Occupant satisfaction with the indoor environment in seven commercial buildings in Singapore
Graphical abstract
Introduction
Sustainable buildings should aim to achieve substantial energy savings and reduce greenhouse gases emission, while also providing good Indoor Environmental Quality (IEQ) that satisfies building occupants. IEQ affects occupants’ health, comfort, well-being and productivity [1,2]. Conducting a post-occupancy evaluation (POE), with a widely adopted and reliable survey tool, could provide valuable information in understanding occupant satisfaction with the built environment, and identify areas in need of improvement.
The Center for the Built Environment (CBE) at the University of California, Berkeley, has been developing and maintaining an effective and reliable occupant survey tool to gather occupant's satisfaction surveys for more than 20 years [3,4]. The latest version of the IEQ survey tool has been implemented in over 900 buildings, with over 90,000 individual occupant responses. The survey aims to collect occupant perceptions of and satisfaction with a space's IEQ as well as characteristics of the target building.
The CBE IEQ Occupant Survey database facilitates studies examining occupant satisfaction with the built environment across a large, diverse sample. For instance, responses within the CBE database have been used to compare occupant's satisfaction in LEED versus non-LEED certified buildings [[5], [6], [7]]; relationships between individual IEQ factors and overall workspace satisfaction [8,9]; comparison of acoustics and temperature satisfaction between radiant and all-air buildings [10]; and exploration of occupant satisfaction and self-estimated performance in relation to IEQ parameters in buildings [11]. Despite the large sample size and building type variety available in the CBE database, the buildings sampled are mainly located in the US.
About 43% of the world's population is now housed in the tropics, and this figure will likely increase to >50% by the year 2050 [12]. An increasing trend in the investment of research and development and scientific publication is observed in the tropics [12]. It is expected occupant satisfaction with the indoor built environment could be different in tropical climate countries due to different building design and construction practices, and occupant preferences, expectations, and cultural norms. For example, satisfaction with regards to the thermal environment could differ due to environmental adaptation [13,14].
Singapore is located at 1.3° N, 103.8° E and belongs to the tropical rainforest climate “Af” based on the Köppen Climate Classification [15]. Throughout the year, the climate in Singapore is warm and humid, with a daily mean outdoor air temperature of 26–29 °C and a daily mean relative humidity of 75–85% [16]. In Singapore, a requirement for the Green Mark certification involves obtaining occupants' satisfaction with a building's environment via post-occupancy evaluation assessment. Green Mark is a rating system designed to evaluate a building's performance and environmental impact [17]. Green Mark recommends that a building achieves an occupant satisfaction level of at least 80%. This 80% level is a macro indicator, and generally represents a substantial majority of people's decisions, similar to ASHRAE 62.1, ASHRAE 55 and ISO 7730 [18,19]- yet it is a precept, instead of a hard mathematical law. This target may be easy to achieve for some environmental parameters, but could be harder for others. One study examining IEQ satisfaction from 367 occupants in 14 buildings in Singapore showed that satisfaction with window view, personal control, temperature, air movement, daylight, visual comfort, visual privacy, air quality, noise level and sound privacy failed to achieve the 80% level, even in Green Mark certified buildings [14]. In fact, occupants' perceived comfort and satisfaction with indoor environmental parameters could differ due to contextual and behavioural factors [20], and singular satisfaction ratings applying to all IEQ parameters may not be adequate.
Another important issue is to understand which parameters, or cluster of parameters, contribute the most to overall environmental satisfaction. Using the CBE database, Frontczak et al. found the most important parameters for workspaces satisfaction were satisfaction with amount of space, followed by noise level and visual privacy [8]. Working with the same database using a multiple regression approach, Kim and de Dear also found that amount of space, noise level and visual privacy affected overall satisfaction the most [9]. In the Cost-effective Open-Plan Environments (COPE) project in Canada, Veitch et al. found that satisfaction with workspaces' environment features can be reduced to three major factors, including “privacy/acoustics”, “lighting” and “ventilation/temperature”, and the satisfactions with these three factors and the overall environment were positively associated [21]. The Workplace Wellness Study surveyed 1601 employees in North America, suggested air quality (58%) was the most highly-rated wellness factor in office, followed by comfortable lighting (50%) and comfortable temperature (34%) [22]. In Singapore, there could be different associations between IEQ parameters and overall environment satisfaction due to different contextual and behavioural characteristics found in the tropics. Through pinpointing which parameters comprise overall satisfaction, this information could help guide policymakers’ decisions on which factors to focus guidelines towards design and operation practices. Understanding how overall satisfaction is achieved also helps building owners, operators, and employers to prioritize how to make decisions to maximize tenant satisfaction in the workspace when resources are limited.
In this study, we surveyed occupant satisfaction in seven commercial buildings in Singapore using a survey adapted from the CBE IEQ Occupant Survey. The objectives are (i) to study occupants' satisfaction level with different IEQ factors and verify which IEQ factors can achieve an 80% target occupant satisfaction; (ii) to understand the reason(s) that caused environmental dissatisfaction; and (iii) to identify which IEQ factors have higher impacts on occupant satisfaction with the overall workspace in Singapore's commercial buildings.
Section snippets
Survey tool design
We modified the original CBE IEQ Occupant Survey [8] to be appropriate for building characteristics and operation in Singapore. The changes have been informed and acknowledged by CBE. In particular, we added questions on satisfaction with humidity and air movement because of the hot and humid climate characteristics in Singapore. Meanwhile, we removed satisfaction with general maintenance and ease of interaction from the original CBE survey, because our survey scope is within workspace, instead
Description of the dataset
Table 1 summarizes respondent and workspaces characteristics. A total of 53% of respondents were male, mainly between 21 and 50 years old, and occupants reported spending more than 30 h per week in their workspace. Most of the occupants were located in open plan offices with low (<1.5 m height) or no partitions. 59% of respondents were located near (within 3 m) an external wall and window.
Occupants’ IEQ satisfaction distribution
Fig. 1 shows the distribution of satisfaction responses for each IEQ factor. Overall, respondents were more
Overall environment satisfaction contributors
In this section we analyse which variables contribute the most to overall environmental satisfaction. We applied correlation analysis on the 18 IEQ satisfaction responses to elicit the relationship between parameters. Next, we conducted principle component analysis (PCA) to identify the possible new factors (or components) that emerge between the multiple IEQ parameters. Lastly, we analysed the significance of the factors in predicting overall environment satisfaction by using multiple linear
Limitations
A major limitation of this pilot study is the small building and individual sample size (7 buildings and 666 respondents). This may influence the accuracy of the analysis, especially for instances in which there is limited variance available in the PCA. The existing database is part of larger longitudinal project. We are continuously surveying buildings with the intention of developing an IEQ benchmarking system for commercial buildings in Singapore. Additionally, our survey tool has been
Conclusions
We modified the CBE Indoor Environmental Quality (IEQ) Occupant Survey to conduct IEQ satisfaction assessments in 7 commercial buildings in Singapore (666 respondents). Overall satisfaction with the environment was 78%. People were most satisfied with flexibility in dress code (S = 86%), electric light (84%) and cleanliness (82%). We found dissatisfaction rates higher than 20%, for sound privacy (D = 42%), personal control (32%), temperature (30%), air movement (27%), overall privacy (26%), and
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This research was funded by the Republic of Singapore's National Research Foundation through a grant to the Berkeley Education Alliance for Research in Singapore (BEARS) for the Singapore-Berkeley Building Efficiency and Sustainability in the Tropics 2 (SinBerBEST2) Program. BEARS has been established by the University of California, Berkeley as a center for intellectual excellence in research and education in Singapore. We would like to thank Tom Parkinson for developing the blue prints of
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