Direct expansion, Enhanced dehumidification, Operational characteristics, Experimental prototype, Mathematical model
Direct expansion (DX) air conditioning (A/C) systems are widely used for controlling indoor air temperature and humidity in various buildings in hot and humid climates since they are simpler and more energy efficient, and generally cost less to own and maintain. However, it is often problematic for a DX A/C system to provide desired humidity control due to the current system design trends, variable weather conditions and the commonly used control strategies for DX A/C systems. Therefore, a standalone DX based enhanced dehumidification air conditioning (EDAC) system is proposed to provide suitable indoor humidity control at different seasons. There are two evaporators in the EDAC system, thus it could act as a dehumidifier (ADO mode) on the days when less or no additional cooling is required by employing one evaporator as a reheating coil, or act as an enhanced dehumidification A/C system (EDAC mode) by functioning two evaporators to separately deal with sensible and latent cooling. A prototype experimental EDAC system was established in a laboratory. The operational characteristics of the EDAC system at ADO mode in terms of the moisture removal capacity (MRC), the specific moisture extraction rate (SMER) and the resulted supply air temperature were investigated and reported in this paper. Firstly, the experimental results on operational characteristics are reported. Secondly, the development of a steady-state mathematical model for the ADO mode of the EDAC system is presented. The developed model was thereafter used to study the influence of different sizes of the evaporator and the reheating coil on the operational characteristic of the EDAC system at ADO mode. The study results could lead to a better understanding of the operational characteristics of the EDAC system, facilitating its design, operation and control.