Development of a novel sorption-based dehumidification system

The required energy to control the temperature and humidity for human comfort is estimated as 50% of the building's total energy consumption. Several serious health problems which are caused by mildew, viruses, and reduction of air quality in buildings are all associated with excessive humidity. Humidity control also plays a vital role in greenhouse food production. Developing a compact and efficient dehumidification system for buildings and greenhouses is a necessity in order to reduce the energy consumption and greenhouse gas (GHG) emissions. Despite the advantages of "thermally-driven" liquid desiccant absorption systems over the other dehumidification systems, the research on them is still limited to laboratory-scale experiments rather than practical applications. The conventional packed-column absorbers in liquid desiccant dehumidification systems have fundamental limitations (a slow absorption process) and practical challenges (solution carryover, crystallization, and corrosion) that hinder their utilization in real dehumidification applications. In this research, a new design concept for absorption reactors is proposed for the dehumidification applications. The proposed reactor concept provides compactness (i.e high moisture removal rates per volume), permits working in the crystallization region, and eliminates the metal corrosion which is associated with the hygroscopic salts. This was achieved by creating spherical microreactors (i.e., microcapsules) that encapsulates the aqueous hygroscopic salt (such as LiBr) solution inside an elastic spherical semi-permeable membrane shell using a custom-built microfluidic device. A compact "packed-sheet" absorber that houses packed spherical microcapsules was designed, built, and tested for dehumidification applications. The results showed that the developed absorber had moisture removal rates per volume (of 75 g/s-m3) that were two folds higher than the conventional packed-column absorbers (35 g/s-m3). In addition, fundamental studies were presented to study the heat transfer from/to spherical particles. Moreover, a one-dimensional model that considers the coupled heat and mass transfer was developed to simulate the transient behaviour of the proposed packed-sheet reactor. The validated model was used to conduct a parametric study to reveal the impact of the various design and operating conditions, and to optimize the design. The results from the optimization study showed that the performance of the proposed design can be maximized to realize moisture removal rates of up to 135 g/s-m3 with a coefficient of performance of 0.25.