Conference Agenda

Conventional methods for producing superhydrophobic passive daytime radiative cooling coatings are considered inexpensive, however the majorities use fluorinated polymer. In this work a novel method, fluorine-free, developed for synthesizing porous structures coating by using low density polyethylene is presented. The method has precise control over the thickness and microstructure. Moreover, the materials and the machinery required to produce the coatings are minimal in comparison to the conventional methods, hence lowering the cost of production. The coating, poly-cool, exhibits superhydrophobic properties as well as radiative cooling capabilities with solar reflectance of 97.4% and emissivity of 91% within the atmospheric window. The coating consists of highly porous polyethylene and PDMS nanoparticles. The high porosity of polyethylene helps improve the reflectivity of solar irradiance whereas the PDMS nanoparticles tune the emissivity of the coating to match that of the atmospheric window (8 to 13m).

The performance of radiative coolers are directly affected by their constituting materials’ optical properties and micro-structures. Here, we investigate the effects of optical properties and microstructure on radiative cooling performance, namely solar reflectance and emittance at 9-13 µm region. The aim is to provide guidance to reach the ideal radiative cooler. Inspected phenomena are included but not limited to Mie resonance, light scattering, effective medium theory.

Daytime radiative cooling has emerged as a promising solution for continuous passive cooling. While significant progress has been made in material developments, questions persist regarding the potential large-scale deployment of this technology. Among the potential applications, two predominant uses of daytime radiative cooling materials are under study: passive roof cooling and water-cooling panels. Passive roof cooling involves the deposition of radiative cooling material on the roof’s surface to passively cool the building by reflecting incoming solar rays. The second application employs outdoor radiative cooling panels to passively cool water, which can be used to assist cooling systems. For instance, cooled water could sub-cool the cooling refrigerant, thereby improving the air conditioner's energy efficiency.

In the present study, a numerical assessment to compare the benefits of both application schemes for radiative cooling materials is conducted. For each application, the model predicts the energy savings achievable by each integration mode. Preliminary results indicate that prioritizing roof cooling applications would be most effective in tropical regions. The deployment of water cooling panels for refrigerant sub-cooling appears to be more beneficial in mid-latitude temperate zones. These findings suggest adjusted approaches based on climatic considerations for the optimal deployment of daytime radiative cooling technologies worldwide.

Remote sensing in thermal infrared bands (TIR) is largely dominated by cumbersome dispersive-type hyperspectral imagers, which usually require expensive and cryo-cooled quantum detectors to make up for their low optical throughput. Here, we present a compact and low-cost TIR hyperspectral camera based on the Fourier-transform approach. It combines an uncooled bolometer detector and a common-path birefringent interferometer made of calomel (Hg2Cl2). It features high optical throughput, an interferometric contrast greater than 90% even for incoherent radiation, spectral resolution tunable up to 4.5 cm-1, robust and long-term interferometric stability. Retrieving in a few minutes the infrared spectrum in all pixels of the TIR image, it could constitute a valuable tool for evaluating radiative cooling materials' spatial and spectral properties over extended areas. We test the capabilities of the instrument by measuring the emissivity map of different butterfly wings, which provide a natural example of radiative cooling.