That is NOT ENOUGH. Sunlight will make the black material very hot and it will transfer into the room. You need thermally interlined curtains. Here with plenty of thermal mass inside the three layer insulating curtains, you cannot believe the heat that spills out when I draw them late on a sunny morning.
No. What you need is insulation *behind* whatever the sun falls onto. Your walls will be fine because they have. You need thermally insulating curtains or blinds
test by sticking a sheet of celotex or poly foam in the window
Even better, the Victorian design of sash windows, open the top sash downwards and the lower sash upwards, createa a circulating ventillation, shame about them being draughty in the winter, but coal-fired days then, so no matter.
That is about as dumb as you can possibly get. Black is a really good absorber of solar radiation which it converts almost entirely into heat.
You want a mirror finish on the outside surface with a thin layer of insulator and then a mirror layer on inside. The side facing the sun still gets mad hot but the inner surface acts as a radiation shield.
Aluminised bubble wrap sold for wrapping boilers isn't too bad if you don't care about appearances.
It heated up the blackout material which then heated up the air in the room. Black is just about optimium for absorbing solar radiation (and also for re-reradiating it).
Mirror finish on both sides or white on the outside and mirror on the inside are about the optimum solutions for minimum thermal load. The thin layer of insulation between the two sides is important.
Look at how the old observatory domes were painted with the whitest possible white in the days before air conditioning to see what works!
These days they are painted a neutral semi-metallic grey so that the surface doesn't supercool at night dripping cold air into the dome and causing unnecessary turbulent air aka "dome seeing".
Since this is a flat/appartment, is there a balcony or any means of accessing the outside of the window ?. Stopping the suns rays from hitting the outside of the glass is what you need to do.
In Brazil and other places where it gets over 30C every summer, tower blocks have external shutters on rails, like patio doors that can be slid across the window to provide this shading.
A couple of sheets of 25mm celotex propped up against the window on the inside would do the job. Get some aluminium tape and seal all the edges and they would last longer.
But on a south-facing wall it is better to keep windows shut during the day, else all that will happens is that the external brickwork gets to well over 50C and creates an updraft of hot air which then gets into the house through an open south window.
Open your north windows during the day and keep windows and curtains closed on all south-facing windows/doors until after about 6PM.
but FTAOD, Management will not allow me to fit anything much on the outside of the block, if that is what you are thinking of
I'll be lucky to get permission to run a drain pipe though the wall to the outside
Though as before, I can't even justify the expense of that for 2 weeks of the year, when sticking the pipe through a crack in window works
Not sure what that means
the rooms are too hot 24/7 for the complete period when it is hot outside, perhaps 4-5 days at a time 2-3 times a year - I'm keeping a diary this year to find out the exact number.
an air con unit located in one room is not going to cool down the other rooms via the door ways
I'd need one unit for each room
retro fitting internal ducting to move the cooing air through the property is completely impractical
I presume because it's permanently screwed to the walls. It will still be taking up space in the room.
I'm not refusing to consider them at all
I just know that Block Management will not allow it
I just love to have Mediterranean style shutters on the outside of my windows. It's not going to happen.
Fitting a simple blind on the outside I may get permission for.
But given the additional expense of fitting external items "at height" even that isn't going to be economically viable for a 2 week a year problem.
If I was on the ground floor, it might be viable. But I'm not
It depends on the tightness of the material against the window. With traditional curtains and blinds they don't fit tightly against the window. So what you have is a material that reflects some heat outside (depending on colour/reflectivity), but the remainder it absorbs. And then you have this hot thing that sets up a convection cell that drives heat around the room, drawing in cold air at the bottom and releasing hot air at the top. Essentially a blind does the same job as a central heating radiator.
Something mounted directly on the window (either baking foil or the foiled bubblewrap/celotex idea) minimises this because the reflector is directly against the glass. That means more heat is reflected back into the glass rather than coming into the room, and there is no air flow taking heat away from the glass into the room.
Of course foiled things are an endpoint - they block all the daylight too. Which may be fine for a few days a year. Or you may decide you can accept some temperature rise in exchange for some daylight, in which case film can do that halfway position. On the other hand, film is hard to remove in winter when you actually want the solar gain.
You can still get secondary double glazing where the glass panels slide from side to side. Fit that and apply the solar reflective film to the sliding glass panels and they can be slid to one side (or removed) for the winter.
For all practical purposes the only way to achieve this is with film stuck on the outside of the window instead of the inside - at perhaps an extra 500 pounds in installation costs (and a lot of aggro getting permission).
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