I have a residential building that needs to be modeled with window
shading on the south side. When I input the shading 24" to each window
on the south side of the building my heating during winter and the pumps
results every month are increased and the shading doesn't help at all.
This doesn't make any sense to me. In the winter time on the south side
during summer the shading should help after theory. In the winter should
help too because the sun will heat the windows and heat up the spaces.
Any help would be appreciated.
Thank you.
Crina Bosch
I'm not sure thats a surprising result. Depending on your window height, you might be over shading your window and reducing some of the passive solar heat gain in winter. I don't see how the shades will help in winter - they will reduce the heat gain.
The trick is always to balance out when your summer benefits outweigh your winter penalty. This is why we model - to optimize these aspects.
Vikram Sami, LEED AP
The ideal overhang depends on your latitude. It is an easy and standard
passive solar calculation. You can google calculators based on your
zip. Your window shade can be designed to exclude the summer sun and
allow the winter sun to enter. Depending on your results you might want
to adjust your window sill height. If your building has fans on 24
hours a day you may not see a big winter benefit due to the heat loss at
night without insulating curtains. If your fans only run during
occupied times you might think you have a benefit but is is only because
eQuest is not calculating the heat loss when the fans are off. At the
end of the day, you have a chunk of wall at R-2. It is actually a
little worse than this, the glass is radiating heat outside at a higher
rate than an insulated wall would as well. This is also why there is
such a game being played with the low E coatings, you can adjust the
selectivity of incoming and out going radiation depending on where you
are and what you are trying to accomplish. One of the glass
manufacturers has what is called "Canadian low E", it maximizes incoming
radiation and minimizes out going, no good in Miami though, you want to
minimize incoming and maximize outgoing(maybe). I don't think eQuest is
totally "tuned" in this area from some of the observations others have
made concerning glass and shading.
Bruce Easterbrook P.Eng.