Numerical Modeling and Performance Evaluation of a Three‐Stage Direct–Indirect–Direct Evaporative Cooler

ABSTRACT This study develops and evaluates a numerical model for a three‐stage evaporative cooling system based on a direct–indirect–direct (DID) configuration. Prior work has mostly examined single‐ or two‐stage systems, leaving three‐stage DID configurations underexplored, especially with stage‐resolved modeling. To address this, a single coupled finite‐difference framework has been developed that links direct evaporative cooling (DEC) and indirect evaporative cooling (IEC) processes to deliver consistent three‐stage predictions of temperature and humidity. The unified model, implemented in MATLAB with a finite‐difference scheme, is used to examine the DID cooler's response to different inlet air velocities, outdoor temperatures, and humidity levels. Simulations show that the three‐stage arrangement can achieve deeper temperature reductions than conventional single‐stage coolers while maintaining stable performance over a realistic range of operating conditions. For representative hot‐weather conditions in Rajshahi, Dhaka, and Khulna, the cooler delivers supply air temperatures up to 22.5°C below the outdoor air, with outlet relative humidity ranging from 67% to 99%. In addition, the volumetric cooling capacity of the three‐stage DID cooler increases almost linearly with inlet air velocity, reaching about 9.37–125.92 kW/m 3 over 0.5–5 m/s and rising further at higher outdoor temperatures. Model predictions agree closely with published experimental data, with maximum deviations around 1.36%, giving confidence in the stage‐resolved description. The results highlight the potential of DID evaporative cooling as a low‐energy option for buildings in hot, dry, or mixed climates, and also point to applications where very low supply‐air temperatures are desirable even at high humidity. The scope of this work is to extend the framework to additional climatic zones, integrate smart control and renewable power options, and explore improved pad and heat‐exchanger materials to further enhance durability and performance.