is below 25 ◦ C, while the winter duration is from 3 December to 4 March. The coldest
day, typically towards the end of January, has an average high temperature of 20 ◦ C and a low of
Sustainability 2017, 9, 640
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11 ◦ C. The daylight hours on the shortest and longest days of the year, 21 December and 20 June,
are respectively 10.5 h and 14 h. From the end of November, the sky starts becoming cloudier, while
from the start of May, it starts appearing clearer. Over the year, relative humidity varies from 15% to
90%. Wind speed typically varies between 0 and 9 m/s. Precipitation occurs in the form of light rain,
moderate
rain and thunderstorms. Mostly, it is observed as moderate rain, which is 6almost
46% of
Sustainability 2017, 9, 640
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the total precipitation days [35]. During summer, from 15 May to 28 September, there is almost a 2%
respectively
and
14 h. point
From the
end ofaNovember,
theprecipitation
sky starts becoming
cloudier,
whilethere
from is an 18%
average
chance 10.5
thathat
some
during
given day,
will occur,
while
the
start
of
May,
it
starts
appearing
clearer.
Over
the
year,
relative
humidity
varies
from
15%
to
90%.
average chance that precipitation will occur at some point during a given day in winter,
which starts
Wind speed typically varies between 0 and 9 m/s. Precipitation occurs in the form of light rain,
from 3 December and ends on 4 March.
moderate rain and thunderstorms. Mostly, it is observed as moderate rain, which is almost 46% of
the total precipitation days [35]. During summer, from 15 May to 28 September, there is almost a 2%
4.2. Riyadh Climate
average chance that at some point during a given day, precipitation will occur, while there is an 18%
average
chance
thatDhahran,
precipitation
will occur
at some
during
day in winter,
whichthroughout
starts
In
contrast
with
Riyadh’s
climate
is point
hot and
dry.a given
Temperature
variation
the
from 3 December
◦ and ends ◦on 4 March.
◦
year is between 8 C and 43 C. The average daily high temperature is above 39 C during summer,
which4.2.
starts
onClimate
14 May and ends on 26 September. The average high temperature is 43 ◦ C, while the
Riyadh
◦
low is 28 C on the hottest day of the year ,which is in August [36]. The average daily high temperature
In contrast with Dhahran, Riyadh’s climate is hot and dry. Temperature variation throughout
is below
24 ◦ C during winter, which lasts from December–February. On the coldest day of the year,
the year is between 8 °C and 43 °C. The average daily high temperature is above 39 °C during
whichsummer,
is typically
January,
the average
low temperatures
are temperature
19 ◦ C and 8is◦43
C,°C,
respectively.
whichin
starts
on 14 May
and endshigh
on 26and
September.
The average high
Like Dhahran,
daylight
is also
available
Riyadh
for almost
10.5[36].
h onThe
theaverage
shortest
day
of the year,
while the low
is 28 °C on
the hottest
day ofinthe
year ,which
is in August
daily
high
is belowwhile
24 °C during
winter,which
which is
lasts
December–February.
Onitthe
dayfor almost
whichtemperature
is 21 December,
on 20 June,
thefrom
longest
day of the year,
is coldest
available
the year,humidity
which is typically
in January,
the average
high
and6%
lowto
temperatures
arethe
19 °C
andbut
8 °C,
14 h. of
Relative
in Riyadh
normally
changes
from
71% during
year,
sometimes,
respectively. Like Dhahran, daylight is also available in Riyadh for almost 10.5 h on the shortest day
it may reach 96% as the high and can drop to 3% as the low. Typical wind speed is between 0 m/s
of the year, which is 21 December, while on 20 June, which is the longest day of the year, it is available
and 7for
m/s.
Mostly,
the wind
is blowing
fromnormally
north almost
time,
and 11%
of time,
almost
14 h. Relative
humidity
in Riyadh
changes17%
fromof
6%the
to 71%
during
the year,
but it is also
coming
from theit northwest.
Tenas
percent
of and
time,
wind
from
the south,
whileis12% of the
sometimes,
may reach 96%
the high
can
dropistoalso
3% coming
as the low.
Typical
wind speed
m/s and 7m/s.
Mostly,
the wind isThere
blowing
17% of the
time, and
of
time, between
it is also0 blowing
from
the southeast.
arefrom
12%north
andalmost
2% average
chances
that11%
moderate
rain
time,
it
is
also
coming
from
the
northwest.
Ten
percent
of
time,
wind
is
also
coming
from
the
south,
occurs during winter and summer, respectively.
while 12% of the time, it is also blowing from the southeast. There are 12% and 2% average chances
that moderate
5. Material
Used rain occurs during winter and summer, respectively.
5. Material
Used we will discuss the material used in this faculty housing project and our proposal
In
this section,
for the green
section.
the external
wall
section,
100 mm-thick
CMUand
blocks
are used on the
In thisroof
section,
we willIndiscuss
the material
used
in this faculty
housing project
our proposal
innerfor
and
of the wall
a 50wall
mm-thick
polystyrene
layerblocks
in the
The thermal
theouter
green side
roof section.
In thewith
external
section, 100
mm-thick CMU
aremiddle.
used on the
inner andvalue
outer for
sidethe
of the
wallsection
with a 50
mm-thick polystyrene
layer2in
middle.
The
thermal
conductivity
whole
is calculated
as 0.530 W/m
K,the
which
is bit
higher,
so a further
2K, which is bit higher, so a further
conductivity
value
for
the
whole
section
is
calculated
as
0.530
W/m
increase in the insulation thickness can reduce the thermal conductivity value of the section. Figure 3
increase in the insulation thickness can reduce the thermal conductivity value of the section. Figure
shows the x-section of the external wall and its thermal properties. Moreover, in partition walls, again,
3 shows the x-section of the external wall and its thermal properties. Moreover, in partition walls,
150-mm
CMU
blocks
are
usedare
with
on both
sides.
again,
150-mm
CMU
blocks
usedplaster
with plaster
on both
sides.
Figure
3. External
x-sectionand
and
properties.
concrete
units.
Figure
3. Externalwall
wall x-section
its its
properties.
CMU,CMU,
concrete
masonrymasonry
units.
In the existing roof section, a 300 mm-thick ribbed concrete slab is used as the structural member,
In the
existing roof section, a 300 mm-thick ribbed concrete slab is used as the structural member,
and above it, cement screed is provided for sloping purposes. The bitumen layer is there above the
and above
it, cement screed is provided for sloping purposes. The bitumen layer is there above the
concrete layer for water proofing. Fifty millimeter-thick polystyrene is used as insulation, which
concrete
layer
for water
millimeter-thick
used
as critical
insulation,
which might
might be less,
as 70% proofing.
of the heatFifty
is absorbed
by the roof, polystyrene
so this may beisthe
most
area that
Sustainability 2017, 9, 640
7 of 18
2017, 9, 640
18
be Sustainability
less, as 70%
of the heat is absorbed by the roof, so this may be the most critical area7 of
that
needs
Sustainability 2017, 9, 640
7 of 18
more
attention.
Above
the
insulation
layer,
again,
the
water-proofing
membrane
is
provided
with
Sustainability
2017, 9, 640 Above the insulation layer, again, the water-proofing membrane is provided
7 of 18 the
needs
more attention.
cement
tile
onattention.
top.tile
The
thermal
conductivity
value,
calculated
for the
section,
0.490
W/m2 K,
needsthe
more
thethermal
insulation
layer,
again,
thecalculated
water-proofing
isisprovided
with
cement
onAbove
top. The
conductivity
value,
forwhole
themembrane
whole
section,
is 0.490
needs
more
attention.
Above
the
insulation
layer,
the
water-proofing
membrane
is is
provided
with
cement
on top.
thermal
conductivity
value,
calculated
for properties.
the whole
section,
0.490
which
is2the
high.
Figure
4The
shows
roofthe
x-section
and
its
thermal
W/m
K,again
which
istile
again
high.
Figure
4the
shows
roof again,
x-section
and
its thermal
properties.
2K,the
with
cement
tile on
top.Figure
The thermal
conductivity
value, calculated
for the
whole section, is 0.490
W/m
which
is again
high.
4 shows
the roof x-section
and its thermal
properties.
W/m2K, which is again high. Figure 4 shows the roof x-section and its thermal properties.
Figure4.4.Existing
Existing
roof
x-section
its properties.
Figure
roof
x-section
andand
its properties.
Figure 4. Existing roof x-section and its properties.
Figure
4. Existing
roofwith
x-section
and its properties.
In windows, low-e double
glazing
is used
an aluminum
frame, which has a U-value of
In In
windows,
low-e
double
glazing isused
used
with an
aluminum frame,
which has a U-value of
windows,
low-e
double
glazing is
with an
which has a U-value of
2K. Figure
2.71 W/m
5 shows
the window
glass section
andaluminum
its thermalframe,
properties.
2 K.
2.71
W/m
Figure
5
shows
the
window
glass
section
and
its
thermal
properties.
2
In windows,
glazingglass
is used
with
anits
aluminum
frame, which has a U-value of
2.71 W/m
K. Figure 5low-e
showsdouble
the window
section
and
thermal properties.
2.71 W/m2K. Figure 5 shows the window glass section and its thermal properties.
Figure 5. Double-glazed window section and its properties.
Figure
5. Double-glazed
Double-glazed
window
section
its properties.
Figure 5.
window
section
and and
its properties.
Double-glazed
window calculations,
section and its no
properties.
Since ceiling sectionFigure
does 5.
not
influence thermal
thermal insulation layer is
Sinceinceiling
section
does Gypsum
not influence
thermal
calculations,
no thermal
is
provided
the
ceiling
section.
board
is
placed
as
a
false
ceiling
with
a insulation
600-mm
airlayer
gap to
Since ceiling section does not influence thermal calculations, no
thermal
insulation
layer is
Since
ceiling
section
does
not
influence
thermal
calculations,
no
thermal
insulation
layer
is
provided
in
the
ceiling
section.
Gypsum
board
is
placed
as
a
false
ceiling
with
a
600-mm
air
gap
to
provide air-conditioning ducts. Figure 6 shows the ceiling section and its properties.
provided
in the
ceiling section.
Gypsum
board
is placed
placedasasa afalse
false ceiling
with a 600-mm air gap to
provided
in the ceilingducts.
section.
Gypsum
board
with a 600-mm air gap to
provide
air-conditioning
Figure
6 shows
theisceiling
section andceiling
its properties.
provide
air-conditioning
ducts.
Figure
ceilingsection
sectionand
and
properties.
provide
air-conditioning
ducts.
Figure66shows
shows the
the ceiling
itsits
properties.
Figure 6. Ceiling section and its properties.
Figure 6. Ceiling section and its properties.
Ceiling section
its properties.
In the floor section, a plain Figure
cement6.concrete
(PCC)and
layer
is provided with ceramic tiles on the
Figure 6. Ceiling
section
and itsisproperties.
In theisfloor
section,
a plain
concrete
(PCC)
with
ceramic
tiles onThe
the
top. PCC
placed
on a layer
of cement
gravel, while
below
thelayer
gravel,provided
compacted
earth
is provided.
In
the
floor
section,
a
plain
cement
concrete
(PCC)
layer
is
provided
with
ceramic
tiles
on
top.
PCC
is
placed
on
a
layer
of
gravel,
while
below
the
gravel,
compacted
earth
is
provided.
The
2
U-value of the section is 0.47 W/m K. Figure 7 shows the floor x-section and its thermal properties. the
top.
PCC
is placed
on
aplain
layer
of2K.
gravel,
while
below
gravel,
compacted
earth
is properties.
provided.
U-value
of
the
section
isa0.47
W/m
Figure
7 shows
thethe
floor
x-section
and its
thermal
In the
floor
section,
cement
concrete
(PCC)
layer
is provided
with
ceramic
tiles onThe
the top.
2K. Figure 7 shows the floor x-section and its thermal properties.
ofon
theasection
is 0.47
W/mwhile
PCC U-value
is placed
layer of
gravel,
below the gravel, compacted earth is provided. The U-value
of the section is 0.47 W/m2 K. Figure 7 shows the floor x-section and its thermal properties.
Sustainability 2017, 9, 640
Sustainability
Sustainability 2017,
2017, 9,
9, 640
640
8 of 18
88 of
of 18
18
Figure 7.
7. Ground floor
floor section and
and its properties.
properties.
Figure
Figure 7. Ground
Ground floor section
section and its
its properties.
In
we
are
assuming
to
the
green
roof
In the
proposedgreen
greenroof
roofsection,
section,
we
assuming
to provide
the
extensive
green
roof
not
the proposed
proposed
green
roof
section,
we
areare
assuming
to provide
provide
the extensive
extensive
green
roof not
not only
only
taking
into
consideration
the
load-bearing
capacity
of
the
existing
structure,
but
also
due
to
only
taking
into consideration
the load-bearing
capacity
of existing
the existing
structure,
to
taking
into consideration
the load-bearing
capacity
of the
structure,
but but
also also
due due
to the
the
maintenance
factor
of
the
green
roof.
It
is
also
important
to
mention
that
a
shallow
soil
depth
may
the
maintenance
factor
of green
the green
is also
important
to mention
a shallow
soil depth
maintenance
factor
of the
roof.roof.
It is It
also
important
to mention
that that
a shallow
soil depth
may
result
in
root
damage
from
heat
and
temperature
may
in plants’
damage
from
heat
and
temperaturefluctuation,
fluctuation,and
and2223/4”
3/4”soil
soil substrate
substrate is
is
resultresult
in plants’
plants’
rootroot
damage
from
heat
and
temperature
fluctuation,
and
3/4”
soil
is
suggested
by
some
of
the
green
roof
companies
for
the
extensive
green
roof;
but,
still
it
is
suggested
of the
roof companies
for the extensive
green roof;green
but, still
it is but,
recommended
suggestedby
bysome
some
of green
the green
roof companies
for the extensive
roof;
still it is
recommended
to
3”
layer.
For
green
provision,
we
to
provide minimum
a 3”minimum
deep soilaalayer.
Forsoil
green
roof
provision,
are considering
green roof
recommended
to provide
provide
minimum
3” deep
deep
soil
layer.
For
green roof
roofwe
provision,
we are
are considering
considering
green
roof
layers
on
existing
conventional
roofs,
where
reinforced
cement
concrete
(RCC
slab)
layers
on
existing
conventional
roofs,
where
reinforced
cement
concrete
(RCC
slab)
is
used
the
green roof layers on existing conventional roofs, where reinforced cement concrete (RCC slab) is
isasused
used
as
the
main
structural
member
and
above
which
bitumen
is
provided
as
the
water-proofing
main
member member
and above
which
bitumen
provided
the water-proofing
membrane.
as thestructural
main structural
and
above
which isbitumen
is as
provided
as the water-proofing
membrane.
same
mm-thick
insulation
layer
the
The
same 50The
mm-thick
polystyrene”
layer is considered
above theabove
bitumen,
membrane.
The
same 50
50insulation
mm-thick “extruded
insulation “extruded
“extruded polystyrene”
polystyrene”
layer is
is considered
considered
above
the
bitumen,
which
is
provided
in
the
existing
roof
structure,
so
the
true
effect
of
the
green
roof
could
which
is provided
the existing
structure,
so the trueso
effect
of the
green
couldroof
be observed.
bitumen,
which is in
provided
in theroof
existing
roof structure,
the true
effect
of roof
the green
could be
be
observed.
The
root
barrier
with
the
water
proofing
membrane
is
provided
above
the
insulation
layer
The
root barrier
with
the water
is providedisabove
the insulation
layer to protect
observed.
The root
barrier
with proofing
the watermembrane
proofing membrane
provided
above the insulation
layer
to
the
and
the
damage.
water
system,
which
the
insulation
and the other
from
any from
damage.
waterThe
drainage
system, which
not
only
to protect
protect
the insulation
insulation
andstructure
the other
other structure
structure
from any
any The
damage.
The
water drainage
drainage
system,
which
not
only
stores
rainwater,
but
also
takes
excessive
water
to
the
gutter,
is
provided
above
the
root
stores
rainwater,
but also takes
to thewater
gutter,
provided
the root
barrier
not only
stores rainwater,
but excessive
also takeswater
excessive
toisthe
gutter, above
is provided
above
thelayer.
root
barrier
layer.
The
drainage
system
is
basically
recycled
plastic
modular
elements,
normally
having
aa
The
drainage
system
is basically
recycled
plastic
modular
elements,
normally
having
a 6-cm
height.
barrier
layer. The
drainage
system
is basically
recycled
plastic
modular
elements,
normally
having
6-cm
Above
drainage
layer,
mm-thick
soil
is
Above
the drainage
layer,
a 150 mm-thick
soil
bed is placed,
and
we are and
considering
150 mm as 150
the
6-cm height.
height.
Above the
the
drainage
layer, aa 150
150
mm-thick
soil bed
bed
is placed,
placed,
and we
we are
are considering
considering
150
mm
as
the
plant
height
above
the
soil
layer.
While
creating
the
green
roof
section
on
the
software
plant
height
above
the soil
layer.
creating
thecreating
green roof
on the
software
ECOTECT,
mm as
the plant
height
above
theWhile
soil layer.
While
the section
green roof
section
on the
software
ECOTECT,
we
aa 300
mm-thick
layer
for
soil
as
are
as
we
are considering
a 300 mm-thick
for soil
and
plants,
as plants,
plants
not available
as material
ECOTECT,
we are
are considering
considering
300layer
mm-thick
layer
for
soil and
and
plants,are
as plants
plants
are not
not available
available
as
material
on
the
software,
and
the
green
roof
main
section
(soil
layer
and
plants)
works
as
thermal
on
the software,
and the green
roof
mainroof
section
layer(soil
andlayer
plants)
asworks
thermal
or
material
on the software,
and the
green
main(soil
section
andworks
plants)
as mass
thermal
mass
or
shading
on
existing
roof
so
thick
can
resolve
the
as
shading
the existing
structure,
so considering
one thickone
layer
canlayer
resolve
problem.
mass
or as
as on
shading
on the
the roof
existing
roof structure,
structure,
so considering
considering
one
thick
layer
canthe
resolve
the
2
2 K W/m
problem.
The
thermal
value
for
green
roof
is
The
thermal
value calculated
for this green
roof
section
0.190 W/m
since
we
did
problem.
Theconductivity
thermal conductivity
conductivity
value calculated
calculated
for this
this
green
roofissection
section
is 0.190
0.190
W/m2K
K since
since
we
did
not
change
the
thickness
of
the
insulation,
as
used
in
the
conventional
roof
section.
The
not
thickness
of the insulation,
as used in
conventional
roof section.
thermal
we change
did not the
change
the thickness
of the insulation,
as the
used
in the conventional
roof The
section.
The
thermal
value
of
the
green
be
improved
changing
the
conductivity
value of the
green
can
furthercan
improved
by changing
theby
specification
thermal conductivity
conductivity
value
ofroof
thesection
green roof
roofbesection
section
can
be further
further
improved
by
changing and
the
specification
and
thicknesses
of
insulation,
soil
layer
and
plants.
Figure
8
shows
the
x-section
of
the
thicknesses
of
insulation,
soil
layer
and
plants.
Figure
8
shows
the
x-section
of
the
proposed
green
specification and thicknesses of insulation, soil layer and plants. Figure 8 shows the x-section of the
proposed
green
roof
its
Since
are
considering
the
extensive
on
roof
and its
properties.
Since
we are considering
green
on the green
existing
structure,
proposed
green
roof and
and
its properties.
properties.
Since we
wethe
areextensive
considering
theroof
extensive
green roof
roof
on the
the
existing
structure,
planned
use
aa combination
forbs,
sedum
and
grasses,
which
we
planned
to use awe
combination
forbs,
sedum and of
grasses,
better
survivability
inbetter
a hot
existing
structure,
we
planned to
toof
use
combination
of
forbs, which
sedumhas
and
grasses,
which has
has
better
survivability
in
climate,
like
Arabia,
as
in
the
climate,
like Saudi
Arabia,
as discussed
the literature
review
survivability
in aa hot
hot
climate,
like Saudi
Saudiin
Arabia,
as discussed
discussed
in[33].
the literature
literature review
review [33].
[33].
Figure
Figure 8.
8. Proposed
Proposed green
green roof
roof
section
and
its
properties.
roof section
section and
and its
its properties.
properties.
6.
6. Thermal
Thermal Analysis
Analysis
All
All analyses
analyses are
are made
made on
on the
the software
software ECOTECT.
ECOTECT. ECOTECT
ECOTECT by
by Autodesk
Autodesk is
is aa unique
unique building
building
performance
analysis
software
that
performs
a
variety
of
analyses
with
simple
and
performance analysis software that performs a variety of analyses with simple and intuitive
intuitive 3D
3D
Sustainability 2017, 9, 640
9 of 18
6. Thermal Analysis
All analyses are made on the software ECOTECT. ECOTECT by Autodesk is a unique building
Sustainability 2017, 9, 640
9 of 18
performance analysis software that performs a variety of analyses with simple and intuitive 3D
modeling. It is user-friendly interface, and compatibility with other software like AutoCAD, REVIT,
modeling. It is user-friendly interface, and compatibility with other software like AutoCAD, REVIT,
etc., makes it popular among designers to use from the conceptual to the design stage. It can perform
etc., makes it popular among designers to use from the conceptual to the design stage. It can perform
analysis like solar stereographic shadows, overshadowing and solar reflection, sun penetration and
analysis like solar stereographic shadows, overshadowing and solar reflection, sun penetration and
shading,
of artificial
lighting,
solar access
photovoltaic/heat
collection,collection,
acoustic reflections
shading,analysis
analysis
of artificial
lighting,
solar and
access
and photovoltaic/heat
acoustic
and
reverberation
times
and
hourly
thermal
comfort
and
monthly
space
loads
with
a weather
toola
reflections and reverberation times and hourly thermal comfort and monthly space
loads with
option
for
a
specific
location
[37].
Especially,
“solar
access
analysis”
to
calculate
the
incident
solar
weather tool option for a specific location [37]. Especially, “solar access analysis” to calculate the
radiation
and the
“shading
design
wizard” to
designwizard”
the proper
shading
make
it prominent
amongit
incident solar
radiation
and
the “shading
design
to design
the
proper
shading make
other
software.
Difficulty
in
creating
complex
geometry
and
lacking
study
of
the
fluid
dynamics
prominent among other software. Difficulty in creating complex geometry and lacking study of are
the
some
limitations
that
this
software
has.
fluid dynamics are some limitations that this software has.
Heating
Heating and
and cooling
cooling loads
loads are
are aa measure
measure of
of energy
energy needs
needs to
to be
be added
added or
or removed
removed from
from aa space
space
by
either
mechanical
or
natural
systems
to
provide
the
desired
level
of
comfort
within
a
space
by either mechanical or natural systems to provide the desired level of comfort within a space [38].
[38].
Heating
Heating and
and cooling
cooling loads
loads help
help in
in choosing
choosing the
the type
type of
of system
system and
and its
its capacity.
capacity. This
This also
also helps
helps in
in
choosing
choosingduct
ductsizes
sizesand
andits
itstype.
type. These
These loads
loads have
have aa direct
direct impact
impact on
on the
the construction
construction and
and operational
operational
cost,
and
building
durability.
To do
analyses,
we prepared
two separate
models
cost,occupant
occupantcomfort
comfort
and
building
durability.
Tothese
do these
analyses,
we prepared
two separate
with
the with
samethe
materials
on the walls,
floors,
ceiling,
windows
and doors,and
as shown
one
models
same materials
on the
walls,
floors,
ceiling, windows
doors, in
asFigure
shown9.inOn
Figure
model,
the
conventional
roof
material
was
applied,
while
on
the
other,
the
green
roof
was
considered.
9. On one model, the conventional roof material was applied, while on the other, the green roof was
Monthly
loadMonthly
discomfort
wasanalysis
run afterwas
making
the zone
settings.
Thesettings.
weatherThe
dataweather
file for
considered.
loadanalysis
discomfort
run after
making
the zone
Dhahran’s
climate
is
not
available
in
ECOTECT,
so
we
are
considering
the
Kuwait
coastal
area
climate
data file for Dhahran’s climate is not available in ECOTECT, so we are considering the Kuwait coastal
for
analysis,
many other
products
do the
same by
area
climate since
for analysis,
sincesoftware
many other
software
products
dodefault.
the same by default.
(a)
(b)
Figure 9.
9. Models
Models of
of faculty
faculty housing:
housing: (a)
(a) with
with conventional
conventional roof;
roof; (b)
(b) with
with green
greenroof.
roof.
Figure

•

•
•
•
•
•
The main considerations while making the analysis, as also shown in Figure 10, were:
The main considerations while making the analysis, as also shown in Figure 10, were:
Design for the full air-conditioning system due to the hot weather of Saudi Arabia, where airDesign
for the
air-conditioning
systema day
due for
to the
hot weather of Saudi Arabia, where
conditioning
is full
required
twenty four hours
12 months.
air-conditioning
is
required
twenty
four
hours
a
day
for
12
months.
Thermostat range: 18–26 °C.
◦
Thermostat
range:24
18–26
C.
Operating hours:
h/day.
Air
speed:
0.50
m/s.
Operating hours: 24 h/day.
Clothing
1.0.
Air
speed:factor:
0.50 m/s.
Air
change
rate:
0.50.
Clothing factor: 1.0.
Wind
sensitivity:
0.25.
Air change rate: 0.50.
•
Wind sensitivity: 0.25.
Sustainability 2017, 9, 640
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Figure 10. Zone setting for both models.
7. Results
Figure 10. Zone setting for both models.
7. Results
analysis informs
informs us about the total energy demand of the building including
Load
discomfort analysis
cooling
loads.
Monthly
load
discomfort
analysis
is made
madeoffor
for
Dhahran
heating and
Monthly
load
discomfort
analysis
is
region while
Load discomfort analysis informs
us about
the total
energy demand
theDhahran
building including
the
Kuwait
coastal
area
weather
data
file,
as
the
Dhahran
weather
data
file
is
notfile
available
considering
the
Kuwait
coastal
area
weather
data
file,
as
the
Dhahran
weather
data
is not
heating and cooling loads. Monthly load discomfort analysis is made for Dhahran region
while
considering
Kuwait
weather
data
file,that
as we
the are
Dhahran
weather
data file
is not
in ECOTECT.
It isthe
also
important
toarea
mention
that
we are
considering
detached
housing
to understand
available
in ECOTECT.
It is coastal
also important
to
mention
considering
detached
housing
to
availablethe
ininECOTECT.
It
also because
important
mention
that
we
are considering
detached
housing
tothese
the reduction
energy demand
oftothe
building
orientation;
otherwise,
these
houses
are
understand
reduction
inisenergy
demand
because
of the
building
orientation;
otherwise,
understand
thein
reduction
in orientations
energy
of theurban
building
orientation;
theseinbrief.
placed
in
orientations
and thedemand
proper
urban
arrangement,
as
discussedotherwise,
in discussed
the project
houses
aredifferent
placed
different
andbecause
the proper
arrangement,
as
the
houses
are
placed
in
different
orientations
and
the
proper
urban
arrangement,
as
discussed
in
The selected
building
is analyzed
four different
orientations,
east facing, west
facing,
project
brief. detached
The selected
detached
buildingwith
is analyzed
with four
different orientations,
eastthe
facing,
project brief. The selected detached building is analyzed with four different orientations, east facing,
northfacing,
facing north
and south
facing.
Initially,
analysis
is made
with the
existing
roof
understand
west
facing
and south
facing.
Initially,
analysis
is made
with
thestructure
existing to
roof
structure
west facing, north facing and south facing. Initially, analysis is made with the existing roof structure
theunderstand
orientation,the
consuming
the maximum
of energy.
Figureof11,
shows Figure
the results
generated
to
orientation,
consumingamount
the maximum
amount
energy.
11, shows
the
to understand the orientation, consuming the maximum amount of energy. Figure 11, shows the
by the
software
with
eastand
north-facing
models
and
with
the
conventional
(existing)
roof.
These
results
generated
by
the
software
with
eastand
north-facing
models
and
with
the
conventional
results generated by the software with east- and north-facing models and with the conventional
results
areroof.
summarized
in
Table
1summarized
and
Figure 12.
(existing)
These
results
areare
in
andFigure
Figure
(existing)
roof.
These
results
summarized
in Table
Table 11and
12.12.
North
with
conventional
RoofRoof
in Dhahran((with
Northfacing
facingbuilding
building
with
conventional
in Dhahran((with
East facing
building
conventional
Roof
Dhahran(with
East facing
building
withwith
conventional
Roof
inin
Dhahran(with
Kuwait
Coastal
area
climate),
SaudiSaudi
ArabiaArabia
Kuwait
Coastal
climate),
Saudi
Arabia
Kuwait
Coastal
area
climate),
Kuwait
Coastal
areaarea
climate),
Saudi
Arabia
MONTHLY
HEATING/COOLING
LOADS
MONTHLY
HEATING/COOLING
LOADS
MONTHLY
HEATING/COOLING
LOADS
MONTHLY
HEATING/COOLING
LOADS
All Visible Thermal Zones
All Visible Thermal Zones
All Visible Thermal Zones
All Visible
Thermal Zones
Comfort: Zonal Bands
Comfort: Zonal Bands
Comfort: Zonal Bands
Comfort: Zonal Bands
Max Heating: 8504 W at 07:00 on 31st December
Max Heating: 8504 W at 07:00 on 31st December
Max
Heating:
8504 W at 07:00 on 31st December
Max Heating:
8504
W
at
07:00
on
31st
December
Max Cooling: 16089 W at 15:00 on 20th August
Max Cooling: 15660 W at 15:00 on 20th August
MaxHEATING
Cooling: 16089COOLING
W at 15:00 on 20th August
Max Cooling:HEATING
15660 W at 15:00
on 20th August
COOLING
TOTAL
TOTAL
COOLING
TOTAL
HEATING
COOLING
MONTH HEATING
(Wh)
(Wh)
(Wh)
MONTH
(Wh)
(Wh)
(Wh) TOTAL
MONTH
(Wh)
MONTH
(Wh)
(Wh) 0
(Wh)
888176
888176
Jan
871656(Wh)
0 (Wh)
871656 Jan
216085
216085 Jan
Feb
225320
0 0
225320888176
888176
Jan Feb
871656
0 0
871656
Mar
4786
48152 0
52938225320
45712
49662 Feb
Feb Mar
2160853950
0
216085
225320
1453126
1453126
Apr
0
148004248152
1480042 52938
4786
Mar Apr
3950 0
45712
49662 Mar
0
4078471
4078471
4033749
4033749 May
Apr May
0 0 1453126
1453126
Apr
0
1480042
1480042
0
5247624
5247624
Jun
0
5212540
5212540 Jun
0
4078471
4078471
May
0
4033749
4033749 May
0
6053633
6053633
Jul
0
5998248
5998248 Jul
Jun
0
5247624
5247624
Jun Aug
0 0 5212540
5212540
0
6837556
6837556
6780110
6780110 Aug
Jul
0
6053633
6053633
Jul
0
5998248
5998248
0
4832337
4832337
Sep
0
4801960
4801960 Sep
6837556
6837556
Aug Oct
0 0 6780110
6780110
Oct
0 0
2655952
2655952
2642203
2642203 Aug
4832337
4832337
Sep Nov
0 411 4801960
4801960
Nov
740 0
120732
121472
121788
122199 Sep
Dec
638493 0
0
638493
628528
628528 Oct
2655952
2655952
Oct Dec
0
2642203 0
2642203
TOTAL
1757515740
31354500
33112016121472
1720630
31089436
32810066
120732
Nov TOTAL
411
121788
122199 Nov
PER M²
7516
134082 0
141598638493
132949
140307 Dec
638493
Dec PER M²
6285287358
0
628528
Floor Area:
233.846 m2
233.846 m2
1757515
31354500
33112016
TOTALFloor Area:
1720630
31089436
32810066 TOTAL
7516
134082
141598
PER M²
7358
132949
140307 PER M²
Figure
11.
Monthly
Loaddiscomfort
discomfort analysis
analysis
in
with
conventional
roof.roof.
Floor Area:
233.846
m2thethe
Floor Area:
233.846
m2
Figure
11.
Monthly
Load
inDhahran
Dhahran
with
conventional
Figure 11. Monthly Load discomfort analysis in Dhahran with the conventional roof.
Sustainability 2017,
2017, 9,
9, 640
640
Sustainability
11 of
of 18
18
11
Table 1. Total Energy demand comparison with four different orientations and the conventional roof in
Table
1. Total Energy demand comparison with four different orientations and the conventional roof
Dhahran.
in Dhahran.
Conventional Roof in Dhahran, Total Energy Demand Comparison
Conventional
in Dhahran,
Total Energy
Demand Comparison
(Monthly
LoadRoof
Discomfort
Analysis)
with Different
Orientation
(Monthly Load Discomfort Analysis) with Different Orientation
Heating Load
Heating Load
Orientation (KWh/m2Y) 2
Orientation
East facing
East facing
North Facing
North Facing
West facing
West facing
South facing
South facing
(KWh/m Y)
7.4
7.5
7.3
7.3
Cooling Load
Cooling Load
2Y)
(KWh/m
2
(KWh/m Y)
132.9
132.9
134.1
134.1
133.3
133.3
134.0
134.0
7.4
7.5
7.3
7.3
Total Energy Demand
Total Energy
Demand
2Y)
(KWh/m
(KWh/m2 Y)
140.3
140.3
141.6141.6
140.6140.6
141.3
141.3
Conventional Roof in Dhahran, Total
Energy demand comparison with
different orientation
Total energy demand (KWh/m2Y )
142.0
141.0
140.0
139.0
East
North
West
South
Figure 12. Total energy demand comparison with four different orientations and the conventional roof
Figure 12. Total energy demand comparison with four different orientations and the conventional roof
in Dhahran.
in Dhahran.
The difference in energy demand for the four orientations is minor with the east-facing one
The difference
in energy
theshown
four orientations
is minor with
east-facing one
2Y as
consuming
the minimum,
140.3demand
KWh/mfor
in Table 1. West-facing
andthe
north-south-facing
2
consuming
minimum,consume
140.3 KWh/m
Y as shown
in141.6
TableKWh/m
1. West-facing
and
2Y and
2Y. It can
orientationsthe
respectively
140.6 KWh/m
be north-south-facing
concluded that the
2 Y and 141.6 KWh/m2 Y. It can be concluded that the
orientations
respectively
consume
140.6
KWh/m
east-west orientation is consuming less compared to the other three because the longitudinal axis of
east-west
orientation
consuming and
less since
compared
to theside
other
threeexposed
because to
thesun
longitudinal
axis
the building
is facing isnorth-south,
the north
is least
and the one
ofofa
the
building
is
facing
north-south,
and
since
the
north
side
is
least
exposed
to
sun
and
the
one
of
a
longer elevation is mostly under shade, so mainly the heat transmission is from the south side only.
longer
elevation
is
mostly
under
shade,
so
mainly
the
heat
transmission
is
from
the
south
side
only.
It also depends on the number of windows provided at different elevations. Furthermore, even if we
It
depends
on thethe
number
windows with
provided
at different elevations.
Furthermore,
evenbetter
if we
arealso
going
to consider
sameof
orientation
the neighborhood,
the results
would be even
are
going
to
consider
the
same
orientation
with
the
neighborhood,
the
results
would
be
even
better
as now, the southern side of the building will also be under shade because of the adjacent building.
as
the southern
of the facing
building
willoralso
be is
under
shade because
of the adjacent
building.
Onnow,
the other
hand, theside
building
south
north
consuming
the maximum
amount of
energy
On
the
other
hand,
the
building
facing
south
or
north
is
consuming
the
maximum
amount
of
energy
since the longitudinal axis is facing east-west, and this will be exposed to sun either in the morning
since
the
longitudinal
axis
is
facing
east-west,
and
this
will
be
exposed
to
sun
either
in
the
morning
or
or in the afternoon; but the front elevation along the south is exposed to sun most of time, as this time
in
the afternoon;
butexposed
the fronttoelevation
alongthe
theshorter
south axis,
is exposed
sun most
of time,
as this time
north,
which is least
sun, is along
so totaltoenergy
demand
is higher.
north,
which
is
least
exposed
to
sun,
is
along
the
shorter
axis,
so
total
energy
demand
is
higher.
The monthly load discomfort analysis in four different orientations with conventional (existing
monthly
load discomfort
analysis
in four
different
with
(existing
roof)The
roofs
are repeated
in the Riyadh
climate,
and
almostorientations
a similar type
ofconventional
trend is observed,
as
roof)
roofs
are
repeated
in
the
Riyadh
climate,
and
almost
a
similar
type
of
trend
is
observed,
as
shown
shown in Table 2 & Figure 13. The east-west-oriented building is consuming a lesser amount of
in
Table 2but
& Figure
13. The east-west-oriented
building
is consuming
a lesser amount
of energy,
but the
energy,
the north-facing
building has the
maximum
energy demand.
It is also
important
to
north-facing
building
has
the
maximum
energy
demand.
It
is
also
important
to
mention
that
in will
this
mention that in this case study, if the building is north oriented, then the south elevation, which
case
if that
the building
is north
oriented,
thenincreases
the souththe
elevation,
which will
that
be thestudy,
rear in
case, has more
windows,
which
energy demand;
thatbeis the
whyrear
thein
northcase,
has
more
windows,
which
increases
the
energy
demand;
that
is
why
the
north-facing
building
facing building has slightly higher energy demand as compared to the south-facing building.
has slightly higher energy demand as compared to the south-facing building.
Sustainability 2017,
2017, 9,
9, 640
640
Sustainability
12 of
of 18
18
12
Table 2. Total energy demand comparison with four different orientations and the conventional roof in
Table
2. Total energy demand comparison with four different orientations and the conventional roof
Riyadh.
in Riyadh.
Conventional Roof in Riyadh, Total Energy Demand Comparison
Conventional
in Riyadh,
Total Energy
Comparison
(Monthly
Load Roof
Discomfort
Analysis)
withDemand
Different
Orientation
(Monthly Load Discomfort Analysis) with Different Orientation
Heating Load
Heating Load
Orientation (KWh/m2Y) 2
(KWh/m Y)
East facing
4.3
East facing
4.3
NorthNorth
Facing
4.4 4.4
Facing
West facing
West facing
4.3 4.3
South facing
4.2
South facing
4.2
Orientation
Cooling Load
Cooling Load
(KWh/m22Y)
(KWh/m Y)
158.2
158.2
159.7
159.7
158.6
158.6
159.6
159.6
Total Energy Demand
Total Energy Demand
(KWh/m2Y)
(KWh/m2 Y)
162.5
162.5
164.1
164.1
162.8
162.8
163.8
163.8
Conventional Roof in Riyadh, Total Energy
demand comparison with different
orientation
Total energy demand (KWh/m2Y )
165.0
163.5
162.0
East
North
West
South
Figure 13.
energy demand
demand comparison
comparison with
with four
four different
different orientations
orientations and
and the
the conventional
conventional roof
roof
Figure
13. Total
Total energy
in
Riyadh.
in Riyadh.
If we are going to compare the total energy demand in two different climates, which are Dhahran
If we are going to compare the total energy demand in two different climates, which are Dhahran
and Riyadh, with the existing conventional roof, then the result generated by the software clearly
and Riyadh, with the existing conventional roof, then the result generated by the software clearly
tells that the total energy demand in Riyadh would be almost 14% higher along different orientations,
tells that the total energy demand in Riyadh would be almost 14% higher along different orientations,
as shown in Table 3. If we are going to compare heating loads in both climates, it is quite clear that
as shown in Table 3. If we are going to compare heating loads in both climates, it is quite clear that
these are high in Dhahran, and this is because of the winter duration, as this is for a greater time
these are high in Dhahran, and this is because of the winter duration, as this is for a greater time period
period in Dhahran. The longer winter period in Dhahran reduces the cooling loads, and hence, total
in Dhahran. The longer winter period in Dhahran reduces the cooling loads, and hence, total energy
energy demand in the Dhahran climate is less than Riyadh.
demand in the Dhahran climate is less than Riyadh.
Table 3. Total energy demand comparison in Dhahran and Riyadh with the conventional roof.
Table 3. Total energy demand comparison in Dhahran and Riyadh with the conventional roof.
Conventional
Roof
Comparisonin
inDhahran
Dhahran and
Total
Energy
Demand
Conventional
Roof
Comparison
andRiyadh,
Riyadh,
Total
Energy
Demand
(Monthly Load Discomfort Analysis) with Different Orientation
(Monthly Load Discomfort Analysis) with Different Orientation
Orientation
Orientation
East facing
North Facing
West facing
East
facing
South facing
North Facing
West facing
Total Energy Demand
Total Energy Demand
Difference in Total
TotalinEnergy
Demand
in Total
Energy
Demand in
Dhahran
with
in Riyadh
with
Energy
Demand in Total
Difference in %
Difference
Conventional Roof
Conventional Roof
Difference
Dhahran2with
Riyadh with
(KWh/m2 Y)
(KWh/m Y)
(KWh/m2 Y)
Energy Demand
Conventional Roof
Conventional Roof
141.6
164.1
140.3
141.6 2Y)
(KWh/m
140.6
140.3
141.3
162.5
164.1
(KWh/m2Y)
162.8
162.5
163.8
22.2
(KWh/m2Y)
22.5
22.2
22.2
22.5
22.5
in %
13.67
13.72
13.65
13.67
13.73
13.72
140.6
22.2
13.65
Now, we replaced the
conventional roof with162.8
the green roof in Dhahran
climate. Table
4 and
South
facing
141.3
163.8
22.5
13.73
Figure 14, show the results generated by the software. In this model, the green roof is placed at
the top instead of the conventional roof, while all other specifications (for walls, floors, windows,
roof
with theisgreen
in Dhahran
climate.
4 and
doorsNow,
etc.) we
are replaced
the same,the
andconventional
a considerable
reduction
notedroof
in the
cooling load,
as it Table
came down
Figure 14, show the results generated by the software. In this model, the green roof is placed at the
top instead of the conventional roof, while all other specifications (for walls, floors, windows, doors
Sustainability 2017, 9, 640
13 of 18
etc.) are the same, and a considerable reduction is noted in the cooling load, as it came down13from
of 18
132 KWh/m2Y to 124 KWh/m2Y, while the reduction in heating demand is less than 1 KWh/m2Y;
which was 7.5 KWh/m2Y before, but became almost 6.8 KWh/m2Y.
from 132 KWh/m2 Y to 124 KWh/m2 Y, while the reduction in heating demand is less than 1 KWh/m2 Y;
2 Y before,
Table
4. Total
energy
demandbut
comparison
with four
different 2orientations
and the green roof
which
was 7.5
KWh/m
became almost
6.8 KWh/m
Y.
Sustainability 2017, 9, 640
in Dhahran.
Table 4. Total energy demand comparison with four different orientations and the green roof in Dhahran.
Green Roof in Dhahran, Total Energy Demand Comparison
Green
RoofDiscomfort
in Dhahran, Analysis)
Total Energy
Demand
Comparison
(Monthly
Load
with
Different
Orientation
(Monthly Load Discomfort Analysis) with Different Orientation
Orientation
Heating Load
Cooling Load
Heating Load
Cooling 2Load
2Y)
(KWh/m
(KWh/m
Y)
Orientation
2
2
(KWh/m Y)
East facing
6.8
East facing
North Facing North Facing6.9
West facing West facing 6.8
South facing
South facing
6.7
(KWh/m Y)
124.3
124.3
125.1
125.1
124.7
124.7
125.0
125.0
6.8
6.9
6.8
6.7
Total Energy Demand
Total Energy Demand 2
(KWh/m Y)
(KWh/m2 Y)
131.1
132.0
131.5
131.7
131.1
132.0
131.5
131.7
Green Roof in Dhahran, Total Energy
demand comparison with different
orientation
Total energy demand (KWh/m2Y )
133.0
132.0
131.0
130.0
East
North
West
South
Figure 14 Total energy demand comparison with four different orientations and the green roof
Figure 14. Total energy demand comparison with four different orientations and the green roof
in Dhahran.
in Dhahran.
Comparing the total energy demand between the conventional and green roof in Dhahran, the
the total6.5%
energy
demand
between
the conventional
and green
roof
Dhahran,
2Y and
2Y,
131inKWh/m
latterComparing
is found to provide
of savings
with
respective
loads of 140 KWh/m
2 Y and
the
latter
is
found
to
provide
6.5%
of
savings
with
respective
loads
of
140
KWh/m
as shown in Table 5.
131 KWh/m2 Y, as shown in Table 5.
Table 5. Total energy demand comparison in Dhahran with the conventional roof and the
Table 5. Total energy demand comparison in Dhahran with the conventional roof and the green roof.
green roof.
Conventional
vs.Green
GreenRoof
Roof in
in Dhahran,
Dhahran, Total
Demand
Conventional
vs.
TotalEnergy
Energy
Demand
(Monthly Load Discomfort Analysis) Comparison with Different Orientation
(Monthly Load Discomfort Analysis) Comparison with Different Orientation
Orientation
Orientation
East facing
North Facing
Westfacing
facing
East
South facing
North Facing
West facing
Total Energy Demand in
Total Energy
Demand in
Dhahran
with Conventional
Roof (KWh/m2 Y)
Dhahran with Conventional
140.3
141.6
140.6
140.3
141.3
Total Energy Demand
Reduction in Energy
Total
Energy
Demand
Reduction in
in
Dhahran
with
Green in
Demand
Roof (KWh/m2 Y)
(KWh/m2 Y)
Dhahran with Green
131.1
132.0
131.5
131.1
131.7
Energy Demand
in %
6.55
6.76
6.50
6.55
6.83
9.1
6.50
Roof (KWh/m2Y)
(KWh/m2Y)
141.6
132.0
9.6
131.5
Saving
9.2
9.6
9.1 9.2
9.7
Roof (KWh/m2Y)
140.6
Saving in %
6.76
Now,
the conventional141.3
roof (existing) is replaced with
South
facing
131.7the green roof in Riyadh,
9.7 and the analyses
6.83
are made in four different orientations. In terms of orientation, the trend of the energy demand is
almost
same
asconventional
the green roofroof
in Riyadh,
as east-west
is with
the most
suitable
orientation
with
Now,
the
(existing)
is replaced
the green
roof
in Riyadh,
andthe
theminimum
analyses
energy
demand,
while
north-south
has
the
maximum
energy
demand
as
shown
in
Figure
15.
Cooling
are made in four different orientations. In terms of orientation, the trend of the energy demand
is
2 Y from 158 KWh/m2 Y to 148 KWh/m2 Y, while the reduction
loads
got
reduced
almost
10
KWh/m
almost same as the green roof in Riyadh, as east-west is the most suitable orientation with the
2 to 4.0 KWh/m2 Y as shown
in
heating energy
loads isdemand,
almost ignorable,
as reduction
from
4.3 KWH/m
minimum
while north-south
has is
the
maximum
energyYdemand
as shown in Figure
in
Table
6.
2
2
15. Cooling loads got reduced almost 10 KWh/m Y from 158 KWh/m Y to 148 KWh/m2Y, while the
Sustainability 2017, 9, 640
14 of 18
reduction in heating loads is almost ignorable, as reduction is from 4.3 KWH/m2Y to 4.0 KWh/m2Y as
shown in Table 6.
Sustainability 2017, 9, 640
14 of 18
Table 6. Total energy demand comparison with four different orientations and the green roof
in Riyadh.
Table 6. Total energy demand comparison with four different orientations and the green roof in Riyadh.
Green Roof in Riyadh, Total Energy Demand Comparison
Green Roof
Riyadh, Total
Energy
Demand
Comparison
(Monthly
Load in
Discomfort
Analysis)
with
Different
Orientation
(Monthly Load Discomfort Analysis) with Different Orientation
Cooling Load
Total Energy Demand
Heating Load
Orientation
Heating
Load
Cooling
Load
Total
Energy
Demand
2
2
2Y)
(KWh/m Y)2
(KWh/m
(KWh/m Y)
Orientation
(KWh/m2 Y)
(KWh/m Y)
(KWh/m2 Y)
East facing
4.0
147.8
151.7
East facing
4.0
147.8
151.7
North Facing
4.1
148.7
152.8
North Facing
4.1
148.7
152.8
3.9
148.1
152.1152.1
West facingWest facing 3.9
148.1
South facing
3.9
148.5
152.4
South facing
3.9
148.5
152.4
Green Roof in Riyadh, Total Energy
demand with different orientation
Total energy demand (KWh/m2Y )
153.0
152.0
151.0
East
North
West
South
Figure 15. Total energy demand comparison with four different orientations and the green roof
Figure 15. Total energy demand comparison with four different orientations and the green roof in Riyadh.
in Riyadh.
Now,
Now, we
we compared
compared the
the results
results of
of conventional
conventional roof
roof with
with green
green roof
roof in
in Riyadh
Riyadh and
and found
found that
that
with
the
east-facing
building,
the
saving
can
be
6.63%
as
compared
to
the
conventional
roof
with the east-facing building, the saving can be 6.63% as compared to the conventional roof in
in the
the
Riyadh
Riyadh climate,
climate, and
and it
it reaches
reaches almost
almost 7%
7% for
for the
the south-facing
south-facing building,
building, as
as shown
shown in
in Table
Table7.7.
Table 7.
7. Total
Total energy
Table
energy demand
demand comparison
comparison in
in Riyadh
Riyadh with
with the
the conventional
conventional roof
roof and
and the
the green
green roof.
roof.
Conventional vs. Green
Roof in Riyadh,
Energy
(Monthly
Discomfort
Conventional
vs. Total
Green
RoofDemand
in Riyadh,
Total Load
Energy
DemandAnalysis) Comparison
with Different Orientation
(Monthly Load Discomfort Analysis) Comparison with Different Orientation
Total Energy Demand in
Orientation
Orientation
East facing
North Facing
East
facing
West
facing
South facing
Total
Energy
Demand in
Riyadh
with Conventional
2
Roof
(KWh/m
Y)
Riyadh
with
Conventional
162.5
2Y)
Roof (KWh/m
Total Energy Demand
Reduction in Energy
Energy
Demand in Demand
Reduction in Saving in %
inTotal
Riyadh
with Green
Saving
2 Y)
2 Y)
Roof (KWh/m
Riyadh
with Green
Roof (KWh/m
Energy
Demand
North Facing
164.1
163.8
151.7
(KWh/m2Y)
152.8
151.7
152.1
152.4
West facing
162.8
152.1
164.1
162.5
162.8
152.8
10.8
(KWh/m2Y)
11.3
10.8 10.8
11.4
11.3
10.8
6.63in %
6.89
6.61 6.63
6.96
6.89
6.61
Comparing
the effectiveness
hot and humid (Dhahran
the hot
South
facing
163.8 of the green roof in the
152.4
11.4climate) and 6.96
and dry climate (Riyadh), we found that the reduction in energy demand is slightly higher in Riyadh
as compared
to Dhahran,
as shownofinthe
Table
8, asroof
is also
suggested
other(Dhahran
studies that
the green
Comparing
the effectiveness
green
in the
hot andby
humid
climate)
androof
the
is
more
effective
in
a
hot
and
dry
climate
[18].
hot and dry climate (Riyadh), we found that the reduction in energy demand is slightly higher in
Riyadh as compared to Dhahran, as shown in Table 8, as is also suggested by other studies that the
green roof is more effective in a hot and dry climate [18].
Sustainability 2017, 9, 640
15 of 18
Table 8. Green roof saving comparison in Riyadh and Dhahran.
Green Roof Saving Comparison in Dhahran and Riyadh
Orientation
Saving in % due to
Green Roof in Riyadh
Saving in % due to
Green Roof in Dhahran
Difference
East facing
North Facing
West facing
South facing
6.63
6.89
6.61
6.96
6.55
6.76
6.50
6.83
0.08
0.13
0.11
0.13
8. Discussion
As part of energy conservation strategies in buildings, a number of systems and materials can
be applied to reduce the energy demand. Walls, floors, roofs and windows can be designed in such a
way that heat losses in winter and heat gain in summer could be minimized. Green roofs are a passive
strategy, which insulate the building rooftop. The vegetation component of the green roof reduces
the heat gain by working as an active dynamic air envelope system. It provides exterior shading to
control the direct solar radiation, thus leading to considerable energy saving. In this research project,
we have considered newly-constructed villas in KFUPM, Dhahran Saudi Arabia, as the case study
and modelled green roof layers above the existing roof structure with the same insulation thickness as
provided in the conventional roof. We considered the extensive green roof for this purpose because of
its low maintenance factor and its structural lightness in terms of weight.
To attain our goals, firstly, we prepared two separate models in the software ECOTECT, one
with the conventional and the other with the green roof. We placed the conventional roof model in
four different orientations facing east, west, north and south and calculated the total energy demand
with the Dhahran climate. Then, we replaced the existing conventional roof with the green roof and
observed the energy savings. We considered the same building in the Riyadh climate and repeated
all analyses to understand the validity of the green roof in two different Saudi climates. Moreover,
to understand the energy savings due to the appropriate orientation, we considered the detached
residential building. It is also important to mention that the effectiveness of the green roof also
depends on the level of insulation provided for the building envelope and windows along with
climatic conditions and building function. We analyzed this building with single and double glazing
although single glazing results are not included in this research paper but after providing the efficient
glazing and better insulated walls, energy saving because of green rooftop became more significant.
With energy savings, the initial cost, maintenance cost and the system’s payback period also need
to be considered. Normally, a green roof costs more than most conventional roofs or cool rooftops.
Green roofs cost depends on its type (intensive or extensive) and its components’ specifications,
like depth of growing medium, type of roofing system, type of drainage system, type of plants, etc.
The cost of the extensive and intensive green roof options has been reported to be $10/ft2 and $25/ft2 ,
respectively [39]. Maintenance expenses of the green roof also need to be considered at the time of
construction, as it mainly depends on the type of plants provided on it. Most of the maintenance cost
emerges in the first year as plants develop, and it can be $0.75–$1.50 for every square foot [40].
Besides energy savings, there are several other benefits that can be attained due to the provision
of the green roof. It can also potentially enhance the property value. Although no such data are
available showing the increment in property value due to the green roof, according to some statistics,
a normal house price can increase by up to 7.1% with close proximity to greenery [41]. It is also
important to mention that the life span of the conventional roof is around 20 years, while for the green
rooftop, it is 40–55 years [42]. The green rooftop also helps with carbon reduction and controlling air
contamination. Dust, particulates and nitrates (NO2 ) are the measure of the air quality, and different
plants have different oxygen-carbon dioxide conversion rates; but, according to a study, 80–85 kg of
toxins per hectare per year can be removed by green roofs [43]. In urban areas, the creation of natural
Sustainability 2017, 9, 640
16 of 18
surroundings is not a typical interest, and the green roof can help with creating such an environment
by providing plants and soil contributing to the richness of the natural habitat. The green roof also
helps with mitigating the urban heat island effect. Urban areas are full of dull surfaces with low
albedo, which is basically the reflection capability of any surface [44]. Dull surfaces and the absence of
vegetation increase the urban air temperature amid summer months [45]. This results in increased
building energy demand and consequently more usage of HVAC systems.
The findings of this work reveal that buildings in Saudi Arabia oriented along east-west consume
the least amount of energy. It is also reported that the total energy demand of buildings is least when
the orientation angle is zero, which means placing the long axis of the building along east-west can be
the most suitable option [46]. Similarly, according to Ghobadian (2006), the most suitable orientation
in Iran is also east-west, as the length of the building should be towards the south, so in winter,
it could gain the maximum solar energy, and in summer, shading devices can be used to protect it from
heat [47].
9. Conclusions
The presented work has investigated the impact of the orientation and green roof on the energy
performance of buildings in the hot-humid and hot-dry climatic conditions of Saudi Arabia. Dhahran
and Riyadh have been used as the representative cities for these two climatic conditions, respectively.
The findings of the modeling work undertaken with the help of ECOTECT software reveal a nominal
difference in the energy performance of the selected building with varying orientations. For example,
in the case of Dhahran, the building consumes 140.3, 140.6, 141.6 and 141.3 KWh/m2 Y, respectively, for
east, west, north and south facing. The total energy demand in the Riyadh climate is however found to
be almost 14% higher than in the Dhahran climate, mainly due to the longer and more intense summer
in the case of the former. The green roof is observed to be marginally more effective in the hot and dry
climate of Riyadh compared to the hot and humid conditions of Dhahran. The results of the analysis
indicate that in the climatic conditions of Dhahran and Riyadh, the green roof can reduce the energy
consumption by 6.7% and 6.8%, respectively.
Acknowledgments: The authors would like to acknowledge the support of Deanship of Scientific Research (DSR),
King Fahd University of Petroleum and Minerals, Saudi Arabia, who sponsored us to carry out this research
project (Reference No. IN141034). Their support allowed us to conduct all modelling and experimental work.
Author Contributions: Hassan Saeed Khan conceived the research idea and did the modeling. Muhammad Asif
and Hassan Saeed Khan jointly analyzed the results and wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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