Lecture 9: Windows and Daylighting Material prepared by GARD Analytics, Inc. and University of Illinois at Urbana-Champaign under contract to the National Renewable Energy Laboratory. All material Copyright U.S.D.O.E. - All rights reserved

2 Importance of this Lecture to the Simulation of Buildings  Every building is different in many ways: Location/exterior environment Construction/building envelope Space usage/interior environment HVAC system  Building consume approximately one-third of all energy used nationally—lighting accounts for about one third of building energy use  Daylighting has the potential to significantly reduce the amount of energy spent on lighting  Proper modeling of windows is important to both daylighting studies and energy analysis since it has a significant impact on both of these areas

3 Purpose of this Lecture  Gain an understanding of how to Specify windows in EnergyPlus Specify and control daylighting features within a zone

4 Keywords Covered in this Lecture  Material:WindowGlass  Material:WindowGas  Material:WindowGasMixture  Material:WindowShade  Material:WindowBlind  WindowShadingControl  WindowFrameAndDivider  WindowGapAirFlowControl  Daylighting:Simple and Daylighting:Detailed

5 Windows glass gas

6 Material:WindowGlass  Non-opaque solid layer used to construct windows MATERIAL:WindowGlass, SPECTRAL PANE, !- Name Spectral, !- Optical Data Type SpectralDataSet1, !- Name of Window Glass Spectral Data Set , !- Thickness {m} 0.0, !- Solar Transmittance at Normal Incidence 0.0, !- Solar Reflectance at Normal Incidence: Front Side 0.0, !- Solar Reflectance at Normal Incidence: Back Side 0.0, !- Visible Transmittance at Normal Incidence 0.0, !- Visible Reflectance at Normal Incidence: FrontSide 0.0, !- Visible Reflectance at Normal Incidence: Back Side 0.0, !- IR Transmittance at Normal Incidence 0.84, !- IR Hemispherical Emissivity: Front Side 0.84, !- IR Hemispherical Emissivity: Back Side 0.80; !- Conductivity {W/m-K} More examples from DOE-2 library in file WindowGlassMaterials.idf

7 Material:WindowGas  Non-opaque gaseous layer used to construct windows Gas type can be: Air, Argon, Krypton, Xenon, or Custom Custom requires properties (curve fit coefficients) for conductivity, viscosity, and specific heat as well as the gas molecular weight MATERIAL:WindowGas, WinAirGap, !- Name AIR, !- Gas Type 0.013; !- Thickness {m} More examples from DOE-2 library in file WindowGasMaterials.idf

8 Material:WindowGasMixture  Allows a custom mixture of gases to construct a non-opaque gaseous layer used for windows Gas type can be: Air, Argon, Krypton, or Xenon User defines up to four gases in mixture Material:WindowGasMixture, MyWinGasMix, !- Name , !- Thickness 2, !- Number of gases in mixture Air, !- Gas Type - Gas #1 0.5, !- Fraction - Gas #1 Argon, !- Gas Type – Gas #2 0.5; !- Fraction – Gas #2

9 Constructing Windows  Same as a regular construction definition except using window glass, window gas, and/or window gas mixture CONSTRUCTION, ELECTRO-CON-DARK, !- Name ELECTRO GLASS DARK STATE, !- Outside Material Layer WinAirGap, !- Material Layer #2 SPECTRAL PANE; !- Inside Material Layer

10 Material:WindowShade  Allows specification of window shades Becomes part of window shading control MATERIAL:WindowShade, MEDIUM REFLECT - MEDIUM TRANS SHADE, !- Name 0.4, !- Solar transmittance 0.5, !- Solar reflectance 0.4, !- Visible transmittance 0.5, !- Visible reflectance 0.9, !- Thermal emissivity 0.0, !- Thermal transmittance 0.005, !- Thickness {m} 0.1, !- Conductivity {W/m-K} 0.05, !- Shade-to-glass distance {m} 0.5, !- Top opening multiplier 0.5, !- Bottom opening multiplier 0.5, !- Left-side opening multiplier 0.0; !- Air-flow permeability More examples from DOE-2 library in file WindowShadeMaterials.idf

11 Material:WindowBlind  Allows specification of window blinds Becomes part of window shading control Example on next slide… More examples from DOE-2 library in file WindowBlindMaterials.idf

12 Material:WindowBlind MATERIAL:WindowBlind,BLIND WITH HIGH REFLECTIVITY SLATS, HORIZONTAL, !- Slat orientation 0.025, !- Slat width [1"] (m) , !- Slat separation [3/4"] (m) 0.001, !- Slat thickness (m) 45.0, !- Slat angle (deg) 0.9, !- Slat conductivity (W/m-K) 0.0, !- Slat beam solar transmittance 0.8, !- Slat beam solar reflectance, front side 0.8, !- Slat beam solar reflectance, back side 0.0, !- Slat diffuse solar transmittance 0.8, !- Slat diffuse solar reflectance, front side 0.8, !- Slat diffuse solar reflectance, back side 0.0, !- Slat beam visible transmittance 0.8, !- Slat beam visible reflectance, front side 0.8, !- Slat beam visible reflectance, back side 0.0, !- Slat diffuse visible transmittance 0.8, !- Slat diffuse visible reflectance, front side 0.8, !- Slat diffuse visible reflectance, back side 0.0, !- Slat IR (thermal) hemispherical transmittance 0.9, !- Slat IR (thermal) hemispherical emissivity, front side 0.9, !- Slat IR (thermal) hemispherical emissivity, back side 0.050, !- Blind-to-glass distance 0.5, !- Blind top opening multiplier 0.5, !- Blind bottom opening multiplier 0.5, !- Blind left-side opening multiplier 0.5, !- Blind right-side opening multiplier, !- Minimum slat angle (deg) ; !- Maximum slat angle (deg)

13 WindowShadingControl  Referenced by exterior window surface definitions  Shading types: Shade (interior, exterior, or between glass)—WindowShade Blind (interior, exterior, or between glass)—WindowBlind Switchable glazing

14 WindowShadingControl (cont’d)  Reference to either a construction or a material name  Many shading control variations: Always on or off or on as per schedule On if high solar, glare, air temperature, cooling load, or combinations of these Meet daylighting illuminance setpoint On at night if heating required or low temperatures with various daytime controls Off at night while on during daytime for cooling conditions and high solar on windows

15 WindowShadingControl (cont’d)  Other controls Various setpoints Glare control Several control options for blind slat angles WINDOWSHADINGCONTROL, WIN-CONTROL-GLARE, !- User Supplied Shading Control Name SwitchableGlazing, !- Shading Type ELECTRO-CON-DARK, !- Name of construction with shading OnIfHighGlare, !- Shading Control Type, !- Schedule Name 0.0, !- Solar/Load/Temp SetPoint {W/m2, W or deg C} NO, !- Shading Control Is Scheduled YES, !- Glare Control Is Active, !- Material Name of Shading Device, !- Type of Slat Angle Control for Blinds ; !- Slat Angle Schedule Name

16 WindowFrameAndDivider  Used to define information about frames and dividers  Can be significant portion of heat transfer characteristics of window  Includes physical properties (width, projections, number of dividers) as well as thermal properties  Example on next slide…

17 WindowFrameAndDivider (cont’d) WindowFrameAndDivider, TestFrameAndDivider, !- User Supplied Frame/Divider Name 0.05, !- Frame Width {m} 0.05, !- Frame Outside Projection {m} 0.05, !- Frame Inside Projection {m} 5.0, !- Frame Conductance {W/m2-K} 1.2, !- Ratio of Frame-Edge Glass Conductance to Center-Of-Glass Co 0.8, !- Frame Solar Absorptance 0.8, !- Frame Visible Absorptance 0.9, !- Frame Thermal Hemispherical Emissivity DividedLite, !- Divider Type 0.02, !- Divider Width {m} 2, !- Number of Horizontal Dividers 2, !- Number of Vertical Dividers 0.02, !- Divider Outside Projection {m} 0.02, !- Divider Inside Projection {m} 5.0, !- Divider Conductance {W/m2-K} 1.2, !- Ratio of Divider-Edge Glass Conductance to Center-Of-Glass 0.8, !- Divider Solar Absorptance 0.8, !- Divider Visible Absorptance 0.9; !- Divider Thermal Hemispherical Emissivity

18 WindowGapAirFlowControl  Used to allow ventilation of air gap in windows with either inside or outside air  Air can be vented to inside or outside  Can be scheduled WindowGapAirflowControl, !- Used to control forced airflow through a gap !- between glass layers Zn001:Wall001:Win002, !- Name of Associated Window InsideAir, !- Airflow Source OutsideAir, !- Airflow Destination 0.008, !- Maximum Airflow (m3/s per m of glazing width) !- (5.2 cfm for 1m x 1m window) AlwaysOnAtMaxFlow, !- Airflow Control Type No, !- Airflow Has Multiplier Schedule? ; !- Name of Airflow Multiplier Schedule

19 Daylighting  DAYLIGHTING:SIMPLE Specify useful fraction of solar gain  DAYLIGHTING:DETAILED Calculates illuminance  Only one type per zone  May use different types in same run

20 Daylighting:Simple  Effectiveness method Fraction beam usable Fraction diffuse usable Schedule  LIGHTS Fraction replaceable All lights on one control

21 Daylighting:Simple Sensible and Latent Beam Solar Sky Diffuse Ground Diffuse Light Control

22 Daylighting:Detailed Methodology  Calculated illuminance level  External factors Sky condition Sun position Ground reflectance External shading and obstructions

23 Daylighting:Detailed Methodology (cont’)  Window factors Size Position Transmittance Shades  Internal factors Interior surface visible absorptance Position of daylighting reference point

24 Daylighting:Detailed Sensible and Latent Beam Solar Sky Diffuse Ground Diffuse Light Control 1 Light Control 2 Uncontrolled Reference Pt 1 Reference Pt 2

25 Daylighting Calculation  Daylight factors Ratios of interior illuminance or luminance to exterior horizontal illuminance Contribution of direct light from each window to each reference point Contribution of reflected light from walls, floor and ceiling Window luminance and window background luminance used to determine glare Factors calculated for hourly sun positions on sun-paths for representative days of the run period

26 Daylighting Calculation (cont’d)  Daylighting calculation performed each heat- balance time step when the sun is up  Daylight factors at each reference point interpolated using the current time step’s sun position and sky condition  Illuminance found by multiplying daylight factors by exterior horizontal illuminance  If glare control, then automatically deploy window shading, if available, to decrease glare below a specified comfort level  Similar option uses shades to control solar gain

27 Electric Lighting Control  Electric lights full-on assumed to provide the setpoint illuminance – regardless of schedule  Electric lighting control system simulated to determine fraction of lighting for each lighting zone  Based on daylighting illuminance level regardless of actual electric lighting input power  Zone lighting electric reduction factor passed to thermal calculation  Heat gain from lights and power input reduced

28 Continuous Dimming

29 Stepped Lighting Control

30 Daylighting:Detailed Inputs  1 or 2 illuminance reference points Specific point(s) in zone (X,Y,Z position) Zone coordinate system – relative to zone origin If zone origins are all 0,0,0, then equivalent to world coordinates  1 to 3 lighting zones Controlled by reference point 1 Controlled by reference point 2 Uncontrolled Specify fraction of lighting power for each zone

31 Daylighting:Detailed Inputs (cont’d)  Illuminance setpoint(s) [lux]  Lighting control type Continuous – stay on at minimum Continuous – turn off at minimum Stepped – automatic Stepped – manual with probability Minimum lighting output and power levels

32 Daylighting:Detailed Inputs (cont’d)  Glare control of window shades Direction of view Maximum glare level

33 Daylighting:Detailed Example DAYLIGHTING:DETAILED, Zone 2, !- Zone Name 1, !- Total Daylighting Reference Points 2.5, 2, 0.8, !- X,Y,Z-coordinates of first reference point {m} 2.5, 8, 0.8, !- X,Y,Z-coordinates of second reference point {m} 0.4, !- Fraction of zone controlled by first ref. point 0.4, !- Fraction of zone controlled by second ref. point 500, !- Illuminance setpoint at first reference point {lux} 500, !- Illuminance setpoint at second reference point {lux} 1, !- Lighting control type 0, !- Azimuth angle of view direction clockwise from 0, !- zone y-axis (for glare calculation) {deg} 22, !- Maximum allowable discomfort glare index 0.3, !- Minimum input power fraction for continuous control 0.2, !- Minimum light output fraction for continuous control 1, !- Number of steps (excluding off) for stepped control 1; !- Probability lighting will be reset in manual control

34 Ground Reflectance  GroundReflectance  12 monthly values  Affects: Solar gains Daylighting  Snow Ground Reflectance Modifiers

35 Daylighting Modeling Guidelines  Do not use window multipliers Different window positions would be lost  Zone multipliers Beneficial to get room proportions correct Can only use if external shading not affected by zone position  Interior surfaces within a zone do not block direct light for daylighting calcs

36 Representative Room with Zone Multiplier

37 Model Unique Rooms as Individual Thermal Zones

38 Multiple Lighting Zones

39 Daylighting in Part of a Thermal Zone First Reference Point A BCD Interior window – no daylighting passes through Exterior window

40 Shading Surfaces for Daylighting  Opaque No daylight transmitted (according to manual, I/O ref. pp ) However, shadowing surface transmittance schedule does impact daylighting currently in some cases (may be a bug)  Black Do not reflect light For example, reflection from top of overhang onto window above not calculated

41 Summary  Windows are a means of providing solar heat gain and natural lighting to spaces within a building  EnergyPlus requires specification of the composition of window components as well as any shading strategy being used  Daylighting calculations can show the possible reduction in electric lighting