| Author: | Zhang, Yanling |
| Title: | Investigation on evaporative cooling-enhanced compact desiccant dehumidification system in hot and humid regions |
| Advisors: | Yang, Hongxing (BEEE) Lu, Lin (BEEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Humidity -- Control Cooling Air conditioning Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Environment and Energy Engineering |
| Pages: | xxix, 219 pages : color illustrations |
| Language: | English |
| Abstract: | The growing demand for energy-efficient and environmentally friendly air-conditioning solutions in buildings has catalyzed the exploration of innovative, efficient, and cost-effective air handling systems. Desiccant cooling systems, recognized for their superior coefficient of performance (πΆππ) relative to traditional mechanical vapor compression refrigeration (πππΆπ
) systems, encounter significant challenges in effectively managing and decoupling indoor heat and humidity loads in hot and humid areas. The complexity inherent in current desiccant cooling technologies often restricts their practical application, highlighting the necessity for a simplified approach that can be validated through experimental methods. This thesis presents an in-depth experimental and numerical investigation of an Evaporative Cooling-Enhanced Compact Desiccant Dehumidification (πΈπΆπΈπ·π·) system. The inclusion of a internally cooled moisture absorption heat exchanger in the system can effectively manage the decoupled indoor heat and moisture loads under high temperature and high humidity conditions. The proposed system simplifies the existing complex indirect evaporative cooling (πΌπΈπΆ) and liquid desiccant dehumidification (πΏπ·π·) systems and enhances their cooling capacity, thereby offering a potential solution for independent treatment of temperature and humidity. Firstly, a dedicated numerical model for counter-crossflow πΌπΈπΆ-assisted πΏπ·π· (ECLD) system to conduct a comprehensive parameter study for performance prediction and parameter optimization. A hexagonal plate heat exchanger (ππ»πΈ) consisting of both counterflow and cross-flow was used as a core in an πΈπΆπΏπ· to ensure efficient heat transfer and facilitate easy installation simultaneously. A numerical heat and mass transfer model was established and validated, and an intensive parameter analysis of the thermal performance of the dehumidifier was conducted. The performance of the newly developed counter-cross flow πΏπ·π· with πΌπΈπΆ-assisted cooling was improved by 16% and 8.4%, respectively, compared to the adiabatic and cross-flow type dehumidifiers. The newly developed πΏπ·πΈπΆ fully used the return air and worked on improving the cooling capacity to reduce the volume of the combined πΌπΈπΆ and πΏπ·π· system. Comparing the heat exchange performance of the ππ»πΈs with multiple flow patterns at different aspect ratios may provide references for optimizing the ππ»πΈs. Secondly, a numerical model of an evaporative cooling-enhanced compact desiccant dehumidification system is developed. A combined system consists of an internally cooled liquid desiccant dehumidification (πΈπΆπΏπ·) and a regenerative indirect evaporative cooling (π πΌπΈπΆ) that can operate without a power-intensive compressor. The internally cooled πΏπ·π· initially removes the latent heat from hot and humid air before it is cooled by the π πΌπΈπΆ. The response surface method (π ππ) and multi-objective optimization were used to optimize and assess the potential and performance of the system. The validated response surface model is used to optimize six critical environmental and operational parameters. An empirical model was proposed for the outlet parameters of the system and proposed an optimization strategy for its operating parameters, as well as the potential and energy performance was assessed through parameter analysis and multifactor optimization. The regional capability was demonstrated in three selected hot and humid regions. Thirdly, an experimental study was conducted to validate the response surface model, analyzing the energy consumption and air handling capacity of the πΈπΆπΈπ·π· system under various hot and humid conditions. The proposed system achieves πΆππ values ranging from 11.3 to 18.4 without compromising indoor comfort or facility compactness. Experimental studies of this new system provide the possibility of achieving high efficiency in air handling over a wide range of temperatures and humidity. Finally, A derivative system using photovoltaic/thermal-assisted desiccant regeneration is proposed based on the πΈπΆπΈπ·π·. The system used exhaust air as the working air source and solar energy as the heat source for desiccant solution regeneration. Two kinds of desiccants were tested in this system. The economics and overall energy performance of the system were analyzed. The key academic contributions derived from this thesis are summarized as follows: 1) Proposing a new dehumidification heat exchanger with counter-cross flow internal cooling, effectively managing indoor heat and moisture loads in challenging conditions. 2) Integration of a regenerative evaporative cooler within the πΈπΆπΈπ·π· system, enhancing energy performance through return air heat recovery. 3) Devlopment of simulation models of the new system and their experimental validations. 4) Detailed performance and applicability analysis of the πΈπΆπΈπ·π· system for typical hot and humid urban environments, demonstrating its capability to efficiently handle indoor heat and moisture loads without compromising comfort or compactness. This study may contribute to the field by demonstrating the practical application and efficiency of liquid desiccant and evaporative cooling technologies in managing air quality in hot and humid climates. |
| Rights: | All rights reserved |
| Access: | open access |
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