Abstract:
This dissertation develops energy-efficient cooling interventions at both micro- and macro-climate scales to enhance thermal comfort (TC) in indoor and outdoor environments, with a focus on elderly populations indoors. For indoor environments, macroclimate solutions involve developing a control strategy to harness natural ventilation potential when adequate, utilize cost-effective alternatives for mechanical cooling systems, and optimize their use when necessary. The strategy activates and regulates the mode of available space conditioning systems to provide thermoneutral indoor conditions while using the least amount of energy. A multi-objective optimization process was then employed to identify building refurbishment parameters that minimize lifecycle costs and the risk of overheating during heatwaves, thereby optimizing energy efficiency and resilience. Elderly bioheat and thermal sensation (TS) models were employed in conjunction to a building energy model when developing these solutions. Microclimate interventions revolve around personal comfort systems (PCS), introducing a novel chair-based PCS design that creates a confined, uniform microclimate around seated users in hot environments. Unlike conventional space conditioning methods that condition entire spaces, this PCS focuses on the immediate vicinity of the user, optimizing energy efficiency and addressing individual differences in TS and TC. The PCS incorporates an air-cooling unit and supply units that utilize a colliding jet configuration for targeted upper body cooling and buoyancy-driven airflow for lower body cooling. Assessment metrics and design criteria are introduced to evaluate the performance of the PCS, followed by an iterative design procedure. A parametric analysis was then conducted to evaluate the effects of adjusting controllable parameters on the microclimate and user TS. To further enhance the system for extreme conditions, an add-on ventilated vest is integrated. This vest draws cool air from the cooled microclimate, providing higher heat dissipation and addressing a limitation of ventilated vest when operating in hot conditions. Computational tools—including computational fluid dynamics (CFD), bioheat models, and TS models—support the design, validated through climatic chamber experiments with human subjects and a thermal manikin. The elderly population has received special attention in this part of the research due to their prolonged periods of indoor occupancy and increased vulnerability to heat stress. A transient TS model that predicts elderly TS from physiological signals is developed and used to customize indoor interventions described for the elderly.
For outdoor environments, the work focuses on innovative solutions that counteract heat stress in both large-scale urban contexts and individual microclimates. At the macro-scale, the research addresses the urban heat island effect, a key contributor to outdoor heat stress in urban regions. Two interventions are explored: i. daytime radiative cooling roof panels with selective longwave emissivity/absorptivity and high shortwave reflectance, and ii. desiccant dehumidification systems integrated with conventional air conditioning, incorporating advanced desiccant materials. The impact of these interventions on city-wide thermal conditions, particularly at pedestrian level, was evaluated using urban simulation tools. Spatial and temporal analyses were conducted to compare the results to baseline scenarios and conventional solutions. At the microscale, the research introduces a novel technology that leverages principles of dynamic thermal perception in humans: fluctuating airflow cooled through misting. By exploiting temporal alliesthesia, this approach aims to induce a cyclic overshooting response in TC. From a fundamental heat and mass transfer perspective, this method offers additional advantages; the inherent increase in turbulence and mixing between water droplets and the surrounding air in fluctuating flows can lead to higher evaporation rates compared to constant flows with the same average velocity. The combination of enhanced TC levels and increased evaporation rates can result in fan energy savings, reduced water usage, and extended TC boundaries in outdoor environments. These concepts were investigated using a combination of experimental and numerical tools. Well-controlled, reduced-scale wind tunnel experiments validated the higher evaporation rates and validated a detailed CFD model. This model revealed underlying principles and aided in studying various fluctuations parameters—such as frequency, amplitude, and fluctuation profile—on evaporation enhancement. Subsequently, transient bioheat, TS, and TC models were employed to predict the TC state when the proposed system is used. Testing and optimization of all outdoor interventions were conducted, targeting the general adult population. This dissertation advances the field of TC by developing sustainable, energy-efficient interventions tailored to specific scales, populations, and environments. By providing scale-appropriate solutions for both indoor and outdoor settings and considering the unique requirements of different populations, the work aim to enhance the knowledge and practical implementation of cooling strategies, fostering human well-being in a warming world.