Author: Kang, Shengxian
Title: A study on acoustic environmental evaluation of open-plan offices in mainland China
Advisors: Mak, Cheuk Ming (BEEE)
Degree: Ph.D.
Year: 2023
Subject: Offices -- Noise
Offices -- Designs and plans
Work environment
Hong Kong Polytechnic University -- Dissertations
Department: Department of Building Environment and Energy Engineering
Pages: xxiii, 186 pages : color illustrations
Language: English
Abstract: An open-plan office is a typical type and has been favoured by architects and builders for ease of information flow, flexibility for layout changes and economic reasons. Noise, especially irrelevant speech, can transmit with few obstacles in large office spaces due to the spatial characteristics of the open-plan office (i.e., without partition walls). This acoustic characteristic results in some acoustic problems, such as poor speech privacy and a noisy environment. For employees who spend long periods of time in open-plan offices, these acoustic problems can lead to poor indoor environment satisfaction, low work productivity, and high job dissatisfaction. Thus, the contradiction between convenient information communication and good acoustic quality requirements of open-plan offices has become a pressing acoustic issue in open-plan offices. This thesis systematically investigated the acoustic environment of real open-plan offices, the impacts of acoustic quality levels, work performance prediction, the impacts of reverberation time and speech intelligibility in Chinese open-plan offices by means of acoustic measurements, objective experiments, subjective questionnaires, and acoustic simulation of open-plan offices. In order to achieve the above research objectives, a number of sub-studies have been carried out: (1) An investigation of acoustic environments in large and medium-sized open-plan offices in China; (2) The effect of room acoustic quality levels on work performance and perceptions in open-plan offices; (3) A prediction model that evaluates how much work performance is decreased by speech noise with different intelligibility in Chinese open-plan offices; (4) The effects of speech intelligibility and reverberation time on the serial recall task in Chinese open-plan offices.
Open-plan offices can be subdivided into small, medium-sized and large open-plan offices depending on the number of employees sharing an office. An investigation of acoustic environment was carried out in 16 Chinese open-plan offices, aiming to (1) study how the design parameters of open-plan offices affect indoor acoustic environments; and (2) explore whether occupants' demands of acoustic environments are different between large open-plan offices (LOPOs) and medium-sized open-plan offices (MOPOs). Both objective measurement and subjective evaluation results that relate to the critical aspects of the acoustic environment (noise level and speech privacy) were collected from seven LOPOs and nine MOPOs in China. The analysed results found that open-plan offices with a lower spatial density of workstations or higher storey height have a higher spatial decay rate of speech (𝐷2,𝑆), lower speech level at 4 m distance (𝐿𝑝,𝐴,𝑆,4π‘š) and shorter comfort distance (π‘ŸπΆ). The perceived noise level has the greatest influence on employees' acoustic satisfaction, and speech interference on employees' re-concentration is the main acoustic reason leading to a work productivity decrease. In terms of the differences in acoustic environment between LOPOs and MOPOs, employees in MOPOs have higher acoustic satisfaction and lower disturbance levels of speech noises. Perceived speech privacy is a significant acoustic factor affecting work productivity in LOPOs, while it is not in MOPOs.
A laboratory experiment was carried out to explore the effects of acoustic quality levels on work performance and perceptions in open-plan offices. The accuracy rate of the serial recall task and the reported perceptions of the 41 participants were tested at two receiving locations in four office scenarios. According to the revised international standard for measuring room acoustic parameters in open-plan offices, ISO 3382Β­-3:2022, the room acoustic qualities of the four office scenarios were classified into four levels (good, high-medium, low-medium, and poor). The results confirm the validity of the acoustic classification criteria in ISO 3382-3:2022 and highlight that people working in offices with good acoustic quality have significantly higher work performance and acoustic satisfaction than those working in offices with poor acoustic quality. Moreover, comparisons of objective and subjective results between the two receiving locations imply that maintaining a greater distance from people speaking improves work performance and acoustic satisfaction in offices with poor acoustic quality. However, this improvement is insignificant when working in offices with good acoustic quality.
Speech intelligibility is an essential index for evaluating acoustic performance in open-plan offices. Both speech-to-noise ratio (SNR) and reverberation time (RT) are critical parameters for determining the STI. Many studies explored the effects of speech intelligibility on work performance and acoustic environmental perceptions in open-plan offices by changing the SNR to obtain various STI conditions. However, few studies research how RT affects speech intelligibility and then influences work performance and perceptions of acoustic environments in open-plan offices. A laboratory experiment was carried out to determine the changing trends of work performance and acoustic environment perceptions with the increase in STI under different RT conditions. In addition, this experiment also explored how room RT affects work performance and perceptions of the acoustic environment under the same STI condition. The acoustic conditions tested in this experiment varied in speech intelligibility (STI of 0.21, 0.42, and 0.61) and reverberation time (RT of 0.4s and 1.4s). The main outcome of this experiment is that occupants working in a long reverberant environment have less mental workload, faster task completion speed, and higher acoustic adaptability than those working in a short reverberant environment at an STI of 0.42. Furthermore, the data show a decreased work performance and an increased speech disturbance with the increase in STI in the short reverberant environment, while that trend was not observed in the long reverberant environment. The effects of STI conditions on occupants may differ by gender and noise sensitivity.
Speech noise can reduce occupants' work performance in open-plan offices. Some models have been created to predict the effect of speech of different intelligibility on work performance. However, few of them consider the effects of speech intelligibility in Chinese environments. Thus, a model was developed to evaluate how much work performance is decreased by speech noise with different intelligibility in Chinese open-plan offices. The data from the abovementioned two laboratory experiments and two previous studies were collected and analysed. These two studies researched the effects of the Speech Transmission Index (STI) on serial recall performance in Chinese environments. STI is an important parameter for the objective prediction of speech intelligibility. A sigmoidal curve shape was used to develop a prediction model to explain the relationship between STI and the performance decrease of serial recall tasks (DP). A comparison of curves between STI and DP with previous studies shows that the STI range for serial recall performance variation in Chinese environments is narrower than in non-Chinese language environments.
Rights: All rights reserved
Access: open access

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