The building sector consumes around half of the global energy produced and air-conditioning processes guzzle over 55% of building sector energy. The conventional refrigerant-based chillers, covering over 90% of the current cooling market, are not only energy-intensive but also have high ozone depletion and global warming potentials. Indirect evaporative coolers were introduced but they were difficult to commercialize due to their practical lower achievable temperature limits. All existing indirect evaporative coolers use hydrophilic interface to provide wet surfaces for evaporative potential. These hydrophilic surfaces not only increase heat transfer resistance but also provide excellent conditions, wet and damp surface, for mold formation. The treatment of mold is almost impossible as the height of the channel is only 3–5 mm and the fungus can be dangerous to health. Therefore, we proposed an innovative indirect evaporative cooling cycle in which there are no hydrophilic surfaces inside the system. The humidification of the working air is carried out before it is introduced into the wet channel. Also, the interface between dry and wet channel is only a thin aluminium foil that boosts heat transfer from supply air to working air in the transverse direction. A generic cell of 1800 mm long and 280 mm wide can produce 182.5 W cooling capacity. The measured coefficient of performance and effectiveness are 45 and 80% respectively for sensible cooling. This basic information of the proposed innovative indirect evaporative cooling system can be used to design a commercial unit as the total capacity is based on number of generic cells.
Bibliographical noteKAUST Repository Item: Exported on 2021-02-21
Acknowledgements: Detailed simulation and experimental investigation have been conducted of an innovative IEC system. The innovative aspects include (i) only external water supply via the WA stream with a humidifier and an induction blower. Hence, the fouling issues from wetted-fibre surfaces are mitigated, (ii) high heat transfer across the non-porous foil barrier is enhanced by direct water film evaporation, and water droplets are entrained in the flowing air of wet channels. Simulation and experimental results have an excellent agreement. The maximum COP value of 45 for the generic cell was recorded at 45 °C outdoor air temperature at 55% PA with respect to the product air. Also, the maximum effectiveness of the generic cell is measured as 80%. However, both COP and effectiveness are decreasing with respect to lower inlet air temperature, as the generic cell IEC is dependent on the evaporative potential of the WA. It is also noted being a passive cooler, capacity control must be supported with close monitoring of temperature and humidity of both working and product air which can then be used as control parameters of the operation of IEC.