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How to model daylighting control in pilotis

asked 2021-07-25 12:25:07 -0500

Keigo's avatar

updated 2021-07-26 01:58:36 -0500

I want to simulate lighting with daylighting control in pilotis on the 1st floor. Please refer to the building layout plan on 1F and section below.

image description

Pilotis is outside, but I think EnergyPlus can't simulate daylighting control for outside space. So, I need to model the Pilotis as an internal Zone that is enclosed by "virtual" windows with Visual Transmittance of 1. Please refer to Case 2 in the following image.

image description

If I add the "virtual" windows to Case1 and change the Pilotis to the internal thermal zone, I can simulate all the End Use of the building at once. And the Pilotis can be excluded from the calculation of Total Floor Area in summary report, but the only problem is that the "virtual" windows can't be excluded from the cauculation of Window-Wall Ratio in summary report. The summary report of Case 2 has incorrect WWR. I think Case 2 can be used only for Exceptional Calculation, and Case 1 should be considered a main energy simulation.

That's why I feel the need to model two cases (Case1 and Case2), but do you think this is the reasonable approach? Is there a better way to do annual energy simulation with just one case including lighting in Pilotis?

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answered 2021-07-26 05:57:24 -0500

updated 2021-07-26 06:41:51 -0500

There would be more than one of doing this IMO, the details of which would depend on whether the EnergyPlus model is being developed by hand (GUI), rather than automated/scripted (e.g. OpenStudio Ruby API). Here's an option that would be fairly straightforward to automate (very similar to what you describe):

  1. First run Case 2 with daylighting controls.
  2. Retrieve and store (from EnergyPlus results) the annual Zone 2 lighting requirements (kW, kWh). Optionally, you could output/post-process the annual time series data for Zone 2 lighting, or for each independently controlled bank of lights in Zone 2.
  3. Run Case 1 without exterior lighting.
  4. Add stored Zone 2 lighting requirements from Case 2 (kW, kWh) to the building's energy requirements in Case 1 (a post-simulation results summation, as you suggest).

More in line with your question, you could instead process the annual Zone 2 lighting time series data (from Case 2, step 2) to generate a Schedule:File, used as an exterior lighting schedule. This would allow Zone 2 lighting power to be synchronized with the Case 1 building power draw at each time step, as well as stay within EnergyPlus' post-simulation results processing.

There are drawbacks to using Case 2 and "virtual" fenestration. I don't believe EnergyPlus will allow VT (SimpleGlazing), or otherwise material visible transmittance, to be set to "1.0", which entails some drop in daylighting levels due to solar incidence angles away from normal (i.e. most of the day). So the approximation would be on the conservative side, but maybe "noise" whether you're modelling (or not) the surrounding landscape and urban environment.

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Thank you for your detailed explanation. I was also thinking about using Schedule:File. That would consolidate all the results into one summary report.

And you're right, I couldn't set VT=1. But I could set VT=0.9999999999, so the "virtual" fenestration should have little effect on the results.

Keigo's avatar Keigo  ( 2021-07-26 21:11:02 -0500 )edit

Even if one sets the Simple Window normal VT to 99.99%, the angle-dependent VT will drop as a function of solar incidence angle (calculated at runtime, as described here). At sunrise/sunset (< 40°), the VT should remain ~99%. At 60°, it should drop down to ~90%. At 70°, ~75%. At 80°, < 50%. A head's up.

Denis Bourgeois's avatar Denis Bourgeois  ( 2021-07-27 06:58:27 -0500 )edit

Thank you for pointing it out. You showed me an example of Curve A (Single: 3mm clear). Now I understood.

I have one more question. What do you think is the best way to minimize the influence of Angular Performance? Should I use WindowMaterial:Glazing rather than WindowMaterial:SimpleGlazingSystem ? The Transmittance equation for WindowMaterial:Glazing looks much more complicated.

Keigo's avatar Keigo  ( 2021-08-06 12:52:02 -0500 )edit

(part 1) I have never tried the following with EnergyPlus - so consider the following as merely suggestions. CTRL-F "If Optical Data Type = SpectralAndAngle" in the Input/Output Reference, and then from here onwards.

Denis Bourgeois's avatar Denis Bourgeois  ( 2021-08-06 14:27:35 -0500 )edit

(part 2) ... It indicates that you can reference 3x Data Set Tables to set the angle-dependent properties of (e.g. a single 3mm pane of glass). CTRL-F "TranmittanceDataSet". I cannot locate examples of such tables elsewhere, and the linked description of the table structure seems insufficient (to me). You'd have to do some trial & error tests, I imagine: once you've figured it out, you could set all angle-dependent reflectances to 0.001 and transmittances to 0.999.

Denis Bourgeois's avatar Denis Bourgeois  ( 2021-08-06 14:28:36 -0500 )edit

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Asked: 2021-07-25 12:25:07 -0500

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Last updated: Aug 09 '21