Design and modeling of area-enhanced, bi-porous, evaporative macrochannel for building facade cooling

Facade-integrated evaporative cooling offers a pathway to high heat rejection for buildings with limited rooftop area. However, it needs to operate under fixed footprint and parasitic power constraints, requiring surface enhancement strategies that enable more efficient heat removal. We develop a fan-power-constrained conjugate heat-mass transfer framework to evaluate facade-integrable evaporative macrochannels. We show that hydrogel-only pin fins enhance evaporation into channels but provide little increase in base heat removal due to high internal thermal conduction resistance. To overcome this bottleneck, we introduce a Hydrogel Overlayer on Metal Scaffold (HOMeS) architecture that separates heat spreading and capillary wetting across pore scales. Bayesian optimization identifies near-optimal pin-fin geometries, which, for a 200 × 200 mm panel at a fan power density of 125 Wm^-2, deliver ~7 × higher base heat removal than a flat evaporating channel. We demonstrate that evaporative texturing provides significant performance improvement only when thermal coupling to the interface is preserved.