Energy-Efficient Dehumidification of Controlled Plant Environments Via the Application of Fertilizer-Based Liquid Desiccants

Abstract

To address food security challenges due to population growth, controlled plant environments have become popular because they ensure crop production throughout the year in contrast to open field farming. However, one of the major hurdles in such environments is humidity buildup which has a detrimental impact on crop quality and productivity. Conventional dehumidification strategies such as ventilation, refrigerant-based systems, liquid or solid desiccants, etc. are deployed to tackle this but are often energy intensive and costly. To address this issue, this dissertation proposes the use of fertilizer solutions as a novel and energy efficient method to dehumidify indoor plant environments. This dissertation establishes the thermodynamic limits and energy saving potential of fertilizer-based liquid desiccant. It then implements transport modeling to provide a more realistic assessment of energy use, followed by comprehensive experimental studies. Finally, it demonstrates the real-time dehumidification of humid air inside the functional plant chamber. From thermodynamic analysis it is found that the fertilizer desiccants consume half the energy required for conventional liquid desiccants systems by eliminating desiccant regeneration. This study also shows energy savings for different crops taking into account the dehumidification load (evapotranspiration) and the fertilizer requirement for each crop. Based on thermodynamic analysis, energy savings for common crops range from 0.2 to 0.7 kWh/plant/day. Building on this, transport modeling examines the influence of fertilizer concentration, temperature and fluid circulation rates on the specific energy of dehumidification of fertilizer-based desiccant systems. The results show that minimum specific work input is minimized to 0.16-0.24 kWh/kg at vapor flux level of 1.2-1.6 g/m2/h by adjusting desiccant temperatures. Following this, the comprehensive experimental study was conducted on a lab-scale test bench to measure the system’s energy use for different fertilizers, concentrations, and temperatures. The experiments confirm competitive energy use as low as 0.29 kWh/kg and pinpoint the importance of managing fertilizer temperature to optimize the system’s energy efficiency. Finally, the real-time application of a fertilizer-based desiccant dehumidification system was demonstrated in a closed plant chamber with hydroponic arugula. The fertilizer desiccant effectively maintained different humidity setpoints inside the chamber over the complete growth cycle of the plants.