Liquid desiccant dehumidification membrane ceiling-displacement ventilation system effectiveness with optimized operational strategy -

Abstract

The performance of the chilled ceiling (CC) displacement ventilation (DV) systems is constrained by latent load removal capacity and associated cost of supply air dehumidification to prevent condensation on the chilled ceiling. In this study, a liquid desiccant dehumidification membrane cycle (LDMC) is introduced and mathematically modeled to replace the chilled ceiling to remove directly both latent and sensible load directly from indoor space through the liquid desiccant ceiling membrane. The desiccant system is coupled with displacement ventilation system to enhance the indoor air quality at 100percent fresh supply air. Solar energy is used as thermal energy source required for the regeneration of the desiccant. The operation of the system is simulated using integrated models of the various components of the hybrid system and an optimized operational strategy is adopted based on genetic algorithm to improve performance while maintaining thermal comfort and good air quality. The optimized parameters for system operation are the DV supply flow rate and temperature and the desiccant temperature at the inlet of the ceiling membrane. The model of the hybrid LDMC-C-DV system and its optimization were implemented for a case study consisting of an office during the month of August in Beirut hot and humid climate. When using optimal set points, a decrease of 49percent in energy consumption is observed when compared to the conventional CC-DV system while comfort and IAQ were satisfied. In addition, a ceiling temperature (as low as 16ºC) was attained by the membrane ceiling which was lower than air dew point temperature when compared to conventional CC system.