Applicability of a dedicated outdoor air system assisted by isothermal dehumidification and evaporative cooling

Abstract

A dedicated outdoor air system (DOAS) assisted by an isothermal dehumidifier and an indirect evaporative cooler is proposed, and its energy-saving potential is evaluated based on detailed simulations. In the proposed system, an isothermal dehumidifier accommodates the latent cooling load and an indirect evaporative cooler assumes a sensible cooling load. The energy performance of the proposed system was evaluated by comparing it with two conventional dedicated outdoor air systems: a DOAS with a desiccant wheel and a DOAS with a cooling coil. The results indicate that the proposed DOAS can accommodate sensible and latent cooling loads, but it consumes 10% more operating energy because of the low coefficient of performance (COP) (0.67) of the isothermal dehumidifier, despite the free cooling operation by the indirect evaporative cooler. For comparable energy performance, the proposed system requires the COP of the isothermal dehumidifier to be greater than 0.78, which is achieved through improvements in the membrane selectivity and vacuum pump (compression ratio and isentropic efficiency).