Practical thermal performance correlations for a wet-coil indirect evaporative cooler

The objective of this research was to develop practical models for predicting the thermal performance of a wet-coil indirect evaporative cooler (IEC). Through statistical analysis of cooling and heat exchange effectiveness data generated by a simple ɛ − NTU (number of transfer units) method, simplified models returning the thermal performance of a wet-coil IEC were developed. Linear regression equations were derived as a function of the major design parameters and interactions that strongly affected the wet-coil IEC's performance. A pilot wet-coil IEC unit was built to validate the proposed models. Effectiveness data were obtained under a controlled range of operating conditions in an environmental chamber. Then, the energy-saving potential achievable by integrating a wet-coil IEC into a conventional variable air volume (VAV) system for pre-conditioning the outdoor air intake was quantitatively evaluated. The experimental results showed that more than 75% cooling effectiveness and 59% heat reclaim effectiveness could be achieved under wet and dry operating conditions, respectively. The experimental data acquired using the pilot unit agreed well with the thermal effectiveness predicted by the proposed models. Consequently, the VAV system integrated with the wet-coil IEC showed more than 45% reduced annual operating energy consumption compared with the conventional VAV system.