Analysis of the temperatures of heating and cooling sources and the air states in liquid desiccant dehumidification systems regenerated by return air

Abstract A typical liquid desiccant (LD) dehumidification system regenerated by return air is driven by a heating source and a cooling source to supply air with the required temperature and humidity ratio. This paper analyzes the specific relationship between the heating and cooling sources and the air states by both an analytical method and simulations. The circulating solution is the medium to transfer heat and mass between the air and the heating and cooling sources. The analytical results demonstrate that certain air states (fresh air, supply air, and return air) correspond to one particular solution circulation, which can only be accomplished by a certain pair of temperatures for the heating and cooling sources. With respect to the temperatures of the heating and cooling sources, the supply air state is more influenced by the latter. At a fixed temperature, a lower humidity ratio of the supply air demands a significant increase in the temperature of the heating source and a slight decrease in the temperature of the cooling source, resulting in a greater temperature difference between the two sources. At a fixed humidity ratio, a lower temperature of the supply air requires lower temperatures for both sources, with a subtle reduction in the temperature difference. For a certain supply air state, the humidity ratio of the fresh air is the major factor that determines the temperatures of the two sources; however, a large change in the temperature of the fresh air has little effect on the temperatures of the two sources.