Energy efficiency of using a novel fertilizer-based liquid desiccant system to dehumidify indoor plant environments: An experimental analysis

Plant cultivation in controlled environments such as greenhouses and indoor farms has several advantages over field agriculture and can therefore be an important part of improving the sustainability of global food systems. Among the requirements for effective cultivation in indoor environments is the need to control humidity, but in general the energy cost associated with dehumidification is high. In this study, we evaluate the energy efficiency of a novel dehumidification concept that uses cold concentrated fertilizer as a liquid desiccant solution in a membrane-based contactor. This is the first ever experimental analysis of the process’ energy efficiency – which we define as the amount of energy required to cool desiccant relative to the amount of water vapor removed from the indoor environment. Specific energy use as low as 1.45 Wh per g of water vapor, is observed during laboratory testing when super concentrated calcium nitrate solution is maintained at 8 °C. Assuming a coefficient of performance of 5, this translates to specific work of only 0.29 Wh/g. As the batch of fertilizer solution is recirculated and concentration drops, specific work is found to increase to 0.40 Wh/g. The need to adjust fertilizer temperature to minimize specific work in response to changing concentration is clearly shown. Testing is also conducted with several multi-ion fertilizer blends, and similar results are observed. These energy efficiency results compare very favorably with other dehumidification technologies and standards, suggesting a promising future for fertilizer-based dehumidification.