[BLDG-SIM] Radiance: no variation to winter afternoon light levels?

[Caroline Prochazka]

I am a graduate student of architecture at the
University of Waterloo. I am using Energy-10, Ecotect
and Desktop Radiance to study the role of daylighting
with respect to heating and cooling energy for two
existing Canadian 'green' buildings. This posting is
only one of my many questions, which recently arose
from closer examination of my models.

RADIANCE: I am trying to assess the effect of changing
glazing types. For buildings in both Vancouver and
Toronto, daylight studies in the late winter afternoon
(based on sun charts and other software, I'm using 4pm
Dec21, where the sun is not yet set, but very low in
the sky), where I have not modelled any surrounding
obstructions such as trees or buildings, my internal
illuminance levels are consistently about 200 lux,
even on the east side of the building. Common sense
tells me there should be MUCH MUCH less light than
this...probably no more than 100 lux. 

Also, when changing glazing types (ie, from clear to
reflective) a significant change is noticed for noon
hour lighting, but the 4pm Dec21 lighting remains at
200 lux. What could I be mis-assuming? According to
weather data and other light simulations in Ecotect,
there should still be some light at 4pm on Dec21, but
for an overcast sky, like I'm using, it should be much
less than 200 lux indoors. Has anyone worked with
overcast, late-day skies and had similar experiences?

Regards,
Caroline

=====
t.    519.822.3832
e.    cjprocha at yahoo.com
web:  http://www.geocities.com/cjprocha

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