Days Im Tutorial

8/12/2019 Days Im Tutorial

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Tutorial on the Use of Daysim/Radiance Simulations for Building Design version: Aug-06 Page 53

5.1 Exercise: Daylighting Analysis of a Single Office

This first exercise introduces you to the DAYSIM JAVA interface and guidesyou through the steps necessary to setup and run a daylighting analysis of asingle office located in Ottawa, Canada. Daylight autonomy, daylight factor, andannual electric lighting use are the daylighting performance measures used inthis exercise.

Your Task

You are involved in the design of an office building located in Ottawa, Canada.The building is mainly oriented along the West-East axis with sixty identicalprivate offices bordering either the North or South facades (Figure 5-1-1). Thetwo facades are not shaded by surrounding buildings or landscape. The officesare connected through a central aisle that runs along the center of the buildingon all three storeys.

Figure 5.1-1:Sketchup Visualization of the investigated office building.

Your Task is to use Daysim to

predict the daylight availability (daylight autonomy and daylight factor) inthe offices and on the central aisle, and

estimate the lighting energy savings from an occupancy sensor versus aregular on/off wall switch.

Step 1: prepare the DAYSIM simulation

Before you start with the Daysim simulation, you need to prepare (a) a CADmodel of the building that can be imported it into Daysim, and (b) a sensor pointfile. Looking at Figure 5-1-1, you will realize that the office building is highlyrepetitive, consisting of 30 identical blocks with each block consisting of aNorthern and a Southern offices linked by a piece of aisle (Figure 5-1-2).


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Figure 5.1-2:Sketchup Visualization one of the thirty identical blocks out of which the building ismade up.

Since the daylight availabilities are identical within each of the individual blocksand since these blocks are as far a daylighting is concerned largelyindependent of each other, you may use the model shown in Figure 5-1-2 foryour analysis.

Note: Working with a smaller model reduces the memory requirements for

your simulation and allows you to use less stringent Radiance parameters, asthe resolution at which the raytracing algorithm scans surfaces within yourscene depends on the size of bounding box of your scene

3. Remember, the

time required to generate a 3 dimensional building model may be substantial.Include only those details into your building model that are relevant for thedaylight simulation.

The model shown in Figure 5-1-2 happens to coincide with the Sketchup modelused in chapter 4.1. Please refer to the relevant sections in chapter 4 to learnwhat to consider when preparing a Radiance/Daysim model in Sketchup andhow to export the Sketchup files into 3d Studio (3ds) format. A 3ds file of thegeometry shown in Figure 5-1-2 is also provided with this design exercise. It isstored under C:\Daysim\projects\Ex5.1DaylightingAnalysisOfASingleOffice/ExternalFiles/.

As mentioned earlier, you also need a sensor point file for your project, i.e. a filewith the coordinates and orientations of the points of interest in the building. Adescription of how to generate the sensor file is given in section 4.1. For this

3 The bounding box of a Radiance/Daysim scene is the smallest cube which holds the

scenes complete geometry.


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exercise you will use the sensor point file from chapter 4.1. A copy is alreadystored under C:\Daysim\projects\Ex5.1DaylightingAnalysisOfASingleOffice/pts/center_line.pts. As explained in 4.1, the file contains a line of sensorsfacing upwards, that are located on the center axis of the offices and the aisle atdesk height (85cm). The sensor are one meter apart from each other. The file isshown in Figure 5.1-3.

Figure 5.1-3:Radiance sensor point file

You will use Daysim to calculate daylight autonomies and daylight factors atthese sensor points. You are now prepared to start Daysim.

Step 2: start DAYSIM

Under Windows:go to START > PROGRAMS > DAYSIM2.1 > DAYSIM or usethe DAYSIM shortcut on your desktop

Under Linux:at the command line type: daysim

The DAYSIM graphical user interface (GUI) should appear on your screen(Figure 5-1-4). The interface functions as:

an editor to read/write a DAYSIM project header file that contains allinformation relevant for your Daysim project.

a platform to execute the different DAYSIM subprograms.

an editor to create shell scripts (Linux) or batch files (Windows) that executethe different DAYSIM subprograms. An overview of the relationship between

the different RADIANCE subprograms is provided in Appendix A.


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Figure 5.1-4:DAYSIM startup screen.

WARNING: In some rare case, you will get an error message that your PCdoes not recognize the JAR file extension. In that case, please refer to thetrouble shooting section in chapter 3.

Step 3: start a new project

Under the FILE > NEW PROJECT dialogue choose NEW and pick a directoryunder which you want to store the files for your new DAYSIM project. As you willbe using the scene and sensor files that were discussed in step 1, please go to/projects/Ex5.1DaylightingAnalysisOfASingleOffice/ and namethe project header file header1.hea (Figure 1-2). The name of the projectheader file will be used as a prefix for the results file created by DAYSIM (seebelow). The project header file contains all the information for your DAYSIMprojects. It is an ASCII file with a number of keywords that are explained in theDAYSIM documentation accessible via the HELP menu. More information will beadded to this file as you enter more information in the different GUI menus. Youcan always view a current version of the file by left-clicking on the FILE menu.

Note:For DAYSIM to run properly, project directories and Daysim header filenames must not have any blanks in them, e.g. call you Daysim projectversion_1 instead of version_1.


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Figure 5.1-5:Create a New Project Directory dialogue box.

In the directory under which you store your project header file DAYSIM

automatically creates the following subdirectories:/rad - imported RADIANCE scene files

/tmp - temporary files

/wea - project climate files

/pts - sensor point file

/res - simulation results

Step 4: load climate data

You now need to import the climate data for Ottawa, Canada. A climate filecontains annual time series of direct and diffuse irradiances. In Daysim, this datais combined with the Perez sky model to predict the luminous distribution of thesky at different times of the year (see also sections 1.6 and 2.1.1). The luminousdistribution is a luminance mapping that describes the amount of daylightincident onto a building from the different parts of the sky. Climate data is storedin test reference years which also include a variety of other climate data.

Under the SITE > NEW SITE dialogue you can specify the climate data for yourbuilding site. DAYSIM supports two climate file formats:

DAYSIM weather file (*.wea)

EnergyPlus weather data file (*.epw)

You can pick these files either directly from your local hard drive or you can firstopen your browser (Figure 1-3) and download weather data for over 680locations world wide from the EnergyPlus weather data site (Figure 5.1-7).


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Figure 5.1-6:Pick a Site dialogue box.

You should save the downloaded epw files under C:\Daysim\wea\ or anyother directory under which you want to stores the raw weather data files for yourDaysim projects

4.

Figure 5.1-7:EnergyPlus weather data site.

Browse to a climate file of your choice and press next.

Figure 5.1-8:Load a climate file dialogue box.

4 You can change the name of your default climate directory under FILE->

PREFERENCES.


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You can pick a simulation time step for your annual daylight simulation between1 minute and 1 hour. For calculations of the electric lighting use you should pick5 minutes (default). Press FINISH and wait until the subprogram ds_shorttermhas created your project weather data file and stored it under the projectsubdirectory /wea. Your final SITE screen should look like Figure 5-1-10.

Figure 5.1-9:Choose Simulation Time Step.

Figure 5.1-10:Final Site dialogue box.

Note: Within the GUI you can left-click on the blue underlined labels for

additional help.

When you chose a time step smaller than one hour, a stochastic auto-correlation model is used to generate down to one minute time series ofdirect and diffuse irradiance from hourly means (see chapter 6.2).

For this exercise the simulation should only take a couple of seconds asthe Ottawa 5 minute file comes with the Daysim distribution. Depending onthe speed of your computer, this calculation can take up to 20 minutes.The resulting short time step weather data file is centrally stored on yourcomputer so that you only need to carry out the calculation once for eachclimate file.


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Step 5: import building model and sensor point file

You now need to import the 3d studio file (*.3ds) that was previously exportedfrom SketchUp (chapter 4.1). Go to BUILDING > IMPORT 3D BUILDINGMODEL. As you can see in Figure 5.1.11, you have the choice of eitherimporting a 3d Studio file, importing a Radiance rif-file or manually importingRadiance material and geometry files. An example of how to import a rif file isgiven in chapter 5.3. To import a Radiance file, please refer to design exercise5.2.

Figure 5.1-11:Import 3D Building Model dialog box.

Choose import a 3D Studio file (*.3ds) and click on continue>>. SelectPrivateOffices.3dsunder subdirectory External Files (Figure 5.1.12).


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Figure 5.1-12:Import 3D Building Model dialog box (continued).

When importing a 3d Studio file, Daysim first converts the file using via the mgfformat into Radiance file format. mgf stands for Materials and GeometryFormat. Once your 3ds file has been successfully converted into the Radianceformat, a filter (rad2daysim.exe) runs over the Radiance scene. The filter eraseall light sources from the building model converts all materials to grayscale. Incase a material layer name corresponds to a material in the Daysim database,the material description used in the 3ds Studio file is replaced with the material

from the Daysim database (see section 4.2 for details).

After a few seconds, the following message screen should appear on yourscreen.

Figure 5.1-13:Report from the conversion from Radiance to Daysim.

The message indicates that the material layers GenIntFloor, GenIntWall,GenIntCeiling, DblGlazSpecSel72, and SingGlazClear90 have been replacedwith the material files of the same name stored in the Daysim material database(default: C:\Daysim\materials).


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By clicking OK you finalize the import of the building model into Daysim. Thebuilding menu should now look similar to Figure 5.1.14.

Figure 5.1-14:Building menu after a successful import of a 3ds file.

On the left hand side you see a visualization of the building model you justimported. At this point you should

verify whether the import into Daysim was complete (was the complete scenegeometry imported into Daysim?) and

review the Daysim material file as described in chapter 4.2.

As discussed in chapter 4.2, the Daysim material file for this building modelalready consists of realistic material properties that have been taken from theDaysim material database.

Next you need to import the sensor point file. As explained above, the sensorpoint file is an ASCII file that contains the location and orientations of particularpoints of interest in the building. Click on PICK A SENSOR FILE to choose

.../ExternalFiles/center_line.pts.


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Figure 5.1-15:Pick center_line.pts.

Note: Tips on how to generate a sensor point file are given in section 4.1.1.

Afterwards you need to specify the unit measured by each sensor in your sensorpoint file using the SPECIFY SENSOR UNITS button that appeared in thebuilding menu after you imported the sensor point file. The corresponding dialogis shown below.

Figure 5.1-16:Specify sensor units dialog.

The dialog file shows the coordinates and orientations of all sensors in thesensor point file. Under sensor unit you can characterize the type of theindividual sensors within the simulation by using a pull down menu. You canchoose between luminance, illuminance, radiance, and irradiance sensors. Bydefault, all sensor are illuminance sensors. In this exercise all sensors areilluminance sensors. Therefore, you can leave dialog 5.1.16 unchanged.

Finally, you need to pick your shading device model using the SHADINGDEVICE MODE pull-down menu. Depending on the amount of detail you want toprovide, DAYSIM allows three modes to model shading devices:


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static shading devices (e.g. light shelves): in this mode DAYSIM eitherassumes that the shading device is already part of your basic RADIANCEscene or that there is no shading device.

dynamic shading device model (simple): in this mode DAYSIM uses asimplified model to consider the effect of a generic venetian blinds system onthe annual daylight availability: DAYSIM uses the basic RADIANCE scene tocalculate indoor illuminances when the blinds are retracted. During times ofthe year when the blinds are lowered due to direct glare, DAYSIM simplyassumes that a generic blind system blocks all direct sunlight and transmits25% of all diffuse daylight. The use of this simulation mode is recommendedat an early design stage as explicitly creating and simulating a geometricblind model is very time consuming.

dynamic shading device model (advanced): in this mode DAYSIM uses anexplicit RADIANCE model of the shading device both in retracted andlowered positions. Please note that choosing this mode can more thandouble the required simulation time since two sets of daylight coefficientsneed to be simulated (shading device open and closed) and additional

raytracing is necessary to simulate a lowered blind system. An example ofhow to use this mode is given in design exercise 5-3.

For this exercise please choose the second option (simple blinds). YouBUILDING menu should now look like Figure 5.1.17. You can now run an actualdaylight simulation.

Figure 5.1-17:BUILDING menu after the building model has been successfully entered.


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Step 6: run a simulation

Under the SIMULATION menu (Figure5-1-18) annual indoor illuminance profilesfor all sensors in the sensor point file are calculated. As shown in Figure A-1 in

Appendix A, this calculation involves the use of two subprograms:

(1) Subprogram gen_dccalculates one or two sets of daylight coefficients forall sensor points depending on the underlying blinds model.

(2) Subprogram ds_illumcombines the daylight coefficients with the projectclimate file to yield annual indoor illuminance profiles for all sensor points.

The second step usually only take a couple of minutes (depending on the size ofyour sensor point file) whereas the first can take hours up to days.

Before starting a simulation you need to pick an adequate set of RADIANCEsimulation parameters. For this exercise, please choose the simulationparameters shown in Figure 5.1-18. The simulation parameters correspond tothose for scene 1 in chapter 2.1.3. The simulation will take about 1 hour on a1GHz processor. In case you first want to get a feeling of how the programworks, you can set the ambient bounces to 2 to bring the simulation time down toa couple of minutes.

Figure 5-1-18:SIMULATION main dialogue box.

Via SIMULATION > RUN A SIMULATION you can start a simulation. The firstdialogue box (Fig 5.1-19) allows you to pick which files you want to generate/re-generate. Usually all two boxes should be activated. Please left-click on NEXT.


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Figure 1-19:First RUN SIMULATION dialogue box.

The second dialogue box (Figure 5.1-20) allows you to start the simulation eitherfrom within the DAYSIM GUI or independently as a batch file under Windows oras a shell script under a Linux/Unix environment.

Figure 5.1-21:Second RUN SIMULATION dialogue box.

Pick the first option and click FINISH. The simulation will take about 1 hour on aPC with a 1GHz processor.

Note: During the simulation under Windows a number of DOS windows willpop up on your screen. These DOS windows mark the different simulationsteps namely:

- calculation of diffuse daylight coefficients: This simulation step isaccompanied with a WARNING: no light sources found. This is perfectlynormal as the Radiance scene does not contain any direct light sourcesduring the calculation of the diffuse daylight contribution.

- calculation of direct daylight coefficients: This simulation step will take thelongest since involves calculations with some 60 direct light sources whichcorrespond to the typical sun position for your building site that appear over

the course of the year.- calculation of annual illuminance/luminance profiles (*.ill)

WARNING:Most Daysim users find out at this point if Daysim has notbeenproperly installed on their computer. In that case the Daysim simulation willusually finish within a couple of seconds and the message below is displayed.


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This failure to run properly execute Radiance is usually the result of either yourpath and/or directory names containing blanks , or that the Windowsinstallation program did not properly set all required environmental variables.To remedy the problem either rename your files or go to the Troubleshootingsection in chapter 3.

Once the simulation is finished, the following result files should be stored in thedirectory C:\Daysim\projects\Ex5.1DaylightingAnalysisOfASingleOffice/res:

header1.dc daylight coefficient file

header1.ill annual illuminance profile (blinds up)header1_down.ill annual illuminance profile (blinds down)

The format of these files is explained in Appendix A. Note that the file prefixcorresponds to the project header file name.

Step 7: carry out a daylighting analysis

After the raytracing run from the previous step is finished and after you verifiedthat the two annual illuminance profiles (*.ill) and the daylight coefficient file(*.dc) are in the res subdirectory of your Daysim project, you can go to the

ANALYSIS menu (Figure 5.1-22). This menu allows you to carry out an in-depthanalysis of the annual daylight availability and electric lighting energy use in theinvestigated building. Entry fields are divided into three groups:


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Figure 5.1-22:ANALYSIS dialogue box.

Occupancy Profile: information on typical hours of occupancy

User Requirements and Behavior: here you need to specify both, the amountof lighting typically required by the users of the space as well as generalbehavioral tendencies of the users: Daysim allows you to choose an activeuser a passive user or an occupant population that is a mix of both basic

user types. An active user considers interior daylight levels when setting thelighting and blinds as opposed to a passive user who keeps blinds loweredlighting switched on during occupied hours. Both behavioral patterns havebeen observed in field studies. Obviously, the two behavior patterns results inconsiderably different energy use. As a designer usually cannot anticipatethe ratio of active to passive users in a future building, a hands-onapproach is to assume an evenly mixed population (default setting: mixof both). If this user behavior is chosen, the electric lighting use is calculatedfor both types of users individually an the predicted energy use correspondsto a mean of both values. This user behavior option is recommended, whenthe investigated building zones can repetitively be found throughout thebuilding. This requirement is met in this exercise, as the two office and the

aisle can be found 30 times in the building (see Figure 5.1-1). lighting and shading control system: These entries allow you to describe the

type of lighting and shading controls investigated. You can enter the installedlighting power density either in Wm

-2or in Wft

-2or in whatever floor unit you

choose. The simulation results will accordingly be in the corresponding unit,i.e. W/m

2 yr or W/ft

2 yr. You also need to specify where the work plane is

located within the space using the button: Specify Work Plane.


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Please take some time to familiarize yourself with the input options by left-clicking on the blue field labels and set the lighting power density and zone sizeto 12Wm

-2and 15m

2respectively.

What is the work plane?

You need to specify which of the illuminance sensors in the sensor point file correspondto sensors on the work plane of the occupant who is switching the electric lighting andmanipulating the shading device. A work plane illuminance sensor is usually facingupwards and located at about desk height (0.85cm). At each time step, Daysim willcalculate the minimum illuminance of all work plane sensors. This minimum work planeilluminance will be used to determine whether the occupant manually activates theelectric lighting at a particular time step.

The work plane sensors are also used to predict the appearance of direct glare. Directglare is detected when direct sunlight above 50Wm

-2 (exterior direct irradiance) is

incident on the work plane. The Daysim subprogram gen_directsunlight predicts foreach time step of the year whether direct glare conditions appear at the work place.This information will be stored under der res subdirectory in a direct glare profile

called (header1.dir) .

Before you start a daylighting analysis, you need to specify the work planesensors. A Daysim simulation report concentrates on one building section at atime. As the daylighting situation and requirements vary in both offices and thecentral aisle, a simulation report has to be generated for all three sectionsindependently.

We will first concentrate on the South office. As shown in Figures 5.1-2 and 5.1-3,the first four sensors in the sensor point file are located in the South office.

Assuming that the occupant will usually be seated between 2 and 3 meter awayfrom the facade, we will choose the second and third sensor to be work planesensors in the South office (see Figure 5.1-23).

Figure 5.1-23:Specify work plane dialogue.


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Note: If you do not specify any work plane sensors, Daysim will assume thatall illuminance sensor in your sensor point file are on the work plane. In thisexercise, this would lead to misleading predictions of the electric lighting useand the shading device setting as illuminance sensors are located in bothoffices and on the aisle.

Once you specified the work plane sensors, please click on Start DaylightingAnalysis using the default options from Figure 5.1-22. This will prompt Daysimto generate a simulation report similar to the one shown below.

Table 5.1-1:Daysim Simulation Report for the South office.

Daysim Simulation ReportNotes...

The predicted annual electric lighting energy use in the investigated zone is:20 kWh/unit areaAssuming a lighting zone size of 15 unit area, this corresponds to a total annual lighting energy use of 300kWh/a

Site DescriptionThe investigated building is located in Ottawa (45.32 N/ 75.67 E). Daylight savings time lasts from April 1st toOctober 31st. The picture below shows a visualization of the building model.

User DescriptionThe zone is occupied Monday through Friday from 8:00 to 17:00. The occupant leaves the office three timesduring the day (30 minutes in the morning, 1 hour at midday, and 30 minutes in the afternoon). The total annualhours of occupancy at the work place are 1805.6.The electric lighting is activated 2356.3 hours per year. Theoccupant performs a task that requires a minimum illuminance level of 500 lux. The predicted annual electriclighting energy use of 2.5 kWh/unit area corresponds to the mean energy use in an ensemble of identicaloffices that are occupied by four user types:

a user who operates the electric lighting in relation to ambient daylight conditions, opens the blinds inthe morning (upon arrival), and lowers them when direct sunlight above 50 Wm-2 hits the seatingposition (to avoid direct glare),

a user who operates the electric lighting in relation to ambient daylight conditions, and keeps theblinds lowered throughout the year to avoid direct sunlight,

a user who keeps the electric lighting on throughout the working day, opens the blinds in the morning(upon arrival), and lowers them when direct sunlight above 50 Wm -2 hits the seating position (toavoid direct glare), and

a user who keeps the electric lighting on throughout the working day, and keeps the blinds loweredthroughout the year to avoid direct sunlight.

The coordinates of work place sensors are marked in blue in the table below.


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x y z daylightfactor [%]

daylightautonomy[%] (activeuser)

daylightautonomy[%] (passiveuser)

annual lightexposure[luxh]

1.500 1.000 0.850 12.1 89.5 71.5 20769910

1.500 2.000 0.850 5.4 78.1 41.8 6436636

1.500 3.000 0.850 3.0 63.4 8.0 3696022

1.500 4.000 0.850 1.9 51.3 0.0 25080531.500 6.000 0.850 0.2 0.0 0.0 278091

1.500 7.000 0.850 0.2 0.0 0.0 261861

1.500 9.000 0.850 1.9 42.0 0.0 1605234

1.500 10.000 0.850 3.0 52.5 0.0 2348671

1.500 11.000 0.850 5.4 62.1 4.1 3758828

1.500 12.000 0.850 12.2 76.0 48.2 7142613

Each report lists some key simulation assumptions followed by a table withsimulation results. Within the results table, the first three columns correspond tothe x, y and, z coordinates of the sensors from the sensor point file. Column 4shows the daylight factors for the individual sensor points. The last column shows

the annual light exposure of the sensor points in luxh for active blind usage.

An analysis of the simulation report is provided in the following.

daylight factor distribution

The daylight factor only depends on the building model and is thereforeindependent of all entry fields in the ANALYSIS menu. Figure 5.1-24 shows anEXCEL graph of the daylight factor distribution from Table 5.1-1

#.

Figure 5.1-24:Daylight factor distribution in the office. (Figure generated with Microsoft Excel.)

The figure reveals that the daylight factor near the work plane lies between 3.0and 5.4% for both offices. Note that the daylight factor distribution is identical in

#Please note that Daysim does not have the capability to display graphs. You have to

import the data generates in the *.el.htm file and import it into a spreadsheet of your choice.


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the North and South office, the reason for this symmetry is that the referenceCIE overcast sky is rotationally invariant. The daylight factor near the workplanes (2-3m from the facade) lies above the 2% mark required by LEED. It risesabove 5% closer to the window, which is relatively high for an office daylightfactor (see Table 1-1 in chapter 1). This finding suggests that there is a need fora glare protection device in the offices for a VDT work place lose to the facade.

The daylight factor analysis further suggests that there is only a negligibleamount of daylight on the central aisle.

daylight autonomy distribution

As discussed in Table 1-1, daylight factor predictions are of limited use fordesign purposes, as they are based on a single sky condition. The daylightautonomy has been developed to provide a more holistic daylighting analysis in abuilding. It depends on the minimum illuminances threshold, the specified useroccupancy, and the type of blind control used. The daylight autonomy is definedas the percentage of occupied hours during the year when the minimumilluminance level is provided at a sensor by daylight alone.

In the default setting, Daysim assumes that the offices are occupied weekdaysfrom 8AM to 5PM with a one hour lunch break and two 30 minute breaksthroughout the day. The minimum illuminance threshold is 500 lux whichcoincides with recommended minimum illuminance levels for type b desk workstipulated by the Canada Labour Code, Part II - Canada Occupational Healthand Safety Regulations. Two daylight autonomies are given in the results table:one for an active and a second for a passive blind user. The results in table 5.1-1refer to the daylight autonomy in the South office, as the work plane chosen islocated in the South office. To calculate the daylight autonomy for the Northoffice as well you need to do the following:

save the Daylight Simulation report for the South office under a different

name change the work plane sensor to a work place in the North office (Figure 5.1-

25)

rerun Start Daylighting Analysis.


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Figure 5.1-25:Reset the work plane sensor for an analysis of the North office.

Finally, to calculate daylight autonomy on the aisle, you need to set the minimumilluminance level to 100 lux which corresponds to the recommended level for aservice area with frequent usage according to the Canada Labour Code. To geta conservative estimate of the daylight autonomy on the aisle, you shouldconfigure the work plan sensors in the South and North office synchronously.

Recommended illuminance levels and maximum lighting power densities

In Daysim the electric lighting system is characterized through the choice oflighting control and the installed lighting power density. Recommended valuesfor according to the IESNA Lighting Handbook, the Canadian Labor Code andGerman DIN 3035 can be accessed by clicking on the minimum illuminancelevellabel. Similarly, recommended maximum lighting power densities can be

accessed under installed lighting power density.

The resulting daylight autonomy distribution in the three spaces are shown in theEXCEL graph below.


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Figure 5.1-26: Daylight autonomy distribution in the offices(minimum illuminance level of 500 luxand manually control blinds) and on the aisle (minimum illuminance level of 100lux). (Figuregenerated with Microsoft Excel.)

The figure reveals that in both office the occupants can in principle work between40% and 80% of the year by daylight alone depending on how they use theirblinds. It is also worth mentioning, that the daylight autonomy in the North officeis marginally larger than in the South office. The reason for this is that glare isless of an issue for the North office. In the South office, reduced window sizeand/or a more advanced shading device such a split blind system might provide

a more effective way to reduce glare than the default venetian blind systeminvestigated in this example.

The figure also predicts a daylight autonomy over 30% on the aisle. This revealsthat sufficient lighting levels are routinely reached on the aisle by daylight alone.

A convenient way to reduce the electric lighting use on the aisle - if allowed bylocal safety regulations - could be through manual switches combined with atimer.

electric lighting use

The second part of your task is to estimate the energy saving potential of anoccupancy sensor in the two offices. The predicted annual electric lighting use is

provided at the beginning of each simulation report. As shown in Table 5.1-1, thepredicted annual electric lighting use for the South office is 20 kWh/ unit areawhich corresponds to 300kWh/a per office assuming an installed lighting powerdensity of 12Wm

-2in the 15m

2offices (width x depth =3m x 5m). If you rerun the

simulation for a switch-off and a switch on/off occupancy sensor, you will get thefollowing lighting energy uses for the north and South office.


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Figure 5.1-27:Annual electric lighting use in the north and South offices for three different lightingcontrol strategies. (Figure generated with Microsoft Excel.)

Figure 5.1-27 reveals that the lighting use for both office orientations will be verysimilar. Introducing an occupancy sensor that switches the electric lighting offwhen absence has been detected for more than 5 minutes saves about 30% oflighting energy in both offices. If on the other hand an occupancy sensor is

installed that switches the electric lighting on and off, the lighting energy userises as such a lighting control systems hinders occupants from ever working bydaylight alone.

Step 8: summing up

The daylight factor analysis in the offices yielded a level between 3 and 5% nearthe work plane. Assuming occupancy during regular office hours (Mo-Fr. 8.00-17.00) and a work that requires a minimum desktop illuminance of 500 lux on thedesk, the occupants could work 40-80% of the year by daylight alone dependingon the type of shading device used. A further going analysis should concentrateon either reducing window sizes or using a more advance shading device. For aninstalled electric lighting power density of 12 Wm-2, the mean annual electriclighting use in all the offices would be around 300kWh/yr in both offices. Anoccupancy sensor that switches the lighting automatically off after a delay time of5 minutes would reduce the mean annual electric lighting use in the offices byroughly 30%. Assuming an additional investment cost of $25 for such anoccupancy sensor and electricity costs of 10cent/kWh, the payback time for theoccupancy sensor would be around 2.8 years.


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Tutorial on the Use of Daysim/Radiance Simulations for Building Design version: Aug 06 Page 76

Note: If you want to present Daysim simulation results in your report, you canopen res/SingleOffice.el.htm directly in MS-Word and quicklyintegrate the simulation report in your standard report format.

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