PhD Oral Exam - Lili Ji, Building Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Under the current and potential impact of climate change, there is a growing concern about extreme heat events and its challenging to human health and building resilience. The indoor heat-stress situation relates to outdoor extreme heat events, building characteristics, and occupants’ vulnerability. The high heat-related mortality rate of older people (aged 65+) and the trend of the population aging worldwide indicate the significant importance of evaluating and predicting heat-stress conditions specifically for older people. Building thermal resilience determines the ability to tolerate extreme heat events and maintain or recover indoor comfort. No consistent index has been proposed to evaluate building resilience to heat and compare different resilient cooling strategies. Models of the relation between outdoor extreme weather data, indoor environment parameters, and human physiological responses are still needed to predict the consequences of global warming.

Therefore, this research aims to evaluate building occupants’ thermal response and quantify building thermal resilience against extreme heat events. The bioheat models applicable to calculating young and older adults’ physiological responses under hot exposure were developed to provide valuable methods to predict thermal responses and the physiological-based heat-stress index for occupants with different heat vulnerability levels. The validation study shows that the simulation results of the proposed models agree well with the published experimental data. The models can also capture the relative difference in physiological responses between older and young people in hot or cold scenarios.

To capture indoor overheating patterns under variable surrounding weather conditions, this thesis proposed a new method of selecting extreme hot years based on the synchronization of indoor and outdoor. The extreme hot year (EHY) was chosen by quantifying the degree of synchronization between outdoor heatwave events and building indoor overheating conditions based on the concept of POS (Percentage of Synchronization). A higher value of POS indicates a higher chance of building indoor overheating occurring based on outdoor heatwave events for many archetype buildings and situations for specific climate zones. Based on the POS concept, it has been proved that in building overheating-centric studies, the EHYs should be better selected according to the severity and intensity of heatwaves defined by the thermal-based index.

Under extreme heat events, a new quantification framework for building thermal resilience was developed. The framework considered the resilience profile, quantification index, and resilience level labeling. The conceptual building thermal resilience curve has the shape of a resilience trapezoid. A resilience parameter, the Thermal Resilience Index (TRI), can be calculated by determining the improvement in relative resilience from original conditions. The zone-level and building-level thermal resilience can be labeled based on the value of TRIz and TRIb, respectively. Each labeled class represents the percentage of improvement in resilience. The Standard Effective Temperature (SET) can be used as a performance indicator to permit defining the building thermal performance curve. The proposed framework has been implemented in a calibrated building model to quantify the building thermal resilience with different passive cooling strategies. With this method, the effect of cooling strategies and their combinations on the building-level thermal resilience, the zone-level resilience on different floors and orientations, as well as the resilience uniformity of zones can be quantified, labelled, and compared, thereby, a detailed design of resilience enhancement strategies to be achieved.

The contributions of the thesis include validated new models and methods to quantify human thermal responses and building resilience to extreme heat events. These new methods and tools contribute potentially significant impacts to the research under different climate zones and future climates covering from a single building to large scales to quantify community or city scale resilience to heat.