Consider thermal radiation to the cold night sky.
FROM: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] ON BEHALF OF adamsrackes
SENT: Tuesday, February 05, 2013 4:24 PM
TO: EnergyPlus_Support@xxxxxxxxxxxxxxx
SUBJECT: [EnergyPlus_Support] Zone colder than outdoors - without
mechanical cooling!
I've noticed something strange in the model I've been working with.
It's one of the Commercial Reference Buildings (CRB), essentially
unmodified: the post-1980 vintage small office in Baltimore. This
building has an attic-type roof, which is modeled as zone, but it has
no heating or cooling. It gets extremely hot in the summer and
extremely cold in the winter.
What doesn't make sense to me is that this attic zone temperature
often falls _below_ the ambient temperature at nighttime. I can't see
any reason why this should ever happen given that: there is no
cooling
system, the zone and outdoor temperature at these times are both
falling and not rising, and all the other zones in the building are
warmer than the ambient. It really doesn't make sense at any time of
year, but it's especially hard to understand in the winter, when it's
below 0 C outside. The difference is not insignificant--frequently up
to about 5 C, or 9 F.
As I said, the model is an unmodified CRB. Those models use the
AnalyticalSolution for ZoneAirHeatBalanceAlgorithm. I've also tried
ThirdOrderBackwardDifference (the default) and a few other things, at
lots of different timesteps. The results do not change.
One of the following is in error, in decreasing order of likelihood:
me, this CRB model, EnergyPlus, or the second law of thermodynamics.
Any ideas how/why?
https://dl.dropbox.com/u/47230322/jan.png [1]
https://dl.dropbox.com/u/47230322/jul.png [2]
Thanks,
a
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