Different Radiance Methods




I just wonder if my understanding of different radiance methods in various tools are correct:

  • “2Phase DDS” is embedded in Daysim, Honeybee, and previous versions of Diva
  • “3Phase” and “5Phase” methods have been added to HoneybeePlus

Now, I want to understand if the method that I am using or have been used is appropriate for having accurate results regarding annual daylight assessment (sDA,ASE). I consider two sets of window: simple and complex.

Simple window (a punch window or a punch window with horizontal or vertical shades): 2Phase DDS, 3Phase and 5Phase methods are all appropriate methods for daylight analysis of this type of windows. This means that annual daylight assessment (sDA and ASE) should be accurate with Honeybee and previous versions of Diva.
BSDF: 2Phase DDS, 5Phase and 6Phase methods are appropriate methods for daylight analysis of this type of window. Therefore, HoneybeePlus should be the approprite tool. But if I use 2Phase DDS (Honeybee), I wonder if the results are still accurate.



This image, which Mostapha had created after a lot of back and forth between me and LBNL, is decent decision tree for determining what sort of simulation might be appropriate:

The underlying method for calculating ASE remains the same irrespective of which “phase” method you use. See the red rectangle below.

Finally, HB[+] isn’t technically using the DDS method. Both Daysim (~ 64 suns) and Daysim DDS versions (2305 suns) approximate the position of sun. In HB[+] we are not approximating and use the actual position of the sun instead. Refer the caption for the figure below. HB[+] uses the white positions corresponding to the actual positions, while Daysim DDS uses the red positions corresponding to 2305 positions (with approximation). Additionally, as far as I am aware there is no GUI-based way of doing DDS simulations. One has to setup DDS simulation through a text-based editor irrespective of which GUI-front end one is using.

As per LM 83-12, the occupancy times are based on 10 hours per day (=3650 hours). In a place like Phoenix, AZ a lot of those hours will have clear skies and we’d end up with a calculation involving almost 3650 suns. However in a place like Seattle, WA which has a fair share of overcast weather, we’d end up with less suns in the calculation. Whether an hour is overcast or sunny is based on the Perez Sky Model. For the hours when the sun is above the horizon, the hour would be assigned as overcast is based on the magnitude of Direct-Normal radiation (which is available from EPW files).