This isn't really a software question but more a question about the application of the software tools to a design.

In the description for Radiation Maps, it says, "This is a powerful tool that can be used on an urban or building scale to identify locations with solar energy conversion potential or areas in need of shading due to excessive solar exposure."

Is there a rule of thumb or process for using these results to determine areas in need of shading?  Is there some kwh/m^2 value that is considered "too much" direct sun, warranting the addition of shades?  I'm trying to understand if there's any quantitative relationship between these things.

Tags: maps, radiation, shading

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Hello Lara,

I think the answer will vary strongly dependent on your climate and building type. I find it most useful to compare seasonal irradiation using the maps. If you use the Hourly Daysim-based Method, a CSV file of hourly irradiation in W/m2 for each point is one of the results -- don't make your node  grid too dense. A little analysis in a spreadsheet tool gets you helpful irradiation (heating season) and 'harmful' irradiation (cooling season). Since these irradiation values are based on TMY3 weather data, you can compare it to hourly thermal simulation results as well.

This same process can also be done graphically with visualizations.

Best,

Alstan

Is there a rule of thumb or process for using these results to determine areas in need of shading?  Is there some kwh/m^2 value that is considered "too much" direct sun, warranting the addition of shades?  I'm trying to understand if there's any quantitative relationship between these things.

I forgot to respond to this part directly. I am sure there are some rules of thumb somewhere, but I am not aware of them personally. Maybe another forum reader knows?

Best,

Alstan

Lara -

I've been looking for similar information for a while now as I do a lot of shading studies. I've heard rumors that window blind manufacturers use a setpoint of 50-150 w/m2  - wherein they lower blinds if the radiation exceeds 150w/m2 incident on the glass, and retract if less than 50. I then took 100 w/m2 as an average of that, and divide through 100 W/m² x 1kw/1000 x 24 = 2.4 kW-hour/m²day. So a very rough number would be:

Shading needed if incident radiation on glazing > 2.4kwh/m2/day.

With that said, I have not yet substantiated this number, and would love to get more information to make more informed decisions.

Alstan, a wishlist item that could assist in this process would be providing the ability to visualize hours of direct sun on nodes. 

Hi Dan,

You can view the annual illuminance profile from a Climate-Based Simulation as a falsecolor temporal map. If you run the simulation for zero ambient bounces, that will directly show you the distribution of direct sun in the year. You can run the new Daysim-based "Radiation Map" calculation and DIVA will give you an organized CSV file.

Cheers,

Alstan

thanks alstan- 

A Falsecolor temporal map would definitely be useful - how do I make that?

What i was suggesting is that the representation could show the number of hours each point in the grid is over a minimum threshold over a particular time period (yearly, seasonally, or specific day), similar to the daylight autonomy calc. Aside from seeing direct sun on fenestration, this would be particularly useful if one is performing agricultural analysis, which tends to operate in the hours-of-sun-per-day metric.

Hi Dan,

You can achieve this by clicking the, Climate-based Falsecolor button from the load metrics dialog in the most recent version of DIVA.

The above is a plot from 1000-1001 lx from a 0 ambient-bounce simulation. Essentially it displays incident direct solar, accounting for weather periods where the sky is cloudy. By the way, if you run an annual calculation with 0-ab and an 'always occupied' schedule, the percentage results equate directly to hours of sunlight. 5% = 8760*.05 = 438 hours of direct sunlight.

Best,

Alstan

Alstan-

this is awesome! 

a few questions:

1. i've mostly been using the grasshopper components and it doesn't look like i can perform this analysis there yet? 

2. i get a rhino script error when i run this (but the image still works fine). the error is attached.

Hi Dan,

A strange error, but it shouldn't cause any serious problems. We tell the shell to wait for the image-generating command to run before it attempts to open it. My guess is that it happens too quickly on your computer and throws this error.

Best,

Alstan

Hi Alstan,

I am trying to design shading devices for a facade using Radiation Maps.I created a grid of nodes in front of the facade but I cannot find the associate CSV file anywhere! Where is it stored?

The other question is about (if it is possible) how to  distinguish betwwen direct and diffuse radiation.

Thanks in advance,

Kostas

Hello Kostas,

Are you using the Daysim-based method? It should always produce a CSV file in the grid-based results folder. If you are using the Cumulative Sky method, it will not.

> The other question is about (if it is possible) how to  distinguish betwwen direct and diffuse radiation.

Not directly. You could run an ab=0  (0 ambient bounces) calculation, which would only capture direct, unreflected sunlight. Then you could run an ab>0 calculation to account for the full irradiation. Some mathematics gets you the diffuse + direct-reflected component separately from the direct component.

Best,

Alstan

When I do the radiation map with ab 0 I get zeros. 

Is this normal ?

Hi Mohamed,

If you are using the cumulative sky based method -- yes, because it places all the solar energy into diffuse light sources which require at least 1 ambient bounce to be sampled. If you are using the Daysim-based method, no, because it uses actual direct solar positions.

Best,
Alstan

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