# Radiation Maps - Grid Based

Hello

It is possible to calculate the solar irradiation entering to the space through a window?

I have seen that DIVA can calculate annual irradiation at node locations (vía Radiation Maps-Grid Based). I have used a grid in the interior of a room with one fully glazed facade . But I have some queries:

1) What solar irradiance spectrum is measured after passing through glass?

2) I have used the following glass material:

# Glazing_DoublePane_Clear781: Tau_vis = 0.781; SHGC= 0.703 ; U-Value= 2.785W/m2K
# visual transmittance: 78.1%
# visual transmissivity: 85.1%
void glass Glazing_DoublePane_Clear_78.1
0
0
3 0.851 0.851 0.851

Those parameters defines the way "visible light" is transmitted through the glass. But, if I want to know the transmitted solar irradiation, do I need to specify the solar transmittance of the glass instead of the visible transmittance?

Abigail

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### Replies to This Discussion

Excellent question, Abigial. For clear glass, visible and solar transmission values are usually within a few percentage points of each other. But if you have a highly spectrally selective material, you should indeed specify the solar transmissivity instead (if you know it). Keep in mind the difference between transmissivity and transmittance. You can get the former from the latter using the equation below:

tn = (SQRT(0.8402528435 + 0.0072522239 * Tn * Tn) - 0.9166530661) / 0.0036261119 / Tn

Best,

Jon

So, are the DIVA results in Wh/m2 or in W/m2?

Do solar irradiation results correspond to the full visible and IR spectrum? or, do they correspond to the full spectral?

Do you know if this tool in DIVA (Daysim-Based Hourly Method) is equivalent to the calculation of solar irradiance by using irradiance sensors in Daysim-Ecotect?

Many thanks

Hi Abigail,

Units are in kWh/m2.

The spectrum type is really defined by whatever weather-station instruments are used in the TMY3 data set.  I'm not 100% sure, but these are probably pyranometers with a response in the ~300-3000 nm range.

Yes, the Daysim-based hourly method is a Daysim run with irradiance sensors (as opposed to a Radiance run with a cumulative sky definition).  Not sure I can speak to the options in Ecotect.

Best,

Jon

Many thanks Jon!!!

I have a question. I hope you can help me to understand.

When I calculate the solar irradiance by using irradiance sensors in Daysim, I obtain certain number of W/m2 at each hour and at each sensor point (as I can see in my *.ill file).

But when I calculate the solar irradiance by using Diva (Daysim-based hourly method) I obtain certain number of Wh/m2 at each hour and at each sensor point (as I can see in my *.csv file).

Do you know what the results are in different units? Are the Diva results a sum of W/m2?

Abigail

Hi Abigail,

Those units are effectively the same, since x W/m2 integrated over one hour = x Wh/m2.  One can interpret the Wh/m2 designation as a useful reminder that each hour of weather data used by Daysim was in fact collected over a 60-minute time interval, and therefore doesn't correspond to a truly instantaneous measurement of power.

Jon

Hi Jon

So, I do not understand why my irradiance results are so different as the attached image shows.

The model used in Daysim has the same materials and dimensions that the model used in Diva. But Daysim calculates less W/m2 than Diva (Wh/m2).

Should I assume that the Daysim and Diva results have to be similar?

I have attached the daysim and diva files if you could check it.

Many thanks again.

Abigail

Attachments:

The sensors are not in the same order.  If you scroll to the right in that ill file you'll see higher values.  Overall the range of values looks pretty similar to me.

You are right about the sensors order.

But I still getting different results as you can see in the attached image where I compared the daysim and diva annual results at each sensor point.

As I can see, most of the sensors look similar, excluding those closer to the window.

Do you know why?

Attachments:

I get different results, actually.  Can you post your "C:\DIVA\Temp\ref100n_st" folder?

Folder attached! Thanks

I have an idea. Maybe the calculation of daylight coefficient is different in Diva.

With Daysim I have three options (figure attached):

- Original daylight coefficient file format (This is which I have used in the model ref100n)

- DDS file format

- DDS file format with shadow testing

What method is Diva using? Are there these options available in Diva?

Attachments:

There's no window in your DIVA simulation.  :)

(I can tell by looking at the rad file.)

FYI, with the window present I get the result below:

DIVA is using the "original" DC format.  You can run the (much slower) DDS calculation, but not through the interface -- you'd have to edit the header file yourself.

If your materials, geometry, nodes, parameters, and weather file are the same between two runs, the results will be the same.  Ecotect is using an older version of Daysim than DIVA is, but you could easily test if this makes any difference by running the exact same rad / hea files.

Jon