[Radiance-general] Calculating scheduled solar gains for EnergyPlus' surfaces

Mon Feb 29 11:51:23 PST 2016

Cool, Andy! Thanks very much... I understand why you did what you did when
using BSDFs.

I have just noticed something: This approach does not require WINDOW, thus
it can be scripted... :)

Best,

2016-02-29 16:46 GMT-03:00 Andy McNeil <mcneil.andrew at gmail.com>:

> German,
> Since you're not using BSDFs, I guess your approach makes sense. Just make
> sure you accurately account for all the surface area in your model,
> otherwise your total solar gain will be off.
> Andy
>
> On Sat, Feb 27, 2016 at 4:35 PM, Germán Molina Larrain <
> germolinal at gmail.com> wrote:
>
>> Hi Andy,
>>
>> thanks for such a very good answer. It is quite clear, or will be once it
>> sinks in.
>>
>> I have one concern though. Let me elaborate.
>>
>> My intention was to, actually, not use BSDFs at all. I would like to
>> account for the irradiance caused by the sky and sun, not using the 3-phase
>> method, but the 2 phase one. Accordingly, I send rays from the walls to the
>> binned sky, not to the window. In such case, I would say that your method
>> is impracticable since there is nowhere to send rays from, and with it it
>> is impossible to account for inter reflections on the (very weird) exterior
>> environment.
>>
>> The idea of using black walls, floor and ceiling surfaces was not to
>> consider inter reflections in the interior space (I understand that energy
>> plus will account for that...?). Why do I need -ab 0? I actually want to
>> account for all the optical phenomena on the exterior.
>>
>> Am I being clear? Am I totally wrong?
>>
>> Kind regards!
>> El 27 feb. 2016 18:33, "Andy McNeil" <mcneil.andrew at gmail.com> escribió:
>>
>>> Also, if you use your approach and use ab>0 then you need to multiply
>>> the irradiance on the surface by solar absorbance of the surface. If you
>>> don't then you will definitely create energy.
>>>
>>> Andy
>>>
>>> On Sat, Feb 27, 2016 at 1:28 PM, Andy McNeil <mcneil.andrew at gmail.com>
>>> wrote:
>>>
>>>> Hi German,
>>>> If you're okay with spatial averaging of the solar gains over a group
>>>> of windows, you could create a BSDF using Radiance to represent the
>>>> complexity in E+. The only caveat is that instances where sunlight coming
>>>> from behind the facade can enter the facade (reflecting off of buildings
>>>> across the street, for example) can not be represented in a BSDF. So you
>>>> site obstructions are best represented as geometry in the energy plus
>>>> model. But overhangs and undulated microperferated screens can now be
>>>> represented as BSDFs.
>>>>
>>>> Now I'll try to compare my approach from 2011 to the approach you
>>>> detail. I traced rays from the window into the space to see what surfaces
>>>> the ray hit. You're creating sensors on surfaces tracing rays from the
>>>> surfaces to the windows to calculate irradiance. Your approach probably
>>>> works fine in most cases, but mine is better :).  With your approach you're
>>>> trying to calculate the average irradiance over a surface. If you have one
>>>> sensor point your estimate of the average will not be very good. So you
>>>> decide to use a grid of sensor points, which improves your estimate, but a
>>>> regular grid will be biased. So you use random points and your estimate is
>>>> very good. Though if you have a complex model, with say furniture, then you
>>>> need to know what hits the furniture too. Good luck putting sensor on all
>>>> the furniture surfaces. So then the next question is what settings are you
>>>> using? where they high enough?
>>>>
>>>> Instead if you send rays from the window into the space, like I did,
>>>> every ray is accounted for, so your total solar gains will be accurate.
>>>> With my approach, I know that the sum of the energy distributed to the
>>>> surfaces equals the sum of the energy transmitted by the window, error in
>>>> my approach is limited to relative distribution between surfaces. With you
>>>> approach you have to do a lot of work to try to make sure the total energy
>>>> in the space is accurate, and I don't know of a simple way to check that
>>>> the sum of energy attributed to surfaces equals the sum of energy
>>>> transmitted by the window.
>>>>
>>>> So while my approach might be trickier to implement, once it's running
>>>> you know you're not destroying or creating energy. Your approach is simple
>>>> to set up, but you're never really sure that the total energy in the space
>>>> is correct.
>>>>
>>>> Andy
>>>>
>>>>
>>>>
>>>> On Sat, Feb 27, 2016 at 4:18 AM, Germán Molina Larrain <
>>>> germolinal at gmail.com> wrote:
>>>>
>>>>> Hi everyone,
>>>>>
>>>>> I am working on a project that requires calculating solar heat gains
>>>>> through (very) complex building envelopes. I am pretty sure that EnergyPlus
>>>>> will not be able to do it...
>>>>>
>>>>> I know EPlus is capable of dealing with CFS by means of BSDF... but
>>>>> that assumes that the CFS is an extra layer in the facade. In my case, you
>>>>> could consider the facade to be just anything.... a moving (ondulated and
>>>>> microperforated) overhang, a tree, a complex exterior environment, etc.
>>>>>
>>>>> My plan is to use Daylight Coefficients and use
>>>>> SurfaceProperty:SolarIncidentInside object in E+. That is, I want to
>>>>> pre-calculate the incident solar radiation using Radiance. *Just the
>>>>> incident! interreflection will be calculated by EPlus (is that correct?)*
>>>>>
>>>>> I understand this could be done as:
>>>>>
>>>>>    1. Create an office with black walls, floor and ceiling... the
>>>>>    exterior and the envelope keep their properties.
>>>>>    2. Create a sensor file for each surface... sensors are normal to
>>>>>    each surface, pointing inside
>>>>>    3. Calculate Daylight Coefficients for each wall
>>>>>    1. cat Wall.pts | rfluxmtx [options] -I+ - white_sky.rad scene.rad
>>>>>       > Wall.dcmtx
>>>>>    4. Calculate irradiance over surface
>>>>>       1. cat weather.wea | dctimestep Wall.dcmtx | averageSensors >
>>>>>       WallSolarRad.txt
>>>>>
>>>>> Now... I am not sure if this is correct, because what ANDY SHOWED IN
>>>>> 2011
>>>>> <http://www.radiance-online.org/community/workshops/2011-berkeley-ca/presentations/day3/AM_Radiance_EnergyPlus.pdf>
>>>>> is sort of different. He calculated a wird View Matrix.... is that an old
>>>>> way of doing this same thing? What am I missing?
>>>>>
>>>>> Best!
>>>>>
>>>>> Germán
>>>>>
>>>>> _______________________________________________
>>>>> Radiance-general mailing list
>>>>> Radiance-general at radiance-online.org
>>>>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>>>>>
>>>>>
>>>>
>>>
>>> _______________________________________________
>>> Radiance-general mailing list
>>> Radiance-general at radiance-online.org
>>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>>>
>>>
>> _______________________________________________
>> Radiance-general mailing list
>> Radiance-general at radiance-online.org
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>>
>>
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20160229/ee4c8fdf/attachment.html>