By Meghan Bialt-DeCelie ’19

Cooling systems are one of the largest and most inefficient consumers of electricity. The goal of cooling systems is to reduce the condenser temperature to below the ambient temperature. Evaporative cooling systems can achieve this, but they require a great amount of water loss to do so.

A new cooling alternative may be within reach as described in a study led by Eli Goldstein, PhD.  Scientists were able to demonstrate the use of radiative sky cooling to reduce the temperature of water used for cooling systems with a minimal use of electricity. This method of cooling uses panels that allow the passive transfer of heat to areas of much lower temperatures in outer space. The panel is comprised of three major components for heat from water to flow through: a radiative cooling surface, heat exchanger, and insulation. These panels are able to function under direct sunlight because they reflect most of the solar radiation and they emit heat in a wavelength within the atmosphere’s transparency window which falls between 8 and 13 μm. If heat is emitted within this wavelength range, it does not get trapped by the earth’s atmosphere.

Over the course of three days the radiative cooling panels were able to cool water flowing at a rate of 0.121 and 0.291 min−1 m−2 between 2° and 3° Celsius below ambient temperature. If used over the summer in a typically hot and dry area, the use of these panels is predicted to reduce electricity use of around 21%. Radiative sky cooling has potential, but its effectiveness should be studied on a larger scale.

References:

1. E. A. Goldstein, A. P. Raman, and S. Fan, Sub-ambient non-evaporative fluid cooling with the sky. Nature Communications 9, 17143 (2017). doi:10.1038/nenergy.2017.143.
2. Image retrieved from: https://commons.wikimedia.org/wiki/File:Air_conditioner.svg