|dc.description.abstract||Freshwater scarcity is a major obstacle of growth and prosperity for many nations in the world. Conventional centralised freshwater supply options in general are depleting and the unanticipated social and environmental costs of alternative solutions are emerging. Similar to energy, water sector may also need to explore renewable decentralised freshwater alternatives such as atmospheric moisture as discussed in this thesis. For hot and humid regions, condensed water is unwillingly discharged out of air-conditioning systems and the energy consumed for condensation to full humidity comfort level is wasted. Only a few limited small-scale experimental studies and no systematic modelling have been found in the literature on atmospheric water capture. This thesis works to fill some of this gap by developing an understanding of the fundamental factors that have and continue to challenge the development of technologies for atmospheric water capture.
In this thesis, a framework is developed encompassing several modelling elements for assessment of feasibilities of moist air dehumidification technologies for atmospheric water capture. This framework integrates technical, meteorological and economic modelling elements. In the technosphere, detailed models of thermoelectric and absorption cooling are developed as potential dehumidification technologies. These models are interfaced to renewable energy input algorithms, namely solar photo-voltaic (PV) and solar-thermal. Solar energy collection technologies are also part of this framework which includes models of solar PV systems and evacuated tube collectors (ETCs). Studies of such integration of solar-assisted dehumidification and associated analysis for atmospheric water capture are limited in the literature. Fundamental solar energy input models are developed and interfaced to meteorological data to provide geographical location specific analysis. In this way the model framework is generic and applicable to any location on Earth where meteorological data is available. Finally, an economic modelling component completes the framework to provide comprehensive techno-economic assessments of different technologies for atmospheric water capture. This framework therefore provides a tool to support decision making related to feasibilities of different technologies associated with water capture from atmosphere.
Along the way to developing the modelling framework, a detailed categorisation of dehumidification systems is established and a model to estimate condensation rates based on local climate data is built. The hurdle of condensation energy requirement is highlighted through simulation results. To alleviate this energy burden, an assessment of renewable solar energy input is then made. Techno-economic challenges for two different climates, Sydney and Abu Dhabi are examined and compared throughout this thesis providing comparisons for water and energy profiles. Several modelling components are developed and presented f or this purpose, requiring implementations in different modelling environments including Matlab, Trnsys, Homer and VBA.
Based on the operation principles, dehumidification techniques are categorised into three categories in this thesis (Fig. 2.2). Gas separation membrane technologies were modelled but are not included in this thesis presentation because initial analysis showed they suffer from several key technical drawbacks primarily associated with the sensitivity to fluctuations in feed air temperature and humidity. Technologies in the cooling surfaces category in general use electrical or mechanical power to circulate and compress a refrigerant and cooling down conductive surfaces or coils. This process aims to decrease the temperature of moist air stream below dew point where water vapour molecules start to bond and settle forming the condensation stream. Amongst a wide range of cooling surface techniques, thermoelectric cooler (TEC) devices are attachable to cooling surfaces without using a refrigerant medium. A conceptual TEC dehumidification system is modelled in this thesis targeted at moist air streams with ambient temperature ranges (10-50) C and relative humidity ranges (10-100) %. For large-scale water production, the energy cost is calculated and found to be the major factor contributing to more than 95% of the total cost of generated water. This model is implemented for Sydney and Abu Dhabi case studies by using their annual typical meteorological weather data. This shows the generic nature of the applicability of the model and in this specific comparison confirms the influence of energy consumption over the cost of generated water in those two very different regions. However, lower local utility rates and favourable climatic conditions for dehumidification in Abu Dhabi show significant differentiation in water cost over Sydney.
To confront excessive energy demands for atmospheric water capture, the idea of facilitating solar energy via PV panels is examined in this thesis. A comprehensive solar algorithm is developed and implemented to optimise solar collector positioning and for calculating solar penetration ratios for Sydney and Abu Dhabi. As far as the author is aware, this is the first time such optimal position calculation for Sydney and Abu Dhabi is done. It is found that optimal surface tilt angles for Sydney and Abu Dhabi are 32 and 22 respectively, while optimal surface azimuth angles for Sydney and Abu Dhabi are 195 and 16 respectively. This algorithm is generic in its structure allowing such calculation to be executed for any city in the world and is later used in this thesis for calculations associated with a new ETC diffuse at reflector (DFR) model. This thesis also presents a detailed economic model for prediction of utility costs with consideration for CAPEX, OPEX, subsidies and carbon taxation. It is found that investing a $338,000 on a PV array of 100 kW at current utility rates can meet 53% of energy demand of proposed dehumidification system and reduce LCOE by 6 c/kWh in Sydney. Solar PV array at current utility rates to feed proposed dehumidification system is found to be uneconomical for Abu Dhabi.
Solar-thermal collectors represent an attractive option for driving refrigeration techniques. Evacuated tube collection technology has progressed significantly over the last few years and this technology is assessed in this thesis as a heat collector for absorption chillers. The role of DFR to improve the performance of ETC is highlighted and modelled. Results showed that DFR can significantly improve ETC performance by an average of 24.1% for Sydney and 22.9% for Abu Dhabi respectively. The optimisation of DFR is therefore an important factor for the enhancement of this solar energy collection technology and the algorithm developed in this thesis is generically applicable across geographical locations.
The concept of solar refrigeration is reviewed and investigated for the implementation of sorption refrigeration. Sorption techniques use low-grade heat sources such as solar energy to convert thermal heat into chilling effect. This function is investigated for dehumidification of a moist air stream via cooling coils. A conceptual absorption model is developed in TRNSYS to calculate overall energy demand and water productivity. An ASHRAE algorithm is developed and implemented to cross validate the TRNSYS model. This absorption model was used in an optimisation analysis and showed water productivity improvement of 29% for Sydney and 34% for Abu Dhabi, while energy demand can be reduced by 22% for Sydney and 55% for Abu Dhabi. Unlike Sydney, the cumulative cost of generated water is declining over time in Abu Dhabi reaching $15 /kL. If this system is projected to work during the day only, solar penetration ratio will substantially increase and could meet the entire diurnal load for dehumidification in Abu Dhabi. If the capital cost of developing such system is affordable, absorption model can be further optimised to specifically match local conditions in respect to solar radiation and energy sources where the cost of generated water can economically compete with other conventional sources. In regions such as Abu Dhabi, the idea of having small-scale dehumidification system where the energy demand is mostly met by solar radiation and the volume of generated water is freely controlled and managed by household seems appealing.||en_AU|
|dc.publisher||University of Sydney.||en_AU|
|dc.publisher||Faculty of Engineering and IT||en_AU|
|dc.publisher||School of Chemical and Biomolecular Engineering||en_AU|
|dc.subject||water-supply engineering technological innovations||en_AU|
|dc.title||Modelling framework of solar assisted dehumidification system to generate freshwater from "Thin air"||en_AU|
|dc.type.pubtype||Doctor of Philosophy Ph.D.||en_AU|
|Appears in Collections:||Sydney Digital Theses (Open Access)|