| Author: | Shen, Yongting |
| Title: | Development and investigation of a solar-driven indoor CO2/H2O capture system for low-carbon buildings |
| Advisors: | Yang, Hongxing (BEEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Air quality Indoor air pollution Ventilation Carbon dioxide Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Environment and Energy Engineering |
| Pages: | xxvii, 167 pages : color illustrations |
| Language: | English |
| Abstract: | Cities account for around 70% of global CO2 emissions, underscoring the pivotal role of urban decarbonization in achieving carbon neutrality. One pivot for decarbonizing the expanding urban area is to develop low-carbon buildings featuring high indoor air quality (IAQ) and low CO2 emissions, yet it remains challenging. The main challenge arises from the trade-off between the two merits, that is, sustaining a high IAQ demands intensive ventilation to remove the exhaled CO2, which inevitably increases the unwanted energy load and associated CO2 emission of heating, ventilation, and air conditioning (HVAC) systems. One potential candidate to circumvent this trade-off is using indoor CO2 capture (ICC) technology that integrates carbon capture with HVAC to directly capture indoor CO2 and recirculate CO2-lean air for maintaining a good IAQ at reduced ventilation needs. Despite recent progress, current ICC systems suffer from low feasibility due to the oversimplified inter-subsystem interactions and insufficient exploration of system design principles. In this thesis, we address these challenges by articulating the complex and dynamic energy-mass exchange between ICC and indoor environment. Specifically, we proposed an innovative solar-driven indoor CO2/H2O capture system (SICC) and systematically investigated its configuration-scenario-performance relationship, aiming to achieve widely feasible and energy-efficient ICC technology to facilitate low-carbon buildings worldwide. First, a novel SICC design is proposed by integrating three subsystems: a two-chamber CO2 adsorption device for capturing exhaled CO2, a building-integrated solar photovoltaic/thermal collector (PV/T) for combined heat and power generation, and an HVAC system for ventilating, recirculating, and conditioning the indoor air. To elucidate the intricate mass-energy exchange dynamics, we developed a time-dependent SICC model based on the fundamental principles of energy, species, and mass conservation laws and validated this model with experimental data from literature. The as-developed model lays the foundation for further exploring the configuration-scenario-performance relationship. Second, the feasibility of the SICC in a wide range of indoor environments is examined through systematic scenario analysis. This analysis involved various indoor environments with different room sizes and crowdedness levels to cover common urban building scenarios. Under the premise of satisfying indoor CO2 regulation demand, this analysis has identified the feasible SICC configurations (capture speed, adsorbent mass, solar PV/T area) for these different working scenarios in Hong Kong. Moreover, the obtained configurations exhibited good performances in CO2 removal and overall energy-exergy efficiency. For instance, in a 40 m2 room with 39 occupants, the SICC can control the indoor CO2 concentration below 800 ppm, capture 40.655 kg CO2/day, and save 38.18% energy consumption compared to conventional air ventilation devices in summer. Third, the feasibility of the SICC on a global scale is demonstrated by considering diverse climate conditions to extend its applicability beyond Hong Kong. Specifically, a 20-city-based global performance analysis was conducted to evaluate the impacts of outdoor climate conditions, including solar irradiance, ambient temperature, and relative humidity, on the effectiveness of indoor CO2/H2O regulation and energy-saving potential. The results indicated that SICC can achieve higher CO2/H2O recovery rates and greater indoor CO2/H2O capture capacity in cities with abundant solar irradiance. Moreover, the SICC exhibits significant energy-saving potential in hot and humid cities with high HVAC energy demand, as exemplified by the highest energy-saving potential of 63.9% in Dakar. Overall, these results offer insights into the practical design and global implementations of the SICC. Finally, a modelling-optimization framework is developed to untangle the interplay between SICC objectives while considering the coupling effects of indoor scenarios and climate conditions. The proposed framework integrated the SICC model with the NSGA-II multi-objective optimization algorithm and translated the building’s merits, i.e., high IAQ, low carbon emission, and low energy consumption into five constrained objectives, which are dictated by eight parameters comprising material types, indoor scenarios, and climate conditions. This framework then articulated the impacts of decision parameters, untangled the connections between objectives, and optimized the mentioned five objectives. We also compared the optimization behaviors between different adsorbents (Zeolite 13X, Mg-MOF-74) and experimentally validated the theoretical comparison. For instance, while maintaining the same indoor CO2 level, the optimized solutions can capture more CO2, with an improvement of 59% and 74% for 13X and MOF, respectively. This framework enhances our understanding of the interplay between the SICC objectives, which can shed light on the further improvement of the techno-economic feasibility of contextual SICC designs. Overall, in this thesis, we proposed a novel SICC system as an innovative strategy for achieving low-carbon buildings, and demonstrated its feasibility in capturing indoor CO2, maintaining IAQ, and saving building energy in a wide spectrum of indoor environments and climate conditions. We also provide a new modeling-optimization framework to untangle the performances’ interplay and help generate contextual SICC designs. The proposed SICC system is poised to offer a paradigm shift in the way we achieve low-carbon buildings for urban sustainability. |
| Rights: | All rights reserved |
| Access: | open access |
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