Engineering, 2013, 5, 56-61
doi:10.4236/eng.2013.51b010 Published Online January 2013 (http://www.SciRP.org/journal/eng)
Assessment of the Energy Impact of Using Building
Integrated Photovoltaic and Electrochromic Glazing in
Office Building in UAE
Mohammad Katanbafnas ab1, Bassam Abu-H ijleh2
1KEO International Consultants, Abu Dhabi-UAE
2Faculty of Engineeri ng & IT, the British University in Dubai, Dubai-UAE
Received 2013
ABSTRACT
The aim of this rese arch was t o explo re the ener gy benefit s and fut ure pote ntial of usi ng Build ing Integr ated P hotovol-
taic (BIPV) and Electrochromic Glazing (EG) within the climatic conditions of the city of Abu Dhabi. The Integrated
Environmental Solutions (IES-VE) energy modeling software was used to assess the energy performance, mainly the
red uct io ns in H V AC and li ghting, for d iffer e nt co n fi gurations and compare that to the base case scenario for south, east,
west, and north facing facades. The results showed that the BIPV is most advantageous on the south façade while the
EC glazing performs best on the north facing windows. Moreover, the change in sensor location increased the energy
savi ngs fo r b ot h ca se s, a lthou gh the c ha nge wa s very margi na l c o mpa re d to the c ha nge o f t he gla s s p r op e rt ie s. U sin g a n
automated light control system with dimming for both models, compared against the standard on-off lighting mechan-
ism in the base case, the BIPV proves to have a higher total annual energy saving potential for most orientations, upto
33.5% while dynamic EC was best suited for the North o rientation re sulting in 7.4% reduction in the total annual e nergy
consumption.
Keywords: Renewable Energy; BIPV; EC Glazing; Office Building; UAE ; Computer Simulation
1. Introduction
During the rapid construction boom, before the global
economic crisis, there were approximately one third of
the world’s construction cranes operating in the UAE.
There has been a tremendous shift in building construc-
tion o ver the past 40 years. I n genera l the s unlight a rchi-
tecture that once tried to avoid solar gain by using small
windows and appropriate shading devices has become
obsolete. Other traditional elements such as the Badgir
which functioned to naturally ventilate the buildings are
now merely a decorative feature used for cultural associ-
ation. The vernacular architecture of this region, based
on high thermal mass and natural ventilation, has been
outdated with modern skyscrapers. In 2010, Dubai
claimed the title for the world’s tallest building with the
opening of the Burj Khalifa, a massive 828 meter tall
structure. The estimated 400 office towers in the dense
Business Bay District follow the concept of daylight ar-
chitecture and try to maximize penetration of natural
light. However, these large glazed areas lead to ineffi-
cient energy consumption and high operating costs.
The se b ui ld in gs func ti o n ma in l y due t o he a v y r el ia nce o n
mechanical support particularly use of air-conditioning
that runs on low cost electricity from fos sil fuel [1].
However, UAE is also one of the most ambitious
amongst the several oil-rich Gulf countries that have
made efforts to find alternative energy sources to meet its
growing need for electricity. After all, in order to main-
tain a life of luxury with indoor ski slopes, chilled
swimming pools, and huge air-conditioned shopping
malls, the dependency on oil primarily might not be such
wise option. Looking at the country’s past, the use of
passive techniques such as the Badgir, and courtyard are
prevalent in its architecture. Such measures were neces-
sary for keeping comfortable environments through in-
ducing stack effect particularly in the hotter months. Un-
fortunately with the accessibility to oil and introduction
of air conditioning, these elements slowly faded. Today,
they are the subject of vernacular architectural study of
the region and regarded as the essence of sustainability.
The research aims to compare benefits in terms of
overall building energy use that can be expected from
adopting two alternative façade technologies. In order to
make the study more focused, office buildings are taken
as the only building typology under consideration, as
they are “the largest energy consumers in the buildings

M. KATANBAFNASAB ET AL.
57
sector” [2]. An assessment will be made of the energy
benefits that might arise from installing EC glazing or
BIPV instead of conventional glass across the vertical
façade. The energy benefit of EC glazing will be quanti-
fied in terms of its capability to reduce the total energy
consumption (from electrical lighting plus building sys-
tem like HVAC) on an annual basis through providing
controlled day-lit environment when compared to stan-
dard glazing with blinds. In the case of the BIPV, the
study will estimate energy balance through the energy
consu me d fo r l i ght in g and H VA C, P V e ne r gy that can b e
generated on site , and the resulting energy equilibr ium on
daily, monthly, and annual basis. Thus the research will
attempt to recognize and quantify the benefits of each
system according to various parameters. These can in-
clude façade orientation, concerned area of façade that
the s ystem i s app lied o n, var ying wea ther co ndit ions (i .e.
clear sky, overcast, etc), and possibly further exploration
of these parameter in different geographical location to
compare with Abu Dhabi.
2. Literatu re Revi ew
Most building’s occupants favor daylight as their primary
light source. Although most developers understand the
higher premium value that normally comes with a space
with more wind ows, the e ffect s o f “exte nsi ve da ylighting
on organizational efficiency” is not as well considered
[3]. In the building sector, an increase in demand for
sustainable energy and strategies for manage ment of nat-
ural light indoors and its relationship with artificial
lighting require ments ha s led to explo ratio n of alternative
façade designs. One of the most active areas in building
design is advancements of technologies related to win-
dows and specifically the glass. The driving forces be-
hind such breakthroughs are issues related to interior
day-lighting enhancement, maximizing occupants view
and comfort, and reducing operational costs. Conse-
quently these also have an environmental impact which
makes the focus on glass worthwhile. In addition, other
factors such as cultural mentality, health regulation, and
occupant expectations have added to the momentum to-
wards “healthy buildings” through use of unconventional
façade designs [4].
2.1. Building Integrated Photovoltaic (BIPV)
Most people associate solar energy with flat-panel PV
systems. They are based on crystalline silicon solar cells
that convert the sun’s rays directly into electricity. The
two types of these cells are mono-crystalline and poly
(multi)-crystalline. The easiest way to visually identify
the difference between them is that the polycrystalline
has a shattered glass look, while the mono-crystalline
cells tend to be uniform in appearance, Figure 1. The
Figure 1. Opaque and semi-transparent polycrystalline PV
module [5].
price and performance of polycrystalline silicon solar
module is lower than that of mono-crystalline and they
are the most common type of these cells. Mono-crystal-
line cells are cut from silicon chunks gro wn from a single
crystal. Their applications are for more expensive types
of solar panels and are more efficient in converting the
sun’s ra ys to electr icit y. A polycr ystalline ce ll is cut from
multifaceted silicon crystal. More surface area is required
due to inherent flaws and these panels are less efficient in
converting the sun’s rays. However, polycrystalline tech-
nology has closed up the performance gap in recent years
with nominal efficiency of 15% compared to 17% in
mono.
PV can be used in a variety of ways on a building sur-
face, combining energy production with other functions
of the b uild ing e nvelo pe suc h as faç ade a nd ro of inte gra-
tion, sun shades, and balcony rails. A type of PV applica-
tion is Building integrated photovoltaic (BIPV) which is
an ideal solution to reduce peak grid-supplied power de-
pendency, and provide new façade design. However, the
energy efficiency of BIPV, for example placed as spand-
rel glass panel, is 50% less compared to “optimally
placed PV module” such as roof-mounted angled arrays
used primarily for power generation [4].
According to the International Energy Agency (IEA),
in order to assess potential of BIPV, an analysis of
building skin suitability is required [6]. This can be de-
fined as two categories: architectural suitability taking
into account limitations due to constructions, shading,
and available surfaces, as well as solar suitability which
considers amount of incident solar flux on the surface
based on orientation, inclination and location and per-
formance of characteristic of the BIPV system. One of
the advantages of BIPV as an alternative façade is that is
produces electricity while allowing daylight to penetrate
the internal spaces. This will further reduce building
energy consumption by providing diffused light that will
ultimately reduce need for artificial lighting and hence
air-conditioning. It offers a variety of possibilities for
building integration given that the panels have the best
orientation toward the sun, usually south facing in the

M. KATANBAFNASAB ET AL.
58
Northern hemisphere. Besides good orientation, which
ensures optimum solar irradiance, another critical design
issues is ade quate ventilation. Without sufficie nt air gaps
on the back of the modules, overheating of the modules
causes reductions in outputs. Another important concern
is ma intai ning a clear o bstr uction from s urround ing b uild-
ing parts or trees that may cause shading. This is crucial
for a continuous optimum performance. Any part that is
shaded will reduce the overall module efficiency. Chaar
et al. [7] discusses the effects of wind-blown sand and
dust on PV arrays in the UAE. Despite the good sunshine
conditions in UAE, Chaar highlights the other climatic
conditions such as high temperatures and occasional
strong winds that cause perpetual sandstorm. Because
these factors tend to produce different results than per-
forming laboratory testing, hence the application of PV
arrays must be studied for its feasibility in such extreme
environment.
2.2. Electrochromic Glazing (EG)
A new type of dynamic glazing, also called smar t window,
can cha nge t ransp arenc y in re spo nse to ex terna l cha nges.
There are three technologies that work on this principle:
liquid crystals, suspended-particle devices, and chromic
materials. There are four categories of chromic devices:
electrochromic (EC) which responds to electrical voltage,
thermochromic that responds to heat, photochromic
which responds to light [8] and gasochromic that reacts
to oxidizing gases like H2 [9]. This paper will focus on
electrochromic type which can be used to control heat
and li ght in windo ws. EC gla zing is part o f a new group
of technologies called switchable glazing or smart win-
dow. Its energy reduction potential can be achieved
through control of solar heat, daylight and glare. There
are various types of EC windows. One of the most com-
mon one is metal oxide EC such as tungsten. Tungsten
oxide (WO3) is well known for it good EC properties
and stability. Figure 2 shows the configuration which is
a fi ve-layer WO3 coating sandwiched between two glass
panes.
This technology works by passing a low-voltage elec-
tric current across a microscopically-thin coating on the
glass surface. This activates the EC layer that causes its
color to change from clear to dark, hence changing the
window’s transparency. A product by one of the leading
manufactures has a dynamic range of 3.5% - 64% [10].
This means that on the low (dark) end, it blocks all but
3.5% of incoming visible light and most of the heat,
while on high (clear) end, it blocks only 36% incoming
lights, and allows in more solar heat. One of the advan-
tages EC glazing is that it only requires electricity to
change its opacity but not to maintain a particular shade.
It has a good durability and can be cycled from clear to
tinted over 100,000 times without any functional loss
[11]. Another advantage is that unlike Low-E coatings
that are only appropriate for one type of climate, this type
of smart glass can regulated depending on the specific
needs. Further, in contrast to blinds, they are capable of
partially blocking light while giving a clear view of out-
side. A performance characteristic of ECG that might
limit its use is its s witching speed . B ecause this transition
takes three to five minutes, the amount of light entering
the room is limited by the delay in the response of the
window. Due to this time needed to tint the glass, the
“standard u se is to co ntrol the system for t wo states: cle a r
and f ully t inted ” [1 1] . Anot he r di sadva nta ge is the inc on-
sistency in the tint change. This is known as the “iris
effect” where color change begins at outer edges of the
window and slowly towards the center [12].
Figure. 2 Layers of EC g lazi ng and t he w orking mechanism
[13].

M. KATANBAFNASAB ET AL.
59
3. Methodology
The advanced computer software program Integrated
Environmental So lutions – Virtual Environment (IES-VE)
was used to run the various configurations. There are
several important criteria in choosing the correct soft-
ware tool for this study. The following are a pre-requisite
that were deemed necessary by the author in a computer
program to be capable of handling this study:
-Ability to model BIPV and mimic characteristic of
EC glazing
-Reliable with validatio n certificates
-Used by other scholars in similar research
-Comprehensive database of various building con-
struction materials
A study by Crawley et al. [14] compared the twenty
simulation programs under a number of functions and
capabilit ies. From the a nal ysis, IES-VE software achie ved
the best score and thus was selected for this study.
3.1. The Simulation Models
The basic model established for this simulation study
represents the common construction practice in the Emi-
rate of Abu Dhabi. The space configuration as well as the
type of materials incorporated into the model is fre-
quently found in UAE building construction. The space
modelled, sho wn in Figure 3, has a rectangular shape of
4m (width), 6m (depth), and 3m (height). There is a ple-
num of 1m height, which brings the total floor to floor
height to 4m. The façade is a typical curtain wall con-
struction, with a flush window size of 4m width and 3m
height consisting of double-glazing unit. Hence, the
façade ratio of glazi n g to solid ( or windo w to wall ratio –
WWR) will be 75% vision glass and 25% solid. The
façade is also modelled with interior roller blinds. The
blinds were either fully up or fully lowered over the
whole window.
Figure. 3 Axonometric of the simulation model.
A ba se -case sit uation will pr ovide the co mmon groun d
from which the energy benefits of both the EC glazing
and BIPV can be established. In this situation, there will
be lights with on and off switch that can provide normal
working conditions up to 500 lux. These lights will only
be linked to an automated sensor that will switch them
off beyond illuminance levels of 500lux. This model uses
roller blinds for daylight control. The operation of blinds
would be triggered by automatic sensors determining
daylight levels going above 2000lux, thus giving protec-
tion from glare. And whenever illuminance levels are
below this value, the blinds would be retracted. Although
this automated control does not match accurate human
behavior, it will primarily be used as a comparison
benchmark.
3.2. Electrochromic Glazing Control Strategy
The software does not have the capability of d yna m ically
changing the glazing properties, based on fluctuations in
illuminance levels. Instead the performance of EC glaz-
ing, as it s witches from bleac hed (high tra nsmission state )
to colored (darkened to a highly tinted state), will be
examined by manually testing various tinting conditions
on an hourly basis. Based on available technology, it is
assumed that the range of visible transmittance in the
model could vary between 3.5% and 62%. For this model,
the standard glazing will be replaced by EC gla zi ng. P re-
vious researches have shown that the best energy per-
formance is achieved by daylight control switching of
EC, mostly because of the “large electric lightning load
reduction from day-lighting” [15]. The lighting mechan-
ism will be si milar to the base-case, where dimming con-
trol will be used to maintai n a constant lighting co ndition
of 500lux levels from natural light with artificial lights
acting as supplementary. In this scenario, the EC glazing
will be considered in full tint mode during non- wo rking
hours and weekends. The objective of this model is to
evaluate the contribution of dynamic glazing and dim-
ming cont rol in the overall energy consumption.
3.3. BIPV Model Strategy
Part of this study is to explore some of these different
Monocrystalline PV technologies to compare their bene-
fits against each other. An annual si mulatio n will id entify
the best type based on total light energy, total electr icity,
total displaced electricity, and the total energy balance.
The models use BIPV that are integrated in va rio us ways
within the facade of a room with similar configuration as
the base office module. The software can quantify the
total annual e lectrical outp ut fr om the BIP V based o n the
measured area on the facade. The outcome of this exer-
cise will form a baseline of optimum BIPV model for
assessment against the EC glazing and the base case

M. KATANBAFNASAB ET AL.
60
model. Table 1 shows the matrix of different scenarios
that will be teste d for this reason.
4. Results and Discussion
The summary of the overall results of the BIPV tests
shown in Table 2 indicate that case no. 5 has the lowest
total energy. Ano ther impor tant aspects is prop er lighting
conditions and glare protection. Glare is commonly
caused by either the excessive luminance values in the
field of view and or too high luminance contrasts. Win-
dows can have a high luminance compared with other
luminances in a room. This gives a strong contrast from
inside to outsid e , potentially causing glare.
Based on the results in Table 2 BIPV case 5 is used
Table 1. Test matrix of BIPV simulation cas e s.
Case
#
Building Model Properties
Transparency Façade Integration Availab le
area (m2)
1 Semi Checkered 7.125
2
Opaque
Horizontal Bands 6
3 Vertical Bands 6
4 Only replaces Spandrel 4
5 Combination Checkered with Spandrel 11.125
Table 2. Energy consumption and production summary of
the diff erent B IPV configur a tions studied.
Case nu mber
Base
model 1 2 3 4 5
Direct Lighting
Energy (MWh) 0.363 0.567 0.463 0.444 0.194 0.567
Cooling Load
Energy (MWh 4.595 3.074 2.912 2.905 3.133 3.074
Total Electricity
Consumption
(M Wh) 4.96 3.641 3.375 3.348 3.327 3.641
Total Energy
Produce by BIP V
(M Wh) NA 0.711 0.598 0.598 0.399 1.109
Net Total Energy
Consumption
(M Wh) 4.96 2.931 2.776 2.750 2.928 2.532
Red u ction in Net
Total Energy
Consumption NA 40.9% 44.0% 44.5% 40.9% 48.9%
for the second part of this research, i.e. comparison with
the use of EC glazing. Seven EC configurations were
tested, the difference being the level of tenting if each
case. The tenting values used were: 15%, 30%, 45%,
60%, 75%, 90% and dynamic tenting (i.e. variable tent-
ing based on the level of natural light available through-
out the day). The modeling was done for four design
days (March 21, June 21, September 21 and December
23) representing the four seasons of the year. The simu-
lations were also conducted for four different orientatio ns
(North, East, South and West). The use of EC is expected
to reduce the energy consumption by reducing the solar
gain in the space. Figures 4 and 5 show the cumulative
annual percentage change in energy consumption for
BIPV case 5 as well as all seven EC configurations for
the South and
North orientations, respectively. EC was able to reduce
the annual energy consumption by as much as 11.2% for
the case of South facing dynamic EC co nfigurati on, Fig-
ure 4. I t is interesting to note that the use of EC can al so
Figure 4. Change in total annual energy consumption, South
facing orientat ion.
Figure 5. Change in total annual energy consumption,
North facing orientation.

M. KATANBAFNASAB ET AL.
61
result in increased annual energy consumption, as much
as 5.4% for the North facing EC with 75% tenting, Fig-
ure 5. This is due to the need for more artificial light
when low natural light reaches the interior of the space
due to the high tenting of the EC The other important
result seen is that BIPV results in lower energy con-
sumption for the South orientation, energy reduced by
33.5% compared to 11.2% for the dynamic EC as seen in
Figure 4. As for the North orientation dynamic EC re-
sulted in 7.4% reduction in energy while the BIPV re-
duced the energy by 1.4% as seen in Figure 5. T he main
rea son for that i s that BIP V do es not functi on we ll in t he
North orientation due to the lack of direct sunlight. The
BIPV results for the East and West orientations fall in
between results of the South and North orientations with
an annual energy savings of 16.7%. On the other hand,
dynamic EC performed poorly in the East and West
orientations with an annual energy reduction of only
1.4%. These results show that BIPV is best suited for
orientations in which there is dir ect sunlight (E ast, South
and West) while d ynamic EC is best suited for the North
direction.
5. Conclusions
This research studied the application of BIPV and EC
glazing as an alternative façade to conventional glazing
and blinds within the climate of Abu Dhabi using the
IES-VE energy modelling software. Three different si-
mulation models were created to test all the configura-
tions with various changing parameters. The study
showed that the BIPV model resulted in the most annual
energy saving amongst for three of the four orientations
(East, South and West) upto 33.5% while dynamic EC
resulted in the most annual energy for the North, upto
7.4%. Improper application of EC could result in in-
creased annul energy consumption, by as much as 5.4%
for the case of South orientation with 75% tenting. The
results can be used to significantly reduce the annual
energy consumption in an office building located in Abu
Dhabi-UAE.
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