Enhancing Green Building Rating of a School under the Hot Climate of UAE; Renewable Energy Application and System Integration

This article explores the sustainable performance of a school in UAE and assesses opportunities for enhanced performance through the application of renewable energy systems. The article discusses the government's sustainability initiative called Estidama and the Pearl Building Rating System (PBRS). The article also highlights the challenges of energy conservation and environmental sustainability of buildings in UAE. The article concludes that integrating RE systems in future schools in hot climatic contexts can significantly improve energy performance.

energies
Article
Enhancing Green Building Rating of a School under
the Hot Climate of UAE; Renewable Energy
Application and System Integration
Joud Al Dakheel, Kheira Tabet Aoul *ID and Ahmed HassanID
Architectural Engineering Department, United Arab Emirates University, P.O. Box, 15551 Al Ain, UAE;
[e-mail] (J.A.D.); [e-mail] (A.H.)
* Correspondence: [e-mail]; Tel.: [phone]
Received: 2 March 2018; Accepted: 5 July 2018; Published: 17 September 2018
Abstract:Similar to many fast growing countries, the United Arab Emirates (UAE) witnessed fast
population and urbanization growth. The building sector accounts for a major share of its electricity
consumption,reaching up to 70%.To encourage sustainable development and reduce energy
consumption and emissions, the government introduced a sustainability initiative called “Estidama”,
which employs the use of the Pearl Building Rating System (PBRS). Government buildings, which
constitute 20% of the built environment, aim to lead the way, and are therefore required to attain
a high level of achievement,based on their PBRS ranking (minimum of two out of five pearls).
Schools, led by Abu Dhabi Educational Council (ADEC), are governmental buildings and aim to
attain a higher level of achievement (three out of five pearls). The ADEC plans to build one hundred
schools to be built by 2020, through its Future Schools Program. Over half of the schools have been
completed, but only 20% reached the targeted rating (of three out of five pearls).The Renewable
Energy (RE) application in the UAE is minimal, although it represents 25% of the local rating code.
The objective of this paper is to explore the sustainable performance of one representative school that
did not reach the desired green rating level, with the objective to assess opportunities for an enhanced
performance. This is done through testing the performance and the application of three RE systems
comprising of photovoltaics (PV) array,an absorption cooling system and a geothermal cooling
system through Transient Systems Simulation (TRNSYS) software. Cumulatively, implementation of
these options results in RE potentially contributing to 19% of the school’s annual energy consumption,
enhancing the school’s performance by up to 14 additional credit points, and reaching the target level
of achievement (a three pearl rating). Furthermore, system integration of RE into the existing school
were also considered. Results indicate the significant potential of integrating RE systems in future
schools in hot climatic contexts, for an improved energy performance.
Keywords:building energy performance; green building rating system; photovoltaic; solar absorption
chiller; geothermal; schools; UAE; TRNSYS
1. Introduction
Fast growing economies often share common traits in terms of population growth and rapid
urbanization, resulting in high energy demand and significant carbon emissions. Abu Dhabi, the capital
of the United Arab Emirates (UAE), has similarly experienced a sharp increase in energy demand,
leaping from 25,423 GWh in 2005 to 62,248 GWh in 2015. This drove similar increases in generation
capacity, as indicated in Figure 1 [1]. The surge in energy consumption, positions the UAE as one
of the world’s largest energy consumers per capita, with the building sector accounting for almost
70% of its total electrical energy consumption [2]. The primary electricity loads in the UAE are, by far,
Energies 2018, 11, 2465; doi:10.3390/en11092465 www.mdpi.com/journal/energies

Energies 2018, 11, 2465 2 of 14
cooling demand, then lighting, refrigeration and other appliance loads. In Abu Dhabi, the residential
electricity load distribution is 47% for cooling (but can exceed 60% during the summer peak), 7% for
lighting, 3% for refrigeration and 35% for other appliance loads [3]. The UAE’s extreme hot climate,
and subsequently high cooling demand, generated a challenging environment for energy conservation
and environmental sustainability of buildings [4].
Energies 2018, 11, x FOR PEER REVIEW 2 of 15
for almost 70% of its total electrical energy consumption [2]. The primary electricity loads in the
UAE are, by far, cooling demand, then lighting, refrigeration and other appliance loads. In Abu
Dhabi, the residential electricity load distribution is 47% for cooling (but can exceed 60% during the
summer peak), 7% for lighting, 3% for refrigeration and 35% for other appliance loads [3]. The
UAE’s extreme hot climate, and subsequently high cooling demand, generated a challenging
environment for energy conservation and environmental sustainability of buildings [4].
Figure 1. Total electricity power production in the Abu Dhabi emirate [1].
In line with worldwide initiatives to implement energy efficiency strategies in buildings, the
UAE governmentintroducedin 2008 a stringentsustainabilitycode, named “Estidama”[5].
Followed in 2010 by the development of a green building rating system, named the Pearl Building
Rating System (PBRS). The latter aligns with the principles of international green building rating
systems, aiming to promote the development of sustainable buildings. The code compliance is
governed by the PBRS, ranging from one to five pearls, ranking the level of achievements across
seven categories. Similarly to most green rating system, PBRS is comparable with Leadership in
Energy and Environmental Design (LEED) and Building Research Establishment Environmental
Assessment Method (BREEAM) rating systems. It rates buildings based on six categories: (1)
Integrated Development Process (10 credit points), (2) Natural Systems (14 credit points), (3) Livable
Communities (35 credit points), (4) Precious Water (37 credit points), (5) Resourceful Energy (42
credit points), and (6) Stewarding Materials (19 credit points)]. The first level of a building
attainment requires meeting all mandatory credits and would gain one pearl, while if it achieves 60
additional credits it will reach the second level of attainment (or two pearls). Reaching 85 credits will
achieve the third level or three pearls, while 115 credits translates to four pearls, and 140 credits
qualifies for five pearls, which is the maximum number of pearls. The PBRS has a manual with
specific guidelines on the methodology and calculation equations that are used to validate each
system in order to achieve the credits [6].
The Precious Water and Renewable Energy categories are the dominant categories, comprising
of the highest number of credit points. Twenty five percent of each of these categories represents a
response to the context: characterized by scarcity of water and the extreme harsh climate that
requires a substantial amount of cooling. The UAE has one of the highest sun exposure rates in the
world, giving it a high potential for renewable energy development [7]. The application of RE in the
UAE has been minimal and needs to be reinforced more in buildings in order to overcome the
current energy challenges. Renewable energy makes up less than 0.1% of the UAE’s total final
energy consumption, which is unsustainable due to global current energy consumption challenges
[8]. The UAE’s RE energy base was non‐existent in 2008. Since then, approximately 150 megawatt
(MW) of solar panels have been installed, and over 300 additional MW have been announced. A
further 100 MW of solar photovoltaic (PV) in Dubai, and 53 MW of waste‐to‐energy in Sharjah, was
constructed. Nevertheless, in the context of other Gulf Cooperation Countries (GCC), the UAE has
30000
40000
50000
60000
70000
2011 2012 2013 2014 2015
GWH
Energy Available Electric Consumption
Figure 1. Total electricity power production in the Abu Dhabi emirate [1].
In line with worldwide initiatives to implement energy efficiency strategies in buildings, the UAE
government introduced in 2008 a stringent sustainability code, named “Estidama” [5]. Followed in
2010 by the development of a green building rating system, named the Pearl Building Rating System
(PBRS). The latter aligns with the principles of international green building rating systems, aiming to
promote the development of sustainable buildings.The code compliance is governed by the PBRS,
ranging from one to five pearls, ranking the level of achievements across seven categories. Similarly to
most green rating system, PBRS is comparable with Leadership in Energy and Environmental Design
(LEED) and Building Research Establishment Environmental Assessment Method (BREEAM) rating
systems.It rates buildings based on six categories:(1) Integrated Development Process (10 credit
points), (2) Natural Systems (14 credit points), (3) Livable Communities (35 credit points), (4) Precious
Water (37 credit points),(5) Resourceful Energy (42 credit points),and (6) Stewarding Materials
(19 credit points)].The first level of a building attainment requires meeting all mandatory credits
and would gain one pearl, while if it achieves 60 additional credits it will reach the second level of
attainment (or two pearls).Reaching 85 credits will achieve the third level or three pearls,while
115 credits translates to four pearls, and 140 credits qualifies for five pearls, which is the maximum
number of pearls. The PBRS has a manual with specific guidelines on the methodology and calculation
equations that are used to validate each system in order to achieve the credits [6].
The Precious Water and Renewable Energy categories are the dominant categories, comprising
of the highest number of credit points.Twenty five percent of each of these categories represents
a response to the context: characterized by scarcity of water and the extreme harsh climate that requires
a substantial amount of cooling.The UAE has one of the highest sun exposure rates in the world,
giving it a high potential for renewable energy development [7]. The application of RE in the UAE has
been minimal and needs to be reinforced more in buildings in order to overcome the current energy
challenges. Renewable energy makes up less than 0.1% of the UAE’s total final energy consumption,
which is unsustainable due to global current energy consumption challenges [8]. The UAE’s RE energy
base was non-existent in 2008. Since then, approximately 150 megawatt (MW) of solar panels have been
installed, and over 300 additional MW have been announced. A further 100 MW of solar photovoltaic
(PV) in Dubai, and 53 MW of waste-to-energy in Sharjah, was constructed. Nevertheless, in the context
of other Gulf Cooperation Countries (GCC), the UAE has maintained the lead in total contracted
capacity and project scale [9]. Early RE feasibility studies for Gulf countries directed their attention
to greenhouse gas emissions as a driver [10,11]. Sustainability and the use of RE is prominent in the

Energies 2018, 11, 2465 3 of 14
strategic plans of the country, in terms of targets that will need to be achieved though RE contribution
to the overall energy sector. Despite the overall intents, there is still a significant gap in the integration
of RE which creates an opportunity for its integration within buildings in the UAE.
The government-sector buildings account for 20% of the building stock. Therefore, there is focus
to adopt energy efficient practices in order to curb energy consumption, as well as establishing better
building practices [12]. Governmental buildings aim to lead the way, and are therefore required to
achieve at least two pearls [6] by adopting energy efficiency measures and integrating RE systems.
Among all public buildings, school buildings have a major social and energy responsibility on account
of their educational purpose.Educational facilities are a vital field to implement the sustainability
practices and energy efficiency programs.Many countries are developing sustainable regulations
and policies for schools building.In order to achieve severalnationalenergy efficiency targets,
the local governments support all possible and effective initiatives to augment the benefits and the
sustainable practices [13,14]. Therefore, the Abu Dhabi Educational Council (ADEC), a governmental
entity, envisaged a promising 10-year strategic plan (2010–2020) named the “Future Schools Program”.
This program seeks to construct 100 new schools with a minimum rating of two pearls (60 out of
140 points), and a strongly targeted higher goal of three peals (85 out of 140 points) [15,16]. To date,
53 schools have been completed that meet the mandatory two pearl requirement. However, only 20%
of these schools have reached the desired target of three pearls.This research aims to uncover the
viability of enhancing the green rating performance of school buildings, through renewable energy
integration. This research explores the performance of one recently built school under the hot climate
of the UAE, which did not reach the desired rating (3 pearls), to serve as a model for the 100 planned
schools that are built, or due to be completed by 2020. The aim of this paper is to explore the sustainable
performance of one representative school in the context of the UAE’s hot climate, with the objective to
assess opportunities for an enhanced performance.
2. Analysis of the School Green Rating System Performance
A review of green rating achievements of a newly built school prototype was carried out based
on the design files and data from the educational council (Figure 2). The school was selected based
on its green rating level of achievement (two pearls).The data included architectural drawings,
design strategy, and technical specifications. The simulated data of the school performance including
building loads, electricity consumption, operational schedules, and used systems. The documentation
review revealed that the school already achieved most credits related to passive building envelope
components, such as insulation, roof, and glazing systems; and active systems such as LED lighting,
sensors, controls, and water efficiency.
Energies 2018, 11, x FOR PEER REVIEW 3 of 15
maintained the lead in total contracted capacity and project scale [9]. Early RE feasibility studies for
Gulf countries directed their attention to greenhouse gas emissions as a driver [10,11]. Sustainability
and the use of RE is prominent in the strategic plans of the country, in terms of targets that will need
to be achieved though RE contribution to the overall energy sector. Despite the overall intents, there
is still a significant gap in the integration of RE which creates an opportunity for its integrati
within buildings in the UAE.
The government‐sector buildings account for 20% of the building stock. Therefore, there is
focus to adopt energy efficient practices in order to curb energy consumption, as well as establishing
better building practices [12]. Governmental buildings aim to lead the way, and are therefore
required to achieve at least two pearls [6] by adopting energy efficiency measures and integrating
RE systems. Among all public buildings, school buildings have a major social and energy
responsibility on account of their educational purpose. Educational facilities are a vital field to
implement the sustainabilitypracticesand energy efficiency programs.Many countriesare
developing sustainable regulations and policies for schools building. In order to achieve several
national energy efficiency targets, the local governments support all possible and effective initiatives
to augment the benefits and the sustainable practices [13,14]. Therefore, the Abu Dhabi Educational
Council (ADEC), a governmental entity, envisaged a promising 10‐year strategic plan (2010–2020)
named the “Future Schools Program”. This program seeks to construct 100 new schools with a
minimum rating of two pearls (60 out of 140 points), and a strongly targeted higher goal of three
peals (85 out of 140 points) [15,16]. To date, 53 schools have been completed that meet the mandatory
two pearl requirement. However, only 20% of these schools have reached the desired target of three
pearls. This research aims to uncover the viability of enhancing the green rating performance
school buildings, through renewable energy integration. This research explores the performance of one
recently built school under the hot climate of the UAE, which did not reach the desired rating (3 pearls
to serve as a model for the 100 planned schools that are built, or due to be completed by 2020. The aim
this paper is to explore the sustainable performance of one representative school in the context of the
UAE’s hot climate, with the objective to assess opportunities for an enhanced performance.
2. Analysis of the School Green Rating System Performance
A review of green rating achievements of a newly built school prototype was carried out based
on the design files and data from the educational council (Figure 2). The school was selected based
on its green rating level of achievement (two pearls). The data included architectural drawings
design strategy,and technicalspecifications.The simulated data of the school performance
including building loads, electricity consumption, operational schedules, and used systems. The
documentation review revealed that the school already achieved most credits related to passive
building envelope components, such as insulation, roof, and glazing systems; and active systems
such as LED lighting, sensors, controls, and water efficiency.
Figure 2. External view of the school [17].
Figure 2. External view of the school [17].

Energies 2018, 11, 2465 4 of 14
The design strategies implemented in the school were based on the local PBRS green rating
requirements. A detailed review of the school’s two pearl rating revealed that it achieved 81 credit—only
4 points short of achieving the desired level of attainment (three pearls). The analysis revealed that the
highest number of unachieved credits (up to 70%) were within the Resourceful Energy category, despite
this being the most weighted PBRS category. The RE credit distribution comprises of 6 sub-categories,
by which 25 credit points were not achieved. The main reasons for this, as indicated in the submission
files, were due to the in the lack of expertise offered in the field, therefore this school provides a good
opportunity for the investigation of the energy performance enhancement of the building.
This scenario provides a promising potential to explore the use of renewable energy generation.
A review of Abu Dhabi’s climatic data revealed that the weather remains predominantly hot and
humid, with peak summer temperatures reaching 48◦C and a relative humidity of 90% [18]. Extreme
weather such as this requires extensive air conditioning, which may contribute up to 75% of a building’s
energy use [19].
This research explores alternative cooling systems that require less energy input, with the goal
of substantially decreasing energy consumption. Solar radiation is plentiful in the UAE, and free to
use. Additionally, preliminary assessments have shown a substantial temperature difference of up to
20◦C between the ground temperature (23◦C) and ambient temperature (48◦C) in the peak summer
months, favoring geothermal cooling system [20]. Weather data revealed a yearly solar radiation is
2370 kWh/m2, i.e., 6.5 kWh/m2 per day [21], which favored the choice of an absorption cooling system,
and photovoltaic energy generation. Geothermal cooling system have also been found promising to
deliver the effective cooling required [21].
The contextual characteristics of the promising renewable energy systems for integration into the
selected school building are summarized in Table 1 [22].
The energy produced by the aforementioned systems is compared to the school’s baseline energy
demand (Table 2), to determine the energy savings and perform the calculation. The predicted energy
savings are then converted into credits earned, based on the PBRS guidelines.The cooling system
performance is compared with the demand in peak months (May–August) in order to determine the
reductions achieved in peak-period cooling capacity and energy use.
Table 1. Renewable energy systems selection in harsh climate.
System/Criteria Advantages Limitations Performance Payback Period versus Life Span
Photovoltaic
system [23]
Annual solar
radiation of
2285 kWh/m2,
expected energy of
850 kW year/m2).
Dust results in radiation
reduction on panel.
High temperature
results in power losses.
Electrical energy
production of
322 kWh/m2-year [24,25].
Pay-back period: 3–5 years [26]
based on unsubsidized tariffs.
Lifespan: 25–30 years.
Solar absorption
cooling system [27,28]
Annual solar
radiation of
182,800 kWh/m2.
High initial cost.
Dust on collectors
results in
radiation reduction.
High temperature
results in power losses.
A cooling energy
production of
1059 kWh/m2-year.
Average payback period:
4–10 years.
Lifespan: 25–35 years.
Geothermal
cooling
system [20,29]
Ground temperature
is used to modulate
interior temperature
(difference up to 20◦C
during summer)
High initial cost.
Land required to install
the loop.
Lower temperature
gradient in
moderate seasons.
Cooling energy
delivered by
46 kWh/year-m length
of borehole [30].
Average payback period:
7–10 years according to the
system size.
Life span: up to 50 years.

Energies 2018, 11, 2465 5 of 14
Table 2. Baseline energy consumption data for the school building [17].
System Peak Capacity (kW) Annual Energy Consumption (MWh)
Space cooling (peak months) 360.5 777.6
Heat rejection 49.4 151
Space heating 79.7 0.066
Pumping energy 42.8 105.7
Interior Fans 304.6 276.9
Interior Lighting 188.3 410
Service Water Heating 200.0 231.8
Receptacle/Process
Equipment 167.5 252
Total 1392.9 2206
3. Methodology
A transientsimulation modelis developed using TransientSystems Simulation (TRNSYS)
software,employing Typical Meteorological Year (TMY) weather data for Abu Dhabi to predict
energy performance for the proposed renewable energy systems [31]. TRNSYS simulation program has
been widely used in literature, and has been proven as an effective program for simulating geothermal
systems [32–34], absorption cooling [35–37] and photovoltaic systems [38–40]. A dynamic model that
couples the solar cooling system with the building was developed in TRNSYS to assess its performance
in an office building in Tunisia [41]. The model predicted a primary energy savings up to 82.3%
compared to a classic air conditioning system, resulting in a CO2 emissions savings of 2947 kg [41].
In another study, a solar powered absorption cycle was modeled in TRNSYS, employing evacuated
tube collectors coupled with a 10 kW ammonia–water absorption chiller. The results showed a cost
and energy saving of up to 24.5% and 35.3%,respectively [42]. A desiccant cooling system and
geothermal heat pump used together in a solar hybrid desiccant air conditioning system were tested
using TRNSYS software in Shanghai.Under typical weather condition, the solar driven desiccant
cooling unit achieved an average cooling capacity of 70 kW, contributing up to 31.4% of the cooling
capacity of the system [43]. A TRNSYS model has been developed to simulate both winter and summer
period. Results showed that using these systems reduced the payback from 14 years to 1.2 years, with
the Primary Energy Savings of about 90% [44].
The PV and absorption cooling systems are based on size of roof area available to install
the PV panels and thermal collectors.Three types of PV systems,namely polycrystalline silicon,
mono-crystalline silicon, and amorphous silicon, are preliminary assessed using the manufacturer’s
data sheets. The analysis revealed that mono-crystalline PV is the most suitable system. This is due to
its high efficiency of up to 20% supporting building integration, and low temperature-based power
loss coefficient (up to 0.38%), making it favorable in hot climates [45]. The geothermal heat exchanger
is chosen based on the size of the land area available around the school to install the loop. The TRNSYS
model of the three systems included several building parameters used for modeling.It included
parameters for a building envelope, HVAC and plug loads.
4. Results and Discussion
4.1. Photovoltaic System Performance
The PV module is tested at various slopes and azimuth angles to represent different pitch angles and
orientations during building integration, either driven by need or design choice. Figure 3 shows energy
produced by PV integrated to building at pitch angles of 0◦ representing flat roof, 24◦ representing
latitude pitch, 45◦ representing regular building pitch, and 90◦ representing building vertical facade.

Energies 2018, 11, 2465 6 of 14
4.1. Photovoltaic System Performance
The PV module is tested at various slopes and azimuth angles to represent different pitch
angles and orientations during building integration, either driven by need or design choice. Figure
3 shows energy produced by PV integrated to building at pitch angles of 0° representing flat roof,
24° representing latitude pitch, 45° representing regular building pitch, and 90° representing
building vertical facade.
Figure 3. Monthly energy produced per panel at various Photovoltaic (PV) slopes representative of
different building integration schemes.
Figure 3.Monthly energy produced per panel at various Photovoltaic (PV) slopes representative of
different building integration schemes.
The highest variation in power output is observed at 0◦, for which the power output is lowest in
winter (December–January) and highest in summer (April–August). This trend can be attributed to the
sun position, which moves near zenith up to 18◦ in summer and shifts away from zenith up to 30◦ in
winter, inducing a substantial drop in output. In summer, the incident radiation is nearly normal to
the plane of the PV panel at horizontally integrated panels (0◦), while in winter the incident radiation
is substantially off normal at the same inclinations. The PV panel produces consistently lower power
at 90◦ fundamentally due to larger deviation of incident angle. At 24◦, the energy produced remains
higher during most of the months (apart from winter) due to lower solar angles. At 45◦, the highest
energy production is witnessed during winter, while a substantial decrease is observed in summer. All
of these observations are in agreement with previous findings [46,47]. Architecturally, integrating PV
at 0◦ offers ease of installation, as no additional cost is incurred for structural support, in contrast to
sloped PV. However, at 0◦ slope the PV panel is prone to increased dust retention compared to the
tilted PV, as dust particles on tilted panels can slide down off the panels under gravity.
These results reveal that energy production peaks at different panel slopes during different times
of year, suggesting that the PV slope should be adjusted monthly, or at least seasonally, to enhanced
energy production.The annual energy production for conventional fixed slopes compared to the
monthly adjustable slopes is presented in Figure 4.It can be observed that the adjustable slope
improves the power by 3% output compared to the optimal fixed sloped (24◦).
Energies 2018, 11, x FOR PEER REVIEW 7 of 15
The highest variation in power output is observed at 0°, for which the power output is lowest
in winter (December–January) and highest in summer (April–August). This trend can be attributed
to the sun position, which moves near zenith up to 18° in summer and shifts away from zenith up
to 30° in winter, inducing a substantial drop in output. In summer, the incident radiation is nearly
normal to the plane of the PV panel at horizontally integrated panels (0°), while in winter the
incident radiation is substantially off normal at the same inclinations. The PV panel produces
consistently lower power at 90° fundamentally due to larger deviation of incident angle. At 24°, the
energy produced remains higher during most of the months (apart from winter) due to lower solar
angles. At 45°, the highest energy production is witnessed during winter, while a substantial
decrease is observed in summer. All of these observations are in agreement with previous findings
[46,47]. Architecturally, integrating PV at 0° offers ease of installation, as no additional cost is
incurred for structural support, in contrast to sloped PV. However, at 0° slope the PV panel is prone
to increased dust retention compared to the tilted PV, as dust particles on tilted panels can slide
down off the panels under gravity.
These results reveal that energy production peaks at different panel slopes during different
times of year, suggesting that the PV slope should be adjusted monthly, or at least seasonally, to
enhanced energy production. The annual energy production for conventionalfixed slopes
compared to the monthly adjustable slopes is presented in Figure 4. It can be observed that the
adjustable slope improves the power by 3% output compared to the optimal fixed sloped (24°).
Figure 4. Annual power production per panel (kWh) for different static slope angles, and an
optimized adjustable slope design.
The optimum PV orientation is reported to be exactly southerly in the northern hemisphere,
representedby 0° [48]; however, the energy loss incurred by deviating from the optimum
orientation is not well known. The building configuration varies substantially depending on design
demands, and architects are often compelled to select a sub‐optimal azimuthal orientation in order
to adhere to the building design, facilitate mobility, or maintain symmetry. In order to predict PV
performance due to sub‐optimal azimuth orientation, the energy produced from a PV panel with an
0
200
400
600
800
0° 24° 45° 90° Titled
adjustable
slope
Annual Power Production (kWh)
Figure 4.Annual power production per panel (kWh) for different static slope angles, and an optimized
adjustable slope design.

Energies 2018, 11, 2465 7 of 14
The optimum PV orientation is reported to be exactly southerly in the northern hemisphere,
represented by 0◦ [48]; however, the energy loss incurred by deviating from the optimum orientation
is not well known.The building configuration varies substantially depending on design demands,
and architects are often compelled to select a sub-optimal azimuthal orientation in order to adhere
to the building design, facilitate mobility, or maintain symmetry. In order to predict PV performance
due to sub-optimal azimuth orientation, the energy produced from a PV panel with an azimuth angle
varying from 90 to−90◦ (with an interval of 45◦) is presented in Figure 5.
It can be observed that 0◦ yields the highest energy production, while declines of 24 kWh/m2
at 45◦ (Southwest) and 45◦ (Southeast) and 65 kWh/m2 at 90◦ (West) and−90◦ (East) are observed.
In order to provide optimal PV power penetration for the school building, half of the available roof
area is allocated to PV installation reserving the rest for PV shading and mobility requirements for
maintenance. Thus, the total area covered by PV panels was found to be 555 m2 that can house 342 PV
panels. The PV array produces 209 MWh of energy, which makes up 10% of the total yearly energy
consumption of the school in 2016.
Energies 2018, 11, x FOR PEER REVIEW 8 of 15
PV panels. The PV array produces 209 MWh of energy, which makes up 10% of the total yearly
energy consumption of the school in 2016.
Figure 5. Total annual power production (kWh) for different PV panel azimuth angles for at latitude
angle of 24°.
4.2. Solar Absorption Chiller Performance
The absorption cooling system is designed to deliver 10% (36 kW) of the building peak cooling
capacity of 360 kW. Considering the typical UAE peak solar radiation intensity of 1 kW/m2 [21] and
absorption cooling system efficiency of 40%, [49,50] a typical thermal collector of 3 m2 area can
produce 1.2 kW of cooling power. Thus, an absorption cooling system comprising of 30 collectors
covering 90 m2 of roof area would be required to generate 36 kW of cooling power. The proposed
absorption system is simulated with varying concentration ratios (i.e., the aperture area: receiver
surface area ratio) and inlet fluid flow rate to achieve the desired fluid temperature of 200 °C at the
collector outlet deemed safe for building integration [51].
The results show that as the concentration ratio increases from 5 to 25, the temperature of the
fluid at collector outlet increases from 150 to 580 °C and the energy delivered increases from 2258
kWh to 58,600 kWh. The optimal temperature of 200 °C [51], is achieved at a concentration ratio of
10 delivering 24,500 kWh (Figure 6a).
The water flow rate through the solar collector affects its useful thermal energy gain and,
consequently, the amount of cooling produced. Optimal system operation therefore depends on
achieving a balance between the temperature of the collector and the useful energy production.
Simulations are conducted in sequential order, maintaining a collector temperature above 200 °C
through the use of optimal flow rates. A collector temperature of 618 °C (much higher than optimal
200 °C) is achieved at 2 kg/h and produces 10.56 kWh of useful energy. With increasing flow rate, the
peak collector temperature decreased, while paradoxically the useful energy gain increased. A
collector temperature of 200 °C is achieved at a flow rate of 8 kg/h, producing 12.11 kWh of useful
energy (Figure 6b).
The proposed absorption cooling system consists of a thermal collector array, covering a net
area of 90 m2, and employs Fresnel lenses to achieve the concentration ratio of 10, and a water
circuitry system to maintain a flow rate of 8 kg/h per collector. The system produced 150,505
kWh/year of cooling energy, which is equivalent to 19.35%of the annual cooling energy
consumption and 7.2% of the total annual energy consumption of the school.
0
200
400
600
0 45 -45 90 -90
Annual Power Production
(kWh)
Figure 5.Total annual power production (kWh) for different PV panel azimuth angles for at latitude
angle of 24◦.
4.2. Solar Absorption Chiller Performance
The absorption cooling system is designed to deliver 10% (36 kW) of the building peak cooling
capacity of 360 kW. Considering the typical UAE peak solar radiation intensity of 1 kW/m2 [21] and
absorption cooling system efficiency of 40%, [49,50] a typical thermal collector of 3 m2 area can produce
1.2 kW of cooling power.Thus, an absorption cooling system comprising of 30 collectors covering
90 m2 of roof area would be required to generate 36 kW of cooling power. The proposed absorption
system is simulated with varying concentration ratios (i.e., the aperture area:receiver surface area
ratio) and inlet fluid flow rate to achieve the desired fluid temperature of 200◦C at the collector outlet
deemed safe for building integration [51].
The results show that as the concentration ratio increases from 5 to 25, the temperature of the fluid
at collector outlet increases from 150 to 580◦C and the energy delivered increases from 2258 kWh to
58,600 kWh. The optimal temperature of 200◦C [51], is achieved at a concentration ratio of 10 delivering
24,500 kWh (Figure 6a).
The water flow rate through the solar collector affects its usefulthermalenergy gain and,
consequently, the amount of cooling produced. Optimal system operation therefore depends on achieving
a balance between the temperature of the collector and the useful energy production. Simulations ar
conducted in sequential order, maintaining a collector temperature above 200◦C through the use of
optimal flow rates.A collector temperature of 618◦C (much higher than optimal 200◦C) is achieved
at 2 kg/h and produces 10.56 kWh of useful energy.With increasing flow rate,the peak collector

Energies 2018, 11, 2465 8 of 14
temperature decreased, while paradoxically the useful energy gain increased. A collector temperature of
200◦C is achieved at a flow rate of 8 kg/h, producing 12.11 kWh of useful energy (Figure 6b).
The proposed absorption cooling system consists of a thermal collector array, covering a net area
of 90 m2, and employs Fresnel lenses to achieve the concentration ratio of 10, and a water circuitry
system to maintain a flow rate of 8 kg/h per collector.The system produced 150,505 kWh/year of
cooling energy, which is equivalent to 19.35% of the annual cooling energy consumption and 7.2% of
the total annual energy consumption of the school.Energies 2018, 11, x FOR PEER REVIEW 9 of 15
Figure 6. Energy and collector outlet temperature produced by the simulated absorption cooling
system under various concentration ratios (a) and fluid flow rates (b) in 2016.
4.3. Geothermal System Performance
The geothermal cooling system is preliminarily assessed by comparing the ground
temperature at a depth of 5 m to the minimum and maximum air temperatures in Abu Dhabi, as
shown in Figure 7. This analysis reveals that the yearly ground temperature fluctuates between 24
°C and 26 °C, which offers huge potential as an ambient heat sink, as peak summer air temperature
measures up to 48 °C.
Figure 7. Peak ambient air temperature and ground temperature at a depth of 5 m.
The parametric influences on the geothermal system are studied to optimize the system energy
output (Table 3).
The geothermal system output is monitored in terms of inlet and outlet fluid temperatures,
fluid‐to‐ground heat transfer rate, and the amount of energy delivered representating the cooling
produced. The simulation results of nine consecutive representative days in the peak summer
month of July are expressed as outlet fluid temperature and energy produced.
0
10
20
30
40
50
Jan Feb March April May Jun July Aug Sept Oct Nov Dec
Temperature (°C)
Max Temp Ground Temp at depth 5 m
Ground Temp at 5 m Depth
Figure 6.Energy and collector outlet temperature produced by the simulated absorption cooling
system under various concentration ratios (a) and fluid flow rates (b) in 2016.
4.3. Geothermal System Performance
The geothermal cooling system is preliminarily assessed by comparing the ground temperature
at a depth of 5 m to the minimum and maximum air temperatures in Abu Dhabi, as shown in Figure 7.
This analysis reveals that the yearly ground temperature fluctuates between 24◦C and 26◦C, which
offers huge potential as an ambient heat sink, as peak summer air temperature measures up to 48◦C.
Energies 2018, 11, x FOR PEER REVIEW 9 of 15
Figure 6. Energy and collector outlet temperature produced by the simulated absorption cooling
system under various concentration ratios (a) and fluid flow rates (b) in 2016.
4.3. Geothermal System Performance
The geothermal cooling system is preliminarily assessed by comparing the ground
temperature at a depth of 5 m to the minimum and maximum air temperatures in Abu Dhabi, as
shown in Figure 7. This analysis reveals that the yearly ground temperature fluctuates between 24
°C and 26 °C, which offers huge potential as an ambient heat sink, as peak summer air temperature
measures up to 48 °C.
Figure 7. Peak ambient air temperature and ground temperature at a depth of 5 m.
The parametric influences on the geothermal system are studied to optimize the system energy
output (Table 3).
The geothermal system output is monitored in terms of inlet and outlet fluid temperatures,
fluid‐to‐ground heat transfer rate, and the amount of energy delivered representating the cooling
produced. The simulation results of nine consecutive representative days in the peak summer
month of July are expressed as outlet fluid temperature and energy produced.
0
10
20
30
40
50
Jan Feb March April May Jun July Aug Sept Oct Nov Dec
Temperature (°C)
Max Temp Ground Temp at depth 5 m
Ground Temp at 5 m Depth
Figure 7. Peak ambient air temperature and ground temperature at a depth of 5 m.

Energies 2018, 11, 2465 9 of 14
The parametric influences on the geothermal system are studied to optimize the system energy
output (Table 3).
The geothermal system output is monitored in terms of inlet and outlet fluid temperatures,
fluid-to-ground heat transfer rate, and the amount of energy delivered representating the cooling
produced. The simulation results of nine consecutive representative days in the peak summer month
of July are expressed as outlet fluid temperature and energy produced.
The pipe length of the horizontal heat exchanger (2000 m) is calculated based on the available land
area. The effect of fluid flow rate is evaluated from 400 kg/h to 4400 kg/h in increments of 400 kg/h.
The results show that the energy delivered increases with increasing flow rate up to 2800 kg/h, deliverin
22 MWh of cooling energy during peak months (Figure 8).
Table 3. Parameters and values pertaining to the geothermal system.
Parameters Values
Fluid Flow rate 400–4400 kg/h in increments of 400 kg/h
Pipe Length 200–2800 m in increments of 200 m
Pipe Diameter 1 inch, 1.25 inches, 1.5 inches, 2 inches
Pipe Material Aluminum, Copper, Polyethylene
Pipe Depth 3 m, 4 m, 5 m, 6 m, 7 m
Pipe Spacing 0.25 m, 0.5 m, 0.75 m, 1 m
Energies 2018, 11, x FOR PEER REVIEW 10 of 15
The pipe length of the horizontal heat exchanger (2000 m) is calculated based on the available
land area. The effect of fluid flow rate is evaluated from 400 kg/h to 4400 kg/h in increments of 400
kg/h. The results show that the energy delivered increases with increasing flow rate up to 2800
kg/h, delivering 22 MWh of cooling energy during peak months (Figure 8).
Table 3. Parameters and values pertaining to the geothermal system.
Parameters Values
Fluid Flow rate 400–4400 kg/h in increments of 400 kg/h
Pipe Length 200–2800 m in increments of 200 m
Pipe Diameter 1 inch, 1.25 inches, 1.5 inches, 2 inches
Pipe Material Aluminum, Copper, Polyethylene
Pipe Depth 3 m, 4 m, 5 m, 6 m, 7 m
Pipe Spacing 0.25 m, 0.5 m, 0.75 m, 1 m
Figure 8. Delivered energy for various pipe flow rates.
The performance of three heat‐exchanger materials (i.e., aluminum, copper, and polyethylene)
are compared in terms of the amount of heat removed as shown in Figure 9a. Aluminum has a
thermal conductivityof 237W/m∙K, copperhas a thermal conductivityof 401 W/m⋅K, and
polyethylene has a thermal conductivity of 0.33 W/m∙K. The delivered energy range of variation is
between 22,100 MWh to 22,400 MWh, showing a negligible variation. However, polyethylene pipe
is expected to last longer due to its higher resistance to corrosion. Thus, polyethylene is used as the
heat exchanger material for further simulations. The effect of pipe depth on delivered energy is
determined for depths ranging from 3 m to 7 m, in increments of 1 m [52]. The results in Figure 9b
show an increase in delivered energy with increasing pipe depth up to 5 m producing up to 39
MWh cooling energy. The effect of heat exchanger loop spacing on the delivered energy is
determined ranging from 0.25 m to 1 m, shown in Figure 9c. The energy delivered increases with
increasing inter‐loop spacing, reaching 39 MWh at 1 m spacing. Finally, the effect of pipe diameter
is determined ranging from 0.75 inch to 2 inches, as shown in Figure 9d. The results indicate that
the energy delivered increases with increasing pipe diameter, reaching 22 MWh at a 2‐inch
diameter.
The optimal arrangement reduced the leaving air temperature by 12 °C, thus resulting in a
5.8% reduction in annual cooling energy, and a 2.8% reduction in annual energy consumption. The
temperature is not expected to increase by the geothermal loop, since the earth has infinite thermal
mass, so the heat will eventually dissipate into the earth. Thus, it is least likely that the temperature
of the earth will rise. Additionally, the spacing between pipes is 1 m; therefore, the temperature will
spread between the pipes. Moreover, the heat exchanger has minimal effect on the earth temperature
comparedto the solar radiation,which is much higher that the earth temperature.Ground
temperature below a particular depth remains relatively constant throughout the year; due to the
high thermal inertia of the soil [53]. At a sufficient depth, the ground temperature is always lower
0
10
20
30
400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600
Delivered Energy (MWh)
Flow Rate (kg/hr)
Figure 8. Delivered energy for various pipe flow rates.
The performance of three heat-exchanger materials (i.e., aluminum, copper, and polyethylene) are
compared in terms of the amount of heat removed as shown in Figure 9a. Aluminum has a thermal
conductivity of 237 W/m·K, copper has a thermal conductivity of 401 W/m·K, and polyethylene has
a thermal conductivity of 0.33 W/m·K. The delivered energy range of variation is between 22,100 MWh
to 22,400 MWh, showing a negligible variation. However, polyethylene pipe is expected to last longer
due to its higher resistance to corrosion. Thus, polyethylene is used as the heat exchanger material for
further simulations. The effect of pipe depth on delivered energy is determined for depths ranging
from 3 m to 7 m, in increments of 1 m [52]. The results in Figure 9b show an increase in delivered
energy with increasing pipe depth up to 5 m producing up to 39 MWh cooling energy. The effect of
heat exchanger loop spacing on the delivered energy is determined ranging from 0.25 m to 1 m, shown
in Figure 9c.The energy delivered increases with increasing inter-loop spacing, reaching 39 MWh
at 1 m spacing. Finally, the effect of pipe diameter is determined ranging from 0.75 inch to 2 inches,
as shown in Figure 9d. The results indicate that the energy delivered increases with increasing pipe
diameter, reaching 22 MWh at a 2-inch diameter.
The optimalarrangement reduced the leaving air temperature by 12◦C, thus resulting in
a 5.8% reduction in annual cooling energy,and a 2.8% reduction in annual energy consumption.

Energies 2018, 11, 2465 10 of 14
The temperature is not expected to increase by the geothermal loop, since the earth has infinite thermal
mass, so the heat will eventually dissipate into the earth. Thus, it is least likely that the temperature
of the earth will rise. Additionally, the spacing between pipes is 1 m; therefore, the temperature will
spread between the pipes. Moreover, the heat exchanger has minimal effect on the earth temperature
compared to the solar radiation, which is much higher that the earth temperature. Ground temperature
below a particular depth remains relatively constant throughout the year; due to the high thermal
inertia of the soil [53]. At a sufficient depth, the ground temperature is always lower than the outside air
in summer. When Ground Source Heat Pump (GSHP) is used, the temperature difference between the
outside air and the ground is utilized to dump heat into the ground during summer to provide cooling.
Our findings are in line with a research done in similar climates as the UAE, in which a mathematical
model was developed and validated experimentally coupling the Solar Cooling System (SCS) with
a Geothermal Heat Exchanger (GHX) in California, USA [52]. The results show that a 12.30 kW cooling
capacity SCS would be necessary to satisfy the maximum cooling load requirement during the summer.
Additionally, between 10 and 23% of the energy demand was met by the systems [52].
Recently,some buildings started integrating geothermal system in the UAE as a pre-cooling
system, and are reported to be effective [54]. In particular, Sheikh Zayed Learning Center, a museum
in Al Ain city, UAE, integrated geothermal system and was able to achieve a five pearls, based on the
PBRS system, and was certified a LEED platinum rating [54].
Energies 2018, 11, x FOR PEER REVIEW 11 of 15
than the outside air in summer. When Ground Source Heat Pump (GSHP) is used, the temperature
difference between the outside air and the ground is utilized to dump heat into the ground during
summer to provide cooling. Our findings are in line with a research done in similar climates as the
UAE, in which a mathematical model was developed and validated experimentally coupling the
Solar Cooling System (SCS) with a Geothermal Heat Exchanger (GHX) in California, USA [52]. The
results show that a 12.30 kW cooling capacity SCS would be necessary to satisfy the maximum
cooling load requirement during the summer. Additionally, between 10 and 23% of the energy
demand was met by the systems [52].
Recently, some buildings started integrating geothermal system in the UAE as a pre‐cooling
system, and are reported to be effective [54]. In particular, Sheikh Zayed Learning Center, a museum
in Al Ain city, UAE, integrated geothermal system and was able to achieve a five pearls, based on
the PBRS system, and was certified a LEED platinum rating [54].
Figure 9. The parametric influence of pipe material (a) pipe depth (b) pipe spacing (c) and pipe
diameter (d) on the delivered energy.
5. Credit Enhancement Verification of the Local Green Rating System
In order to verify the result of the study with the local PBRS rating system, an analysis has
been done to calculate the contribution of the studied systems to the overall credits achieved.
The number of RE‐1 credits achieved through the integration of the renewable energy systems,
discussed in Section 4, are calculated by applying Equation (1) which comes from Estidama manual:
1
100 2,088,493.2 kWh
yrh 1,684,467.2 kWh
yrh
2,088,493.2 kWh
yrh
19.35% (1)
The proposed systems reduce building energy consumption by 19.35%, earning 4 additional
credits points, and thus achieving all of the 5 credits allocated to the RE category in the PBRS.
The Estidama PBRS also awards additional RE‐5 credits for peak cooling capacity reductions as
given in Equation (2). The annual average electrical load is calculated in Equation (3).
Peak Reduction Peak Load
Average Electrical Load (2)
Figure 9.The parametric influence of pipe material (a) pipe depth (b) pipe spacing (c) and pipe
diameter (d) on the delivered energy.
5. Credit Enhancement Verification of the Local Green Rating System
In order to verify the result of the study with the local PBRS rating system, an analysis has been
done to calculate the contribution of the studied systems to the overall credits achieved.
The number of RE-1 credits achieved through the integration of the renewable energy systems,
discussed in Section 4, are calculated by applying Equation (1) which comes from Estidama manual:
RE− 1 =
100× 2, 088, 493.2kWh
yrh − 1, 684, 467.2kWh
yrh
2, 088, 493.2kWh
yrh
= 19.35% (1)
The proposed systems reduce building energy consumption by 19.35%,earning 4 additional
credits points, and thus achieving all of the 5 credits allocated to the RE category in the PBRS.

Energies 2018, 11, 2465 11 of 14
The Estidama PBRS also awards additional RE-5 credits for peak cooling capacity reductions as
given in Equation (2). The annual average electrical load is calculated in Equation (3).
Peak Reduction= Peak Load
Average Electrical Load (2)
Annual Average Electrical Load= Cooling Load kWh
180 days× 24 hr
day
+ Other Loads kWh
180 days× 9 hr
day
(3)
A system achieving a peak cooling load-to-average electrical load ratio of 1.8 or below qualifies
for two additional credits.The proposed systems reduce the peak-cooling-to-average load ratio to
1.7, thus earning two additional credits. The school analyses in this article is already producing 5% of
its energy through RE systems.Adding 19.3% energy generated from the proposed three systems
would bring the total RE penetration to 24.3%,nearly reaching the ceiling of 25% allowed by the
PBRS. This would lead to additional 14 credit points, increasing the school’s current rating from 81 to
95 credit points: Thus enabling it to reach the desired three pearl rating (which requires a minimum of
85 credit points).
6. System Integration
The school building is being served by a central chiller as a cooling system. The geothermal and
absorption chiller energy systems are designed to work together with the existing cooling system of
the school. Solar thermal panels, used to heat water, would be used directly for heating water in the
building during winter, and to pass the water to the absorption chiller, to cool the building during
summer (Figure 9).During summer, the air coming from outside would be monitored as it passes
through geothermal system, and is then cooled through the Air Handling Unit (AHU) before entering
the building.At the same time, the hot water passes through the absorption chiller system to cool,
and then passes through the AHU before being used. If hot water entered the absorption chiller, it will
be cooled down but still will not be comfortable, thus, it would enter the chiller compressor to be
chilled water, before passing through the AHU, ready to be used in the school. During winter, the air
will go directly to the AHU and there will be no cooling demand, thus the thermal panels will be used
to heat the water inside the building (Figure 10).
Energies 2018, 11, x FOR PEER REVIEW 12 of 15
Annual Average Electrical Load
Cooling Load kWh
180 days24 hr
day
Other Loads kWh
180 days9 hr
day
(3)
A system achieving a peak cooling load‐to‐average electrical load ratio of 1.8 or below qualifies
for two additional credits. The proposed systems reduce the peak‐cooling‐to‐average load ratio to
1.7, thus earning two additional credits. The school analyses in this article is already producing 5%
of its energy through RE systems. Adding 19.3% energy generated from the proposed three systems
would bring the total RE penetration to 24.3%, nearly reaching the ceiling of 25% allowed by the
PBRS. This would lead to additional 14 credit points, increasing the school’s current rating from 81
to 95 credit points: Thus enabling it to reach the desired three pearl rating (which requires a
minimum of 85 credit points).
6. System Integration
The school building is being served by a central chiller as a cooling system. The geothermal
and absorption chiller energy systems are designed to work together with the existing cooling
system of the school. Solar thermal panels, used to heat water, would be used directly for heating
water in the building during winter, and to pass the water to the absorption chiller, to cool the
building during summer (Figure 9). During summer, the air coming from outside would be
monitored as it passes through geothermal system, and is then cooled through the Air Handling
Unit (AHU) before entering the building. At the same time, the hot water passes through the
absorption chiller system to cool, and then passes through the AHU before being used. If hot water
entered the absorption chiller, it will be cooled down but still will not be comfortable, thus, it would
enter the chiller compressor to be chilled water, before passing through the AHU, ready to be used
in the school. During winter, the air will go directly to the AHU and there will be no cooling
demand, thus the thermal panels will be used to heat the water inside the building (Figure 10).
Figure 10. Renewable energy system integration.
7. Conclusions
This paper investigates opportunities of integrating renewable energy strategies to enhance the
energy performance of governmental schools, under the harsh climate of the United Arab Emirates.
Figure 10. Renewable energy system integration.

Energies 2018, 11, 2465 12 of 14
7. Conclusions
This paper investigates opportunities of integrating renewable energy strategies to enhance the
energy performance of governmental schools, under the harsh climate of the United Arab Emirates.
Specifically,it aims to improve the local green building rating performance of a public schools in
Abu Dhabi (UAE) by taking it from two pearls to three pearls. This is done through gaining credits
in the PBRS’ResourcefulEnergy category,which represent one-fourth of the obtainable credits.
This particular category has not been optimally integrated in the newly built public buildings, despite
its potential.
The technicalfeasibility ofrenewable energy systems,namely photovoltaic,solar-powered
absorption chiller and geothermal systems, were studied. The systems were evaluated using TRNSYS
Simulation Software under UAE climatic conditions to test their performance. Relevant parameters and
variables in each energy system were optimized in order to maximize energy savings, while remaining
grounded in qualitative design terms, special requirement, and cost constraints. The geothermal system
yields an annual cooling energy reduction of 5.8%, and a total energy reduction of 2.2%.The solar
absorption cooling system results in 19.35% reduction in annual cooling energy use, and 7.2% reduction
in total annual energy use. The photovoltaic system contributes 10% of the total energy consumption
(or a 10% energy savings). The total energy savings from the combined three systems can reach 19.35%
which leads to an additional 14 PBRS credit points.The rating enhancement is found feasible in
terms of energy,and special provisions involving photovoltaic,solar-powered absorption cooling,
and geothermal renewable energy systems.Thus,integrating these systems will allow the school
to improve its pearl rating from the current level of performance to the next i.e.,from two pearls
to the desired three pearls.Furthermore, this study considered the RE system integration into the
existing cooling system of the school. The investigated solar systems hold an applicability enhancement
potential that spans to most similar buildings under the same, or similar settings.
Author Contributions:All authors conceived the subject of this paper, J.A.D. carried the literature review and the
simulations and wrote the initial manuscript. K.T.A. and A.H. verified the scholastic depth of the paper, carried
out a critical review of the structure and content, and also supervised the analysis and findings of this work.
All authors discussed the results and contributed to the final write up.
Funding:The authors gratefully acknowledge financial support from the United Arab Emirates University
through the Emirates Centre for Energy and Environment grant number [31R054] and grant number [31R102].
Conflicts of Interest: The authors declare no conflict of interest.
References
1. Statistics-Center. Energy and Water Statistics. 2015. Available online: http://ecocci.org/images/stories/
ECO_data/Announcement/Energy_and_Water_Statistics_2015.pdf (accessed on 12 September 2017).
2. Lin, M.; Afshari, A.; Azar, E. A data-driven analysis of building energy use with emphasis on operation and
maintenance: A case study from the UAE. J. Clean. Prod. 2018, 192, 169–178. [CrossRef]
3. Mokhtar,M.; Ali, M.T.;Bräuniger,S.;Afshari,A.; Sgouridis,S.; Armstrong,P.;Chiesa,M. Systematic
comprehensive techno-economic assessment of solar cooling technologies using location-specific climate
data. Appl. Energy 2010, 87, 3766–3778. [CrossRef]
4. Friess, A.W.; Rakhshan, K. A review of passive envelope measures for improved building energy efficiency
in the UAE. Renew. Sustain. Energy Rev. 2017, 72, 485–496. [CrossRef]
5. Estidama. Available online: http://estidama.upc.gov.ae/estidama-and-pearl-rating-system.aspx?lang=en-US
(accessed on 22 January 2017).
6. Estidama. The Pearl Rating System for Estidama. Available online: http://estidama.upc.gov.ae/template/
estidama/docs/PBRS%20Version%201.0.pdf (accessed on 18 April 2016).
7. Sgouridis, S.; Griffiths, S.; Kennedy, S.; Khalid, A.; Zurita, N. A sustainable energy transition strategy for the
United Arab Emirates: Evaluation of options using an integrated energy model. Energy Strategy Rev.2013, 2,
8–18. [CrossRef]

Energies 2018, 11, 2465 13 of 14
8. Sgouridis, S.;Abdullah, A.;Griffiths, S.;Saygin, D.;Wagner, N.;Gielen, D.;Reinisch, H.;McQueen, D.
Re-mapping the uae’s energy transition: An economy-wide assessment of renewable energy options and
their policy implications. Renew. Sustain. Energy Rev. 2016, 55, 1166–1180. [CrossRef]
9. Alnaser, W.E.; Alnaser, N.W. The status of renewable energy in the GCC countries. Renew. Sustain. Energy Rev
2011, 15, 3074–3098. [CrossRef]
10. Doukas, H.; Patlitzianas, K.D.; Kagiannas, A.G.; Psarras, J. Renewable energy sources and rationale use of
energy development in the countries of GCC: Myth or reality? Renew. Energy 2006, 31, 755–770. [CrossRef]
11. Patlitzianas,D.K.; Doukas,H.; Psarras,J. Enhancing renewable energy in the Arab states of the gulf:
Constraints & efforts. Energy Policy 2006, 34, 3719–3726.
12. Taleb, H.; Al-Saleh, Y. Applying energy-efficient water heating practices to the residential buildings of the
united arab emirates. Int. J. Environ. Sustain. 2014, 9, 35–51.
13. Berg,A. Not roadmaps buttoolboxes:Analysing pioneering nationalprogrammes for sustainable
consumption and production. J. Consum. Policy 2011, 34, 9–23. [CrossRef]
14. Cincera, J.; Krajhanzl, J. Eco-schools: What factors influence pupils’ action competence for pro-environmental
behaviour? J. Clean. Prod. 2013, 61, 117–121. [CrossRef]
15. Central-Intelligence-Agency. United Arab Emirates Electricity Consumption. Available online: http://www.
indexmundi.com/g/g.aspx?c=tc&v=81 (accessed on 19 January 2017).
16. ADEC. Educational Facilities Design Manual; Abu Dhabi Education Council: Abu Dhabi, UAE, 2010.
17. ADEC. Sheikha Bint Sroor Public School Data; Dakheel, J.A., Ed.; ADEC: Abu Dhabi, UAE, 2016.
18. World-Weather.Abu Dhabi Monthly Climate Average, United Arab Emirates.Available online:https://ar.
worldweatheronline.com/abu-dhabi-weather-averages/abu-dhabi/ae.aspx (accessed on 14 January 2017).
19. Radhi, H. Evaluating the potential impact of global warming on the uae residential buildings—A contribution
to reduce the CO2 emissions. Build. Environ. 2009, 44, 2451–2462. [CrossRef]
20. Climate-Consultant. Ground Temperatures of Abu Dhabi. In Climate Consultant, version 5.5; United States
Department of Energy: Washington, DC, USA, 2017.
21. Hasan, A.; Sarwar, J.; Alnoman, H.; Abdelbaqi, S. Yearly energy performance of a photovoltaic-phase change
material (PV-PCM) system in hot climate. Sol. Energy 2017, 146, 417–429. [CrossRef]
22. Hayter,S.; Kandt,A. Renewable Energy Applications for Existing Buildings;NationalRenewable Energy
Laboratory: Golden, CO, USA, 2011.
23. Walwil, H.M.;Mukhaimer, A.;Al-Sulaiman, F.A.;Said, S.A. Comparative studies of encapsulation and
glass surface modification impacts on PV performance in a desert climate. Sol. Energy2017, 142, 288–298.
[CrossRef]
24. Emziane, M.; Al Ali, M. Performance assessment of rooftop PV systems in Abu Dhabi. Energy Build.2015,
108, 101–105. [CrossRef]
25. Al Ali, M.; Emziane, M. Performance analysis of rooftop PV systems in Abu Dhabi. Energy Procedia2013, 42,
689–697. [CrossRef]
26. Radhi, H. Energy analysis of façade-integrated photovoltaic systems applied to UAE commercial buildings.
Sol. Energy 2010, 84, 2009–2021. [CrossRef]
27. Shirazi, A.;Taylor, R.A.;Morrison, G.L.;White, S.D. A comprehensive,multi-objective optimization of
solar-powered absorption chiller systems for air-conditioning applications.Energy Convers.Manag.2017,
132, 281–306. [CrossRef]
28. Bellos, E.; Tzivanids, C.; Symeou, C.; Antonopoulos, K.A. Energetic, exergetic and financial evaluation of
a solar driven absorption chiller—A dynamic approach. Energy Convers. Manag.2017, 137, 34–48. [CrossRef]
29. Fong, K.F.; Lee, C.K.; Zhao, T.F. Effective design and operation strategy of renewable cooling and heating
system for building application in hot-humid climate. Sol. Energy 2017, 143, 1–9. [CrossRef]
30. Salem, A.; Hashim, H. A feasibility of geothermal cooling in Middle East. Latest Trends Sustain. Green Dev.
2010, 105–112.
31. TRNSYS. What Is TRNSYS? Available online: http://www.trnsys.com/ (accessed on 14 February 2017).
32. Chargui, R.; Sammouda, H.; Farhat, A. Geothermal heat pump in heating mode: Modeling and simulation
on trnsys. Int. J. Refrig. 2012, 35, 1824–1832. [CrossRef]
33. Cocchi, S.; Castellucci, S.; Tucci, A. Modeling of an air conditioning system with geothermal heat pump for
a residential building. Math. Probl. Eng. 2013, 2013, 781231. [CrossRef]

Energies 2018, 11, 2465 14 of 14
34. Safa, A.A.; Fung, A.S.; Kumar, R. Heating and cooling performance characterisation of ground source heat
pump system by testing and TRNSYS simulation. Renew. Energy 2015, 83, 565–575. [CrossRef]
35. Florides, G.A.; Kalogirou, S.A.; Tassou, S.A.; Wrobel, L.C. Modelling and simulation of an absorption solar
cooling system for Cyprus. Sol. Energy 2002, 72, 43–51. [CrossRef]
36. Kim, B.; Park, J. Dynamic simulation of a single-effect ammonia—Water absorption chiller.Int. J. Refrig.
2007, 30, 535–545. [CrossRef]
37. Asim,M.; Dewsbury,J.; Kanan,S. TRNSYS simulation of a solar cooling system for the hot climate of
Pakistan. Energy Procedia 2016, 91, 702–706. [CrossRef]
38. Li, Y.; Jing, D. investigation of the performance of photovoltaic/thermal system by a coupled TRNSYS and
CFD simulation. Sol. Energy 2017, 143, 100–112. [CrossRef]
39. Vuong,E.; Kamel,R.S.;Fung,A.S. Modelling and simulation of BIPV/T in EnergyPlus and TRNSYS.
Energy Procedia 2015, 78, 1883–1888. [CrossRef]
40. Quesada, B.; Sánchez, C.; Cañada, J.; Royo, R.; Payá, J. Experimental results and simulation with TRNSYS of
a 7.2 KWp grid-connected photovoltaic system. Appl. Energy 2011, 88, 1772–1783. [CrossRef]
41. Soussi,M.; Balghouthi,M.; Guizani,A.; Bouden,C. Model performance assessment and experimental
analysis of a solar assisted cooling system. Sol. Energy 2017, 143, 43–62. [CrossRef]
42. Al-Alili, A.; Hwang, Y.; Radermacher, R.; Kubo, I. Optimization of a solar powered absorption cycle under
Abu Dhabi’s weather conditions. Sol. Energy 2010, 84, 2034–2040. [CrossRef]
43. Dai, Y.; Li, X.; Wang, R. Theoretical analysis and case study on solar driven two-stage rotary desiccant cooling
system combined with geothermal heat pump. Energy Procedia 2015, 70, 418–426. [CrossRef]
44. Angrisani, G.; Diglio, G.; Sasso, M.; Calise, F.; d’Accadia, M.D. Design of a novel geothermal heating and
cooling system: Energy and economic analysis. Energy Convers. Manag. 2016, 108, 144–159. [CrossRef]
45. Alchemie. Solar Cells. Available online: http://www.solar-facts-and-advice.com/solar-cells.html (accessed
on 13 March 2017).
46. Gunerhan,H.; Hepbasli,A. Determination of the optimum tilt angle of solar collectors for building
applications. Build. Environ. 2007, 42, 779–783. [CrossRef]
47. Jafarkazemi, F.; Saadabadi, S.A. Optimum tilt angle and orientation of solar surfaces in Abu Dhabi, UAE.
Renew. Energy 2013, 56, 44–49. [CrossRef]
48. Assi, A.; Jama, M.; Al Kathairi, K.; Al Shehhi, I.; Fattahi, S. Predicting the electrical behavior of grid-tied
photovoltaic systems in al ain-uae/model and case study.In Proceedings of the 2008 IEEE International
Conference on Sustainable Energy Technologies, Singapore, 24–27 November 2008; pp. 443–447.
49. Ernst,W.D.;Shaltens,R.K.Automotive Stirling Engine Development Project;Mechanical Technology,Inc.:
Latham, NY, USA, 1997.
50. Kong, X.Q.; Wang, R.Z.; Huang, X.H. Energy efficiency and economic feasibility of CCHP driven by Stirling
engine. Energy Convers. Manag. 2004, 45, 1433–1442. [CrossRef]
51. Syed,A.; Izquierdo,M.; Rodriguez,P.; Maidment,G.; Missenden,J.; Lecuona,A.; Tozer,R. A novel
experimental investigation of a solar cooling system in Madrid. Int. J. Refrig. 2005, 28, 859–871. [CrossRef]
52. Acuña, A.; Lara, F.; Rosales, P.; Suastegui, J.; Velázquez, N.; Ruelas, A. Impact of a vertical geothermal heat
exchanger on the solar fraction of a solar cooling system. Int. J. Refrig. 2017, 76, 63–72. [CrossRef]
53. Lee, K.S. Underground thermal energy storage. In Underground Thermal Energy Storage; Springer: Londo
UK, 2013; pp. 15–26.
54. IRENA. District Heating and Cooling; IRENA: Abu Dhabi, UAE, 2017.
©2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).