Original title: Round-the-Clock Sub-Ambient Cooling via Dynamic Sky View Factor Steering
Qiuyu Chen, Minghao Dong, Zheng Zhang, Xiaodonog Zhao +2 · September 2026
Cooling things down usually takes electricity. Passive daytime radiative coolingA way of cooling an object by radiating heat away as infrared light, which can escape through the atmosphere to space. cools objects without power by sending heat into cold outer space. Most cooling setups lie flat, so they cannot adjust as the sun moves or clouds pass, which wastes cooling potential over the 24-h cycle. Inspired by how sunflowers track the sun, researchers built a dynamic sky view factorA measure of how much of the sky an object can see; more sky means more heat can escape. steering system. It works by actively tilting the cooling surface to the best angle throughout the day and night. This movement allows even a near-blackbody surface to achieve sub-ambientBelow the temperature of the surrounding air. cooling during a hot noon. When tested with a selective surface, the steering system increased cooling power by 135% over a static setup, potentially saving up to 200 kWh/m^2 of annual electricity in cities worldwide.
Imagine trying to keep a bowl of soup cool on a sunny windowsill. If you leave it in the sun, it warms up, so you want to keep it in the shade. But the shade moves as the sun crosses the sky, so you keep sliding the bowl to stay in the shade. In this paper, the bowl is the cooling panel, the sun is the heat that warms it, and the system tilts the panel to keep it facing the cold sky instead of the sun.
Air conditioning and refrigeration guzzle electricity, especially during peak daytime hours. This device cools without any electricity input, and it works even under the hot sun, so it could cut energy use in buildings and cold chains. The projected savings of up to 200 kWh per square meter per year in some cities show the scale of the opportunity.
The abstract doesn't say how much energy the tilting mechanism itself consumes, how durable it is over years, or how the 135% improvement scales to other emitters and climates. The 200 kWh/m^2 saving is a modeled maximum from case studies, not a measured annual figure, and the experiments are limited to a typical hot noon rather than a full year.
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Round-the-Clock Sub-Ambient Cooling via Dynamic Sky View Factor Steering — Qiuyu Chen, Minghao Dong, Zheng Zhang et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.