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daylighting algorithm in use?

asked 2017-01-05 15:17:16 -0500

Matt Koch's avatar

updated 2017-01-06 14:42:18 -0500

This post may be moot as the change from OpenStudio 1.14 to OpenStudio 2.1 is imminent. However, here goes.

I created a simple building with some thermal zones - let's call this case "no DLC". Then I copied that building and added illuminance maps and daylighting controls to all thermal zones. When I run this latter configuration without the Radiance Daylighting Measure, let's call this case "w/o DLC", when I run it with the Radiance Daylighting Measure, let's call this case "w/ DLC". So we have three cases for the same identical building.

The "no DLC" case has a high site EUI, the "w/ DLC" case a low site EUI, the "w/o DLC" has an even - but only slightly - lower site EUI. I would have thought that the results of the "no DLC" and "w/o DLC" would be identical, but instead the "w/o DLC" case is even slightly better than the "w/ DLC" case.

Is that because when the OpenStudio model has illuminance maps and daylighting controls, but the Radiance Daylighting Measure is omitted from the run, OpenStudio automatically uses some built-in EnergyPlus daylighting algorithm, which cannot be turned off separately? And when the Radiance Daylighting Measure is included, OpenStudio uses the Radiance daylighting algorithm?

My hope was to simulate an active DLC case (w/ DLC) and an inactive DLC case (w/o DLC) in Parametric Analysis Tool, simply by adding the Radiance Daylighting Measure to one, but not to the other. But I suspect either way I have daylighting going on, just with different algorithms, and the EnergyPlus algorithm yields slightly more savings than the Radiance algorithm, at least for these cases.

That means in order to compare active to inactive DLC, I cannot use Parametric Analysis Tool after all, but must compare a straight OpenStudio run for "no DLC" to one for "w/o DLC" or "w/ DLC" (the latter two depending on whether I trust Radiance or EnergyPlus more)?

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answered 2017-01-06 18:03:32 -0500

updated 2017-01-06 18:04:35 -0500

Your assessment is correct: if you add daylighting controls to an OpenStudio but do not include the Radiance Measure, the daylighting will be done using EnergyPlus' internal daylighting calculations.

So in order to do the analysis you want (daylighting vs. no daylighting), some options are:

  1. Write a Measure to add daylighting controls (or use this Measure)
  2. Add the daylighting controls by hand, and write a simple Measure to set the fraction of lighting for each zone controlled by daylighting controls to zero. Add this Measure to PAT. Here is the basic code you'd need:


model.getThermalZones.each do |zone|
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Thank you aparker. I had come across the Add Daylighting Controls measure before, and hoped this would do the trick. However, though I may have misinterpreted the error reports at the time, this would not suffice unless I also added Illuminance Maps. I suppose one way around that may be to enhance the Add Daylighting Controls measure by automatically adding a map whenever a control is created and have the map be small enough to fit within the thermal zone. I do like the "set fraction of daylighting" approach, but the challenge is more in creating maps and controls, which you still would need.

Matt Koch's avatar Matt Koch  ( 2017-01-09 07:02:56 -0500 )edit

If you aren't using the Radiance measure, you don't need the illuminance maps; EnergyPlus will be happy to calculate the "daylighting" without them. What errors were you seeing?

P.S. There is a version of that "Add Daylighting Controls" measure that does add maps. It's not perfect, but it may be useful even if only a starting point: Add Daylighting Controls measure

rpg777's avatar rpg777  ( 2017-01-09 11:59:26 -0500 )edit

answered 2017-01-09 12:38:50 -0500

Matt Koch's avatar

The following is what comes up after applying the "Add Daylight Sensor at the Center of Spaces with a Specified Space Type Assigned" measure and then the Radiance Daylighting Measure. Note that several of the spaces of this particular building do not have exterior windows, and the first of the two measures mentioned therefore does not add daylight sensors to those spaces. Perhaps that is the cause for this error. image description (Sorry, this is not really an answer, but I did not know how to add an image otherwise).

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Again, the Radiance measure requires maps, but EnergyPlus' daylighting does not. The only published measure that adds controls AND maps is the branched one I linked to in my answer. I'm betting you still don't have maps in these spaces and that is why the measure is complaining about non-configured (for Radiance) spaces. I should add that the Radiance Daylighting measure does not work on OpenStudio 2.0 at the moment, on any models. Are we having fun yet?

rpg777's avatar rpg777  ( 2017-01-12 10:37:34 -0500 )edit

P.S. You really should post your debug images somewhere (e.g. Dropbox) and link to them in a comment rather than creating an 'answer' here.

rpg777's avatar rpg777  ( 2017-01-12 10:39:03 -0500 )edit

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Asked: 2017-01-05 15:17:16 -0500

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Last updated: Jan 09 '17