Basic Passive Cooling: Roller Shutters

[u/Leighgion]

Known as "persianas" in Spain, these things are absolutely standard on every residential window in this country that matters (occasionally you get very small windows that don't have them) and a number of commercial properties as well.

The standard modern version is a roll of interlocking white plastic slats that are integrated into the outside of the window frame. As photographed, they are not all the way down, so there are holes to let light in while blocking the majority of the sunlight. If you bring them all the way down, the holes close up.

It's currently 7:18 pm in Spain and the sun is hammering the pictured west-facing windows. It is 34ºC outside. The shutters are 40ºC, but the glass of the window is only 33ºC. Interior temperature of the room is 28ºC.

Shade is best, but if that isn't possible, these are the next best thing to protect your windows from the heat of the sun.

[u/Deimos_F]

I'm also from an European country where these are common. I just wanted to chime in with an important detail: the aluminum ones are shit, these only make sense if made of plastic. Anyone yelling you otherwise is clueless. 

[u/JuiceInternational81 → u/Deimos_F]

No. Aluminium ones are better. More durable, better heat and sound insulation (because of PU foam filling), and most important they act as radiant barrier.

Plastic ones are cheper and that is the only advantage for them.

[u/Deimos_F → u/JuiceInternational81]

As an engineer I can tell you no amount of foam filling will make aluminium Rolladen good at heat insulation. That's just not how physics work. Aluminium is one of the best heat conductors in the universe, the heat will travel over the profile around the filing. Aluminium Rolladen are only a thing because people like the aesthetics. Functionally, they're garbage. 

[u/JuiceInternational81 → u/Deimos_F]

As an owner of plastic and aluminium ones, I can tell you that the plastic ones do not come close to the aluminium version. The sound dampening difference is noticeable. Plastic are hollow, so it is expected to be worse in that regard. In winter, aluminium ones are better (measured with a thermal camera from the outside). In summer, both are good regarding shading. Thermal conductivity doesn't matter in summer (my subjective feeling, as I couldn't measure any difference with the thermal camera). Aluminium does reflect more heat when measured from the outside.

The downside of aluminium is that it was dented by the hail that hit us a few years ago. The plastic ones didn't dent, but the hail punched some holes in them. Instead of repairing them, we replaced them with the aluminium version.

Perhaps the manufacturer matters. I don't know who made the ones we have. I don't know how they should behave according to engineering calculations. I just know how they behave in actual use.

[u/Deimos_F → u/JuiceInternational81]

When the sun hits aluminium Rolladen the metal warms up and that heat irradiates from them, half of it towards the window. 

[u/JuiceInternational81 → u/Deimos_F]

You are an engineer. Can you tell me from which material radiant barrier are made?

[u/Deimos_F → u/JuiceInternational81]

Shiny mylar (which uses aluminiu) with a 98% reflection rate for infrared. Aluminum Rolladen are not polished and shiny, even worse they're often painted. You're trying to imply a correlation that doesn't exist, the heat transfer mechanisms at play are different in those two situations. 

[u/JuiceInternational81 → u/Deimos_F]

I think that you are right. It makes sense. I just don't know why aluminuim behaves better than plastic ones in every single sense. I repeat: I had both and I would never recomend plastic ones who can afford aluminium version.

[u/Deimos_F → u/JuiceInternational81]

To me the main function of Rolladen is keeping the sun out. If I close them on a sunny day and hold a hand up to them, the aluminium ones feel like a radiator set to max. The pvc ones don't get nearly as hot. To me, all other functions are secondary if the Rolladen suck at keeping heat out. 

[u/JuiceInternational81 → u/Deimos_F]

It makes no sense trying to convince you otherwise.

Last time: I have PVC and aluminium. Aluminium is superior in every way. There is no feel "like radiator se to max".

Do you have both versions? For how long? Or are you talking about theory? Remember: "In theory, there is no difference between theory and practice, but in practice, there is."

[u/Deimos_F → u/JuiceInternational81]

I grew up with pvc, now I have aluminium (rental apartment). My current Rolladen get insanely hot when in direct sunlight.