It's quite common that attic temperatures can fall below the outdoor air temperature on clear cold nights due to night sky radiation from the roof. I've seen measured data for residential attics where the temperature depression is around 3-5 F in California and 1-2 F in Florida. 5C or 9F seems pretty large, but not outside the realm of possibility. I don't know what night sky radiation model is currently in EnergyPlus, but in DOE-2 it was based on work done by Marlo Martin at LBNL back in the early 1980's and produced similarly large attic temperature depressions (10F below ambient in some runs I did for California houses) that I have found doubtful. Joe Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx www.whiteboxtechnologies.com (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips" On 2/5/2013 3:26 PM, Griffith, Brent wrote:
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