Why not radiate it instead of the surrounding air, like Air conditioners? I know an air conditioner does not transfer/dump heat to the outside by radiation, but by phase transformation-specifically condensation..but AC's do dump heat into their immediate environment. not up to space/upper atmosphere. This question is in regards to Sky cool systems (https://www.youtube.com/watch?v=CMaZfuInd9c&lc=Ugzi8-NoZHgor7JAa1V4AaABAg.9f29-BNHdQR9f2mwQeWzRI) which makes meta material film to be used on rooftops of buildings to cool the building directly-or to cool water pipes. The film is made out of meta materials,that in addition to reflecting away all sunlight incident on it, also radiates away infrared in the 8-13 micrometer range. These mid infra red wave lengths are not "trapped" by greenhouse gases in the lower atmosphere so radiate straight into upper atmosphere or space.
Is it because if the material was radiating/emitting infrared merely into the surrounding air (instead of radiating out to space)- part of that radiation would just be returned back to the surface/material radiating it after being absorbed and re emitted by the gases in the surrounding air? Thus the requisite cooling would not happen in daytime direct sunlight? So is this sort of like an inverse greenhouse gas effect? Is it necessary to radiate away in the spectrum where the infrared escapes to space, to achieve the requisite cooling?
Or is it because passive radiative cooling cannot transfer heat from the inside (colder) to the outside (sunny and warm) air-only to the further colder environment of space or the upper atmosphere... For transferring heat from cold to warm one needs to work against entropy. Air conditioners/heat pumps overcome entropy by using electric power to compress vapors. By using meta materials Sky cool is essentially a creating a heat channel to space...
Also how is this approach of using metamaterials (which radiate away in the specific wavelength bands of mid infrared, that are not absorbed by GHGs),different from using regular infrared reflective paint (which I presume radiates away at all wavelengths of the infrared)? Are my questions clear?