Comparative LB and HB average and cumulative radiation analysis

being pretty excited with the new features introduced with LBT 1.3.0, I tried to run a comparative assessment of cumulative and average radiation using 3 methods:

  1. LB Incident Radiation
  2. HB Cumulative Radiation
  3. HB Annual Irradiance.

I have run a simple test, with an external courtyard surrounded by basic building massing.
Similar results could be observed between LB and HB for cumulative radiation, whereas the 2 Radiance/based assessment (options 2 and 3) differ substantially. Summary as follows:

Method | Cum Radiation | Avg Irradiance
1 LB | 745 kWh/m2 | n/a
2 HB Cum | 793 kWh/m2 | 90.6 W/m2
3 HB Irr | 1191 kWh/m2 | 136 W/m2

Should this be interpreted as a notable underestimation by 1 and 2, and if so why? (734.3 KB)

Simulation settings were:

  1. Reinhart (high density sky)
  2. rfluxmtx - medium detail level - default shade rad modifier
  3. same as 2)

@andrea.botti ,

The accuracy depends entirely on which sensor you are looking at. If it’s a sensor that’s frequently in direct sun, then the difference can be pretty substantial since both “LB Incident Radiation” and “HB Cumulative Radiation” don’t model direct sun very accurately. For these two methods, the sun gets smeared out over 4 patches (as you see in the “LB Sky Dome”) and so this results in some inaccuracy in order to get a faster calculation.

Out of all 3 modeling methods, the “HB Annual Irradiance” is the most accurate on a timestep-by-timestep basis. It’s also the most time consuming since it models the direct sun at each timestep by tracing a ray directly from the sensor to the sun vector. So you should judge the accuracy of the other two methods based on option 3.

FYI, here’s an image showing you what each calculation method looks like at an individual timestep. Methods 1 and 2 model radiation the way the DAYSIM does (on the left). The “HB Annual Irradiance” component uses the Improved DC method (in the middle). And modeling a Point-in-Time study is the most accurate way to assess an individual timestep


Thanks Chris, I find this quite eye opening

This is really helpful, thanks for spelling it out.

Hi everyone,

If I understand well the difference between the 3 calculation methods on your answer @chris , it is highly possible that the DAYSIM (used in LB Incident Radiation) gives us higher values than “measurable reality” ?
We’re currently trying to compare EPW data with data from Incident Radiation, on the same control zone, without any geometry blocking rays and we have 70% higher values with LB Incident Radiation. I was wondering if we’re supposed to have thoses very differents results ?

Also, maybe a change in the SkyMatrix, or the type of the measure zone (_geometry parameter in LB Incident Radiation, can be either a Mesh (1 result) or a Brep (several results depending the size of the brep and the _grid_size param)) can have an influence on those comparisons.

Thanks for your answers !


Hi @MCOVale,

Are you able to share a picture of your model setup, script, and what epw variables you’re comparing the output with?

The sky dome used by Incident Radiation is generated from the EPW file, so they should align well - albeit potentially not perfectly due to the process of creating the sky dome.


Hi Chris
since this topic refers to radiation analysis, I mention my problem too:
I’m looking for an equation, python script, component, or any simulation tool that calculate the exact amount of longwave radiation of a complex surface of a wall on a human body in outdoor.
To make it clear I need that equation take the human body as an object made of several surfaces attached to each other and all the wall components which have centimeters dimensions as distinct surfaces.
then I wanna calculate the heat map of each these surfaces of wall to meet the exact number of longwave emittance of them.
and after that I wanna see which surfaces of human body absorb longwave radiations emitted from described wall and how much of these radiation would be absorbed based on the distance and position of the human body?

I will appreciate your time and help.

Hi Charlie, thanks for your answer.

There are below the files I use :
Irradiance (102.7 KB)
pleins0.3dm (690.7 KB)

The EPW file I use is this following one : (301.3 KB)

I compare the results of the 2 methods with the 14th column (N) which I believe is the global irradiance.

We will continue investigations on thoses results to find where the difference is from, if I have some news I’ll edit this.