Cascaded liquid desiccant system for humidity control in space conditioned by cooled membrane ceiling and displacement ventilation

Abstract

Displacement ventilation (DV) combined with liquid desiccant membrane cooled ceiling (LDMC-C) is an efficient Heating, ventilation and Air conditioning (HVAC) system. However, the LDMC-C/DV has limited performance in office spaces located in hot and humid climates or characterized by high internal latent loads due to the inability to control the humidity. This study proposes a cascaded liquid desiccant system in which the liquid desiccant flow exiting the LDMC-C is directed into a liquid desiccant heat and mass exchanger in the DV supply duct to control the humidity in the space and conserve energy. To achieve this goal, an integrated model for different components of the cascaded liquid desiccant system is developed to predict the comfort level and the air quality inside the space as well as the energy consumption of the system. The model was validated experimentally in a climatic chamber. The validated integrated system model was applied to a case study to assess the effectiveness of the system in hot and humid climate. Two configurations of the LDMC-C and mass exchanger were simulated and found to provide acceptable humidity for comfort in the occupied zone of the space. Moreover, the cascaded system cooling and heating energy were found lower by 21.25% and 16.23% respectively in August when compared to a LDMC-C/DV, and to DV membrane exchanger system with different configuration. The cooling and heating energies were also lower in the cascaded system compared to a LDMC-C/DV while using conventional supply air dehumidification method.