Humidity control in a space conditioned by a liquid desiccant membrane chilled ceiling with displacement ventilation system.

Abstract

The combined liquid desiccant membrane cooled ceiling (LDMC-C) with displacement ‎ventilation (DV) removes humidity directly from the space. It is an effective method for ‎providing thermal comfort and good air quality since it can operate at lower ceiling temperatures ‎compared to conventional chilled ceiling. However, LDMC-C-DV system does not control ‎humidity in the lower occupied zone which may lead to discomfort and health problems if ‎humidity increases due to changes in occupancy or to high humidity in supply air. ‎ In this work, a method for humidity control is proposed where fraction of the dehumidified ‎cool dry air adjacent to the LDMC ceiling is extracted from the exhaust stream and mixed with ‎the DV supply air stream. The strategy reduces the moisture content of the mixed DV supply air ‎without the need to use any other dehumidification technique in the supply duct. This leads to re-‎establishing of the thermal comfort conditions in the occupied zone; reducing the cooling ‎requirements of the DV system, and resulting in energy savings. To study the system ‎performance during transient loads, a time-dependent mathematical model of the LDMC-C ‎system was developed and validated experimentally. The validated LDMC-C transient model ‎was then integrated to the mixed DV space model and was applied to a case study to ‎demonstrate its effectiveness in providing acceptable humidity and air quality in the occupied ‎zone and to assess its energy performance. It was shown that during high latent load hours, the ‎relative humidity dropped by an average of 8.72percent in the occupied zone within a period of 12 ‎minutes. In addition, when mixing strategy is adopted, energy savings of 24percent were achieved ‎compared to conventional dehumidification in the supply duct.‎