[Radiance-general] Help analyzing/calibrating a Radiance model to match simulated and measured illuminance

[Vaib]

Dear Lars, Prof.Mardaljevic, Ehsan,

Thank you for your last replies. It gave some ground to the conundrum I had
since long.

Could you please suggest me some reference papers etc. that further
describes the difference between sky luminance distributions of sky models
from Perez (gendaylit) and sky-scanner? Or something similar. So that I can
refer that in my thesis report. Thank you!

Best regards,
Vaib


On 14 May 2014 21:16, Vaib <vaibhavjain.co at gmail.com> wrote:

> Thank you Ehsan, Lars, Prof.Mardaljevic !!
>
> Now, the reason behind weak correlation for cloudy sky conditions (with
> measured values) makes sense.
> Apart from that I couldn't think of any other modeling parameter (surface
> property, geometry, or ambient parameter etc.) that can be tweaked to
> further improve the results.
>
> I have also followed all the modeling best practices mentioned in Building
> Simulation for Design and Operation<http://www.amazon.com/Building-Performance-Simulation-Design-Operation/dp/0415474140> book.
>
>
> I will go ahead and conclude the thesis research with these results.
> Better results can be expected when sky-scanner is used to give
> better/precise sky luminance distribution for the sky model.
>
>
> Ehsan, Thanks!
>
> It would be great if you can provide me sky-scanner's data, so that I can
> have a quick test to support the conclusion. Will discuss more about the
> vertical irrad. sensor that you said.
>
> Best regards,
> Vaib
>
>
>
>
>
>
>
> On 14 May 2014 13:21, Ehsan M.Vazifeh <em.vazifeh at gmail.com> wrote:
>
>> Hi Vaib,
>>
>> There is a simple solution also to check if the errors caused by the
>> distribution of the diffuse or not. pick up the data for vertical
>> irradiance sensor and compare them to virtual sensors in Radiance. then if
>> there is similar trends as your result, you can infer that using gendaylit
>> model you cant get better performance as you already have.
>>
>> Cheers,
>> Ehsan
>>
>>
>> On Tue, May 13, 2014 at 12:31 PM, Ehsan M.Vazifeh <em.vazifeh at gmail.com>wrote:
>>
>>> Dear Vaib,
>>>
>>> I will prepare sky files based on sky scanner measurements for the
>>> period you mentioned in your presentation.
>>>
>>> The reason you get acceptable values for horizontal irradiance outside
>>> is that gendaylit is based on direct and diffuse data therefore you will
>>> get similar values in simulation. As Lars also mentioned distribution of
>>> diffuse is an-isotropic specially in case of breaking clouds. So after I
>>> send you the files please re-simulate again and let us know if you see any
>>> improvement in interior sensors values in comparison to the measured values.
>>>
>>> Cheers,
>>> Ehsan
>>>
>>>
>>> On Tue, May 13, 2014 at 11:52 AM, Lars Grobe <grobe at gmx.net> wrote:
>>>
>>>> Dear Vaib,
>>>>
>>>> thank you for sharing the presenatation with us!
>>>>
>>>> After a quick look at it, one potential source for the observed
>>>> mismatch may be the sky luminance distributions. You use a model of the
>>>> sky, which has a rather complex luminance distribution, based on only
>>>> diffuse horizontal and direct normal illuminance. These to values tell you
>>>> little about the luminance distribution not within the narrow angle
>>>> obtained by the sun, instead you use a theoretical model to reconstruct the
>>>> distribution. This means that for sunny sky conditions, when you know where
>>>> a huge fraction of luminous flux entering your scene is coming from (you
>>>> measure it and you know the sun position), you have a good estimate on the
>>>> sky distribution - while especially for sky conditions where the
>>>> distribution is far from uniform, but mostly diffuse, you really do
>>>> guess-work. E.g. clouds tend to give you a rather high variance in real
>>>> world, but get approximated as a smooth distribution with the sky models
>>>> you use.
>>>>
>>>> The sky models you use with the measured illuminance readings were ment
>>>> to be used for annual simulations. The generated distributions match the
>>>> average over a year. For single time-steps, which is what you compare, I
>>>> would expect deviations.
>>>>
>>>> Cheers, Lars.
>>>>
>>>>   Hello everyone!
>>>>
>>>> May I request you to please give some insight on the study I did to
>>>> match simulated and measured illuminance.
>>>>
>>>> Draft report: http://bit.ly/1nCpjU3
>>>>
>>>> Please have a look at the report.
>>>>
>>>> In this draft report I have tried to explain the model, and results
>>>> using different statistics. Also I have highlighted some areas in the
>>>> time-series graph, where the model is systematically (occurring during the
>>>> same time) under-estimating the illuminance. I don't know why?
>>>>
>>>> Do you think, there is still some scope of fine-tuning the model, or
>>>> the systematic error is uncertain to hypothesize?
>>>>
>>>> Do you think the results correlate well enough with other similar
>>>> benchmark daylight studies that used Radiance?
>>>>
>>>> I observed that the model correlates better in the case of "observed
>>>> sunny sky" as compared to "observed cloudy sky." But I couldn't understand
>>>> the reason behind this. ?
>>>>
>>>> Request you to please ask me if I missed to provide any info. about the
>>>> model.
>>>>
>>>> Thank you in anticipation.
>>>>
>>>> Best regards,
>>>> Vaib
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>>>
>>>
>>>
>>
>>
>>
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