I think the problem lies in your input solar radiation, where the direct normal and diffuse horizontal are given as constant values for all sunlight hours:
This is simply wrong. The diffuse horizontal should be the same
as the global horizontal minus the direct normal * sine (solar
angle). In your case, I see that the diffuse horizontal is higher
than the global horizontal for an hour at sunrise and for two
hours before sunset, which are impossible. Also, the (direct
normal)/sine (solar angle) cannot be larger than the global
horizontal. I haven't bothered to check that but I guess is
you've also violated that for a number of hours. If you're using
the EnergyPlus WeatherConverter to create the epw file, I'm
actually surprised that it did not catch conditions that are
outside of physical reality.
A correct or more plausible (:-) ) clear sky profile should look something like this (Phoenix AZ average October day) :
The current ASHRAE Clear Sky Model allows you to create such profiles for more than 5,000 locations around the world, so you should just use that to get a more realistic solar radiation profiles for your particular location.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 205A Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx http://weather.whiteboxtechnologies.com for simulation-ready weather data (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
Hello,
I am having hard times with the way EP treats incoming solar radiation.
I created a simple test case: a cubic building, perfectly aligned on the north direction, only red-brick, no surrounding objects, ideal loads, constant internal room temperature, constant air temperature, constant wind speed, constant humidity. The only thing that varies is the incoming solar radiation.
I used a model to determine the clear-sky radiation in my location, the TMY3 may contain some weird effects due to the clouds' presence.
I set EP to output "Surface Outside Face Incident Solar Radiation Rate per Area [W/m2]" on each surface.
I checked out January 1 (the first 24h of the year) and something weird happens.
All the surfaces except west and east show a symmetrical collection of radiation during the day, as expected. You can see that in the picture attached.
East and West are not supposed to be symmetric, they receive direct radiation in different parts of the day. However, the peak of incoming radiation for the west side is much higher than the peak for the east side.
How is it possible? What possibly can alter the collection of solar radiation on those 2 surfaces?
Note the material of each surface is the same.
Attached you can find the .idf and the .epw file if you want to replicate the analysis.
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Posted by: Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx>
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