Are Humans Good Sensors? Using Occupants as Sensors for Indoor Environmental Quality Assessment and for Developing Thresholds that Matter
The indoor environmental quality (IEQ) of buildings can have a strong influence on occupants’ productivity and health. Post occupancy evaluation (POE) is the first step in assessing IEQ, and typically relies on subjective surveys of thermal quality, air quality, visual quality, and acoustic quality. However, the practice of conducting POE, from data collection during field studies to data coding, analyses and visualization, is very labor intensive. In addition, there is often a significant discrepancy between major IEQ standards and actual human perception. The Center for Building Performance and Diagnostics (CBPD) at Carnegie Mellon University (CMU) has expanded POE to include both objective IEQ measurements and records of the TABS that may affect indoor environment and user satisfaction. The suite of three tools including user satisfaction survey, technical attributes of building system and workstation IEQ measurements in the National Environmental Assessment Toolkit has been deployed in over 1600 workstations in 65 buildings, generating a rich database for statistical evaluation of the possible correlations between the physical attributes of workstations, measured environmental conditions, and user satisfaction. The database also supports a number of critical hypotheses relative to the complexity and depth of field data needed, the critical factors that must be collected, and the possibility that humans are indeed good sensors for many variables. The major statements that have been drawn from the research are as follows: (1) Because human health and performance outcomes are a result of an integration of indices, IEQ evaluation must include thermal, air, visual, and acoustic measures. (2) While POE with IEQ measurement is an ideal approach to assessing the full suite of environmental characteristics that impact human satisfaction, health and performance, field measurements are labor and cost intensive. (3) Building occupants can provide critical insights and even real measures of IEQ, and contribute to updating IEQ standards to reflect integrated realities. As such, this research revealed an integrated approach to POE +M by leveraging occupants as sensors to quickly capture IEQ conditions in a work environment. This approach can identify critical factors in the physical environment that impacts building occupant comfort and satisfaction. This approach provides practical IEQ assessment methods and procedures centered on the occupants’ perspective. The ultimate outcome of this research will contribute (1) correlations between occupant perception and measured data, (2) a refined survey method to assess building IEQ capable of robust prediction of building performance, and (3) metrics and guidelines for IEQ standards that capture new IEQ thresholds that impact building occupants’ comfort. The hypotheses tested in this thesis are summarized as follows: Hypothesis 1: Humans are effective sensors for POE+M. Combining occupant responses with key IEQ attributes can provide insight that is comparable to complex field instrumentation. Hypothesis 2: User satisfaction can inform design decisions. Comparing user satisfaction to instrumented IEQ measurements can inform acceptable thermal, air, visual, and acoustic design for occupant satisfaction. Hypothesis 3: Environmental thresholds are not adequate. Comparing user satisfaction to instrumented IEQ measurements can inform acceptable thermal, air, visual, and acoustic quality l conditions for occupant comfort. Multivariate regression, multiple correlation coefficient, and Pearson correlation statistical analysis of the database of 1600 workstations revealed the relationship between measured and perceived IEQ indices, interdependencies between IEQ indices and other satisfaction variables of significance. This research can contribute correlations between occupant perception and measured conditions, and metrics and guidelines for IEQ standards that capture new IEQ thresholds that impact building occupants’ comfort. The key findings of the IEQ data analysis are as follows: The result of the thermal quality revealed that smaller thermal zone, greater window quality, a level of control, measured air temperature at 60 cm from the floor, and radiant temperature asymmetry between exterior and interior walls are critical factors of temperature satisfaction. For air quality, operable windows, window quality, partition height, dedicated exhausts for printer and copy area, return air density are critical factors for overall air quality satisfaction. User satisfaction of the visual quality showed that seated view in the workstation is the most critical factor for user’s overall visual quality satisfaction. In addition, better ceiling fixture, ceiling lens type, window type and managing illuminance level on the work surface are important. Lastly, to ensure the acoustic quality satisfaction in both background noise and frequency from distraction from other people, bigger workstation, more partition sides, higher partitions and management of distributed noise source are critical for user comfort and perceived productivity. Overall, this thesis identified opportunities to improve the process of IEQ assessment by engaging occupants in POE, and define critical indicators for building occupant satisfaction. The results will contribute to the ongoing database of engaging humans as IEQ sensors. In the future, the findings and framework described here may be applied in different aspects of the building delivery process, such as building life cycle evaluation, building design, and the construction stage, to improve occupants’ thermal, air, visual, and acoustic conditions in the building.