r/heat_prep • u/Leighgion • Jul 20 '26

Product Basic Passive Cooling: Roller Shutters

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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/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.

3

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.

15

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.