View Full Version : The effect of North/South facing windows when calculating heat load

07-03-2012, 12:14 PM

I understand a room will absorb a heat load from solar energy through windows, but in the northern hemisphere, why is it important to note whether their is a north or south facing window? I was always led to believe "the sun rises in the east and sets in the west". what effect would east/west facing windows have?

Any help would be great as I'm just curious

07-03-2012, 01:01 PM
Read here

07-03-2012, 01:13 PM
why is it important to note whether their is a north or south facing window?

It is important to calculate the peak summertime solar gain.

In order to do this you need to calculate the angle of incidence of sun rays in summer to the window and this depends heavily on window orientation. This means that the effective area of the window is reduced to capture sun’s rays.

For north facing windows angles of incidence will be of about 40 thus transmittance is reduced.
For a perfect south orientation you don’t need to take this into account unless there is a building in front of it affecting your window by its reflectivity.

". what effect would east/west facing windows have?

Angle of incidence is less important on east-west facing windows because you will have to take into account 100% of the total window area and your transmittance will be close to 100% too.

07-03-2012, 11:10 PM
Sun rises in the East and travels West via the Southern skyline, put simply.... ;)

08-03-2012, 01:40 AM
Bryan_UK reminded me that I live in the southern hemisphere, so for me is the nothern skyline.

Please transpose the words north and south in my previous post.


10-03-2012, 09:38 PM
South facing windows will affect your winter heating requirements as they allow some solar radiation to supplement the heating input. If the windows are not shaded, and as Aramis has correctly pointed out, with the sun low in the southern sky during the winter - traversing the sky from SE to SW, the extra solar gain through those windows can make a substantial difference.

Even in the summer, if you are far enough north, (ie: well north of the Tropic of Cancer) the sun will always be traversing to the south of your position and the South facing windows will be a significant source of heat gain during the summer which will need to managed if we want comfortable conditions.