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 Proceedings of the

International Conference on Chemical Engineering 2014ICChE2014, 29-30 December, Dhaka, Bangladesh 

*Corresponding Author: Md Jahangir Alam,

E-mail: jahangirche@gmail.com 

EFFECT OF EXTERNAL SHADING AND WINDOW GLAZING ONENERGY CONSUMPTION OF BUILDINGS IN BANGLADESH

Md. Jahangir Alam*, Biplob Kumar Biswas Department of Chemical Engineering, Jessore University of Science and Technology,

Jessore- 7408, Bangladesh

Mohammad Ariful IslamDepartment of Mechanical Engineering, Khulna University of Engineering & Technology,

Khulna-9203, Bangladesh

Energy efficiency of buildings is attracting significant attention from the research community as the world is

moving towards sustainable buildings design. Energy efficient approaches are measures or ways to improve

the energy performance and energy efficiency of buildings. External shading and window glazing influence

the solar energy on a window and the conveyed energy within the room through the window. In present

study, the effect of advanced glazing and overhangs on the solar energy transmitted into or lost from the

room through the fenestration areas have been evaluated for typical residential buildings in Bangladeshusing EnergyPlus software. It was found that appropriate overhangs or side fins in the south, west and east

windows would lead to the optimal reduction of the annual energy transferred into the buildings and can

have an energetic behavior equivalent to high performance glazing. The results have been summarized to

easy selecting the best window with different glazing, overhangs and side fins based on energy evaluation.  

1. INTRODUCTION

Population growth and economic progress have led

to an increase in the demand for energy. The

worldwide increase in demand for energy has put

rising pressure on identifying and implementing

ways to save energy. In global context, Buildings

account for a surprisingly high 40% of worldwide

energy consumption (Krarti, 2012). If the energy

consumed in manufacturing steel, cement,

aluminum and glass used in construction of

 buildings is being considered, this consumption

would be more than 50% (www.wbcsd.org).

Energy efficient buildings is an important factor

related to the energy issue; according to Omer

(2008) a building has three parameters directly

related to energy consumption: thermal comfort(thermal conditioning), visual comfort (lighting)

and air quality (ventilation). Energy consumption

analysis of buildings is a difficult task because it

requires considering detailed interactions among

the building, HVAC system, and surroundings

(weather) as well as obtaining mathematical or

 physical models that are effective in characterizing

each of those items. The dynamic behavior of theweather conditions and building operation, and the

 presence of multiple variables, require the use of

computer aid in the design and operation of high

energy performance buildings (Zhu, 2006, Catalina,

et. al., 2008).

Windows have long been used in buildings for  day-lighting and ventilation.  Many studies have even

shown that health,  comfort,  and  productivity are

improved due to well-ventilated indoor

environments and access to natural light. However,

windows also represent a major source of unwanted

heat gain/loss, discomfort, and condensation problems.  But in recent years, windows have

undergone a technological revolution. High-

 performance, energy-efficient window and glazing

systems are now available that can dramatically cut

energy consumption and pollution sources: theyhave lower heat gain/loss, less air leakage, and

warmer window surfaces that improve comfort and

minimize condensation. These high-performance

windows feature double or triple glazing

specialized transparent coatings, insulating gas

sandwiched between panes that reduce the energylost through windows. In addition, well-designed

shading devices features reduce heat transfer,

cooling requirements of buildings. Shading devices

can also improve user visual comfort by controlling

glare and reducing contrast ratios. This often leads

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to increased satisfaction and  productivity.  Shading

devices offer the opportunity of differentiating one

 building facade from another. This can provideinterest and human scale to an otherwise

undistinguished design (http://www.wbdg.org).

Rahman and Satyamurty (1999) investigate the

difference between the values of shading factors for

windows with overhangs calculated under

extraterrestrial and terrestrial conditions and

showed that the shading factor values evaluated

under terrestrial conditions can differ by 25%

compared to the extraterrestrial values for non-

south facing windows shaded by over hangs.

Francis and Milorad (2006) evaluated the impact ofusing switchable glazing on energy use for space

cooling. Using software EnergyPlus, he found that

application of switchable glazing would lead to a

reduction in annual cooling electricity consumption

 by up to 6.6% where the actual amount depends on

existence of overhangs, orientation of buildingwings, types and locations of rooms. Milorad and

Francis (2007) also evaluated the energy saving that

can be achieved by applying advanced glazing to a

typical high-rise residential building in Hong Kong

using the simulation software EnergyPlus. It wasfound that application of low-E glazing would lead

to a reduction in cooling electricity use by up to

4.2%. The saving due to application of low-E

reversible glazing would be up to 1.9%; double

clear glazing up to 3.7%; and clear plus low-Eglazing up to 6.6%. The achievable saving woulddepend on orientation of building wings, and type

and location of rooms.

Singh (2009) investigated the energy rating of

different window glazing available in the Indian

market. This rating is helpful in selecting the best

window for a given building and a given climate.

He developed energy rating equations for different

glazing, buildings and climates by regression

analysis. Weir (1998) suggested the embodied

energy of the four main materials used in the

construction of an inert gas filled, double-glazedwindow.

In the above mentioned research papers, it can be

concluded that the energy transferred through the

window depends on many parameters such as typeof the window, overhangs and side fines and

selecting the optimum window is very difficult.

However, there is no significant information were

found in the literature about building performance

in the weather condition of Bangladesh. In present

study, in the first stage, the effects of applying

overhangs and side fins have been investigated on

the single clear glazing window, and then theoptimal condition has been obtained for Bangladesh

weather condition. At the second stage, the effect of

advanced glazing windows optimized and in the

final stage the results have been summarized to

simple selecting the best window with differentglazing, overhangs and side fins based on energy

rating.

2. Simulation Technique

The global increase in demand for energy has

generated pressure on saving energy. Consequently,Energy efficient buildings are an important factor

related to the energy issue. Various building energy

simulation softwares are used now-a-days to

simulate building energy consumption and to design

energy efficient building such as EnergyPro,

EnergyPlus, EAB, REScheck etc. Among themEnergyPlus is developed by US department of

Energy and it is getting popular to simulate anddesign of energy efficient building.

2.1 Simulation software:The building energy simulation program

EnergyPlus was used in present study to predict

annual energy use in the residential buildings of

Jessore district in Bangladesh. EnergyPlus (version-

32 8.1.0.009) is made available by the LBNL in

USA. EnergyPlus calculates thermal loads of

 buildings by the heat balance method. This method

takes into account all heat balances on outdoor and

indoor surfaces and transient heat conduction

through the building. The simulation results ofEnergyPlus have been validated through numerous

analytical, comparative and empirical tests.

Although EnergyPlus is capable of simulating

heating, ventilation, and air conditioning (HVAC)

systems, the details of HVAC systems are not

modeled since the primary objective of the study

was to examine the influence of windows on

thermal loads of buildings. In EnergyPlus, the heat

transfer by radiation, convection and conduction is

calculated at each time step. The U-values are not

constant through the simulation because theradioactive and convective heat transfer is

calculated by algorithms that take into account parameters such as temperature difference between

the surface and the air [Energyplus engineering

document, 2006].

2.2 Description of the building:The thermal performance of a residential one

storied  building (Fig. 1) including 1 m2  windowshave been located at the center of the wall of zones

1, 2, 3, 4 (south, east, west, and, north zone

respectively) that has been evaluated by computer

simulation. All the zones have been assumed to be

maintained at the same temperature in the second

floor and the energy is transferred only withexterior walls and windows into the zones. The

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thermal properties of the wall, ceiling and floor

materials have been considered as ideal.

(a)  Plan of the building

(b)  Isometric view of the building

Fig. 1: Computational building

Effect of four types of windows has been studied as

follow:

  Single clear glazing (S.Clear)  Double low-E Opaque glazing (D.L.O)  Double low-E Clear (Argon) glazing

(D.L.C)

 

Double clear glazing (D.Clear)

In the present study, the effects of window shading

have been investigated for three cases:

(1) Windows without overhangs and side fins.

(2) Windows with overhangs and without side fins.

(3) Windows with overhangs and side fins.

Simultaneously the depth, the width and thedistance above the window of the overhangs and

the depth of side fins have been changed. In present

study, window energy transfer (E) has been used

for the declaration of the results and has been

determinate from the following equation (i).

(i)

Hourly windows annual heat gain (or loss) has been

calculated by EnergyPlus program and they have

 been declared as follow: Window Heat GainEnergy, the total heat flow to the zone from the

glazing, frame and divider of an exterior window

when the total heat flow is positive. The total

window heat flow is the sum of the solar and

conductive gain from the window glazing. Window

Heat Loss Energy, the absolute value of the total

heat flow through an exterior window when the

total heat flow is negative.

Also, the cp (coefficient of performance) index has

 been used for evaluating the shading effect and

using of advanced glazing window that it has been

determined from the following equation.

(ii)

In equation (ii) Ea  is the total energy that it is

transferred into the building from the single clear

 pane glazing window without overhangs or sidefins (reference model). Also E b  is the total energy

that it is transferred into the building from the

window (new model). In this new model the type of

window, overhang and side fin are different with

the reference one. Results have been shown in

Table 1 for all Models.

Table 1: Overhang and side fin configurations in all

direction

The overhangs and side fins have been applied only

at single clear glazing windows. Also the cp  index

for heating, cooling periods or for the year has been

calculated. Taking into consideration the formula ofthe cp, it can be concluded that, increasing the cp 

index, leads to a decrease of the total energy

transferred into the building from window. An

assumption was made that all zones were ideally

controlled by thermostats such that the zone

temperatures would be kept steadily at 230C in the

year.

Case

Overhangs

(m) Distanceabove

the

window

(m)

Side fin with

1 m width

Width Depth

Depth

of theright

side

(m)

Depth

of theleft

side

(m)

1 1.1 0.5 …  …  … 

2 1.1 1 …  …  … 

3 2 1 …  …  … 

4 2 1 0.2 …  … 

5 2 1 …  1 … 6 2 1 …  …  1

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3. Result and Discussion:

In this section, the cp index has been calculated for

the heating and cooling periods or for the whole

year. The results have been shown in Figs. 2 – 5 for

each direction of the windows.

For the south window (Fig. 2), the best performance application case of overhangs and side

fins is the case 6 (overhang with 2 m width, 1 m

depth without distance above the window and a

side fin in the left side of the window and 1 m2 

area). With attention to cases 1 – 6, it can be

concluded that using of overhangs increase the

annual average cp  index (from 19% up to 44%).

Also with increasing the cp  index the energy

consumption would lead to a decrease.

Fig. 2: Results for south window 

For the north window (Fig. 3), the best

 performance is obtained in the case 5 (overhang

with 2 m width, 1 m depth without distance above

the window and with a side fin in the right side of

the window and 1 m2  area). With taking into

consideration the cases 1 – 6, it can be concluded

that using overhangs increase the annual average cp

index (from 18% up to 38%).

Fig. 3: Results north window

For the east window (Fig. 4), the best performance

application case of overhangs is the case 4

(overhang with 2 m width, 1 m depth and 0.2 mdistance above the window and without side fins of

the window). With attention to cases 1 – 6, it can be

indicated that using of overhangs increase the

annual average cp index (from 15% up to 30%).

Fig. 4: Results east window

For the west window (Fig. 5), the best performance

has been obtained in the case 4 (overhang with 2 m

width, 1 m depth and 0.2 m distance above the

window and without side fins of the window). And

With attention to cases 1 – 6, it can be concluded

that using of overhangs and side fins, the cp indexhas only 9-20 % change during the heating or

cooling periods.

Fig. 5: Results west window

Using of advanced glazing systems i.e., Double

low-E Opaque glazing (D.L.O), Double low-E

Clear (Argon) glazing (D.L.C), Double clear

glazing (D.Clear) window, the ef index increase for

each direction of the windows but Double low-EClear (Argon) glazing (D.L.C) give highest  cp

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index for south facing window and also save more

energy.

4. Conclusion:

The final results have been evaluated  to simpleselecting the best window with different glazing,

overhangs and side fins based on energy rating of

 building at Jessore in Bangladesh. With attention to

these values, following conclusion remark can be

formulated:1.  For the south windows of a single clear glazing

window with an overhang (with adding the

width) and side fin window is the best solution

for case 6. Also, it can be noticed that using of

appropriate overhang and side fin will lead to

similar performance to the advanced glazingwindows and a reduction of the cost.

2. 

For the north windows, using of overhangs orside fins (the case 5 especially) useful for

heating, cooling periods. Also, it can be

concluded that using of appropriate overhangand side fin will lead to similar performance to

the advanced glazing, but using of double low-

E clear (argon) glazing window is more useful.

3.  For the west windows, using of overhangs or

side fins (the case 4 especially) useful for

heating, cooling periods. Also, it can be seenthat using of appropriate overhang and without

side fin will lead to similar performance to the

advanced glazing, but using of double low-E

clear (argon) glazing window is more useful.4.  For the West windows, using of overhangs or

side fins does not a significant change in the

energy transferred through the window into the

 building for heating or cooling periods.

Although, using of the double clear glazing,

Double low-E Opaque glazing and double low-

E clear (argon) glazing window can lead to a

considerable energy transfer reduction.5.  Using of the most appropriate overhang or side

fin that has been established for the single clear

 pane glazing is more useful for any direction of

window than the advanced glazing windows

(double clear glazing, low-E glazing).

Reference:

1.  Bojic, M., and Yik, F. (2007), Application of

advanced glazing to high-rise residential

 buildings in Hong Kong,  Building and

 Environment . 42, pp. 820 – 28.

2.  Catalina, T., Virgone, J., and Blanco, E.

(2008), Development and validation of

regression models to predict monthly heating

demand for residential buildings.  Energy and

 Buildings, 40, pp. 1825 – 1832.

3.  Krarti, M. (2012), Weatherization and energy

efficiency improvement for existing homes: An

Engineering approach.  Mechanical and

 Aerospace Engineering Series, pp. 0-434.

4.  Omer, A. M. (2008), Renewable buildingenergy systems and passive human comfort

solutions.  Renewable & Sustainable Energy

 Reviews, 12, pp. 1562 – 87.

5.  Rahman, A.N. M. Mizanur, and Satyamurty,

V.V. (1999), Overhang shading factor values

for windows of general azimuthal angle

evaluated under extraterrestrial and terrestrial

condition,  International Journal of Energy

 Research. 23, pp. 235-245.

6.  Singh, M. C., and Garg, S. N. (2009), Energy

rating of different glazings for Indian climates,

 Energy, 34, pp. 1986 – 92.7.  Weir, G., and Muneer, T. (1998), Energy and

environmental impact analysis of double-

glazed windows,  Energy Conversion and

 Management . 39, pp. 243-256.

8.  Yik, F., and Bojic, M. (2006), Application of

switchable glazing to high-rise residential buildings in Hong Kong,  Energy and

 Buildings. 38, pp. 463 – 71.

9.  Zhu, Y. (2006), Applying computer-based

simulation to energy auditing: a case study.

 Energy and Buildings, 38, pp. 421 – 428.10.  Energy Efficiency in Buildings, (2009).

Retrieved from www.wbcsd.org

11.  Energyplus engineering document, The US

department of energy. (2006), Retrieved from:

.12.  'Whole Building' Design Guide, A program of

the national institute of building sciences.

Retrieved from:

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