Performance analyses of a new system for water harvesting from moist air that combines multi-stage desiccant wheels and vapor compression cycles

Abstract

This paper discusses effective ways to harvest water from air for residential use in dry climate area. An air handling process was proposed to humidify the air through multi-stage desiccant wheels before being dehumidified by the evaporator to harvest water. This approach not only increases the evaporating temperature but also increases the water harvesting rate (WHR) greatly. Two configurations of multi-stage desiccant wheels were compared, and proper desiccant wheel structure, length and number of stages were suggested. As for the energy system, two configurations of heat pump system (HPS) were compared and heat recovery is highly recommended, which can increase the system performance by around 70%. Effects of condensing temperature and outlet humidity ratio of air after water harvesting on WHR and water harvesting efficiency (WHE) were studied. When the ambient condition is 40 °C and 5 g·kg−1, it is suggested to be operated under the condition that ωreg,out is 6 g·kg−1 and tC is 90 °C. WHR and WHE can reach 32.5 kg·h−1 and 1.26 kg·kWh−1, respectively. Performances of the system, which adopts MSDW-2 and HPS-2, under different ambient conditions were studied and ωreg,out ranges with high WHE were summarized for different ranges of ωambi.