The motivation of this research project was in response to problems of re-condensation in drying, reduced drying rate encountered by the food and beverage packaging industry which led to the aim of developing a better performing drying system as well as achieving high energy efficiency. A hybrid dryer suited for rapid drying applications is designed, constructed and experimentally tested and considered in atmospheric environment only. The system employs a heat pump in conjunction with a heat reactivated desiccant wheel to provide an efficient drying capability and supply low dew point temperature (DPT) conditions. The combined system utilises the heat dissipated by the condenser in regenerating the desiccant wheel, to increase the economic feasibility of such a hybrid system. Up to 60% heat energy can be saved by using the hybrid system in the rapid surface drying applications. Mathematical models are developed to obtain the correlations among the design operating and performance parameters of the dehumidification systems. The mathematical models can be used to estimate the performance of the hybrid system as well as the performance of the individual components of the system. A prototype model was designed, fabricated and tested. The experimental facility consisted of a heat pump desiccant dehumidifier with the new ecological R134a as a refrigerant which used the heat dissipated by the condenser. An analysis of the experimental data was conducted to determine the practical relationship between the operational parameters (COP, ma and TR) and performance parameters (SMER, DPT and ε) of the system. The observed behaviours of the test cases are suggested to be governed by a specific combination of the operation parameters. The analysis shows that the proposed hybrid system can deliver supply air at a much lower DPT compared with the single refrigerant circuit and a desiccant wheel. It is shown that the specific moisture extraction rate (SMER) for conventional dryers is 0.5 - 1 kg/kWh and SMER for heat pump based system is 3 - 4 kg/kWh whereas the hybrid system achieves SMER >5 kg/kWh. By operating the combined system in tandem, a greater amount of dehumidification could be realised due to the improved ratio of latent to the total load. The present research also confirms the importance of improving heat recovery to improve the performance of a heat-pump-assisted drying system.

Controlled environment agriculture allows the production of fresh food indoors from global locations and contexts where it would not otherwise be possible. Growers in extreme climates and urban areas produce food locally indoors, saving thousands of food import miles and capitalizing upon the demand for fresh, tasty, and nutritious food. However, the growing of food, both indoors and outdoors, consumes huge quantities of water - as much as 70-80% of global fresh water supplies. The utilization of liquid desiccants in a closed indoor agriculture cycle provides the possibility of capturing plant-transpired water vapor. The regeneration/desalination of these liquid desiccants offers the potential to recover fresh water for irrigation and also to re-concentrate the desiccants for continued dehumidification. Through the utilization of solar thermal energy, the process can be completed with a very small to zero grid-energy footprint. The primary research in this dissertation focused on two areas: the dehumidification of indoor environments utilizing liquid desiccants inside membrane contactors and the regeneration of these desiccants using membrane distillation. Triple-bore PVDF hollow fiber membranes yielded dehumidification permeance rates around 0.25-0.31 g m-2 h-1 Pa-1 in lab-scale trials. A vacuum membrane distillation unit utilizing PVDF fibers yielded a flux of 2.8-7.0 kg m-2 hr-1. When the membrane contactor dehumidification system was applied in a bench scale controlled environment agriculture setup, the relative humidity levels responded dynamically to both plant transpiration and dehumidification rates, reaching dynamic equilibrium levels during day and night cycles. In addition, recovered fresh water from distillation was successfully applied for irrigation of crops and concentrated desiccants were successfully reused for dehumidification. If applied in practice, the liquid desiccant system for controlled environment agriculture offers the potential to reduce water use in controlled environment agriculture by as much as ~99%.

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