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RE: [EnergyPlus_Support] sky luminance

Hi, Jia
I have not read the new findings, however, it is not really that important to made the solar information current in the EPlus weather file for general use.
TMY is typical information for the last 30 years compiled/selected  into  averaged one hour period data.  There is a warning that it is not to be used for wind power, solar power simulation.  IWEC is specially compiled to satisfy the annual energy consumption model.
This is why Mr. Ooi is looking for and doing some measurements himself.  However, after looking at the 10 second interval values for Global Horizontal, etc.  he is convinced that the room temperature, etc. will not be affected very much.  However, the lighting in the room will follow the fast variation of the sky illuminating conditions.
Mr. Ooi has not finalized on how he is going to measure all these different components.  I suggest to him that it is no use looking at the whole sky.  He should only quantify components through the windows, while he is carrying out subjective tests on comfort conditions.

If your  interest is in lighting, etc.  more detailed solar  information would be required.
For annual energy calculation, the current IWEC weather file data is sufficient.
I am not against updating the sky luminance distribution model in EPlus.  However, I do not see how to improve it without having more input data.
Dr. Li  


To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: hujia06@xxxxxxxxx
Date: Wed, 3 Feb 2010 11:01:59 -0500
Subject: Re: [EnergyPlus_Support] sky luminance

Hi  Linda:
Of course, because there are not enough studies to quantify the sky type recognization, it is not easy to convert new models into code now.
if EPlus code changed the model of its reference, its prediction may be unreliable if without prior validation of new models. In that page, EPlus cited the reference where the model appears, it is probably that EPlus follows the approach of its reference. Hope to check it out and make it clear.

On Wed, Feb 3, 2010 at 8:51 AM, Linda Lawrie <linda@fortlawrie.com> wrote:

A new sky luminance model is not in the enhancement list queue. 

If you were a collaborative developer, you could develop one and submit it to the team for potential inclusion.

Many times there will be changes when one takes a reference idea and has to fit it into code.  As code is not provided by references (nor have they stood test of time).

Why would the sky model need to be changed?

At 10:52 PM 2/2/2010, Hu,Jia wrote:
After reading one orginal ref. of Eng. Ref . I feel  some inconsistency maybe exists between Eng.Ref. and original source.
In Page 152 (PDF 191), it interpolates the two sky luminance distributions, but in its reference, Perez (1990)  interpolated the "geometrical factor ", which is the ratio of sky luminance distribution to Zenith luminance. In different sky types, Zenith luminance is different even if sky conditions are the same
I do not know how EPlus actually works in this case. if it follows the Engineering Ref. some errors may occur. But it probably follows the method of the reference.
Many other sky models are developed now.  is it possible to update the sky luminance distribution model in EPlus?

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