Dynamic performance evaluation of porous indirect evaporative cooling system with intermittent spraying strategies

Air-conditioning systems consume a large amount of energy with the rising thermal requirement of indoor environments. Indirect evaporative cooler (IEC), which is recognized to partially substitute conventional airconditioning devices, has been studied extensively to supply the cool air at the cost of less energy in buildings. Existing literature reveals the benefits of employing porous media in a variety of heat exchangers. However, research on the utilization of porous material in the plate-type cross-flow IEC is still seldomly carried out in the area of its dynamic variation process and water spraying system optimization. In this paper, a simulation model of IEC with porous material on the secondary air channel surface (PIEC) is proposed with experimental validation. Effects of various parameters on the dynamic variation of the primary air outlet temperature have been quantitatively analyzed. Results show that the PIEC can produce cool air without spraying water for a period due to the water retention ability of porous media, rather than the conventional IEC that relies on consistent water spray to maintain the water film for evaporation. Thus, intermittent operational strategies of the PIEC water system could be achieved, and the energy consumption would be less compared with the traditional spraying mode. The longest non-spraying duration of the studied PIEC is 2410 s, which reduces 95.2% of water pump operation time compared with the conventional consistent spraying plan. The maximum coefficient of performance is up to 146.3, corresponding to 14.5 Hong Kong dollars daily operation costs saving simultaneously. In summary, the PIEC can contribute to a better performance with periodic water spraying modes, which is a competitive approach for cooling production.