Elsevier

Building and Environment

Volume 57, November 2012, Pages 194-204
Building and Environment

Building façade design for daylighting quality in typical government office building

https://doi.org/10.1016/j.buildenv.2012.04.015Get rights and content

Abstract

Daylighting is one of the potential passive strategies to improve energy performance and users' visual comfort in existing offices without expensive installation and operational cost. For the first time, empirical study of daylighting performance was conducted for an existing typical government office building designed by Public Work Department (PWD) in Malaysia. Daylight field measurement of external illuminance and internal work plane illuminance was carried out. The findings demonstrated that internal daylight level in the building was insufficient despite the abundance of external daylight availability in the tropics which can achieve as high as 130 klx. Validation of simulation using Radiance-based software against the measurement under actual tropical sky indicated significant Pearson correlation of 0.709. Then, modification of window glazing and shading devices was experimented with simulation. The findings evidenced that light shelf increased daylight distribution uniformity, but failed to reduce glare on vertical plane when direct sunlight patches occurred. Integration of light shelf with partial blinds tilted at 45° showed improved performances of mean Guth Visual Comfort Probability (VCP) and CIE Glare Index. This paper concludes that simple modification of window glazing and shading device is able to provide significant improvement in tropical daylighting quantity and quality for visual comfort.

Highlights

► Empirical daylighting study of a typical government office building in Malaysia. ► Internal daylight level was low despite high daylight availability in the tropics. ► Validation of simulation against measurement indicated Pearson correlation 0.709. ► Light shelf increased daylight distribution uniformity but failed to reduce glare. ► Integration of light shelf and blinds increased Guth VCP; reduced CIE Glare Index.

Introduction

Since 2000's, there are arising awareness and concerns towards energy efficiency in office buildings among the government and policy makers in Malaysia. A few prominent energy efficient buildings were designed and constructed by the government as showcase buildings to the building profession as well as the public. These include the Low Energy Office (LEO), Putrajaya in year 2004, Green Energy Office (GEO), Bangi in year 2007 and Energy Commission (EC) Diamond Building, Putrajaya in year 2010. All these buildings have successfully achieved significant reduction in energy consumption (with BEI 65 to 135 kWh/m2/yr) in comparison with the typical office buildings (with BEI 250 kWh/m2/yr) in Malaysia [1], [2].

To promote energy efficiency in Malaysian government office buildings, Public Work Department (PWD) plays an essential role as the driving forces on development and construction of government buildings. PWD has designed standard office building for federal and states governments since 1960's. However, many of these standard designs were developed for cost and space efficiency without considering energy efficiency. This has led to high energy consumption among the existing typical government office buildings. Hence, extensive efforts are urgently needed to study and improve the energy performances in the existing typical government offices. Existing buildings are more constrained in comparison with new buildings in applying energy efficient design strategies. Thus, feasible retrofit is needed with less cost effects. Thereby this paper suggests means of energy efficiency measures by modifying the glazing types and solar shading to improve the building daylighting and visual performances.

Daylight is more efficient in providing light in comparison with electric light while producing less heat for the same amount of light [3]. Zain-Ahmed et al. [4] mentioned that minimum energy savings of 10% can be achieved by using daylighting strategies alone. Besides, daylight is the full-spectrum of light that matches closest to human visual response. Quality of daylight is much better than electric light. Lesser amount of daylight is needed to perform a task than performing the same task under electric light. Apart from that, daylight also gives better colour rendering and visual environment that enables the occupant to see objects properly in a room [3].

As the use of computers and video display terminals (VDT) has proliferated, visual comfort has become an important issue in office design [5]. Galasiu and Veitch [6] reviewed several surveys and concluded that most of the responders believed daylight is superior to electric light in its effects on people. Besides, human has greater tolerance to daylight uniformity in comparison with electric light [7]. Daylighting gives better visual comfort to the occupants.

The major drawback to harvest daylight in tropical climate is high intensity of solar radiation which will result unwanted solar heat gain. Record from Subang Jaya Meteorological Station showed that the annual maximum intensity of solar radiation falling on horizontal is about 1000 W/m2 and on vertical surface is about 850 W/m2 for east and west facing surfaces [8]. Apart from that, uncontrolled daylight can lead to excessive glare especially when working with computer task [9]. Dubois [7] suggested that absolute work plane illuminance (WPI) higher than 500 lx is too bright for computer work. However, the global illuminance in tropical sky can be higher than 100 klx [10]. Thus, high tropical daylight availability will cause discomfort glare to the occupants.

As tropical sky is predominant by intermediate sky with clouds [10], [11], the sky can be bright with patches around the edges of the clouds. Direct glare problem occurs when the occupants look to the high sky luminance through the windows. While the sun is not obscured by the clouds, direct sunlight patches falling on the interior spaces also cause non-uniform daylight distribution, resulting great contrast and visual discomfort. Consequently, the challenge in tropical daylighting is not about achieving the daylight quantity, but to control the daylight quality. Occupants need to avoid direct exposure to the sky component and direct sunlight patches by using shading devices [12], [13].

Inappropriate use of the shading devices will sacrifice natural daylighting and create discomfort glare. Many building users close up their windows totally with blinds in order to avoid glare. As a result, the abundance of daylight in tropical climate is yet to be utilised [14]. Therefore, the balance among the prevention of heat gains, control of discomfort glare and harvesting of daylight is very crucial in order to develop energy efficient and visual comfortable design solutions [13], [15], [16], [17].

The design of typical government office buildings in Malaysia is constrained by the organisational requirement as stated in Economy Planning Unit (EPU) Standard in Malaysia [18]. According to Malaysian Ministry of Work, there are total of 64 federal government office buildings designed by PWD and located at different states of the country [19]. The conventional space planning locates the individual officer's rooms at the perimeter of the building, thus limiting the potential of daylight utilisation. Tinted glazing and overhangs are commonly applied for all building façades without considering the orientation. Internal blinds or curtain are widely used to control glare problem. This kind of standard design is continuously duplicated for many government office buildings for more than 50 years. However, there is lack of daylighting research on these buildings.

A recent survey of lighting conditions in 5 Malaysian government office buildings with different design typologies had been conducted by the authors [20], [21]. The findings evidenced that all the selected buildings showed full dependency on electric lighting although there was sufficient external daylight availability in the tropical region. When the electric lights were switched off, all the 5 buildings failed to meet MS 1525:2007 lighting recommendation [22]. The research concluded that all the 5 office buildings were not designed for daylight utilisation, with average daylight factor lower than 1.5% and poor daylight distribution uniformity. Therefore, investigation on the daylighting performance in typical government office buildings to improve energy efficiency and visual comfort is critically demanded. This paper presents an empirical daylighting study for the first time in an existing typical government office building designed by PWD. Building façade modification was proposed to improve the daylighting performance.

WPJB is an existing typical government office building designed by PWD and completed in year 1978. This building is located at the city centre of Johor Bahru with latitude 1°27'37"N and longitude 103°45′30"E. This building was selected for study because it shows the design typology (floor layout, building form, building height and façade design) which is commonly employed by PWD. It is orientated with linear façades facing north-east and south-west. The building is 10-storey high with total lettable area of 19,694 m2 and ceiling height of 2450 mm. It is free from shadow casting from adjacent buildings and vegetation.

As shown in Fig. 1, the building façade is clothed with extensive use of external shading device with overhang and vertical screen for all orientations. This kind of shading device is a common element in many typical government office buildings in order to avoid direct solar heat gain and glare problem. Survey by the authors had identified at least 18 typical government office buildings located throughout Malaysia with similar building façade design as shown in Fig. 2. However, the potential of this shading device for daylighting demands further investigation. Apart from that, the common glazing types employed in these buildings are tinted glazing with low visible transmittance (VT).

Section snippets

Field measurement

As shown in Fig. 3, a typical individual officer's room in WPJB facing south-west (220°N) was selected for daylight measurement. The selected room is at the top floor and the blockage from adjacent building or vegetation is minimised. This room has deep plan geometry with room depth (D) to width (W) ratio 2.2 (as shown in Fig. 4), where the diminishing effect of side-lighting is significant. The floor area of the room is representative to the office room size for all government staffs with

Field measurement

As shown in Fig. 8, the internal WPI was influenced by the external illuminance. Generally, 27 March 2011 and 3 April 2011 showed higher external illuminance in comparison with the other days. The highest recorded external illuminance was about 130 klx during noon time, while the lowest during office working hour was approximately 20 klx. This demonstrated that there is abundance of daylight in Malaysian tropical sky.

The high quantity of external illuminance failed to illuminate the officer's

Discussion

The validation of simulation against field measurement suggested that adaptive application of the Radiance-based simulation software is needed in order to accurately predict the tropical daylighting performance. As shown by previous research [29], simulation performance criteria using relative ratio (such as daylight factor) was more reliable than using the absolute value (such as WPI). In this paper, the Pearson correlation between the simulated and measured daylight ratio was significant.

Conclusion

This paper has presented empirical study of daylighting performance for the first time in an existing typical government office designed by PWD in Malaysia. The findings urged reconsideration on the typical façade design that was in fact not appropriate for tropical daylighting. This paper demonstrates that simple modification of the external shading device and glazing type could provide significant improvement in the indoor daylight quantity and quality. However, flexible internal shading

Acknowledgement

This research is funded by the Public Works Department Malaysia (PWD) and Universiti Teknologi Malaysia (UTM) through a collaborative research grant, Vote 73751. The authors would also like to acknowledge the assistance from the PWD and UTM research teams in conducting the research.

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