Experimental evaluation of a commercial scale dew-point cooler with different air distribution configurations

Abstract

Dew-point evaporative coolers based on the Maisotsenko cycle (M-cycle) offer significantly higher energy efficiency than conventional vapor-compression cooling systems while avoiding refrigerant emissions. However, their performance depends on airflow configuration, working air ratio, and the recirculation strategy used to generate evaporative cooling. In this study, a commercial-scale cross-flow M-cycle indirect evaporative cooler with a maximum cooling capacity of 12.2 kW (3.5 tons) was experimentally evaluated under different airflow and recirculation configurations. The system incorporated two controllable recirculation stages that allowed independent adjustment of the working air ratio, r, and a newly defined working air distribution ratio, r_d, representing the distribution of recirculated air drawn from upstream and downstream sections of the dry channel. Experiments were conducted across a wide airflow range (100-11,000 m^3/hr) and varying inlet humidity conditions while maintaining constant inlet temperature. The results show that increasing the working air ratio enhances the temperature drop and dew-point effectiveness but reduces the coefficient of performance (COP) due to increased fan power consumption and pressure losses. An optimal working air ratio of r=0.33 was identified for maximizing cooling capacity and COP. The study further demonstrates that preferentially drawing equivalent volumes of recirculated air from downstream and upstream of the dry channel significantly improves performance. The optimal working air distribution ratio was found to be 1.1 <= r_d <=1.3, yielding the lowest product air temperature and highest COP. These findings highlight the importance of airflow distribution design in M-cycle heat exchangers and provide guidance for optimizing recirculation strategies in large-scale dew-point cooling systems.