Regenerator Inlet Air Relative Humidity Effect
Figure 3.21 presents the effect varying the inlet air relative humidity from 20 to 80 % has on the performance of the regenerator. Figure 3.21a demonstrates that the outlet solution temperature and concentration are inversely proportional to inlet air relative humidity. Furthermore, Fig. 3.21b demonstrates that as the relative humidity of inlet air increases, the air absolute difference and latent effectiveness reduces. This is due to the fact that as relative humidity increases, the vapour pressure of the air increases. This results in a smaller vapour pressure differential between the solution and air, and thus less mass transfer. Lower inlet air relative humidity means the desiccant solution at a specified inlet condition can be regenerated to a higher concentration.
Fig. 3.22 a, b Inlet air temperature effect on regenerator performance
Regenerator Inlet Air Temperature Effect
Figure 3.22 presents the effect varying the inlet air temperature from 20 to 35 °C has on the performance of the regenerator. Similar to the relative humidity effect, the vapour pressure of the inlet air increases with rising temperature. Figure 3.22a demonstrates that the outlet desiccant solution mass concentration is lower with increasing inlet air temperature i.e. it is re-concentrated to a lesser degree. Figure 3.22b demonstrates that the air absolute humidity difference and latent effectiveness reduces as inlet air temperature increases.
Although good cooling capacity has been demonstrated in hot and humid climatic conditions, regeneration capacity reduces with increasing inlet air relative humidity and temperature. The successful application of liquid desiccant air conditioning is therefore location and climatic specific. When operating the regenerator on fresh outside air, liquid desiccant system performance will be poorer in hot and high humid climates.
In this parametric study, the inlet air condition to the regenerator has been assumed to be equal to the fresh air used in the dehumidifier. However, as highlighted in Sects. 3.5.2.1 and 3.5.2.2 regeneration capacity is higher with a lower inlet air relative and temperature. In a building application, fresh conditioned air is supplied to the space from the dehumidifier. The mass of supply air must be balanced with extract to remove internal gains and prevent pressurisation of the space. The extracted room air will be stale, thus it cannot be used again for human comfort purposes. However it can be used for regeneration purposes. This is favourable as it will have a lower temperature and relative humidity than the outside fresh air, thus improving the performance of the regeneration process (Dwyer 2014).
