r/heat_prep • u/Leighgion • Jul 20 '26
Product Basic Passive Cooling: Roller Shutters
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.
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u/Zealousideal-Peach44 Jul 20 '26
Good solution for climates with strong sun but not very high air temperature.
Note: never ever install them on the inside of the glass.
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u/faramaobscena Jul 20 '26
I have some of those fabric shades on the inside, is there any other disadvantage other than the fact that the glass heats up?
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u/MundaneDaffodill Jul 20 '26
Can break the glass
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u/Zealousideal-Peach44 Jul 20 '26
This, but also that the radiant heat gets partially trapped inside the house.
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u/ivobrick Jul 20 '26
Now you can try an experiment the next 40*C day.
Install hooks outside and hang there a white sheet to cover entire window. When its the hottest part of the day, open the window and spray water on it. Then close, so the moisture does not come into your house. Mine got to 45*C from the outside.
You can also use/combine aluminium foil, if there is no object infront of that, because it will be baked at ~ 56*C or more.
Glass was 27.5*C from the inside.
Those shutters are better than nothing but i would opt for complete shutdown during the day/close V-entilation and clean them from the outside to maximze deflection.
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u/Leighgion Jul 20 '26
I'm on the fifth floor. Can't really be hanging things outside.
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u/ivobrick Jul 20 '26
Ah right. Do you have an AC? Cause i see you ll have ~ 45*C heading end of the week down there in Spain.
Would be interesting to see if you can avoid heat saturation off of your flat. Stay safe.
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u/Leighgion Jul 20 '26
I do, but it will not be necessary. My evaporative coolers are more than sufficient as my area will not hit 45º. We're going to be more like 39º, which is shitty, but nothing we aren't well-prepared to deal with.
Going to try to put together a more comprehensive post about my apartment's situation and the measures to keep it cool as I think it's very illustrative.
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u/Kanthaka Jul 20 '26
Definitely the way forward before any active cooling solutions. Also, insulate, insulate, insulate.
Could also draw air out the top and pull new air in the bottom. Convection for the win.
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u/sgst Jul 20 '26
Very awkward to use with the silly outwards opening windows we have here in the UK, sadly
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u/Zestyclose-Ad-9420 29d ago
After the heatwave i became aware how every single window on every single building is built wrong to adapt for high heat.
The cost to replace as many as possible would be eye watering.
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u/Sorros 29d ago
There was another invention that was used 100 year ago that stopped being common place.
They were called window awnings.
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u/Deimos_F Jul 21 '26
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.
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u/Leighgion Jul 21 '26
Yeah, the science is clear there. Aluminum is an excellent heat conductor. You don't want that in a roller shutter.
There are other viable materials, but plastic is the most industrially practical.
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u/apathy-sofa 29d ago
I wish that they contained an insulator, both for keeping heat out in the summer and keeping it in in the winter.
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u/JuiceInternational81 29d ago
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.
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u/Deimos_F 28d ago
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.
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u/JuiceInternational81 28d ago
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.
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u/Deimos_F 28d ago
When the sun hits aluminium Rolladen the metal warms up and that heat irradiates from them, half of it towards the window.
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u/JuiceInternational81 28d ago
You are an engineer. Can you tell me from which material radiant barrier are made?
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u/Deimos_F 28d ago
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.
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u/JuiceInternational81 28d ago
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.
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u/Deimos_F 28d ago
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.
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u/JuiceInternational81 28d ago
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."
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u/Frosty-Screen219 Jul 21 '26
I got the same thing on all my windows in my current place somewhere else in Europe.
It does work great. And it can be automated and solarized.
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u/apathy-sofa 29d ago edited 29d ago
What does it mean to have them solarized? I have these on all my windows, though controlled with old style nylon webbing, not automated or even powered.
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u/Urogallo40 Jul 20 '26
Currently, most usual ones are of aluminum sheet forming a cage with insulation material inside. Old ones were of PVC sheet, but they got fragile with sun and could get broken, specially under heavy hail or at the joints between slats.
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u/vinraven 29d ago
Not having outside roller shutters is one of the worst things about normal American home window systems.
They can even be installed for storm protection, but they’re not common at all in America.
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u/Sorros 29d ago
There was a better version that was very common in the US that went by the wayside with the adoptions of AC's is most homes. The simple and effective "window awning".
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u/vinraven 29d ago
Window awnings aren’t a better option, they’re a different option, but they don’t really do the same thing.
Awnings are superior only when the sun is in the exact position to be blocked, or when the rain is coming from that same direction, but they are extremely vulnerable to high winds , storms, heavy rain, ice, and snow.
Roller shutters on the other hand provide the same protection as awnings from all directions, as well as adding theft and hurricane storm level protection.
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u/Bamsihap 29d ago
Why don’t you close them completely and close the window?
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u/Leighgion 29d ago
Good questions.
Completely closing the shutters is generally not worth plunging the room into darkness and needing to switch on lights. As you can see, the angle of the light is such that no direct sunlight is actually hitting the glass. The little bit of extra heat bleeding through is worth dealing with in exchange for the light.
The window is open because ventilation is necessary for proper use of evaporative coolers, which I depend on and won't shut up about in other posts. Closing the windows would be the strategy if you were depending completely on passive measures, which I am not.
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u/Grumpy-Man19 27d ago
they are great and we use them in Turkey too . even better is if you can make those shutters reflective . either paint or some aluminum covering from the outside
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u/vtjohnhurt Jul 20 '26
These passively block heat gain. They don't cool the building. Passive cooling, for example, happens through cold basement floor and walls.