Analysis of desiccant dehumidification and evaporative cooling in hot and humid climates

Abstract

Although it is generally accepted by academics that the interior distribution of specific humidity is uniform, literature or specific research on the spatio-temporal distribution of humidity is lacking. This work aims at studying the use of a time-varying humidity inlet such as that due to an evaporative cooling and desiccant dehumidification system to examine the resultant specific humidity variation in an internal space containing a number of sensible and latent heat sources. As part of this research, this study has carried out an experimental campaign in a test chamber using a number of temperature and humidity sensors to measure these parameters at particular points inside the chamber. A numerical model was then set up and validated to understand the flow physics and species transport occurring in the room, with a focus on investigating the specific humidity distribution in such a confined space. The numerical model shows that in regions of higher air velocities close to the test subjects, a lower mass of water vapour was detected. Particularly under low inlet velocities, and therefore low mixing, stratification of humidity was noticed with the denser, less humid air at the lower levels. When low mixing is present, and when the initial inlet and room humidity values are similar, a high humidity source results in the formation of a bubble of humid air at low level which eventually reaches a breaking point, after which mixing of humidity occurs throughout the room. On the other hand, when the inlet and room humidity are greater than 30% relative humidity at the start of the experiment, then the breaking point has already been exceeded, segregation of humidity does not occur, and mixing of the interior space ensues. The results from this thesis can find important applications in the fields of HVAC design, building conservation and electronics environmental design.