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

[Vaib]

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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