In recent years, people prefer to work from their home for many reasons, such as saving time, increasing productivity and flexibility, reducing commuting and facilities costs, independence, etc. Hence, the prospect of residential offices has obtained a reputation over the years.
The fast development of communications technology and computer capabilities was the main reason for the increase of home-based offices. Hence, this trend has increased in parallel with the rapid development of technology.
Home-based office has been recently focused by the government in Malaysia to encourage the citizens to work from their residential units.
A recent survey in several residential buildings in Malaysia shows that most of the occupants (approximately 70 percent) carried out computer-related tasks in addition to other household tasks in their residential units during the daytime (9 am to 5 pm).
Overall, desk-related tasks (reading, writing, and computing) are frequently done by workers in their residential working rooms during the daytime. Based on the Green Building Index (GBI) for residential buildings, daylighting is a major criterion under the category of indoor environmental quality since a quarter of the total points is devoted to daylighting. Thus, considering visual comfort in residential buildings is as significant as providing visual comfort for workers in office buildings.
While previous daylighting studies in Malaysia merely focused on office buildings, this study investigates daylight distribution in existing residential buildings.
Daylighting is a significant passive design strategy, especially for reducing energy consumption in buildings. Based on previous studies, efficient design of daylighting can substantially provide a healthy indoor environment, energy savings in terms of lighting, and preferable visual comfort for the residents.
In the tropics, daylight always brings more heat compared to electric lighting. Daylighting is a major design strategy that needs to be implemented in buildings by architects at the beginning design stages.
Daylighting is essential to be utilised for building design in tropical areas due to severe sunlight penetration, changeable formation of clouds within a minute, and high external illuminance. Previous research studies in tropical climates argue that external illuminance under the tropical skies could be as big as 140000 lux.
Zain-Ahmed, Sopian indicates that minimum 10 percent energy could be saved through implementing daylighting strategies in buildings under tropical skies.
Recent studies investigated passive design parameters that can influence daylight distribution in a building, such as the colour of the external façade, window-to-wall ratio, window glazing, external obstructions, window orientation, atrium, self-shading strategy, automated solar shading, light pipe, etc.
These strategies should be implemented in buildings at the preliminary stages of design. However, end users are unable to retrofit those fixed parameters after occupancy in their houses, but they can alter interior design parameters, such as the internal shading device, furniture, etc.
Previous studies explain different internal shading devices that can considerably influence indoor daylight performance. This study focused on the impacts of furniture—as a typical interior design element—on indoor daylighting performance in residential buildings.
Furniture has a great influence on daylighting efficiency in buildings through reflecting or shading solar light. Indoor environmental qualities, in terms of thermal and visual comfort, may be changed through different arrangements of furniture in buildings.
A study by Dubois shows that by inserting furniture in a room in temperate climates, the difference of illuminance levels between a furnished and an unfurnished room can remarkably fluctuate by 35 percent.
Every arrangement of furniture makes a specific light distribution; therefore, furniture can obviously influence indoor illuminance level. Thus, it is essential to investigate the impact of furniture on daylighting as the physical surfaces and masses may considerably affect indoor daylight distribution.
In order to accurately simulate daylighting condition in a residential working room, it is important to consider suitable furniture arrangements.
Since a wide range of various furniture arrangements can be existed, it is improper to consider a casual layout as the representative for all the others. On the other hand, it is infeasible to consider all the available furniture layouts in a residential working room for analysis of indoor daylight level.
For this reason, furniture has been mostly overlooked in previous studies on daylight simulation experiments in buildings under a tropical sky. Thus, in this paper, typologies of mostly used furniture layout (MUFL) in residential working rooms should be employed to have better generalization on furniture.
A questionnaire survey on furniture arrangements in working rooms was conducted by Mousavi, Khan in 11 residential buildings in Johor Bahru, Malaysia.
As desk-related tasks had the highest usage among home workers and the focus of this research is on such activities in a working room, typologies of MUFL were determined based on different locations of a desk in a typical working room.
Accordingly, three locations were frequently selected by home workers to place a desk in their working room (along a wall at the window, along a wall opposite the window, and along sidewalls). Among the typologies of furniture layout, plan A had the highest usage by respondents.
The location of other possible furniture was determined based on their most selected position in the working room. For example, when the location of a desk is near the sidewalls, a bed was frequently positioned near the window wall; a drawer was mostly positioned near the rear wall, while a bookshelf and a storage cabinet were often located near the sidewalls.
For the remainder of the study, these three typologies of MUFL were considered for daylight simulation experiments in the case room.
In summary, due to the rapid development of home-based computing workspaces in Malaysia, it was essential to improve indoor visual comfort in existing residential buildings, which constituted a vast majority of building types in main urban regions in Malaysia.
Beside office buildings, visual comfort and daylighting design should be considered in existing residential buildings. Although the furniture was overlooked in previous daylighting studies in tropical areas, this study focused on furniture as an important interior design element affecting indoor daylight distribution. Thus, this paper aimed to show the impact of the furniture layout on the qualitative and quantitative performance of tropical daylight in the existing residential buildings in Malaysia.
The field measurement shows that the Radiance-IES simulation engine could properly simulate a furnished room for the tropical skies. It is questionable to directly use the CIE sky types, which are employed in the Radiance-IES program, for evaluating tropical daylighting.
The reason is that the value of outdoor illuminance in the tropical climate of Malaysia could be as big as 120000 lux, whereas the simulated value was up to 20000 lux under CIE sky.
This was in line with previous research stated that the CIE skies had outdoor illuminance of lower than 20000 lux while this value was higher than 80000 lux for the Malaysia’s tropical sky.
However, before using the Radiance-IES software for a tropical climate, it needed to be validated because of the different characteristics of CIE and tropical skies. While there were huge differences between the simulated and measured values of the absolute values (E0 and WPI) in the furnished room, the Pearson correlation between the two sets of results were significant only for relative ratios (DF and DR).
This was in accordance with previous studies that indicated Radiance-based software can accurately be used for the tropical daylight simulation for the relative ratios, but not absolute values.
The minimum value of mean DR was more than one percent, which is the allowable lower daylight limit, for all the simulated tests, except the west orientation on March 21st at 12 pm This implies that the indoor daylight availability was substantially adequate in the existing working rooms in residential buildings in Malaysia.
Although the DR results in the case room steadily fluctuated during the day under the north and south orientations, these values drastically changed under the east and west orientations. This is in accordance with a study by Lim, Ahmad that indicates the highest inconsistent daylighting patterns could be recorded for the rooms with east orientations in tropical regions.
The DR values were reduced for all the simulated experiments by adding furniture in the case room. This decrease of indoor daylight level was more sensible when the furnished room (especially type B) receives direct sunlight compared with indirect sunlight.
The mean IUR values in the unfurnished room during all simulated tests were much lower than the recommended threshold. However, differently furnished types (MUFLS) not only improve indoor daylight uniformity but also deteriorate the condition.
Moreover, the IUR values had much more potential rather than DR values to fluctuate drastically by changing the arrangement of furniture in the case room. This shows that the furniture layout has a major influence on daylight distribution uniformity in the room. The findings of GVCP and CGI showed that the daylight quality in the case room (without furniture) for all the simulated experiments was lower than the allowable ranges for transient and sedentary conditions.
By furnishing the case room, even with different arrangements, the indoor visual comfort not only improved, but also it worsened the situation in terms of glare problems. Previous studies used relative differences to compare two daylight variables under different conditions.
On average, all three furnished types reduce the mean DR values approximately 11 percent compared with the base type. This is in line with an investigation in temperate climates that indicates furniture may reduce daylight levels in a room.
The difference of IUR values between furnished and unfurnished conditions was obviously distinct for each furniture arrangement. Accordingly, type C recorded the high difference of 86 percent while type B had a 15 percent decrement of IUR results compared with the base type.
It can be reasoned that various layouts of furniture in a room could greatly influence indoor daylight distribution uniformity. Thus, high reduction of daylight distribution uniformity in a building is the main impact of furniture on indoor daylighting performance.
The mean relative difference of GVCP and CGI results was nearly similar in quantity for each furnished type. By furnishing the case room, on average a 12 percent decrement of GVCP values and a slight two percent increment of CGI values can be observed. Therefore, furnishing a room, irrespective of its arrangement, could increase glare and visual discomfort.
Overall, type B compared with the other furnished types had better indoor daylighting performance, particularly for illuminance-related metrics since whenever sunlight directly came inside the furnished room (type B), it dropped somewhere between the window and the bed.
Therefore, the bed affected the daylight level reaching the rear space of the room that caused a reduction in the average indoor daylight level. Based on the solar angle and furniture position, furniture may reflect direct sunlight further in buildings or shade it from the rest.
While the occupants of residential buildings in the context of Malaysia have more tendencies for choosing type A to furnish their residential working rooms, in this paper, type B represented better indoor daylight performance than the other furnished conditions.
This indicates that the social needs of people had a higher priority over the environmental needs, especially daylight utilisation, when furnishing their residential working rooms.
This paper focused on the impact of different furniture layouts on the quantitative and qualitative daylighting performances in residential working rooms. Though a vast majority of furniture arrangements could be discovered in reality, in order to have a better generalisation, the MUFLs in a typical working room of residential buildings in Malaysia were employed in this study.
The field measurement under a tropical sky only validated the relative ratios of the daylighting variables in the Radiance-IES. Therefore, IUR and DR as illuminance-related metrics, CGI and GVCP as glare metrics were employed to assess indoor daylighting condition.
Based on the findings of field measurement, the outdoor illuminance under a tropical sky can be as high as 120 klux (third day of measurement at 1 pm).
This extreme outdoor illuminance under the tropical sky can cause high indoor daylight levels, especially for the east and west orientations.
The study showed that different furniture layouts can decrease the indoor daylight availability on average by approximately 11 percent. The importance of furniture layout on the reduction of the indoor light level is more sensible when it is placed in a way that decreases the depth of the daylighting space by preventing sunlight from reaching the hind space of a room.
By changing the layout of the furniture in the case room, daylight distribution uniformity recorded the biggest fluctuations among the other daylighting variables.
It can be concluded that while various furniture arrangements may even slightly decrease the extreme daylight quantity (DR) in the tropics, they can also deteriorate the indoor daylight quality (IUR, GVCP, and CGI) compared with an unfurnished space. Thus, furniture as an interior design element could not improve tropical daylight performance in a building.
Future studies can investigate the impacts of different interior design variables (such as surface reflectance, glazing tinting and internal shading controls) on indoor daylighting performance.