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Building Science

This Radiative Cooling Material Could Supplant Traditional Air Conditioners

A new study shows a breakthrough in the cooling effect of a material that’s easy to manufacture

This plastic film promotes daytime radiative cooling.
Image Credit: University of Colorado at Boulder

When it’s hot out, we want cold. At night, we like to be able to turn on the lights. During the daytime, it can be hard to find the darkness.

All these things — hot and cold, day and night, light and dark — can seem like opposites. Chinese philosophy suggests, however, that these opposing forces, known collectively as the yin and the yang, aren’t separate. And science has proved it. Let me tell you about the latest yin and yang science and how it could revolutionize air conditioning.

Willis Carrier’s air conditioner

For a hundred years we’ve been using these mechanical systems called air conditioners to remove heat and humidity from buildings. It was one of many revolutionary technologies to come out of the twentieth century. Because of air conditioning, places like Orlando and Phoenix have far higher populations than they probably would otherwise.

An air conditioner works by cycling the indoor air through a box that contains a fan to move the air and a cold coil to cool and dehumidify the air. It pulls in air from the home, sends it over the cold coil, and then sends that cooler, drier air back into the house. Wonderful!

But what happens to the heat? The heat from the indoor air goes into that cold coil. The coil is filled with a refrigerant, a material that can get cold. After it absorbs the indoor heat, the refrigerant travels to the outdoor unit (in a typical split system). The outdoor unit uses a compressor and another coil to dump the heat into the outdoor air. Yes, other types of air conditioners exist, but the vast majority are of the type I just described: split-system, air-source air conditioners. (For more detail on how they work, see my…

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One Comment

  1. Charlie Sullivan | | #1

    I'd rather have the reverse
    The similar concepts I've seen before attempt to do the reverse: block solar radiation, ideally by reflecting it, and transmit thermal radiation. Then you can have a surface beneath the film radiating to the sky while being protecting from incoming heat, including incoming solar radiation, and incoming convection from the outdoors. That allows cooling to below ambient temperature.

    On the other hand, the way they tested this film, by keeping it at a temperature equal to the air temperature, illustrates that it would be difficult to use it to cool anything below ambient temperature.

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