This might be a way to increase the efficiency of data centers.
The Stanford mirror was designed in such a way that it reflects 97% of the visible light that falls on it. But more importantly, it works as a thermal radiator. When the mirror is warmed up, it releases heat at a specific wavelength of infrared light that passes easily through the atmosphere and out into space.
Fan said that the mirror could cool buildings – or other objects – simply by putting it in direct contact with them. Coating the roof of a building with the mirror would prevent heating from sunlight but do little to remove heat from its interior. More likely, the mirror would be used to cool water or some other fluid that would then be pumped around the building.
buildings are insulated, so “putting it in direct contact with them” would accomplish little or nothing, and even then, only on the top floor
the article also fails to mention any comparison of these mirrors to simply applying a white coating/stone/shingles on the roof (which would be massively less expensive)
simply cooling water as suggested in the article seems like a goofy idea - if ambient is 90 F, then the water could only be cooled to that temp, assuming 100% efficiency
The commerical product is an array of rooftop panels which use the mirror/thermal-radiator material. That array is then used as a heat sink for an existing air-conditioning system.
There are different types of heat sinks available. Compared to a cooling tower, the panels don’t consume water. And, the panels are cooler than an air-cooled radiator. So, there are potential savings in water consumption or in thermal efficiency. The case studies at skycoolsystems.com give specific data.
As you pointed out, 90°F water can’t be used directly. But, the video at The Engineering Mindset shows condenser water temperatures between 27°C and 32°C. So, bringing the coolant temperature below ambient air temperature would be useful as part of an air-conditioning system.