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# Daylighting performance metrics in EnergyPlus

I am trying to model daylighting in EnergyPlus (not OpenStudio). I am just wondering what are the Daylighting performance metrics that can be modeled in EnergyPlus for simulation time (not time steps), or if we can model for time steps then can we get some meaningful results for simulation time (weekly, daily, Run period etc.). For example we can use Daylight autonomy (DA) for analyzing daylighting, but how we can model this in EnergyPlus?

Also, what are the available EMS sensors for Daylighting?

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Sorry for updating this after some time. I used EMS to report number of hours when daylight illuminance was between 100 and 2000 lux (i.e. useful daylight). A value of less than 100lux means it is too dark and a value of 2000 lux means it is too bright (can't remember the publication title but one of the authors was Christoph Reinhart of MIT).

EnergyManagementSystem:Sensor,
BlockIllumminance,      !- Name
Block1:Zone1,                !- Output:Variable or Output:Meter Index Key Name
Daylighting Reference Point 1 Illuminance;  !- Output:Variable or Output:Meter Name

EnergyManagementSystem:ProgramCallingManager,
Illu3,  !- Name
EndOfZoneTimestepBeforeZoneReporting,  !- EnergyPlus Model Calling Point
IlluProg3;     !- Program Name 1

EnergyManagementSystem:Program,
IlluProg3,     !- Name
IF (BedOcc2 > 0) && ((BlockIllumminance >2000)  || (BlockIllumminance <100)),
SET ZoneIllu3 = ZoneTimeStep,
ELSE,
SET ZoneIllu3 = 0,
ENDIF;

EnergyManagementSystem:GlobalVariable,
ZoneIllu3;

EnergyManagementSystem:OutputVariable,
Zone Illuminace Between 100 and 2000 Wile Occupied,  !- Name
ZoneIllu3,         !- EMS Variable Name
Summed,                  !- Type of Data in Variable
ZoneTimestep;            !- Update Frequency

more

Thanks for documenting your solution.

( 2015-07-25 11:50:18 -0600 )edit

Dear Waseem,

I am dealing somehow with the same process you had, May I know what kind of "Output:Variable" you used for you sensor?

Block1:Zone1, What is it? This is exactly my problem that energy plus can not recognize this input name ..

( 2019-03-28 01:35:40 -0600 )edit

I had to do a little homework myself to be able to provide a reasonable answer.

(DA) is the percentage of the time-in-use that a certain user-defined lux threshold is reached through the use of just daylight. DA is usually given as an annual value but seasonal, monthly and daily presentations can be made. For more historic details, see the Daylighting Pattern Guide site.

There are two forms of reporting. Time series reports are available when using Output:Variable statements and summary results are provided in various formats (e.g., html, tabular, etc).

All available time series reporting are described in the Input Output Reference document at the end of the section that describes the object (e.g., Daylighting:xxxxxxxx). From these descriptions, it appears that post-processing of results will be required to ascertain the results your looking for.

Summary reports are described in the OutputDetailsAndExample document. I don't think DA is available.

EMS sensors are described in the EMSApplicationGuide document, or if you include simple EMS instruction in your input file (e.g., EMS global variable statement [see EMS example files]), all available EMS actuators and sensors will be reported to the EMS data dictionary (edd) file. A quick review of this document did not show anything related to daylighting.

These are the available time series reporting options:

Daylighting Output

The following daylighting-specific outputs are (mostly) available for Daylighting:Controls:

Output:Variable,*,Site Exterior Beam Normal Illuminance,hourly;
Output:Variable,*,Site Exterior Horizontal Beam Illuminance,hourly;
Output:Variable,*,Site Exterior Horizontal Sky Illuminance,hourly;
Output:Variable,*,Site Beam Solar Radiation Luminous Efficacy,hourly;
Output:Variable,*,Site Sky Diffuse Solar Radiation Luminous Efficacy,hourly;
Output:Variable,*,Site Daylighting Model Sky Clearness,hourly;
Output:Variable,*,Site Daylighting Model Sky Brightness,hourly;
Output:Variable,*,Daylighting Window Reference Point 1 View Luminance,hourly;
Output:Variable,*,Daylighting Window Reference Point 1 Illuminance,hourly;
Output:Variable,*,Daylighting Reference Point 1 Illuminance,hourly;
Output:Variable,*,Daylighting Reference Point 1 Glare Index,hourly;
Output:Variable,*,Daylighting Reference Point 1 Glare Index Setpoint Exceeded Time,hourly;
Output:Variable,*,Daylighting Reference Point 1 Daylight Illuminance Setpoint Exceeded Time,hourly;
Output:Variable,*,Daylighting Window Reference Point 2 View Luminance,hourly;
Output:Variable,*,Daylighting Window Reference Point 2 Illuminance,hourly;
Output:Variable,*,Daylighting Reference Point 2 Illuminance,hourly;
Output:Variable,*,Daylighting Reference Point 2 Glare Index,hourly;
Output:Variable,*,Daylighting Reference Point 2 Glare Index Setpoint Exceeded Time,hourly;
Output:Variable,*,Daylighting Reference Point 2 Daylight Illuminance Setpoint Exceeded Time,hourly;
Output:Variable,*,Daylighting Lighting Power Multiplier,hourly;

more

@rraustad: Thanks for the answer. I don't know why I forgot to answer my question here. I used EMS to calculate DA for my problem. I am answering my question as it may be useful for someone else.

( 2015-07-25 11:23:40 -0600 )edit

Hey Waseem, just FYI in your initial question/post you mentioned wanting to calculate "useful daylight", and you defined that as horizontal illuminance between 100 and 2,000 lux. This is an old definition of useful daylight illuminance or UDI. A couple of years ago the upper limit was raised to 3,000 lux. Looks like you ended up calculating regular old daylight autonomy (DA) based on your follow ups. There is also a spin on that metric (Rogers) called "continuous daylight autonomy", which gives partial credit for illuminance not quite at the DA threshold.

( 2015-07-27 11:14:06 -0600 )edit

Also FYI OpenStudio will calculate DA, DAcon, and UDI for you, if you use Radiance for the daylight simulation instead of EnergyPlus. OpenStudio will calculate lighting schedules based on the Radiance-calculated daylight availability and seamlessly transfer those to the EnergyPlus model.

( 2015-07-27 11:15:46 -0600 )edit

@rpg777: Rob, Thanks for the info mate. Is not 3000 lux too bright (I will read the paper but I think this is too bright). Is this upper limit dependent on zone type (office, classroom etc.) or not? Also, is there a way to calculate cDA (continuous daylight autonomy) through EnergyPlus (not by using OpenStudio or Radiance)?

( 2015-07-27 14:05:45 -0600 )edit

@Waseem, the upper threshold was raised to 3,000 lux in light of newer research and the advent of flat monitors (less susceptible to veiling reflections than the old curved and specular CRTs). I don't have a reference handy but John Mardaljevic's the guy you wanna look up. UDI is intended for use in classroom and office type spaces. There is no built-in way to calculate these metrics with EnergyPlus, but it can generate the required illuminance data for them (geometrically limited as it may be).

( 2015-07-31 15:41:55 -0600 )edit