Two-stage air-dehumidification system for the tropics - experimental and theoretical analysis of a lab system
In tropical climates, a rising demand for active air-conditioning leads to a strong increase of electricity consumption. Compared to the energy demand for the sensible cooling of air the high humidity (in the order of 20 g water per kg dry air) in the tropics results in a significantly high air-dehumidification load. Handling the dehumidification load and sensible cooling load separately can reduce the electricity demand for air-conditioning considerably if the dehumidification is driven by heat energy (e.g. solar thermal or waste heat) instead of electricity. At the Solar Energy Research Institute of Singapore (SERIS), an experimental two-stage air-dehumidification system consisting of a membrane unit and an adsorption based desiccant unit, has been installed and analysed. The membrane unit pre-dehumidifies the ambient air, which is then further dehumidified and simultaneous evaporatively cooled by an Evaporatively COoled Sorptive (ECOS) dehumidification and heat exchange unit. The aim of this study is to evaluate the dehumidification performance of the two-stage air-dehumidification system under tropical climate conditions and different operating parameters such as air flow rate and regeneration air temperature. A numerical model was developed for the ECOS and the membrane unit in MATLAB which was then coupled with TRNSYS software in order to create a model for the two-stage dehumidification system. The results of our investigations show that the two-stage system is able to dehumidify ambient air by 8 to 10 g water per kg of dry air under the warm and humid climate conditions of Singapore. Thermal COP of up to 0.6 was obtained.