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Do homes increase in temperature due to solar gain with curtains open if it's overcast?

In other words, Does having curtains closed reduce the temperature of the home on an overcast day?

In other words, Does an overcast day prevent the warming effect of the sun hitting a homes window and raising it's temperature?

In other words, Closing the curtains on a sunny clearly keeps a room cooler. Does closing the curtains on an overcast day have the same effect? Why?

Thank you for your time.

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  • $\begingroup$ Yes - you can have a warm day... $\endgroup$ – Solar Mike May 6 '18 at 18:13
  • $\begingroup$ @SolarMike Not what I am asking. Closing the curtains on a sunny clearly keeps a room cooler. Does closing the curtains on an overcast day have the same effect? Why? $\endgroup$ – NitrusInc May 6 '18 at 18:18
  • $\begingroup$ Improve your question - more info in your comment than the original question... $\endgroup$ – Solar Mike May 6 '18 at 18:20
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    $\begingroup$ @SolarMike Alright. It's alright if you don't have the answer. Thank you anyway. $\endgroup$ – NitrusInc May 6 '18 at 18:23
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    $\begingroup$ I’m trying to get you to see the answer for yourself, I designed and built a very low energy house, passive solar, pv, solar thermal, super-insulated ... but ... $\endgroup$ – Solar Mike May 6 '18 at 18:25
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Closing the curtains will help even on a cloudy day.

Assuming there is minimal heat transfer from the curtain to the room due to infrared radiation of the curtain and assuming minimal convection of hot air trapped between the curtain and the glass, overflowing the curtain rail into the room, the curtain will help by reflecting some of the sun's rays that have penetrated through the clouds and also some of the infrared radiation caused by the clouds.

The difference between a cloudy day and a sunny day is some of the solar radiation energy reflects back into space by the clouds, but not all of it. It depends on reflection index of the cloud. The part of radiation which is not reflected partially heats up the cloud causing infrared radiation to earth and partially reaches the surface of the air.

So having the shades closed still helps even during cloudy days.

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