Re: [EnergyPlus_Support] Re: Weather Converter Direct Solar Radiation Spikes

[Joe Huang <YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx>]

I had found problems in how the weather converter calculated the direct normal that I brought that to E+ Team's attention last year, and thought that  it had gotten fixed.

Please note that these three radiation values are closely related. The direct normal is calculated using various direct/diffuse split models (Perez, Gompertz Function, etc.), all of which calculate the direct normal as a function of the KTbar (ratio of total horizontal to extraterrestrial horizontal). Therefore, if the total horizontal goes down, expect the direct normal to go down much faster.

The diffuse horizontal is even easier to compute,  it's simply the total horizontal - direct horizontal,  which is the direct normal * sine (solar altitude).

None of these models or calculations would produce spikes.  That, as I suggested previously, occurs when the sun location is inconsistent with your measured solar radiation.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
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On 4/8/2014 2:12 PM, Sankey, Maxim L wrote:
>  
How do I let the program "fix" it itself?
> 
> I've reviewed my custom weather file with the location's TMY2 file. It appears that the 'Horizontal Infrared Radiation Intensity from Sky' is much lower than the TMY2, the 'Direct Normal' is much lower than the TMY2 (except for the spikes), and the 'Diffuse Horizontal Radiation' is much higher than the TMY2. The 'Global Horizontal Radiation' I input to the converter is on par with the TMY2 file, as is the dry bulb temperature. It appears that the direct normal is spiking as you each have mentioned, but it is also dividing the diffuse and direct radiation incorrectly.
> 
> Max
> 
> From: <mailto:linda@xxxxxxxxxxxxxx>linda@xxxxxxxxxxxxxx
> To: "EnergyPlus Support" <mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx><EnergyPlus_Support@xxxxxxxxxxxxxxx>
> Sent: Tuesday, April 8, 2014 5:01:00 PM
> Subject: [EnergyPlus_Support] Re: Weather Converter Direct Solar Radiation Spikes
> 
>  
I believe this is just exhibiting a typical problem that happens at Sundown.  You can let the program "fix" the data or fix it yourself.

> 



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