Hi Jan
To compute trasnmissivity (tn) from transmittance (Tn), I should use:
tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
But, how can I compute the solar transmissivity from the solar
transmittance?
Besides, can you help me with the following:
- What is the way in Daysim to customize all sensor points in the
file *.pts as irradiance sensors? This last in order to avoid
customizing all sensors, one by one, in the sensor type column of the
Daysim interface.
- I am new in Diva-for-Rhino, but I have seen that it can calculate annual
irradiation at node locations (radiation maps-grid based). Is this
equivalent to the calculation of the solar irradiation in Daysim?
Many thanks
···
------------------------------
Message: 2
Date: Thu, 11 Aug 2016 11:49:22 +0200
From: Jan Wienold <[email protected]>
To: DAYSIM discussion <[email protected]>
Subject: Re: [Radiance-daysim] Radiance-daysim Digest, Vol 26, Issue 1
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"Radiance and Daysim do internally not raytrace spectrally - there are
calculating simply in channels (RGB for Radiance, Daysim just one). That
means:what you put in you will get out :If you use a weather file with solar spectrum AND your material
properties are valid for that range (that means using solar
transmittance, solar reflectance) then you also get solar irradiance as
output.That means for your last question: Yes, you should insert the "solar
transmissivity" (must be calculated from the solar transmittance). Don't
forget to use also solar reflectance values for all your surfaces.
Usually they are very similar to the visible, but there are exceptions.But please consider, that Radiance (and daysim) are raytracers! They do
not consider any change in wavelength for a ray. That means they do NOT
consider the heating up of a surface when it is absorbing radiation and
emitting it in the IR.That's why you CANNOT calculate the "real" SHGC of a window system. You
can just calculate the solar transmittance. Depending on your glazing
system the difference between the SHGC and the solar transmittance could
significant (I guess more than 40% is possible in general, typically the
difference for a normal glazing is in a range of 10-20%)!E.g. if you check a typical glazing from Interpane (Tau_vis=0.76,
Tau_solar=0.48, SHGC=0.55, see here:
http://www.interpane.net/interpane2013/teweint.php?lang=de&site=10331.html
),
the difference is 13%. For a combination of Planilux/Planitherm of St.
Gobain I calculated with Window 7 (LBNL software) Tau_vis 0.75,
Tau_solar=0.48 and SHGC of 0.59 (19% difference).Jan
On 11/08/16 10:17, Abigail Chi wrote:
> Hi Christoph and many thanks for your answer. I have the following
> queries.
>
> - I choose a material (in this case a glass) and specify its
> transmissivity as follows:
> mod glass id
> 0
> 0
> 3 rtn gtn btn
> This defines the way "visible light" is transmitted through the glass.
> I think this is useful when I use illuminance sensors.
> But, if I use the irradiance sensors, do I need to specify the solar
> transmittance of the glass instead of the visible transmittance?
>
> - What is the way in Daysim to customize all sensor points in the file
> *.pts as irradiance sensors? This last in order to avoid customizing
> all sensors, one by one, in the sensor type column of the Daysim
> interface.
>
> - I am new in Diva-for-Rhino, but I have seen that it can calculate
> annual irradiation at node locations (radiation maps-grid based). Is
> this equivalent to the calculation of the solar irradiation in Daysim?
>
> Thanks in advance.
> Abigail