radiative cooling

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Comfort Problems Related to Radiation

On cold winter nights, we can feel chilly when our skin radiates heat toward cold window glass

Posted on Jun 16 2017 by Martin Holladay

Our homes include insulation to reduce heat flow through floors, walls, and ceilings. Some parts of our homes’ thermal envelopes (for example, insulated ceilings) are well insulated and have a high R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. ; other parts (like windows) have a much lower R-value. But during the winter, as long as we have an adequate heating system that keeps the indoor air temperature at 72°F, we should be comfortable — right?

Not quite. Even when the air temperature is held to a steady 72°F, occupants can be cold during the winter — especially if they are standing or sitting next to a large window.

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Image Credits:

  1. Images #1 and #2: Charlie Huizenga, Hui Zhang, Pieter Mattelaer, Tiefeng Yu, Edward Arens

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Night Sky Radiation

On a clear, windless night, roofing and window glass can get colder than the outdoor air temperature

Posted on May 26 2017 by Martin Holladay

Let’s say you walk into an unheated room. The air temperature is only 50°F. There is a wood stove in the room, but the wood stove is unlit.

Your body is at about 98°F. Since your body is warmer than absolute zero, it is radiating heat in all directions. (All objects that aren’t at absolute zero emit infrared radiation). The wood stove is cool — it’s at 50°F. Still, the wood stove is also radiating heat in all directions.

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Image Credits:

  1. Image #1: Aaswath P. Raman
  2. Image #2: Graham Finch - RDH Building Engineering

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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

Posted on Feb 22 2017 by Allison A. Bailes III, PhD

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.

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Image Credits:

  1. University of Colorado at Boulder

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