effect of different balcony shading configurations on

DUET Journal 27 Volume 5, Issue 1, June 2019

Effect of Different Balcony Shading Configurations on Daylighting Residential Dining Spaces in Tropical Climate

Fariha Seraj1*, Md Ashikur Rahman Joarder2

1Department of Architecture, Dhaka University of Engineering & Technology, Gazipur, Bangladesh2Department of Architecture, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh

ABSTRACT

Balconies, inseparable and distinctive element of residential apartments representing local architecture, are designed as overhangs that determine not only the relationship between building, environment and occupants but also influence various mechanisms for example- sun-control and daylighting. This paper investigates the effect of various types of shading configurations for balconies on the daylight availability at the deepest part of the residential apartments of Dhaka. Dynamic daylight simulation technique is used to assess the performance of different shading configuration of balconies for four orientations. Simulation results indicate that among studied configurations, single horizontal canopy and horizontal louvers in vertical plane are most feasible for north and south orientation respectively. For east and west facing balconies, horizontal louvers on horizontal plane are most feasible to incorporate daylight in the dining considering dynamic daylight metrics.

*Corresponding author’s email: [email protected]

1. InTRoDuCTIon

Residential building sector consumes more than one- third of the total global energy consumption and the scenario of Dhaka is similar [1]. As indicated by the Annual Report of DESCO 2017, 90% consumer of Dhaka are residential consumers and they consume 49% of the total electricity consumption [2]. Among this 41% electricity is used for lighting purpose [3]. The residential apartment buildings in Dhaka are often poorly planned. Sometimes to meet the demand of huge population, existing residential buildings in Dhaka were constructed disregarding the building codes and setback rules set by RAJUK and neglect their physical, environmental and socio- cultural effects on the overall condition of the city environment.

Dining space, the most visually integrated central space of the contemporary apartments is chronologically evolved from the traditional courtyard [4]. Poor access to daylight and windowless dining space are major problems that found in most of the apartment buildings in Dhaka due to its central location and insufficient distance between buildings. Lack of sensitive design resulting in poor daylighting condition inside apartment buildings increase the use of supplementary artificial lighting which accelerates the energy consumption in buildings and finally contribute to higher urban energy demand. This can be avoided by implementing passive design strategies such as daylighting. Electricity consumption can be reduced by 25- 50% with advanced lighting sources, design strategies and controls; and 75% by incorporating daylight [5]. Balconies are essential for creating a good indoor- outdoor relationship of a space and also for

physiological and psychological benefits which cannot be attain with electric lights. It can provide useful daylight by reducing the discomfort glare, cooling load and overall energy consumption. According to Chan and Chow [6], a south- west facing balcony with a clear glazed window can substantially reduce 12.3% annual energy consumption. Studies related to daylighting through balconies are very limited and focused on the bed rooms only. To improve the daylighting condition and maintain good indoor- outdoor relationship of the residential dining, effect of the shading configuration of balconies need to be studied.

This paper aims to investigate the impact of different shading configurations of balconies to increase daylight availability inside the dining space of residential apartment of Dhaka.

This paper is divided into three parts. The first part describes the codes and standards related to illumination condition inside the residential dining space and shading design of balconies. The second part describes the methodology of the dynamic daylight simulation technique applied and the last part discusses the result of the simulation with conclusion.

2. BALConY SHADInG AnD DAYLIGHTInG

Balconies are projected overhangs or extension roof of the residential apartments above ground level that offer the occupants quick access to outdoor environment. It may be found in buildings over the globe but it is more distinctive feature of buildings situated in tropical areas. Balcony-

EffEct of DiffErEnt Balcony ShaDing configurationS on Daylighting rESiDEntial Dining SpacES in tropical climatE


a covered and hanging platform at a height of minimum 2.286 m from the plinth level of a building, should be accessible from respective floor level, open to outer environment by three sides up to 2.6 m high and edges should be protected with guards [7]. In Dhaka, balconies are often placed with bedrooms, living and dining areas with a clear glass door to provide access to natural light and ventilation (Fig. 1). Balconies are arranged in series on the apartment façades to provide a breathing space as well as to provide shading for the opening beneath it. Balconies can reduce discomfort glare, undesirable summer light, harmful ultraviolet rays and offer a reduction in the cooling and lighting energy loads [8]. Xue et. al., conducted a questionnaire survey on 340 residents of highrise apartment buildings of Hong Kong and found that daylight hours and uniformity of indoor illuminance decreases with the use of balconies. The questionnaire survey also revealed that presence of balconies force occupants to use internal shading and artificial lighting [8]. Kim and Kim showed that availability of daylight and distribution of indoor illuminance strongly depends on the depth of the balcony [9]. Area, height of the parapet and shading design of the balcony considerably affect user’s behavior pattern and luminous comfort [8]. Most of the studies related to residential balcony are confined to thermal comfort and ventilation rather than daylighting. Therefore, the effect of the shading design of balconies on indoor daylight availability need to be studied.

Fig. 1: Facades of the multi storied apartments buildings of Dhaka with balconies.

3. CoDES AnD STAnDARDS

Daylight could reach to the central part of apartment building, i.e. dining space. The minimum recommended illumination level of 150 lux need to be maintained on the table top of the dining at 0.75 m height from the finished floor level (Fig. 2) [7]. If the illumination level falls below 150 lux then supplementary artificial lighting should be provided. Where works take place over the whole area of a room, the uniformity ratio between maximum and minimum illumination level should be 0.7 [7].

For balconies, regulations related to the maximum allowable area within the setback area and height of the parapet (2.06 m) are mentioned in the Building Construction Act 2008. Total allowable area of cantilevered balconies, side and rear balconies of a residential building can be measured by the following equations-

Total allowable area of Front balconies (m2) = Front width of the building (m) x 1m

Total allowable area of rear and side balconies = 2.5% of each floor area.

Fig. 2: Illuminance measuring heights for residential dining Space

4. CoMPuTER SIMuLATIon METHoD

Dynamic daylight simulation (DDS) technique, an alternative to Daylight Factor (DF) approach, is used to measure the performance of different shading configurations for balconies. DDS is based on time series of illuminaces or luminaces within a building and these time series extend over the whole year based on external annual solar radiation data for the building site [10]. The main advantage of DDS is it considers both quantity and character of daily and seasonal variations of daylight for a building site along with irregular meteorological events. To ensure occupant’s comfort and benefit, a suitable



simulation tool for evaluating daylight is necessary which has following capabilities [11].

a) High prediction capability for indoor daylight distribution

b) Modelling capacity of complex geometry with surrounding environment

c) Capability of providing Climate Based Daylight Metrics (CBDM) as output.

DAYSIM is selected as simulation tool as it satisfies the above-mentioned criteria [11]. The initial 3D model was constructed using ECOTECT V 5.20 simulation software. Then it was exported to DAYSIM 2.1P4, a RADIANCE based simulation tool that can calculate illumination on specific points on an hourly basis by CBDM method using an annual climate file. DAYSIM, validated successfully for daylight analysis [10], can calculate illumination level on any point as a function of outside daylight availability and can provide 8760 (365 x 24) hours data for each sensor point considering Perez all weather sky illuminance models [12- 13]. Simulations are performed to calculate the Daylight Factor (DF), and dynamic daylight performance metrics: Daylight Autonomy (DA), Continuous Daylight Autonomy (DAcon), Maximum Daylight Autonomy (DAmax) above 5%, Useful Daylight Illumination (UDI) and illumination on the specific points of the case space on an hourly basis.

4.1 Simulation Parameters

For DDS, calculations are performed using DAYSIM for the whole year considering the daylight time of nine hours from 8 a.m to 5 p.m without no lunch or intermediate break and daylight savings time. The minimum design illuminance level is considered as 150 lux at the analysis grid at 0.75m height from the finished floor level according to BNBC [7]. The dynamic simulation parameters are shown in Table I.

The non-default RADIANCE parameters are: 5 ambient bounces, 1000 ambient divisions, 20 ambient sampling, an ambient resolution of 300, a specular threshold of 0.15, and a direct sampling of 0.0 [10].

Table I: Daylighting simulation parametersSl. no Parameters Specifications

1. Location Dhaka

2. Longitude 90.40° N

3. Latitude 23.80° E

4. Local Terrain Urban

Sl. no Parameters Specifications

5. Precision High

6. Time Zone +6 GMT

7. Simulation Time 8.00 to 17.008. Date Whole Year9. Sky Illumination Model Perez all possible sky model

round the year10. Unit of Dimension SI metric (m, cm, mm and

Lux, cd/m2)11. Daylight properties of

glaze portionTransmission: 90%Pollution factor: 0.70Framing factor: 0.90Maintenance factor: 0.85

4.2 Description of Case Space

Dhaka is one of the densely populated cities in the world with 45% population of middle and upper- middle income group [14]. These middle-income group prefer apartments comprising 92.9-111 m2 and their preferred locations are Mirpur, Uttara, Mohammadpur, Dhanmondi, Bashundhara, Banasri, Tejgaon among the planned residential areas of Dhaka [15]. On a previous research on residential apartment of this middle-income group of Dhaka, three types of living- dining layout were identified: attached, continuous and separate living- dining [4]. Among these, the number of attached type living- dining layout in the middle-income group’s apartment was significant. To select a typical building that represents the majority of Dhaka’s buildings following selection criteria were fixed for the case space.

a) It should be in the preferred location of the middle-income group of Dhaka comprising area within 92.9-111 m2.

b) Living- dining layout of the case apartment should be attached type living- dining.

c) Dining should be located at the center of the apartment surrounded by other functional spaces.

d) There should be a balcony with an aperture for daylighting to study the effect of different shading configurations for the balcony.

Following convenience sampling method, which is a type of nonprobability or nonrandom sampling where subjects are selected because of their convenient accessibility and proximity to the researcher [16], a nine storied residential building on Tejgaon Bijoy Shoroni Link Road was selected as the case residential building as it satisfies the above-mentioned criteria.



The building is rectangular in shape with typical floor plans. The dining space (13.8m2) of the rear flat on the first floor with an opening of 2.1m height (with an adjacent balcony) was selected as case space for simulation study as the daylighting condition is critical in the lower story. The building has a 9m wide road on the north and 10, 6 and 4 storied buildings on south, east and west sides respectively (Fig. 3 and 4). The material properties for simulation are shown in Table II.

Fig. 3: Site and surroundings of the case dining space of the 9- storied residential apartment (dining area

marked by hatch).

Fig. 4: Conceptual sections through XX’ and YY’ directions showing location and surrounding of case space.

It is difficult to isolate impact of one single variable on daylighting of a space because of synchronous effect of numerous other variables. Daylighting simulation permits

to study the impact of one single variable on the daylighting of a space by keeping the other variables steady. To investigate the effect of the shading configurations on daylighting of the dining space, surroundings of the case space is considered as vacant [17].

5. PERFoRMAnCE EVALuATIon PRoCESS

For comparative study, performance metrics are essential to guide the design. For the performance evaluation process, the total floor of the case dining space was divided into 60 sensor points at 0.75m height considering the work plane height for residential space [7] (Fig. 5). Letter and number system were used to code the intersection points. The total floor area was divided into 6 axes on XX¢ direction and 10 axes on YY¢ direction with an equal distance of 0.5 m between them [10]. The position of the dining table was considered at the center of the dining space just opposite the door of the balcony and six core sensor points were selected on the table top at 0.75 m height. According to the “core work plane sensor” approach, DF, DA, DAcon, DAmax and UDI values of these were evaluated [19].

Performance of ten different shading devices that are mostly used in buildings [20-22], were examined by placing them alternatively as balcony shading at 2.1 m height to improve the daylighting of the dining space.

Table II: Material properties for dynamic daylighting simulation [18].

Material Properties

Wall

Material: 110mm brick with 10mm plaster in both sides.U Value: 2.620Solar Absorption: 0.418Thermal Decrement: 0.7

Window

Material: Single pane of glass with aluminium frame (no thermal break).U Value: 6.000Solar Absorption: 0.94Thermal Decrement: 1.74 (refractive index of glass)

Roof

Material: Concrete Roof AsphaltU Value: 0.896Solar Absorption: 0.9Thermal Decrement: 0.58

Floor

Material: 100mm thick concrete slab on ground.U Value: 0.880Solar Absorption: 0.467Thermal Decrement: 0.3

Shading device

Material: Concrete Roof with plasterU Value: 0.896Solar Absorption: 0.9Thermal Decrement: 0.58Material: TimberU Value: 0.773Solar Absorption: 0.636 Thermal Decrement: 1



Configurations of the nine shading devices are coded as SC-1 to SC- 10 (Table III) and their performance were examined in four orientations: north, south, east and west.

6. RESuLTS

To find out the best possible shading configuration for balconies on four different orientations, rating system [10] can be done as it is the simple method to identify the best option among many. Mean values of the dynamic metrics of the core sensor points were considered. Rating system was done considering 9 point to 0 point to suggest the configurations from 1st to 10th place. The results of the dynamic daylight performance metrics (DF, DA, DAcon, DAmax and UDI) along with rating point distribution for ten shading configurations for east, west, south and north facing balconies are presented in Table IV, V, VI, VII respectively.

Horizontal louvers on horizontal plane was found as the most feasible shading configuration for both east and west directions as it scored highest. It is capable of providing better UDI100-2000, also reduce the amount of UDI<100 compared to other options. Horizontal louvers in vertical plane scored second highest points in the dynamic performance metrics for south orientation. It provides higher values of DF, DA and DAcon compared to other options. Brise- soleil semi façade scored considerably the lower than other configurations for east orientation. Horizontal canopy double scored second highest point for west orientation as it allows better UDI100-2000 and DAmax values than the other. The north facing balconies does not receive any direct sunlight so there will be no problem of glare. Among the ten studied options, horizontal canopy single scored highest considering dynamic performance metrics for north orientation.

Fig. 5: Plan and section showing sensor points on the case dining space.

Table III: ECOTECT Modelling of case space with ten selected shading configurations for balconies

SC- 1: Horizontal Canopy Single

SC- 2: Horizontal Canopy Double

SC- 3: Canopy Inclined Single

SC- 4: Canopy Inclined Double

SC- 5: Horizontal Louvers in

Horizontal Plane



Table III: Contined.

SC- 6: Horizontal Louvers in Vertical

PlaneSC- 7: overhang

Vertical PlaneSC- 8: Brise- Soleil

Full FacadeSC- 9: Brise- Soleil

Semi FacadeSC- 10: Vertical

Louvers

Table IV: Summary results and rating point distribution of annual daylighting simulation of the shading configurations for east facing balcony

Shading Device Configurations DF [%] DA [%] DA con [%] DAmax [%] uDI<100 [%] uDI100-2000 [%] uDI>2000 [%] Total Rating

Points Rank

SC- 1 Value 2.2 94.3 97.5 10 3.5 91.3 5 36 7th

Rating 9 9 9 0 9 0 0

SC- 2 Value 1.4 92 96.2 1.7 5.5 93.8 0.7 44 3rd

Rating 4 5 6 8 5 8 8

SC- 3 Value 2.2 94.3 97.5 10.5 3.5 91.5 5 42 4th

Rating 9 9 9 3 9 3 0

SC- 4 Value 1.2 90 95.3 0 6.2 93.8 0 41 5th

Rating 3 4 4 9 4 8 9

SC- 5 Value 1.7 93 96.5 3.8 4.5 94 1.3 49 1st

Rating 7 7 7 6 7 9 6

SC- 6 Value 1.9 93.8 97.3 7.2 4 92.7 3.5 47 2nd

Rating 8 8 8 4 8 7 4

SC- 7 Value 1.5 92.3 96.5 2 5.2 94 0.8 47 2nd

Rating 5 6 7 7 6 9 7

SC- 8 Value 1.6 92.3 96.3 4.5 5.2 92.3 2.3 39 6th

Rating 6 6 5 5 6 6 5

SC- 9 Value 0.9 85.8 93.8 0 8.2 91.8 0 28 8th

Rating 0 3 3 9 0 4 9

SC- 10 Value 0.9 85.3 93.7 0 8 92 0 26 9th

Rating 0 0 0 9 3 5 9

Table V: Summary results and rating point distribution of annual daylighting simulation of the shading configurations for west facing balcony


Points Rank

SC- 1 Value 2.2 96.5 98 13.3 2.5 89.5 7.8 37 6th

Rating 9 9 9 1 9 0 0

SC- 2 Value 1.5 94.5 97.2 4 3.5 94 2 43 2nd

Rating 5 5 6 6 7 8 6

SC- 3 Value 2.2 96.5 98 13.7 2.5 89.5 7.8 36 7th

Rating 9 9 9 0 9 0 0

SC- 4 Value 1.2 93.2 96.5 2 4.5 94.7 0.8 40 4th

Rating 3 4 5 7 5 9 7

SC- 5 Value 1.7 94.8 97.5 6.3 3.5 93.7 3 44 1st

Rating 7 7 8 4 7 7 4

SC- 6 Value 1.9 95.5 97.5 9.7 2.8 91.3 5.5 41 3rd

Rating 8 8 8 2 8 5 2

SC- 7 Value 1.4 94.5 97.2 4.2 3.7 94 2.3 39 5th

Rating 4 5 6 5 6 8 5

SC- 8 Value 1.6 94.7 97.5 7.7 3.5 91.5 4.7 39 5th

Rating 6 6 8 3 7 6 3

SC- 9 Value 0.9 90.2 95.5 1.5 5.8 93.7 0.7 34 8th

Rating 0 3 4 8 4 7 8

SC- 10 Value 0.9 89 95.2 0.7 6 93.7 0 25 9th

Rating 0 0 0 9 0 7 9



Table VI: Summary results and rating point distribution of annual daylighting simulation of the shading configurations for south facing balcony


Points Rank

SC- 1Value 2.2 96 97.7 13.3 2.5 93 4.5 39 7th

Rating 9 9 8 0 9 4 0

SC- 2Value 1.4 92.8 96.5 0 4.3 95.7 0 43 5th

Rating 5 4 4 9 5 7 9

SC- 3Value 2.2 95.8 97.8 13.3 2.5 92.8 4.3 41 6th

Rating 9 8 9 0 9 0 6

SC- 4Value 1.2 92 96.2 0 4.8 95.2 0 38 8th

Rating 4 3 3 9 4 6 9

SC- 5Value 1.7 94.2 97.2 3.7 3.7 95.7 0 49 2nd

Rating 7 6 6 7 7 7 9

SC- 6Value 1.9 95.2 97.5 6.3 3.2 96.3 1.2 50 1st

Rating 8 7 7 5 8 8 7

SC- 7Value 1.4 93.5 96.8 0.3 4 96 0 47 3rd

Rating 5 5 5 8 6 9 9

SC- 8Value 1.6 93.5 97.2 4.3 3.7 95.7 0.5 45 4th

Rating 6 5 6 6 7 7 8

SC- 9Value 1 89 95.2 0 6.7 93.3 0 33 9th

Rating 3 2 2 9 3 5 9

SC- 10Value 0.9 88.7 94.8 0 7 93 0 22 10th

Rating 0 0 0 9 0 4 9

Table VII: Summary results and rating point distribution of annual daylighting simulation of the shading configurations for north facing balcony

Shading Device Configurations DF [%] DA [%] DA con [%] DAmax [%] uDI<100[%] uDI100-2000 [%] uDI>2000 [%] Total Rating

Points Rank

SC- 1Value 2.2 94.2 97.5 0 3.5 96.5 0 63 1st

Rating 9 9 9 9 9 9 9

SC- 2Value 1.5 91.8 96.3 0 5.2 94.8 0 43 6th

Rating 5 3 7 9 5 5 9

SC- 3Value 2.2 94 97.5 0 3.7 96.3 0 60 2nd

Rating 9 8 9 9 8 8 9

SC- 4Value 1.2 90.2 95.5 0 6.2 93.8 0 36 7th

Rating 4 2 6 9 3 3 9

SC- 5Value 1.7 92.8 96.5 0 4.5 95.5 0 51 4th

Rating 7 6 8 9 6 6 9

SC- 6Value 1.9 93.5 96.5 0 4 96 0 55 3rd

Rating 8 7 8 9 7 7 9

SC- 7Value 1.5 92.3 96.3 0 5.2 94.8 0 45 5th

Rating 5 5 7 9 5 5 9

SC- 8Value 1.6 92 96.3 0 5.3 94.7 0 43 6th

Rating 6 4 7 9 4 4 9

SC- 9Value 0.9 85.3 93.7 0 8 92 0 22 9th

Rating 0 0 0 9 2 2 9

SC- 10Value 0.9 86.2 93.8 0 8.2 91.8 0 24 8th

Rating 0 1 5 9 0 0 9



Table VIII: Distribution of DA (Daylight Autonomy) of the dining space by the most feasible shading configurations of balconies for four orientations

Horizontal louvers on horizontal plane for east

oriented balcony

Horizontal louvers on horizontal plane for west

oriented balcony

Horizontal louvers on vertical plane for south

oriented balcony

Horizontal canopy single on north oriented

balcony

The shading devices Brise-soleil semi façade and vertical louvers scored lower than other configurations in four orientations. These two shading devices provide better shading as they scored highest DAmax in four orientations. But it provides less illumination as it scored lowest DF, DA and DAcon values. The distribution of DA on the dining space by the three feasible shading configurations of balconies on four orientations are presented in Table- VIII.

7. ConCLuSIon

This paper represents a daylighting research method that is appropriate for designing shading for balconies of the residential buildings and also other building types. In residential building design, usual practice is to design one single type of shading device for four orientations. This study has shown that different types of shading configurations are sensible for effective daylighting for four orientations.

For the case space, it was found that horizontal louvers on horizontal plane is appropriate for east and west oriented balconies. Horizontal louvers on horizontal plane and horizontal canopy single were found as feasible for south and north orientations respectively. Though vertical louvers scored lowest on almost all four orientations it

will provide better indoor illumination if operable. It is expected that, the results of this study and the method will be helpful for architects to design shading devices effectively for residential balconies.

This research shows the effect of shading design of balconies on indoor illumination while most of the previous studies were limited to ventilation and thermal comfort only. This study will be helpful for architects and designers to design better shading devices for luminous comfort and also the city planners to take decisions regarding shading and balconies for harmonization view. The limitation of this research is it deals with the fixed shading devices only. Further research can be conducted to study the effect of operable shading devices on the thermal and luminous comfort as well as energy consumption of residential apartments.

ACKnoWLEDGMEnT

We would like to thank all of the people who helped make this study possible, in particular Dept. of Architecture, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh and Department of Architecture, Dhaka University of Engineering & Technology (DUET), Gazipur for technical supports.



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