1. American Journal of Energy Science
2015; 2(3): 21-27
Published online May 30, 2015 (http://www.openscienceonline.com/journal/energy)
Performance of Fixed Shading Devices on Daylight
Penetration in the Tropical City Like Dhaka
Mahbuba Afroz Jinia1, *
, Syma Haque Trisha2
, Taqir Mahmood1
1
Dept. of Architecture, Stamford University Bangladesh, Dhaka, Bangladesh
2
Dept. of Architecture, Bangladesh University of Engineering & Technology, Dhaka, Bangladesh
Email address
arch_majinia@yahoo.com (M. A. Jinia), symahaque@gmail.com (S. H. Trisha), taqir33arch@yahoo.com (T. Mahmood)
To cite this article
Mahbuba Afroz Jinia, Syma Haque Trisha, Taqir Mahmood. Performance of Fixed Shading Devices on Daylight Penetration in the Tropical
City Like Dhaka. American Journal of Energy Science. Vol. 2, No. 3, 2015, pp. 21-27.
Abstract
External shading devices have been utilized very extensively in the buildings of tropics to control the amount of daylight and
direct sun light flowing into interior spaces. It is now widely accepted that architects should encompass the environmental task
of reducing fossil fuel energy consumption in response to climate change. Day light is a blessing of nature. Effective daylight
reduces the need of artificial light at day time and thus reduces the overhead cost of energy. Proper luminous environment
confirms sufficient daylight which is very good for both physical and mental health. But too much or unguided daylight cause
glare and light pollution. For the purpose of examiningthe day lighting design in a residential building in the tropics
likeBangladesh, this paper discussesthe effects of different types of fixed external shading devices on daylight flow
intobuildings. The investigation was carried out by the use of ECOTECT for day lightingsimulations. A building having south
facing openings has been fundamentally chosen as case study. The luminous level of different points in the study room has
been collected as field survey. After studying the existing day light condition, daylight simulations have been conducted using
several types of shading devices based on the study area. More importance has been given on useful daylight illumination for
visual tasks to study the effects of different types of shading devices.
Keywords
Shading Device, Luminous Level, Daylight Illumination, Simulation, Dhaka
1. Introduction
Natural daylight is a vital element in creating a more
efficient and eminently more rewarding interior
environment. Daylight is important for its quality, spectral
composition and the variability that it provides to any
space. It provides high luminance and permits excellent
color discrimination and color rendering and fulfils two
very basic human requirements: to be able to see both a task
and the space well and to experience some environmental
stimulation.
Natural light stimulates biological functions that are
essential to human health. Windows receive a large amount
of energy from the sun and usually most of the sunlight gets
concentrated in certain areas of the space and may even result
in glare on work surfaces. A large amount of direct sunlight
can be a source of great discomfort when concentrated on a
spot, but is extremely useful if distributed to all parts of the
room equally. For controlling the effects of day lighting, the
focus is usually directed to the use of shading devices.
Shading devices are utilized to block the solar radiation
before it reaches the indoor environment, especially at south
faced in the tropical countries. Recently, computer based
modeling and simulation has become more popular and
important for day light prediction. Computational lighting
simulations can predict indoor luminance more accurately
than manual methods even though computational methods
have rarely been validated for real buildings with real
occupancy. Based on these facts, this study seeks to evaluate
the effects of different types of shading devices on day light
conditionin indoor working environment of residential
building at Dhaka.
2. Objectives
The study focuses on the effect of different types of fixed

2. 22 Mahbuba Afroz Jinia et al.: Performance of Fixed Shading Devices on Daylight Penetration in the Tropical City Like Dhaka
external shading device in interior at south façade opening
having commonly used opening sizes in residential buildings
at Dhakacity. Particular emphasis of the study has been given
on the type of the shading device to search more suitable type
of shading for the specific study model.
3. Methodology
3.1. Study Model
The study model fundamentally chosen is located at
Malibagh in Dhaka. This is a residential building of a Govt.
colony. One of the room at 2nd floor (floor level is 21’ above
ground level) of this building having at least one opening at
south has been selected for study.
Table 1. Parameters of Study Model
Study model parameters
Room dimension 14’-1” X 12’-4”
Floor height 10’-6”
Opening orientation South facing, open green field at south, no significant ERC(externally reflected component)
Opening dimension 6’ X 4’-6”
Window frame Wooden frame
Window swing Clear glass with wooden frame
Depth of existing shading device 2’, “U” type, no vertical fin
Wall 10” brick-plaster wall, off-white colour in interior
Ceiling Concrete slab, white colour
Floor Mosaic floor
Secondary opening Closed, blocked by furniture
Working plane 2’-6” above floor
Model of light meter for field surey Digital Lux Meter, model:AR813A, manufactured by Smart Sensor
Time period of data collection
10.00am-04.00pm (this time range delivers the most effective day light in the context of Bangladesh. For
convenient, this time range have been divided into four segment. They are: 10.00am, 12.00pm, 2.00pm
and 4.00pm)
Total number of points for light measurement
on working plane
18
a) b) c)
d)
planeA
planeB
planeC
closed
window
working plane
floor
at 21' above
ground1
2
3
4
5
6
123456
plan elevation section

3. American Journal of Energy Science 2015; 2(3): 21-27 23
e)
Figure 1. (a) Floor plan of the study model, (b) exterior view of the building, (c) Interior view of existing condition, (d) plan, section and elevation of study
model showing points of measurement, (e) resurch methodology
Figure 2. (a) Shadow pattern of different types of shading device
3.2. Limitations of the Study
The research conducted in this paper has some limitations,
e.g.
1 The luminous level found from field survey and
simulation used here are only the data of a specific day
having a clear sunny sky.
2 The luminous data of some specific times of the day has
been used here for convenient.
3 The investigation is done on the basis of illumination
level. Different geometric pattern of fixed shading
devices, different variables such asglare, thermal
radiation, material, color, obstruction of both interior &
exterior space are considered very lightly.
But this paper has the potentiality for further research on
this topic by collecting and analyzing the data on the
different months of the year and other different times of a
day.
3.3. Shading Device and Daylight in the
Tropics
Once the window size has been established the most
effective method of reducing solar heat gain and excessive
daylight is to prevent the transmission of shortwave radiation
through the glass by external shading.The appropriate choice
from a wide range of fixed and movable shading systems will
depend on location, orientation, building type and the overall
cooling, heating and day lighting strategies adopted in the
design phase of the building.
3.4. Types of Shading Devices
Shading devices are broadly classified into three categories
based on its integration with the window (Goulding, 1992;

4. 24 Mahbuba Afroz Jinia et al.: Performance of Fixed Shading Devices on Daylight Penetration in the Tropical City Like Dhaka
Steemers et al, 2002; Lechner, 2001). They are classified
again within these categories by their morphological
characteristics and physical forms. The broad categories of
shading devices are:
1. Retractable or removable shading device, 2. Moveable
or adjustable shading device, 3. Fixed shading device.
Fixed shading devices are classified into three categories:
1. Vertical shading device, 2. Horizontal shading device, 3.
Egg crate shading device
3.5. Useful Daylight Illuminance
Real daylight illuminances across the work-plane exhibit
large variations both spatially and temporally. For example,
daylight illuminances typically diminish rapidly with
increasing distance from windows. Equally, daylight
illuminances at a point can vary greatly from one moment to
the next due to changing sun position and/or sky conditions.
Illuminances that fall within the bounds of minimum and
maximum are called here Useful Daylight Illuminances. The
rationale for the UDI range limits determined from the
survey is summarized as follows:
Table 2. UDI Level
Day light level Sufficiency of day light
Daylight illuminance< 100 lux Insufficient
Daylight illuminance 100 lux - 500 lux effective
Daylight illuminance 500 lux - 2000 lux desirable or at least tolerable
Daylight illuminances>2000 lux
visual or thermal discomfort,
or both
Thus, it is proposed that any daylight illuminance in the
range 100 lux to 2000 lux should be considered as offering
potentially useful illumination for the occupants of the space.
3.6. Calculation for Optimum Shading
The depth of the overhang of the shading devices depends
on the opening height and it is independent of the window
width. The performance of the horizontal shading device
increases with the increase of the depth of the overhang. The
important factor is the ratio between the depth of the
overhang and the height of the opening.
For optimum shading, the ratio between depth of overhang
and height of the opening is,
D = 7/16 x H (1)
Where, D = depth of overhang, H = height of opening
The ratio between the side offset from opening edge of
overhang and height of the opening is,
W = H/2 (2)
Where, W = Side offset from opening edge, H = height of
opening
Optimum shading can also be determined by the ratio
between Depth of overhang and opening height,
D = H / tanØ (3)
Where vertical shadow angle = tanØ
Figure 3. Schematic diagram showing parameters of horizontal shading device
Table 3. Calculating depth of overhang from Vertical shadow angle (VSA) data of study model
Minimum VSA (tanØ)
Opening height
H
Minimum Depth of overhang
D = H / tanØ
113.7 o
4.5’ or 54 inch 1.97’ < 2’
3.7. Calculation of Depth of Shading for
Existing Condition
At first, the requirement of horizontal overhang for an
opening height of 4.5’ has been checked.
D = 7/16 x 4.5 = 1.96’
As the existing overhang is 2’; so, theoretically it should
be adequate for optimum shading performance during the
warmest part of the day.
The minimum requirement has also been checked by the
calculation of vertical shadow angle. Minimum vertical
shadow angle data has been taken between 10 P.M. to 4 P.M.
for the analysis.
3.8. Study of Simulation Models
The luminous levels on the different points found from
field survey and simulation are as follows.
In the table-04, it is observed that the deviation between
field survey and simulation result is very low. Therefore the
simulation results can be considered for the resurch.
D=7
16H
H
sun W=H/2 W=H/2
H
H
sun
D
VSA = tan?

5. American Journal of Energy Science 2015; 2(3): 21-27 25
Table 4. Daylight Level of Existing Condition
Time Measuring points
Plane A Plane B Plane C
Field survey Simulation Simulation Field survey Simulation
10.00am
1 3020 3056 5400 5423 1510 1572
2 2070 2095 2605 2641 1310 1369
3 1305 1352 1450 1456 990 1032
4 920 971 950 1001 785 824
5 755 767 720 774 620 688
6 610 662 615 667 560 608
Difference from point 1 to 6 2410 2394 4785 4756 950 964
12.00am
1 2200 2236 5600 5648 2200 2239
2 1750 1787 2890 2910 1770 1803
3 1200 1240 1600 1644 1210 1263
4 905 958 1050 1109 920 977
5 740 789 820 866 750 800
6 620 692 710 741 655 702
Difference from point 1 to 6 1580 1544 4890 4907 1545 1537
02.00pm
1 1550 1577 5450 5496 3060 3113
2 1310 1383 2690 2718 2055 2112
3 990 1038 1440 1492 1320 1375
4 765 814 990 1018 950 1002
5 650 711 750 797 750 806
6 595 632 640 699 610 685
Difference from point 1 to 6 955 945 4810 4797 2450 2428
04.00pm
1 1000 1050 34900 34952 33400 33429
2 890 919 1800 1835 1700 1736
3 645 698 980 1017 1005 1049
4 505 562 680 712 700 751
5 435 485 500 551 545 593
6 595 435 415 488 450 501
Difference from point 1 to 6 405 615 34485 34464 32950 32928
Table 5. Daylight Level FromSimulaion With Horizontal Type Shading
Device
Time
Measuring
points
Plane A Plane B Plane C
10.00am
1 3065 6325 1554
2 2059 2538 1340
3 1339 1397 1022
4 952 971 809
5 747 767 680
6 661 645 597
Difference from point 1 to 6 2404 5680 957
12.00am
1 2294 5760 2271
2 1843 2655 1857
3 1287 1658 1293
4 967 1143 995
5 815 891 821
6 713 754 720
Difference from point 1 to 6 1581 5006 1551
02.00pm
1 1565 5425 3149
2 1372 2753 2135
3 1020 1528 1379
4 808 1025 1007
5 683 797 794
6 612 692 681
Difference from point 1 to 6 953 4733 2468
04.00pm
1 1091 34878 33502
2 944 1950 1755
3 725 1083 1099
4 573 738 782
5 497 591 611
6 447 506 516
Difference from point 1 to 6 644 34372 32986
Table 6. Daylight Level FromSimulaion With Vertical Type Shading Device
Time
Measuring
points
Plane A Plane B Plane C
10.00am
1 62419 7003 2262
2 3333 3776 2071
3 2064 2175 1618
4 1484 1494 1285
5 1199 1175 1103
6 1032 1040 959
Difference from point 1 to 6 61387 5963 1303
12.00am
1 3725 76863 3657
2 3117 4367 3084
3 2156 2618 2208
4 1728 1908 1748
5 1465 1571 1486
6 1299 1371 1300
Difference from point 1 to 6 2426 75492 2357
02.00pm
1 2298 66786 64693
2 2095 3909 3479
3 1648 2268 2175
4 1314 1608 1590
5 1126 1289 1276
6 1022 1114 1110
Difference from point 1 to 6 1276 65672 63583
04.00pm
1 1661 4935 3159
2 1422 2530 2105
3 1061 1400 1260
4 791 923 835
5 652 711 655
6 566 599 560
Difference from point 1 to 6 1095 4336 2599

6. 26 Mahbuba Afroz Jinia et al.: Performance of Fixed Shading Devices on Daylight Penetration in the Tropical City Like Dhaka
Figure 4. (a) Daylight levels of existing condition, (b) simulation result with hosizontal type shading, (c) simulation result with vertical type shading, (d)
simulation result with eggcrate type shading
Table 7. Daylight Level FromSimulaion With Eggcrate Type Shading Device
Time
Measuring
points
Plane A Plane B Plane C
10.00am
1 3192 5519 1926
2 2179 2790 1705
3 1433 1640 1280
4 1070 1144 1014
5 868 912 843
6 747 766 725
Difference from point 1 to 6 2445 4753 1201
12.00am
1 2687 6150 2712
2 2268 3293 2283
3 1609 2011 1669
4 1278 1445 1310
5 1065 1147 1081
6 924 985 935
Difference from point 1 to 6 1763 5165 1777
02.00pm
1 1964 5668 3291
2 1679 2290 2229
3 1311 1704 1533
4 1027 1209 1143
5 868 945 934
6 759 817 787
Difference from point 1 to 6 1205 4851 2504
04.00pm
1 1216 3620 2150
2 1036 1771 1365
3 748 983 899
4 582 669 646
5 481 512 506
6 426 444 436
Difference from point 1 to 6 790 3176 1714
4. Result
Analyzing from the above charts it is observed that in the
existing condition daylight level in interior is very high after
04.00pm which in very discomfort level. From the simulation
model, horizontal type shading also is showing the
discomfort levels in the afternoon. Vertical type shading
device showing an opposite results, luminous level is very
high before afternoon. The uniformity of daylight level is not
balanced. Last of all, eggcrate type shading showing a better
condition, distribution and uniformity of daylight is
moderate. The differences from point 01 to 06 are lower from
the others. The graphs given below better describes the
overall results.
5. Discussion
At present, varieties types of shading devices are being
used in the residential apartment buildings at Dhaka. Among
them, many are properly working, but the rest are creating
discomfort to the users. It is very important to design a
proper shading device for healthy living environment. Lack
of light or access light both hampered our daily life activities.
In this paper the effect of general three types of shading
devices are analysed through computer simulation. From the
simulation results it is observed that eggcrate type shading
renders better interior dalight condition than the others. This
study may be a design guideline for the architects to design
proper shading system for the openings.
Acknowledgement
This paper is based on the research work done in M. Arch

7. American Journal of Energy Science 2015; 2(3): 21-27 27
Course ARCH 6103 (Luminous Environment and Built
Form) under the supervision of Dr ZebunNasreen Ahmed in
Department of Architecture, Bangladesh University of
Engineering & Technology.
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