Library Subscription: Guest
Home Archives Officers Future meetings American Society of Thermal and Fluids Engineering
Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Passive directional daytime radiative cooling system

Bikram Bhatia
Department of Mechanical Engineering, Massachusetts Institute of Technology

Yichen Shen
Department of Physics, Massachusetts Institute of Technology

Melissa Gianello
Department of Mechanical Engineering, Massachusetts Institute of Technology

Arny Leroy
Department of Mechanical Engineering, Massachusetts Institute of Technology

Marin Soljačić
Birck Nanotechnology Center, Electrical & Computer Engineering, 1205 W. State St., West Lafayette, Indiana; Department of Physics, Massachusetts Institute of Technology

Evelyn N. Wang
Device Research Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Abstract

Air conditioning and refrigeration constitute a significant portion of our energy needs. Passive approaches exploiting high atmospheric transparency in mid-infrared wavelengths (8-13 µm) to cool terrestrial objects by radiating heat to the low temperature upper atmosphere offer a promising low-cost refrigeration solution. Few recent studies have demonstrated passive daytime radiative cooling to below ambient temperatures by using spectrally selective photonic crystal emitters [1,2]. In this work, we show that higher cooling powers of up to 100 W/m2 and minimum temperatures of 17 °C below ambient during daytime are possible using a simple blackbody emitter. Unlike previous work on daytime radiative cooler designs that rely on complex photonic structures we use a polished aluminum reflector, physically separated from the emitter, to reflect the direct solar radiation. In addition, we use a ZnS nanoparticle-infused polyethylene membrane which reflects ~80% of the diffuse solar radiation and also serves as a convection cover. The proof-of-concept radiative cooler was tested under the sun and at night and its performance was analyzed based on the relative contributions of different heat transfer pathways − incoming and outgoing atmospheric radiation, incoming solar irradiation and conduction and convection losses to the surroundings. Overall, we show cooling performance enhancement by decoupling the reflector from the emitter to minimize the effect of solar absorption which is the biggest bottleneck to the performance of state-of-art photonic emitters. The simple geometric optics based approach demonstrated in this work could lead to low-cost, high-performance passive radiative cooling solutions.

Check subscription Publication Ethics and Malpractice Recommend to my Librarian Bookmark this Page