Temperature inside an enclosed space

[black hole 123]

its summer where i live and the ceiling space gets extremely hot, much hotter than ambient outdoor.

under a shade outdoor, the air temp beneath shade will be colder than air temp in sunlight. yet in a space with no air flow, the temp is always hotter from my experience. why is this? this isn't a greenhouse like inside a car where infrared comes through and becomes trapped. does microwave or longer wavelength pierce the ceiling and get trapped?

i want to shade my air con outdoor unit, what material is best used for this? want to reflect as much sunlight as possible

 

[davenn]

this isn't a greenhouse like inside a car where infrared comes through and becomes trapped

Yes it is a form of greenhouse. Regardless of the roof type, concrete / slate tiles, corrugated iron, etc Those materials get hot and
reradiate IR (heat) into the roof-space and because that heat can't escape ( even worse if there is ceiling insulation ... batts, insulfluff
etc it will heat up even more

 

[256bits]

under a shade outdoor, the air temp beneath shade will be colder than air temp in sunlight

Not necessarily..
The shade blocks the sunlight from you, or anything within the shade. Thus there is less of direct heating from solar to a surface.
Air moves around, so an exchange of air from outside the shade with the air within the shade will occur.
It is true though that the air temperature closer to a surface in a shade will be cooler than the air closer to a surface in direct sunlight.

Have you calculated the amount of "saving" you would expect if you shade your air conditioner?

 

[black hole 123]

ok, i didn't know about the reradiate in IR wavelength.

i have another question. if i put the same aluminium foil on a thermal conductor and a thermal insulator, and place both under the sun, suspended above ground with aluminium facing upwards, after many hours will the air beneath the thermal conductor be hotter or the same as for the thermal insulator? sorry if this sounds really dumb...