Transient modeling framework of indirect evaporative coolers under intermittent spraying operation

초록

This study proposes a transient modeling framework for an indirect evaporative cooler (IEC) operating under intermittent water spraying conditions. Most existing indirect evaporative cooler models rely on fully wetted steady-state assumptions or complex computational fluid dynamics (CFD), which restrict their practical application in spray-cycle design and control. A simplified transient modeling approach is presented as an alternative to computationally intensive simulation methods by employing thermodynamic equilibrium equations to predict the dynamic supply air temperature during wetting and drying cycles. The framework is based on three experimentally determined transient coefficients: wetting-phase time constant (α), drying-phase time constant (β), and dimensionless coupling parameter (τ). These coefficients are expressed as polynomial regression correlations of inlet air conditions and flow rates, and the model was evaluated within the tested operating domain. For independent validation conditions, the model reproduced the dynamic supply air temperature with a mean absolute deviation of 0.3 K relative to experimental data. For the evaluated control cases, intermittent spraying increased the maximum coefficient of performance (COP) to 12 while reducing pump operation time by 97%. A marginal cooling capacity penalty of approximately 2.4% is observed; however, the substantial reduction in energy input provides a more favorable balance for sustainable design. Finally, this study provides a practical low-complexity tool for developing threshold-based control strategies, supporting the advancement of more intelligent and responsive evaporative cooling systems.

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