Passive radiative cooling below ambient airtemperature under direct sun (2014) [pdf]

Post by spearo77 » Fri, Jul 09, 2021, 6:29 PM UTC

oezi wrote: post #31

PaulHoule wrote: post #15

Earlier quoted context omitted.

Opening the windows at night and running fans to equalize the temperature, then putting space blankets over the windows for the day works wonders on hot days in upstate NY.

One question that I always wonder when hot days strike: Given that I only have one portable fan, what is the best setup at night if it is colder outside than inside: 1. Open the windows and put fan so that it blows air out of one window 2. Open the windows and have fan mix the air inside the room 3. Open the windows and put fan on balcony to blow air from outside in.

Post by PaulHoule » Fri, Jul 09, 2021, 6:36 PM UTC

eloff wrote: post #38

PaulHoule wrote: post #16

Earlier quoted context omitted.

The weakness it has it that it needs a clear sky to work. For overcast muggy days or even a high coverage of cumulus clouds, performance will be absent or degraded. It works at night, however, and for best results you could maximize insulation and "thermal mass" inside the building and minimize radiative transport through the windows. The best thing about air conditioning, however, is de-humidification and that is a…

Adhesives are not built for high-humidity environments. My parents live in the tropical rainforest of Panama. One of the challenges is that anything stuck together with adhesive usually comes apart over time. The glass panel on the door of my mom's oven fell off.

Post by coolradmab » Fri, Jul 09, 2021, 7:32 PM UTC

hatsunearu wrote: post #29

coolradmab wrote: post #12

I've been actively working on this technology, goal is making it cheaper and simplify installation. Stanford's a highly reflective surface ~95% combined with stacks layers of silica oxide on a wafer under vacume. The trick too achieving bellow ambient temperature is too reflect nearly all solar energy while emitting strongly in the "atmospheric window". Most silica compounds are well suited as emitters, however the h…

wouldn't large scale usage of a device like this essentially increase the planetary albedo and help fight climate change? especially if you just skip the "environmental heat transfer" part

Post by coolradmab » Fri, Jul 09, 2021, 7:40 PM UTC

etskinner wrote: post #39

PaulHoule wrote: post #16

Earlier quoted context omitted.

The weakness it has it that it needs a clear sky to work. For overcast muggy days or even a high coverage of cumulus clouds, performance will be absent or degraded. It works at night, however, and for best results you could maximize insulation and "thermal mass" inside the building and minimize radiative transport through the windows. The best thing about air conditioning, however, is de-humidification and that is a…

I'm having trouble understanding why a clear sky is important. Surfaces radiate based on their temperature and emissivity only, right? So why would it matter what the surface is emitting toward? Perhaps what I'm missing is that clouds emit some radiative heat back to the surface, whereas a clear sky emits very little, so the net heat loss from the surface under a cloudy sky would be lower.

Post by jryb » Fri, Jul 09, 2021, 7:53 PM UTC

leoedin wrote: post #4

To compare to an air conditioner. This device has about 40W of cooling per m2. Apparently in Australia you should size between 80 and 120 W/m2 of air conditioning (I think this is cooling watts rather than power usage watts) - https://www.google.com/amp/s/www.crownpower.com.au/blog/choo... So that means every square meter of living space needs 2 square meters of radiative cooling (assuming no other passive cooling in…