[Radiance-general] Irradiation on standing subject with Radiance

[Greg Ward]

Well, the projected area of a cylinder is roughly the diameter times the height times the sine of the angle between the cylinder's axis and the sky patch (or solar disk) direction.  This would work if you didn't have the complex urban surroundings.  With the surroundings, there's no way I know to avoid a more complete view factor calculation, which is what rcontrib gives you.

-Greg

> From: Ruggiero Guida <ruggiero.guida at gmail.com>
> Subject: Re: [Radiance-general] Irradiation on standing subject with Radiance
> Date: September 20, 2015 3:24:39 PM PDT
> 
> Thanks Greg,
> 
> The subject is inside a complex urban environment and the calculation is performed for a whole year or fraction of a year. However I need to keep the hourly granularity because the irradiation information is used to calculate other comfort parameters.
> 
> I would like to avoid the use of a cylinder all together if possible. For example, for the direct solar radiation, I could simply have:
> 
> S_irrad = Id * fp(solar_altitude)
> 
> where:
> 
> - S_irrad is the irradiation on the subject,
> - Id the direct radiation from the the sun
> - fp(solar_altitude) the projected area of the subject in the direction of the sun
> 
> My idea is to consider a dome around the subject: if I can calculate the irradiation contribution for each direction I can then apply the projection factor to each of these contributions and sum them up. This should give me the total irradiation falling on the subject.
> 
> Thanks
> Ruggiero
> 
> 
> 
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> 
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> 
> 
> On 20 September 2015 at 23:23, Greg Ward <gregoryjward at gmail.com> wrote:
> Hi Ruggiero,
> 
> Is the standing subject inside a complex space?  Do you need this for an annual simulation?
> 
> If the answer to either of these questions is "no," then you can simplify the problem a bit.  If the answers are both "yes," then your third option of a daylight coefficient calculation will be the most efficient.  You basically want to compute random positions on the cylinder with the surface normal facing outwards, and give these to rcontrib to compute an integrated daylight coefficient for sky patches (and ground).
> 
> If you confirm that this is what you need, I can help you with the appropriate command chain if you like.
> 
> Cheers,
> -Greg
> 
>> From: Ruggiero Guida <ruggiero.guida at gmail.com>
>> Subject: [Radiance-general] Irradiation on standing subject with Radiance
>> Date: September 20, 2015 4:06:46 AM PDT
>> 
>> Hi,
>> 
>> I am trying to calculate the total radiation on a standing subject using Radiance rtrace, but I am a bit stuck.
>> 
>> The first approach that comes to mind is to integrate over an idealised vertical discretized cylinder, but this would be too computationally expensive. I have to do the same calculation for several locations.
>> 
>> The second approach that comes to mind is to apply a bulk reduction factor, but this would not be very accurate in the presence of direct radiation or anisotropic diffuse radiation. 
>> 
>> A third way could be to use rtrace to calculate the contribution to the irradiation from the various sky patches and use the projection factor for each one of them. As far as I understand though, rtrace provides the total directional irradiation on an ideal surface placed in the point of interest and perpendicular to the ray under examination. This corresponds to the radiation generated from the portion of the sky visible from the surface.
>> 
>> Has anyone tried something similar? Do you have any recommendation?
>> 
>> Thanks
>> Ruggiero
> 
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