Does indirect solar light have any warming effect in a house?
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| Posted in General Questions on
Hello, I recently started renting a house that has huge north-facing windows. Looking at online shade maps, it will not get any direct sunlight in the coldest months. As I prepare for the winter, I am wondering if there will be any benefit to opening the blinds on the south-facing windows during the day in the winter. Will indirect sunlight warm the house at all or will I just lose heat out those windows too? Thank you.
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Unless the blinds are outside the glass, opening or closing them won't make any difference.
Once the light is through the glass it will be converted to heat when it hits something and is absorbed. The same amount of heat is absorbed by the light hitting the blinds as by hitting the wall or the floor, and that heat goes into the room.
DC,
Just thinking out-loud...
Isn't the difference between curtains or blinds absorbing the heat, and other surfaces further into the room, that half the heat the window covering absorb will be emitted back out towards the window?
Every object radiates heat. The spectrum of the radiated heat depends on the temperature of the object, it has to be pretty hot --glowing-- to radiate in the visible spectrum. The surface of the sun is about 10,000F, which is why it produces light that appears white to us.
The blinds aren't going to be very hot at all, 100F would probably be on the high end. The radiation they are going to be producing will be in the very sub-infrared spectrum. The glass in windows is typically 50% or so transparent in the visible spectrum, but pretty opaque in the infrared, so there would be little radiation through the glass at that spectrum.
Of course there are other factors, the opaque glass absorbs some of the radiation and some of it gets conducted through the glass outside. Some gets reflected back into the room. The blinds reflect some of the visible light, and some of that does go back out through the glass. The area around the blinds is warmer than it would be if they were raised, which increases conduction and convection losses in that area.
And it's hard to put a number on all of those things. The only one that would be expected to be significant would be the reflection of visible light, and blinds tend not to be very reflective. Even with reflection, only about half of what is reflected is going to pass through the glass.
The general idea is that once the light goes through the glass, it's not going back, and the energy in that light is in the room, regardless of what happens to it after it passes through the glass.
It's also why it doesn't matter if you paint your walls white or black, or if your floors are wood or tile.