performance of fixed shading devices on daylight penetration in the tropical city like dhaka

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 Mahmood

1

1Dept. of Architecture, Stamford University Bangladesh, Dhaka, Bangladesh 2Dept. of Architecture, Bangladesh University of Engineering & Technology, Dhaka, Bangladesh

Email address

[email protected] (M. A. Jinia), [email protected] (S. H. Trisha), [email protected] (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

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)

pla

ne

A

pla

ne

B

pla

ne C

clo

se

d

win

do

w

working plane

floor

at 21' above

ground1

2

3

4

5

6

123456

plan elevation section

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;


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=716H

H

sun W=H/2 W=H/2

H

H

sun

D

VSA = tan?


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


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


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


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


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


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


Table 6. Daylight Level FromSimulaion With Vertical Type Shading Device

Time Measuring


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


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


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


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



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


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


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


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


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


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


Course ARCH 6103 (Luminous Environment and Built

Form) under the supervision of Dr ZebunNasreen Ahmed in

Department of Architecture, Bangladesh University of

Engineering & Technology.

References

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[3] SHAILY RUNGTA & VIPUL SINGH. 2011. Design Guide: Horizontal Shading devices and Light Shelves.

[4] O.H. KOENIGSBERGER. 1975.Manual of Tropical Housing and Building

[5] B. GIVONI. 1969.Man, Climate and Architecture.

[6] AL-MOFEEZ and ABDUL. 1991. Insulation in the Opaque Envelope: Effects on Thermal Performance of Residential Building in Hot-arid Climates, Dissertation for degree of Doctor of Philosoph,Texas A&M University, UMI dissertation information service, Michigan.

[7] DUBOIS,M. C.2000. A Simple Chart To Design Shading Devices Considering The Window Solar Angle Dependent Properties, Proceedings of the Third ISES Europe Solar Congress: Eurosun 2000, 19-22 June, Copenhagen (Denmark).

[8] STEEMERS,K.,andBAKER.N.2002. Daylight Design of Buildings, James & James Ltd, London

[9] HIEN,W.N.,andISTIADJI,A.D.2003. Effects Of External Shading Devices On day lighting And Natural Ventilation, proceedings of Eighth International IBPSA Conference, Eindhoven, Netherlands

[10] S. H. TARIQ & M. A. JINIA. 2013. Performanceof Fixed Horizontal Shading Devices in South Facing Residential Buildings in Dhaka, Global Science and Technology Journal, Vol. 1. No. 1. July 2013, Issue. Pp.88-99.

performance of fixed shading devices on daylight penetration in the tropical city like dhaka

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