At night sure, in the day time the sun is adding heat across a wide band of frequencies. This heats up less, but does not drop below ambient temperature in full sunlight.
The advantage of targeting the IR window is that it would work even with clouds and water vapor in the atmosphere whereas, plain old thermal radiation needs a clear night to be effective.
Of course it won't pump heat backwards into the sun but they propose a water circulation system, which I imagine could store some daytime heat to release it at night. That and masonry of the walls of the building would store even more.
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At night sure, in the day time the sun is adding heat across a wide band of frequencies. This heats up less, but does not drop below ambient temperature in full sunlight.
PS: You don't actually need a thing special at night to get this effect: http://www.asterism.org/tutorials/tut37%20Radiative%20Coolin...
The advantage of targeting the IR window is that it would work even with clouds and water vapor in the atmosphere whereas, plain old thermal radiation needs a clear night to be effective.
Of course it won't pump heat backwards into the sun but they propose a water circulation system, which I imagine could store some daytime heat to release it at night. That and masonry of the walls of the building would store even more.