Effective desiccant dehumidification system with two-stage evaporative cooling for hot and humid climates

This study examines the design and operation of a hybrid air conditioning system that uses 100% fresh air and integrates a solid desiccant dehumidification system with a two-stage evaporative cooling system to optimize the system operation with respect to energy and water consumption while maintaining occupant thermal comfort. The first stage consists of cooling a fraction of the dehumidified air stream using an evaporative cooling pad, mixing the cooled air with the remaining bypassed air fraction and then supplying it to the space in order to minimize water consumption and limit the indoor relative humidity to acceptable levels. The second stage consists of locally cooling the occupant's microclimate using a personalized evaporative cooler (PEC) that will allow for higher room bulk air temperatures. The system was implemented in an office space in Beirut and the optimization was carried using a derivative free genetic algorithm that handled three variables: the regeneration temperature; the air mass flow rate; and the fraction of air entering the evaporative cooler. The two-stage system achieved a 16.15% reduction in energy consumption and a 26.93% reduction in water consumption compared to a single-stage evaporative cooling system at the same thermal comfort level.